Java-1.indb

A GUIDE TO

PROGRAMMING IN

Java

™

2 Platform Standard Edition 5

Beth Brown

JAVA

™

A Guide to Programming

in Java

™

Java

™

2 Platform Standard Edition 5

Beth Brown

First Edition

ISBN 1-58003-071-8 (softcover)

ISBN 1-58003-072-6 (hardcover)

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Preface iii

We have strived to make this the clearest and most comprehensive

Java text available. Our primary objective in this text is to present mate-

rial in clear language with easy to follow examples. To meet this objective,

we use our teaching experiences as well as the feedback, comments, and

suggestions from other experienced instructors to determine how best to

present programming concepts.

For the best classroom experience for both the student and the instructor,

our comprehensive text book includes hands-on reviews, critical-thinking

questions, and exercises of varying difficulty levels. Additionally, our

Teacher Resource Materials correlate directly to the text book and offer

teaching hints for explaining difficult concepts, additional lessons and

exercises, and a comprehensive question bank for creating tests, quizzes,

and reviews. The Teacher Resource Materials include the applications,

Case Studies, and vocabulary from the text book, as well as answers to

all the reviews and exercises.

It is our belief that learning to program offers the student an invaluable

opportunity to develop problem-solving skills. The process of defining a

problem, breaking it down into a series of smaller problems, and finally

writing an application to solve it exercises a student’s logical abilities.

Additionally, the student is made aware of the capabilities and limita-

tions of a computer and soon realizes that the programmer—the human

element—is more important than the machine.

A Guide to Programming in Java is written for a one-term or two-term

course. No previous programming experience is required or assumed. It

is our goal that this text provide students the best possible introduction

to programming using Java and to prepare them for further study in the

IT/programming/computer science field.

Preface

iv A Guide to Programming in Java

Design and Features

Programming Concepts This text emphasizes the fundamental concepts

of programming so that this knowledge can be applied to other program-

ming languages.

Problem Solving From the very beginning, students are taught to imple-

ment programming solutions with proper algorithm design and code

conventions.

Programming Style Throughout the text, proper programming style

is emphasized so that students can make their applications easy to read,

modify, and debug.

Demonstration Applications and Runs Many demonstration applica-

tions are included, complete with sample runs, so that students are shown

both proper programming techniques and the output actually produced

by an application.

Reviews Numerous reviews are presented throughout each chapter to

provide immediate reinforcement of newly learned concepts. Solutions to

the reviews are included on the Teacher Resource Materials CD.

Case Studies Most chapters end by stating a problem, developing an

appropriate algorithm, and then implementing the solution. The process

of specification, design, implementation, and debugging and testing is

clearly outlined.

Chapter Summaries Each chapter ends by summarizing the concepts

and statements covered in the chapter.

Vocabulary Sections Each chapter contains a vocabulary section that

defines new terms. A separate section lists Java keywords, statements,

and classes.

Critical Thinking Written response questions that require critical think-

ing from the student are included at the end of each chapter.

Exercises Each chapter includes a large set of exercises of varying diffi-

culty, making them appropriate for students with a range of abilities. Most

exercises include a demonstration run to help make clear what output is

expected from the student’s application. Exercises based on previous work

are marked with a ö symbol. Answers to the exercises are included on

the Teacher Resource Materials CD.

Indexes In addition to a standard index, an index of the applications

presented in the text is also included.

Appendix A chart of Unicode symbols is included.

Online Resources Materials that complement and extend this text are free

for download and distribution in your class. Information about various

Java compilers is available. Supplemental chapters cover operating systems,

personal finances, introduction to computers, and keyboarding skills are

also provided. Students can download all the files needed to complete the

reviews and exercises from www.lpdatafiles.com.

Preface v

Teacher Resource Materials

Our Teacher Resource Materials correlate directly to the text book and

provide all the additional materials required to offer students an excellent

computer applications course. The Teacher Resource Materials feature:

• START_HERE.htm Help files and a guide for using the text and

resource materials.

• Lesson Plans Lessons in PDF format keyed to the chapters in the

text. Each lesson includes assignments, teaching notes, worksheets,

and additional topics.

• Tutorials Flash movie files that provide animations to illustrate

searching and sorting concepts. Each movie is keyed to the text.

• PowerPoint Presentations Topics keyed to the text are in

PowerPoint files for presentation.

• Vocabulary Word files of the vocabulary presented in the text.

• Rubrics Rubrics keyed to exercises in the text for assessment.

• Worksheets Programming assignments that supplement the exer-

cises in the text provide additional reinforcement of concepts.

• Critical Thinking Answers Answers for the critical thinking

questions presented in the text.

• Data files All the files the student needs to complete the reviews

and exercises in the text, as well as the files needed to complete

the worksheets and tests.

• ExamView

Software Question banks keyed to the text and the

popular ExamView

software are included to create tests, quizzes,

and additional assessment materials.

• Answer files Answers to the reviews, exercises, worksheets, and

tests.

Acknowledgments

Special thanks to the many instructors who used this text in their

classroom as it was being written. I would especially like to thank the

following instructors for their many comments and suggestions:

Paul Massey Hanna-Westside Extension Campus

Edward Sapienza Peabody Veterans Memorial High School

Timothy Strohm Churchville-Chili Senior High School

Jackie Kyger Marine Military Academy

Jan Marrelli, a Lawrenceville Press author and editor, has contributed

much to this text. She has used this text as it was being written in her

classroom. The many comments and suggestions from her and her stu-

dents have helped to make this text so clearly written. Jan, an experienced

instructor, has also written many of the critical thinking questions, exer-

cises, and reviews.

vi A Guide to Programming in Java

Elaine Malfas, senior technical editor at Lawrenceville Press, has pro-

duced the format and layout for this text. The many illustrations have been

created by Elaine as well.

Thanks also to Joseph Dupree in our Customer Relations Department

for some of the original drawings included in this text.

The success of this and all of our texts is due to the efforts of Heidi Crane,

Vice President of Marketing at Lawrenceville Press. Joseph Dupree and

Christina Albanesius run our Customer Relations Department and handle

the thousands of orders we receive in a friendly and efficient manner.

Michael Porter is responsible for the excellent service Lawrenceville Press

offers in the shipping of orders.

About the Author

Beth A. Brown, a Computer Science graduate of Florida Atlantic

University, is director of development at Lawrenceville Press where she

has coauthored a number of programming and applications texts and

their accompanying Teacher Resource Materials. She has taught computer

applications and programming at the high school level.

Preface vii

Chapter Expectations

Chapter 1 – An Introduction to

Computers

After completing Chapter 1, students

will be able to:

1. Compare and contrast various input, output,

and storage devices.

2. Identify hardware components and explain

their function.

3. Demonstrate knowledge of operating systems.

4. Discuss different computer classifications and

compatibility issues.

5. Differentiate among the levels of programming

languages.

6. Describe communication and networking

components.

7. Understand the binary number system.

8. Describe how data is stored in memory and in

files.

9. Use Internet services to access information and

share resources.

10. Demonstrate proper etiquette and knowledge

of acceptable use policies when using a

network.

11. Discuss social and ethical issues associated

with computer use.

Chapter 2 – Applets and Web

Programming

After completing Chapter 2, students

will be able to:

1. Define terminology associated with the World

Wide Web.

2. Discuss the impact of programming on the

World Wide Web community.

3. Create HTML documents.

4. Explain how a web browser interprets an

HTML document.

5. Use JavaScript to demonstrate how scripts can

enhance a website.

6. Create simple Java applets.

7. Specify custom values for a Java applet that has

been placed in an HTML document.

8. Apply a style sheet to an HTML document.

Chapter 3 – Introducing Java

After completing Chapter 3, students

will be able to:

1. Define terminology associated with object-

oriented programming.

2. Explain why Java is a widely used

programming language.

3. Create Java applications.

4. Describe the process involved in executing a

Java application.

5. Display and format program output.

6. Annotate code properly with comments,

formatting, and indentation.

7. Explain the importance of using code

conventions.

8. Demonstrate algorithm design as a problem-

solving strategy.

9. Use visual organizers to design solutions.

Chapter 4 – Variables and Constants

After completing Chapter 4, students

will be able to:

1. Declare and initialize variables and constants

using the appropriate data type.

2. Choose legal identifiers that follow good

programming style.

3. Differentiate between primitive and abstract

data types.

4. Explain how to access Java packages.

5. Demonstrate how to read data from an input

stream.

6. Write numeric expressions.

7. Apply type casting.

8. Format numeric output.

9. Identify Java keywords.

10. Differentiate between syntax and logic errors.

11. Understand run-time exceptions.

12. Read and understand a problem description,

purpose, and goals.

viii A Guide to Programming in Java

Chapter 5 – Conditional Control

Structures

After completing Chapter 5, students

will be able to:

1. Demonstrate the use of decision structures to

control the flow of a program.

2. Describe how a roundoff error can occur.

3. Generate random numbers.

4. Write compound Boolean expressions.

5. Access methods in the Math class.

6. Modify existing code.

7. Develop code with correct and efficient use of

conditional control structures.

8. Select appropriate test data.

9. Create and modify solutions to problems.

Chapter 6 – Loop Structures and

Strings

After completing Chapter 6, students

will be able to:

1. Demonstrate the use of repetition control

structures.

2. Explain how infinite loops can occur.

3. Differentiate between counters and

accumulators.

4. Use various tools and techniques to debug an

application.

5. Manipulate and compare strings using the

String class and its methods.

6. Develop code with correct and efficient use of

repetitive control structures.

7. Apply problem solving strategies.

Chapter 7 – Chapter Methods

After completing Chapter 7, students

will be able to:

1. Use top-down development and procedural

abstraction to develop problem solutions.

2. Write methods.

3. Use method parameters.

4. Demonstrate the use of method overloading.

5. Return values from a method.

6. Write appropriate method documentation,

including pre- and post-conditions.

7. Identify boundary cases and generate

appropriate test data.

8. Describe code conventions that apply to

methods.

Chapter 8 – Classes and Object-

Oriented Development

After completing Chapter 8, students

will be able to:

1. Understand and instantiate objects.

2. Design and implement a class.

3. Apply functional decomposition.

4. Apply appropriate naming conventions to a

class.

5. Explain the difference between accessor,

modifier, and helper methods.

6. Write constructors.

7. Compare and contrast instance and class

members.

8. Understand class specifications and the

relationships among the classes.

9. Understand and implement a given class

hierarchy.

10. Apply encapsulation.

11. Identify reusable code from existing code.

Chapter 9 – Inheritance and

Polymorphism

After completing Chapter 9, students

will be able to:

1. Extend a class using inheritance.

2. Explain an is-a relationship.

3. Implement a subclass.

4. Define and demonstrate polymorphism.

5. Understand abstract classes.

6. Declare and implement an interface.

7. Extend existing code using inheritance.

Chapter 10 – Arrays

After completing Chapter 10, students

will be able to:

1. Describe types of problems that benefit from

the use of arrays.

2. Create one and two dimensional arrays.

3. Include array parameters in a method

declaration.

4. Understand how to implement arrays with

meaningful indexes.

5. Apply offset array indexes.

6. Manipulate characters in a string.

7. Understand the digital code, Unicode.

8. Apply search algorithms to an array.

9. Use methods in the ArrayList class.

10. Demonstrate the use of the Wrapper classes.

Preface ix

Chapter 11 – GUIS and Event-Driven

Programming

After completing Chapter 11, students

will be able to:

1. Design graphical user interfaces.

2. Use component classes in the Java swing

package.

3. Create event-driven applications.

4. Control the layout of an interface using layout

managers.

5. Use text fields and combo boxes to obtain user

input.

6. Apply color and add images to an interface.

Chapter 12 – Files and Exception

Handling

After completing Chapter 12, students

will be able to:

1. Use the File class to create objects that

represent a file.

2. Write exception handlers.

3. Understand file streams.

4. Read the contents of an existing file.

5. Process numeric data.

6. Create an output file stream.

7. Explain the object serialization and

deserialization processes.

Chapter 13 – Recursion and

Advanced Algorithms

After completing Chapter 13, students

will be able to:

1. Implement the selection sort algorithms.

2. Sort objects using the Comparable interface.

3. Implement the insertion sort algorithm.

4. Define and demonstrate recursion.

5. Implement the mergesort algorithm.

6. Implement the binary search algorithm.

7. Explain the recursive technique, depth-first

searching.

8. Analyze algorithms for efficiency.

9. Design and document sequential search

algorithms.

Chapter 14 – Data Structures

After completing Chapter 14, students

will be able to:

1. Explain how data structures, such as stacks

and queues, can be used to organize data.

2. Use and implement well known data

structures.

3. Describe standard operations associated with

data structures.

4. Choose appropriate data structures.

5. Differentiate between a LIFO and FIFO

structure.

x A Guide to Programming in Java

Table of Contents xi

Table of Contents

Chapter 1 – An Introduction to

Computers

Desktop Computing .................................................1

Operating Systems and Environment ....................2

Mobile Computing ....................................................4

Programming Languages ........................................5

Networks ....................................................................6

Number Systems .......................................................9

Storing Data in Memory ........................................ 10

What is a File? ......................................................... 11

Storage Devices ........................................................12

Intranet, Extranet, Internet ....................................13

Telecommunications ............................................... 14

Internet Services: Web, E-mail, and

Mailing Lists ............................................................ 15

Finding Information on the Web and

Downloading Files .................................................. 16

Internet Privacy Issues ........................................... 18

Internet Acceptable Use Policy .............................19

The Social and Ethical Implications of

Computer Use .......................................................... 19

Protecting Computer Software and Data ............20

The Ethical Responsibilities of an IT

Professional ..............................................................22

Chapter Summary ..................................................22

Vocabulary ...............................................................25

Review Questions ...................................................29

Exercises ...................................................................32

Chapter 2 – Applets and Web

Programming

The World Wide Web ..............................................35

HTML ......................................................................36

Creating an HTML Document .............................. 37

Review: hello_world.htm ..................................38

Review: Computer Viruses Website –

part 1 of 6 .............................................................38

JavaScript ..................................................................38

Review: welcome.htm ........................................39

Review: Computer Viruses Website –

part 2 of 6 .............................................................39

Using Scripts to Enhance a Website .....................40

Review: Computer Viruses Website –

part 3 of 6 .............................................................41

Review: System Check – part 1 of 2 .................41

Java Applets .............................................................41

Creating Java Applets .............................................41

Drawing Shapes and Adding Color .....................43

Review: Hot Air Balloon ...................................44

Placing an Applet in an HTML Document ........44

Applet Parameters ..................................................44

Review: System Check – part 2 of 2 .................45

HTML Tags ..............................................................45

Review: Computer Viruses Website –

part 4 of 6 .............................................................47

Hyperlinks, Tables, and Images ............................47

Review: Computer Viruses Website –

part 5 of 6 .............................................................49

Style Sheets ..............................................................49

Review: Computer Viruses Website –

part 6 of 6 .............................................................51

Chapter Summary ..................................................51

Vocabulary ...............................................................53

HTML Tags ..............................................................54

Critical Thinking .....................................................55

Exercises ...................................................................56

xii Table of Contents

Chapter 3 – Introducing Java

Why Program in Java? ............................................59

Objects, Classes, and Packages .............................59

A Java Application .................................................. 61

Executing a Java Application .................................62

Review: Greeting ................................................62

Displaying Output ..................................................63

Review: AboutMe – part 1 of 2 .........................64

Formatting Output ..................................................64

Review: AboutMe – part 2 of 2 .........................65

Code Conventions ...................................................65

Algorithm Design ...................................................66

Chapter Summary ..................................................67

Vocabulary ...............................................................69

Java ............................................................................70

Critical Thinking .....................................................71

Exercises ...................................................................72

Chapter 4 – Variables and

Constants

Declaring Variables .................................................77

Using Variables ........................................................78

Review: RectanglePerimeter .............................79

Primitive Data Types ..............................................79

Review: Distance – part 1 of 2 ..........................79

Abstract Data Types ................................................80

Java Packages ...........................................................80

Obtaining a Value from the User .......................... 81

Review: Distance – part 2 of 2 ..........................82

Numeric Expressions ..............................................83

Review: Digits .....................................................84

Type Casting ............................................................84

Review: GradeAvg – part 1 of 2 .......................85

Review: TempConverter ....................................85

Formatting Numeric Output .................................86

Assignment Operators ...........................................86

Review: GradeAvg – part 2 of 2 .......................87

Using Named Constants ........................................87

Identifiers and Keywords ......................................88

Review: CircleCircumference – part 1 of 2 .....88

Programming Errors ..............................................88

Chapter 4 Case Study .............................................90

Chapter Summary ..................................................93

Vocabulary ...............................................................95

Java ............................................................................96

Critical Thinking .....................................................97

Exercises ...................................................................99

Chapter 5 – Conditional Control

Structures

The if Statement ..................................................... 105

Roundoff Error ...................................................... 106

Review: SurfsUp – part 1 of 3 ......................... 106

The if-else Statement ............................................. 106

Review: SurfsUp – part 2 of 3 ......................... 107

Review: CircleCircumference – part 2 of 2 ... 107

Nested Statements ................................................. 107

Review: Stages .................................................. 107

The if-else if Statement ......................................... 108

Review: SurfsUp – part 3 of 3 ......................... 108

Review: Discriminant ...................................... 108

The switch Statement ............................................ 109

Review: Hurricane ........................................... 110

Generating Random Numbers ............................ 110

Review: RandomNum ..................................... 111

Compound Boolean Expressions ........................ 112

Review: Delivery .............................................. 113

The Math Class ...................................................... 113

Review: PerfectSquare ..................................... 114

Chapter 5 Case Study ........................................... 114

Review: RPS – part 1 of 2 ................................ 118

Review: RPS – part 2 of 2 ................................ 118

Chapter Summary ................................................ 119

Vocabulary .............................................................120

Java .......................................................................... 121

Critical Thinking ...................................................122

Exercises .................................................................123

Chapter 6 – Loop Structures and

Strings

The while Statement ............................................. 131

The do-while Statement ....................................... 131

Infinite Loops ........................................................ 132

Review: Prompter ............................................133

Counters and Accumulators ................................133

Review: Evens ...................................................134

Review: NumbersSum ....................................134

Review: PercentPassing ...................................134

The for Statement ..................................................135

Review: Factorial ..............................................136

Review: OddSum ............................................. 136

Debugging Techniques ........................................ 136

Review: Variable Trace .................................... 137

The String Class ....................................................138

Review: AccountSetup .................................... 139

Comparing Strings ................................................ 140

Review: FormalGreeting ................................. 141

Table of Contents xiii

Chapter 6 Case Study ........................................... 141

Review: WordGuess ......................................... 146

Chapter Summary ................................................ 146

Vocabulary ............................................................. 148

Java .......................................................................... 148

Critical Thinking ................................................... 149

Exercises .................................................................150

Chapter 7 – Methods

Program Development Using Methods ............. 157

Writing Methods ................................................... 159

Review: TimeConverter ................................... 160

Method Parameters ............................................... 160

Review: SpanishNumbers .............................. 161

Review: DisplayBox – part 1 of 2 ................... 162

Method Overloading ............................................ 162

Review: DisplayBox – part 2 of 2 ................... 163

The return Statement ............................................ 163

Review: Exponentiation .................................. 164

Documenting Methods ........................................164

Review ............................................................... 165

Chapter 7 Case Study ........................................... 165

Review: GradeConverter ................................. 171

Chapter Summary ................................................ 171

Vocabulary ............................................................. 173

Java .......................................................................... 173

Critical Thinking ................................................... 174

Exercises ................................................................. 175

Chapter 8 – Classes and Object-

Oriented Development

What is an Object? ................................................179

Designing and Writing a Class ........................... 180

Review: Circle – part 1 of 4 ............................. 182

Review: Coin – part 1 of 2 ............................... 182

Writing Constructors ............................................ 183

Review: Circle – part 2 of 4 ............................. 184

Review: Rectangle – part 1 of 5 ......................184

Instance and Class Members ............................... 184

Review: Circle – part 3 of 4 ............................. 185

Review: Rectangle – part 2 of 5 ......................185

The Object Class .................................................... 185

Review: Circle – part 4 of 4 ............................. 187

Review: Rectangle – part 3 of 5 ...................... 187

Review: Coin – part 2 of 2 ............................... 187

Classes Using Classes ........................................... 187

Review: Bank .................................................... 191

Object-Oriented Development ............................ 191

Review: Carnival .............................................. 195

Chapter 8 Case Study ........................................... 196

Review: RPS2 – part 1 of 2 ..............................202

Review: RPS2 – part 2 of 2 ..............................202

Chapter Summary ................................................202

Vocabulary .............................................................204

Java ..........................................................................205

Critical Thinking ...................................................206

Exercises .................................................................208

Chapter 9 – Inheritance and

Polymorphism

Extending a Class .................................................. 213

Implementing a Subclass ..................................... 214

Review: Puck – part 1 of 2 ............................... 216

Polymorphism ....................................................... 217

Review: Music – part 1 of 2 .............................221

Abstract Classes ....................................................222

Review: Music – part 2 of 2 .............................225

Interfaces ................................................................225

Review: Disk .....................................................227

Review: Puck – part 2 of 2 ...............................227

Review: Rectangle – part 4 of 4 ......................227

Review: Rectangle – part 4 of 5 ......................227

Chapter 9 Case Study ...........................................227

Review: SalesCenter .........................................234

Chapter Summary ................................................234

Vocabulary .............................................................236

Java ..........................................................................236

Critical Thinking ...................................................237

Exercises .................................................................238

Chapter 10 – Arrays

Declaring Arrays ...................................................239

Using Arrays ..........................................................240

Review: StudentRoster .................................... 241

Review: Squares ............................................... 241

Review: Reverse ............................................... 241

Array Parameters .................................................. 241

Arrays with Meaningful Indexes .......................242

Review: DiceRolls – part 1 of 2 .......................243

Review: DiceRolls – part 2 of 2 .......................243

Review: NumberCounts .................................. 243

Characters and Arrays .........................................244

Review: CountLetters ...................................... 246

Review: NameBackwards ...............................246

Searching an Array ...............................................246

Review: FindName .......................................... 247

Two-Dimensional Arrays .....................................247

The ArrayList Class ..............................................252

xiv Table of Contents

Wrapper Classes ....................................................253

Review: HighestGrade ....................................255

Chapter 10 Case Study .........................................255

Review: LocalBank ..........................................264

Chapter Summary ................................................264

Vocabulary .............................................................265

Java ..........................................................................265

Critical Thinking ...................................................266

Exercises ................................................................. 267

Chapter 11 – GUIs and

Event-Driven Programming

What is a GUI? .......................................................275

The Swing Package ............................................... 275

Review: Name – part 1 of 2 .............................278

The JButton Class ..................................................278

Handling Events ....................................................279

Review: Name – part 2 of 2 .............................281

Review: NumClicks ......................................... 281

Controlling Layout ................................................281

Review: Sunflower ...........................................284

Review: Riddle ..................................................284

Getting Input from the User ................................285

Review: DivisibleBy3 .......................................287

Combo Boxes .........................................................288

Review: MetricConversion ..............................290

Changing Colors ................................................... 291

Adding Images ......................................................292

Review: Roll ......................................................294

Using Nested Classes to Handle Events ............295

Chapter 11 Case Study .........................................298

Review: BreakAPlate .......................................303

Chapter Summary ................................................304

Vocabulary .............................................................305

Java ..........................................................................306

Critical Thinking ...................................................307

Exercises .................................................................309

Chapter 12 – Files and Exception

Handling

What is a File? ........................................................ 311

The File Classes ..................................................... 311

Review: MyFile – part 1 of 2 ........................... 312

Handling Exceptions ............................................ 312

Review: MyFile – part 2 of 2 ........................... 313

The File Streams .................................................... 313

The FileReader and BufferedReader Classes .... 314

Review: Assignment ........................................ 315

Processing Numeric Data .................................... 316

Review: Stats – part 1 of 2 ............................... 317

The FileWriter and BufferedWriter Classes ...... 317

Review: Stats – part 2 of 2 ............................... 319

Object Serialization ............................................... 319

Review: Roster ..................................................322

Chapter 12 Case Study .........................................323

Review: LocalBank2 ........................................328

Chapter Summary ................................................ 329

Vocabulary .............................................................330

Java ..........................................................................330

Critical Thinking ................................................... 331

Exercises .................................................................332

Chapter 13 – Recursion and

Advanced Algorithms

Selection Sort .........................................................337

Sorting Objects ......................................................339

Review: ArrayListSort .....................................341

Insertion Sort .........................................................341

Review: ObjectsInsertionSort .........................343

Recursion ................................................................343

Review: RecursiveFactorial .............................345

Mergesort ...............................................................345

Review: ObjectsMergesort ..............................348

Binary Search .........................................................349

Review: SearchLocations ................................351

Review: ObjectsBinarySearch ........................ 352

Review: BinarySearch2 ...................................352

Depth-First Searching ..........................................352

Review: DetectColonies – part 1 of 3 .............356

Review: DetectColonies – part 2 of 3 .............356

Review: DetectColonies – part 3 of 3 .............356

Algorithm Analysis ..............................................356

Chapter Summary ................................................357

Vocabulary .............................................................358

Java ..........................................................................358

Critical Thinking ...................................................359

Exercises ................................................................. 361

Chapter 14 – Data Structures

The Stack Data Structure .....................................365

The Stack Class ......................................................366

Review: Stack2 ..................................................368

Review: Stack3 ..................................................369

The Queue Data Structure ...................................369

The Queue Class ................................................... 370

Review: Queue2 ................................................372

Review: Queue3 ................................................372

Table of Contents xv

The Linked List Data Structure ..........................373

The LinkedList Class ............................................ 374

Review: LinkedList – part 1 of 3 .................... 376

Review: LinkedList – part 2 of 3 .................... 376

Review: LinkedList – part 3 of 3 .................... 376

Chapter Summary ................................................377

Vocabulary .............................................................377

Critical Thinking ................................................... 378

Exercises ................................................................. 379

Appendix A – Unicode

Unicode ................................................................... 381

Index

Index .......................................................................383

xvi Table of Contents

Chapter 1 An Introduction to Computers 1

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This chapter discusses current computing technologies, networks, the

Internet, and the World Wide Web. Issues related to computers, including

privacy, viruses, and copyright are also discussed.

Desktop Computing

A desktop computer and its components are designed to fit on or under

a desk:

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• The physical components of the computer, such as the monitor and

system unit, are called hardware.

• Data and instructions are entered into the computer using input

devices, such as a keyboard, mouse, scanner, microphone, digital

camera, CD-RW/DVD drive, and disk drive.

• A PC becomes much more versatile when peripheral devices, such as

printers and scanners, are added. A peripheral device is attached

to a port on the computer. There are different types of ports, such

as serial, parallel, FireWire, USB, and Bluetooth ports.

• Computers process data into meaningful, useful information.

Processed data is conveyed using output devices. Monitors and

printers display data, CD-RWs, disk drives, and memory keys store

data, and speakers communicate audio output.

The base unit also contains the motherboard, which is the main circuit

board. The motherboard contains several components:

• Expansion boards are circuit boards that connect to the motherboard

to add functionality to the computer. Examples include sound

cards and video adapters.

TIP Desktop computers are

referred to as either PCs or

MACS.

Scanner

A scanner is an input device

that uses a laser to create a

digital image from artwork

such as photos and drawings.

The digitized image can then

be incorporated into an elec-

tronic document.

Printers

A laser printer uses a laser and

toner to generate characters

and graphics on paper. An ink

jet printer uses an ink cartridge

to place very small dots of ink

onto paper to create characters

and graphics.

Chapter 1

An Introduction to Computers

2 Chapter 1 An Introduction to Computers

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• The CPU (Central Processing Unit) or processor processes data

and controls the flow of data between the computer’s other units.

Within the CPU is the ALU (Arithmetic Logic Unit), which can

perform arithmetic and logic operations. It can also make com-

parisons, which is the basis of the computer’s decision-making

power. The ALU is so fast that the time needed to carry out a single

addition is measured in nanoseconds (billionths of a second). The

speed at which a CPU can execute instructions is determined by

the computer’s clock rate. The clock rate is measured in megahertz

(MHz, million of cycles per second) or gigahertz (GHz, billion of

cycles per second).

• A bus is a set of circuits that connect the CPU to other components.

The data bus transfers data between the CPU, memory, and other

hardware devices on the motherboard. The address bus carries

memory addresses that indicate where the data is located and

where the data should go. A control bus carries control signals. All

data flows through the CPU:

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• Memory in the form of integrated circuits (ICs) stores data

electronically. ROM (Read Only Memory) contains the most basic

operating instructions for the computer. The data in ROM is a

permanent part of the computer and cannot be changed. RAM

(Random Access Memory), also called primary or main memory,

is memory where data and instructions are stored temporarily.

Data stored in RAM can be written to secondary memory, which

includes any type of storage media, such as a floppy disk, hard

disk, memory key, or CD-RW. Secondary memory must be copied

into primary memory before it is processed by the CPU. SRAM

(Static Random Access Memory) is high-speed memory referred

to as cache (pronounced “cash”). This memory is used to store

frequently used data so that it can be quickly retrieved by an

application.

Operating Systems and Environment

A desktop computer also contains programs, or software. Operating

system (OS) software is run automatically when the computer is turned on

and is used to control processing and peripherals, run application soft-

ware, and control input and output, among other tasks. Desktop operating

system software includes Windows, Mac OS X Tiger, Unix, and Linux.

Each of these operating systems have different features and functions.

Applications software is written by programmers to perform a specific task,

such as a word processor.

The type of OS a computer can run depends on the computer hardware,

and can be multiuser, multiprocessing, multitasking, multithreading, or

Integrated Circuits

Integrated circuits, also called

chips, are created from silicon

wafers which are etched with

intricate circuits and coated

with a metallic oxide to allow

the circuits to conduct elec-

tricity. The silicon wafers are

housed in special plastic cases

that have metal pins. The pins

allow the integrated circuits

to be plugged into circuit

boards.

BIOS

BIOS (basic input/output sys-

tem) is firmware that contains

the computer’s start-up instruc-

tions. Firmware is instructions

or data that is written onto

ROM.

CPU Manufacturers

Intel and AMD are two proces-

sor manufacturers. Processors

are identified by a model name

or number, such as Pentium

4, Itanium

2, and Opteron™.

The Intel Pentium 4 (P4) CPU

has a clock rate of 3.06 GHz.

The AMD Opteron CPU has a

clock rate of 2.4 GHz. These

CPUs contain more than 40

million transistors on a single

chip.

Real-time Clock

A battery chip called a real-

time clock keeps track of the

date and time in a computer

even when the computer is

off.

Chapter 1 An Introduction to Computers 3

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real time. A multiuser OS is supported by mainframes and minicomputers

and allows for two or more users at the same time. The terms multiprocessing

and multitasking are often used interchangeably when referring to an

OS that allows for multiple applications (“processes” or “tasks”) to run

at the same time. This type of OS determines how to divide processor

time between running applications. A multiprocessing OS should not be

confused with a multiprocessing computer system, which has more than

one processor and performs parallel processing because the processors are

used simultaneously for multiprocessing. Multithreading refers to an OS

that can execute different parts of a single program, called threads, at the

same time. A real-time OS responds to input immediately. This type of

OS is used in situations where immediate feedback is required, such as

navigation systems or medical monitoring equipment.

Environment refers to a computer’s hardware and software configura-

tion. For example, a Windows XP environment means that the computer is

running the Windows XP Professional OS software and hardware includes

a 300MHz processor or better, 128MB of RAM or more, and at least 1.5GB

of hard disk space. The hardware requirements are based on what will

be needed to allow the OS software to properly manage the computer’s

tasks. The term platform is sometimes synonymous with environment.

Environment types vary widely and can refer to the computer type or

the way the user interacts with the computer as well as the software/hard-

ware configuration. A desktop environment refers to a desktop or notebook

computer running an OS designed for the typical hardware found in a

desktop or notebook computer. A multiuser environment is sometimes called

time sharing because each user gets a portion of the processor’s “time.”

A distributed environment shares the load of processing among several

computers. When discussing environments, a distinction is usually made

between multiprocessing and multitasking. A multiprocessing environment

means that more than one processor is being used for executing an appli-

cation, and a multitasking environment is one in which processing time for

multiple applications is divided among one processor. Most environments

run an OS with a graphical user interface (GUI):

Windows XP Operating System

Mainframes and

Supercomputers

A main fra me is a large

computer system that supports

multi-user applications and

tasks that require the storage

an d pr oce ssing of huge

amounts of information. Large

corporations, airlines, banks,

government agencies, and

universities use mainframes.

A supercomputer is the fastest

and most powerful type of

computer. Supercomputers

focus on executing a few

programs as fast as possible

and are used for weather

forecasting and nuclear energy

research.

TIP For information on a

specific operating system, refer

to the appropriate chapter at

Lvp.com.

4 Chapter 1 An Introduction to Computers

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The functions of an OS are based on the intended OS platform.

Functionality is implemented through utility programs that are written

as part of the OS. A utility program has one clearly defined task, unlike

an application which can usually perform many different tasks. Utility

programs are run by the OS to manage input and output, read and write

to memory, manage the processor, maintain system security, and manage

files and disks. One type of utility program, called a device driver, is needed

for printing, viewing graphics, using a CD/DVD drive, and using periph-

erals in general. Some utility programs load when the computer starts and

are called memory-resident because they are always in memory.

Features are added to an OS by incorporating utility programs to per-

form tasks that are in addition to the tasks required to run the computer.

For example, an OS intended for a desktop or notebook environment will

often include utilities for disk defragmentation, text narration and other

accessibility tools, and system restore and backup tools. For example:

Windows XP Utilities

Mobile Computing

Improved technology has allowed the miniaturization of computer

components and special long-lasting batteries. Computers now come

in many shapes, sizes, and with many levels of features. Among these

computers are notebooks, tablets, handhelds, smart phones, and wearables.

Because of their portability, these types of computers are classified as

mobile computing devices:

• A notebook computer is a portable, lightweight computer with a

CPU, memory, and hard disk space comparable to that of a typical

desktop computer.

• A tablet PC is a computer designed similar to a pad of paper and

a pencil. Users simply “write” on a screen with a device called a

stylus that is shaped like a thin pencil. Handwriting recognition

software is used to interpret a user’s handwriting. A keyboard can

also be attached.

Bluetooth

Blue t o o t h i s a wire less

technology used to allow

mobile computing devices to

communicate.

utility program

memory-resident

Chapter 1 An Introduction to Computers 5

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• Handheld computers, also called PDAs, are palm-sized and contain

applications for storing contact information, schedules, lists, and

games. Handhelds come with a stylus for input and have a screen

that is several inches vertically. Many types of application software

have been written for handhelds, including spreadsheets and word

processors. Some handhelds recognize handwriting, have a built-in

keyboard, include a cellular phone, and provide Internet access.

• Smartphones are cellular phones that are able to send and receive

e-mail messages and access the Internet. Some smartphones have

digital camera, MP3 player, and color display capabilities.

• Wearable computers vary greatly in size and application. MP3 play-

ers have been incorporated into clothing, and one type of wearable

computer includes voice recognition. Wearable computers are also

in the form of goggles, which incorporate a monitor, digital camera,

ear bud, and microphone. Wrist-top computers are worn like a tra-

ditional wrist watch and work as a pager, provide Internet access,

and contain other features usually found in a handheld PC.

One issue involved with using so many types of PCs is cross-platform

connectivity, which is the ability for one type of PC to link to and share

data with a different type of PC. Notebook and desktop PCs typically have

good cross-platform connectivity because their file formats can be used on

either computer. Tablets and handhelds use a different OS and generate

different file formats, requiring special hardware and software to use their

files on a desktop or notebook PC. Wearable computers typically have a

cable that allow a connection to other types of PCs, but special software

must be used to communicate between the devices.

Programming Languages

A programming language is a set of words, codes, and symbols that allow

a programmer to give instructions to the computer. Many programming

languages exist, each with their own rules, or syntax, for writing these

instructions.

Programming languages can be classified as low-level and high-level

languages. Low-level programming languages include machine language

and assembly language. Machine language, which is referred to as a first

generation programming language, can be used to communicate directly

with the computer. However, it is difficult to program in machine language

because the language consists of 0s and 1s to represent the status of a

switch (0 for off and 1 for on). Assembly language uses the same instruc-

tions and structure as machine language but the programmer is able to

use meaningful names or abbreviations instead of numbers. Assembly

language is referred to as a second generation programming language.

High-level programming languages, which are often referred to as third

generation programming languages (3GL), were first developed in the late

1950s. High-level programming languages have English-like instructions

and are easier to use than machine language. High-level programming

languages include Fortran, C, Basic, COBOL, and Pascal. In order for the

computer to understand a program written in a high-level language, pro-

grammers convert the source code into machine language using a compiler

or an interpreter. A compiler is a program that converts an entire program

Fourth and Fifth

Generation Languages

Fourth generation languages

(4GL), such as SQL, have

higher English-like instructions

than most high-level languages

and are typically used to access

databases. Fifth generation

languages are used for artificial

intelligence.

Handheld Computers

Handheld computers are

widely used in occupations

that require constant travel,

such as parcel delivery, meter

reading, and sales.

cross-platform connectivity

6 Chapter 1 An Introduction to Computers

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into machine code before the program is executed. An interpreter translates

and executes an instruction before moving on to the next instruction in

the program.

In the 1980s, object-oriented programming (OOP) evolved out of the need to

better develop complex programs in a systematic, organized approach. The

OOP approach allows programmers to create modules that can be used

over and over again in a variety of programs. These modules contain code

called classes, which group related data and actions. Properly designed

classes encapsulate data to hide the implementation details, are versatile

enough to be extended through inheritance, and give the programmer

options through polymorphism. Object-oriented languages include Java,

C++ and Visual Basic .NET.

Networks

A network is a combination of hardware and software that allows

computers to exchange data and share software and devices, such as

printers. Networks are widely used by businesses, universities, and other

organizations because a network:

• allows users to reliably share and exchange data

• can reduce costs by sharing devices such as printers

• offers security options including password protection to restrict

access to certain files

• simplifies file management through centralized software updates

and file backups

• provides e-mail for network users

Networks are classified by their size, architecture, and topology. A

common size classifications is LAN (Local-Area Network), which is a

network used to connect devices within a small area such as a building or

a campus. A WAN (Wide-Area Network) is used to connect devices over

large geographical distances. A WAN can be one widespread network or

it can be a number of LANs linked together.

The computers and other devices in a LAN each contain an expansion

card called a network interface card:

Network interface card

MAN and HAN

A MAN (Metropolitan Area

Network) and a HAN (Home

Area Network) are network

technologies classified by the

size of a network. A MAN is a

high-speed network that typi-

cally connects LANs within a

city or town. A HAN is used

to connect personal devices

within the home.

interpreter

object-oriented programming

Chapter 1 An Introduction to Computers 7

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A cable plugs into the adapter card to connect one device to another to

form a LAN. Cables are not required for network cards that have wireless

capabilities. Network interface cards are available for desktop and mobile

computers and take various other forms including an adapter card, a PC

card, or a Flash memory card

Along with the physical, or hardware, aspects of setting up a network,

there is also the software aspect. A network operating system is software that

allow users and devices to communicate over the network. A networked

environment refers to a set of networked computers running an OS that can

handle the communication between the computers. The operating system

installed must be capable of supporting networking functions, such as

security access features and support for multiple users. Operating systems

capable of network functions are available for Linux, Windows, Unix, and

Mac. The network architecture, discussed next, must also be considered

when choosing a network OS.

Network architecture includes the type of computers on the network and

determines how network resources are handled. Two common models are

peer-to-peer and client/server. In a peer-to-peer network, each computer on

the network is considered equal in terms of responsibilities and resource

sharing. A client/server network consists of a group of computers, called

clients, connected to a server. A server is a computer with more RAM, a

larger hard disk, and sometimes multiple CPUs that is used to manage

network functions.

Physical topology refers to the arrangement of the nodes on a network.

A node is a location on the network with a device capable of processing

information, such as a computer or a printer. There are three common

physical topologies:

• The bus topology is a physical LAN topology that uses a single cen-

tral cable, called the bus or backbone to attach each node directly:

LAN using a bus topology

Ethernet

The Ethernet LAN protocol was

developed by Bob Metcalfe in

1976. Ethernet uses a bus or

star topology with twisted-

pair wiring, coaxial cable,

or fiber optic cable transmis-

sion media. Newer protocols

include Fast Ethernet, which

operates at 100 Mbps, Gigabit

Ethernet which operates at

1 Gbps, and 10G Ethernet,

which operates at 10 Gbps.

Transmission Media

Computers must be con-

nected in order to transmit

data between the nodes. Cable

transmission media includes

twisted-pair wiring, coaxial

cable, and fiber optic cable.

Wireless transmission media

includes infrared signals,

broadcast radio, cellular radio,

microwaves, and communica-

tions satellites.

The amount of data and the

speed at which data can travel

over a media is called band-

width, which is measured in

bits per second (bps). Each

transmission media has a spe-

cific length or range restric-

tion, data transmission rate,

and cost.

8 Chapter 1 An Introduction to Computers

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• In a star topology, each node is attached to a hub, which is a device that

joins communication lines at a central location on the network:

LAN using a star topology

• In a ring topology, each node is connected to form a closed loop.

A LAN with a ring topology can usually cover a greater distance

than a bus or star topology:

LAN using a ring topology

• Wireless networks use high frequency radio waves or infrared sig-

nals instead of cables to transmit data. A router/wireless access

point device is used to allow nodes to transfer data wirelessly.

Another type of topology is logical topology, which refers to the way data

is passed between the nodes on a network. A LAN’s logical topology is

not always the same as its physical topology.

Baseband and

Broadband Technology

Most LANs use baseband

technology which means the

transmission media carries one

signal at a time. Broadband

technology allows for data

transmission of more than one

signal at a time and is found in

cable television transmission.

Wi-Fi

Wi-Fi (Wireless Fidelity) is

a term used to describe an

802.11 network, which is a

specification or protocol for

wireless networks.

logical topology

Chapter 1 An Introduction to Computers 9

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Network users are given a user name and password to log on to a

network through a computer connected to the network. Users are also

assigned a level of access to maintain security. Network users should

follow a certain etiquette referred to as netiquette:

• Do not attempt to access the account of another user without

authorization.

• Do not share your password, and change it periodically.

• Use appropriate subject matter and language, and be considerate

of other people’s beliefs and opinions.

Number Systems

The electrical circuits on an IC have one of two states, off or on. Therefore,

the binary number system (base 2), which uses only two digits (0 and 1), was

adopted for use in computers. To represent numbers and letters, a code

was developed with eight binary digits grouped together to represent a

single number or letter. Each 0 or 1 in the binary code is called a bit (BInary

digiT) and an 8-bit unit is called a byte.

Our most familiar number system is the decimal, or base 10, system. It

uses ten digits: 0 through 9. Each place represents a power of ten, with

the first place to the left of the decimal point representing 10

, the next

place representing 10

, the next 10

, and so on (remember that any number

raised to the zero power is 1). In the decimal number 485, the 4 represents

4×10

, the 8 represents 8×10

, and the 5 represents 5×10

. The number 485

represents the sum 4×100 + 8×10 + 5×1 (400 + 80 + 5):

Decimal Base 10 Equivalent

485 4×10

+ 8×10

+ 5×10

= 400 + 80 + 5

The binary, or base 2, system works identically except that each place

represents a power of two instead of a power of ten. For example, the

binary number 101 represents the sum 1×2

+ 0×2

+ 1×2

or 5 in base ten.

Some decimal numbers and their binary equivalents are:

Decimal Binary Base 2 Equivalent

0 0 = 0×2

+ 0×2

= 0×2 + 0×1 = 0 + 0

1 1 = 0×2

+ 1×2

= 0×2 + 1×1 = 0 + 1

2 10 = 1×2

+ 0×2

= 1×2 + 0×1 = 2 + 0

3 11 = 1×2

+ 1×2

= 1×2 + 1×1 = 2 + 1

4 100 = 1×2

+ 0×2

= 1×4 + 0×2 + 0×1 = 4 + 0 + 0

The hexadecimal system is used to represent groups of four binary

digits. The hexadecimal, or base 16, system is based on 16 digits: 0 through

9, and the letters A through F representing 10 through 15 respectively.

Each place represents a power of sixteen. For example, the hexadecimal

number 1F represents the sum 1×16

+ 15×16

. Some decimal numbers and

their hexadecimal equivalents are:

Decimal Binary Hexadecimal Base 16 Equivalent

0 0000 0000 0 = 0×16

= 0×1 = 0

10 0000 1010 A = 10×16

= 10×1 = 10

25 0001 1001 19 = 1×16

+ 9×16

= 1×16 + 9×1 = 16 + 9

30 0001 1110 1E = 1×16

+ 14×16

= 1×16 + 14×1 = 16 + 14

binary number system

bit

byte

base 10

base 2

base 16

netiquette

10 Chapter 1 An Introduction to Computers

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For clarity, a non-base 10 number should have the base subscripted after

the number. For example, to show the difference between 100 in base 10

and 100 in base 2 (which represents 4), the base 2 number should be writ-

ten as 100

Every letter of an alphabet (Latin, Japanese, Cherokee, and so on) and

symbols of every culture (=, @, ½, and so on) have been given a representa-

tion in a digital code called Unicode. Unicode uses a set of sixteen 1s and 0s

to form a 16-bit binary code for each symbol. For example, the uppercase

letter V is Unicode 00000000 01010110, which can be thought of as the base

10 number 86 (86

). Lowercase v has a separate code of 00000000 01110110,

or 11810.

Storing Data in Memory

Computer memory is measured in bytes. For example, a computer might

have 512MB of RAM. In computers and electronics MB stands for megabytes

where mega represents 2

or 1,048,576 bytes and GB stands for gigabytes,

which is 2

or 1,073,741,820 bytes.

Data stored in memory is referred to by an address. An address is a

unique binary representation of a location in memory. Therefore, data

can be stored, accessed, and retrieved from memory by its address. For

data to be addressable in memory, it must usually be at least one byte in

length. For example, to store JIM in memory each character is converted

to Unicode and stored in two bytes of memory with each memory location

designated by its address:

Because JIM is a character string, it will probably be stored in adjacent

memory addresses.

Bits grouped in units of 16 to 64 (2 to 8 bytes) are called words. Data

stored in a word is also located by an address. The size of a word depends

on the computer system.

The binary representation of an integer number is usually stored in four

bytes of memory. Because an integer is stored in four bytes, the range of

integers that can be stored is –2,147,483,648 to 2,147,483,647. An overflow error

occurs when the number of bits that are needed to represent the integer is

greater than the size of four bytes.

Real numbers, also called floating point numbers, are numbers that contain

decimal points. The binary representation of a real number is usually 4 to

8 bytes of memory. The binary number 111.10 is equivalent to the real deci-

mal number 7.5 and is stored in memory as the binary number 0.11110×2

In this form, the bits that represent the mantissa (fractional part) are stored

in one section of a word and the exponent, in this example 3 (11

), is stored

in another section of the word:

ASCII and EBCDIC

ASCII (American Standard

C o d e f o r I n f o r m a t i o n

Interchange) and EBCDIC

( Ex tended Binary Coded

Decimal Interchange Code)

are two other digital coding

schemes. Unlike Unicode,

ASCII and EBCDIC are not

large enough to support Asian

and other languages that use a

different alphabet.

words

overflow error

real numbers

mantissa

exponent

Chapter 1 An Introduction to Computers 11

sample

The overflow problem discussed for integers can also occur in real

numbers if the part of the word storing the exponent is not large enough.

A roundoff error occurs when there are not enough bits to store the

mantissa.

What is a File?

A file is related data stored on a persistent media. A file can be an appli-

cation (program) or the product of an application. For example, a word

processor application is used to create document files. As another example,

a digital camera is used to create photo files. A file is stored on a persistent

media so that it is retained even after the computer or computerized device

is turned off. A file can be used over and over again whenever the data it

stores is needed.

A file is really just 1s and 0s because it is stored in binary code. Computers

are programmed to translate bytes and words into symbols. Depending

on the file type, these symbols are either human-readable or computer-

readable after translation. Human-readable files are called text files, and

computer-readable files are called binary files. Simple files, such as a text

document, can be measured kilobytes, for example 64K. The K comes from

the word kilo and represents 2

or 1,024. Therefore, a 64K file uses 65,536

bytes (64×2

) of storage.

File types are distinguished by the extension that comes after the file

name. An application adds a unique extension to the files it creates. For

example, MyResume.doc is a document file type. A DOC file is a binary file

created by Microsoft Word. Executables are EXE files and are also binary

files. A file named TestData.txt is a plain text file. A TXT file contains

only letters, numbers, and common symbols readable by humans. Folders

are used to organize commonly related files.

Binary files are more complex than text files and often contain data for

photos, formatted text, spreadsheets, sound, and so on. The disadvantage

of binary files is that they require another application to interpret the

contents. A binary file may have content similar to:

ÿÿñU_ÿÿþ}9UTýÿ–÷}]Ï_ñÿÑßÿÿý�ÿ×_ÿ÷Äõÿ

ÿ ÿ ð – U _ ÿ ÿ w u s U U ü w ] U/ U _ ñ ÿ U W w w t w w U W w w D õ ÿ

þ»ÿÿúªî¿þÿþûïûüÿ¾þïìÿ

þÿÿï¿¿ÿïìôÿ UÿÿüET_ÿÿ÷wìÿ–þ»ÿÞþïýÿþøÿ¯ÿëÿúþÿ«ºòÿþýÿûÿûèôÿ

ÿÝþ_ÿÿ�ÿwþuUuWýw÷÷ÿ{þÿß¿ß÷ÿuWwwu÷uuUUwwDõÿþ»ÿÌ®è�lïÿþ

>«~ï®¿þÿ

ýUÝUUÕ]UU]UÕ]Õ]æÝDôÿ¿Îÿàôÿøÿ

ßýÕW_ý_õW_ÕÕ]uåÿDõÿþ¿óÿïþÿÿþáÿèôÿøwÿuþWuWUUwWþUåwDõ

ÿþ

A binary file is computer-readable

roundoff error

TIP The original form the file

is saved in is referred to as the

native format.

File Size Limitations

File size can be decreased

o r c o m p r e s s e d u s ing a

compression program, such

as WinZip. This technique is

often used to accommodate

storage device and e-mail

account limitations.

Extensions

Common extensions include:

.xls - Excel file

.class - Compiled Java file

.java - Java file

.zip - compressed file

.gif - GIF image file

.bmp - Bitmap graphic

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Storage Devices

Storage devices use a persistent media to maintain files. These devices,

which are also referred to as drives, mass storage, and auxiliary storage, can

be categorized in three ways:

• internal or external

• removable or permanent media

• magnetic, optical, or solid state technology

Internal devices are drives mounted inside the PC case. These devices

can include hard disk, CD/DVD, disk, tape, Zip, and Jaz drives. Except for

the Iomega

RRD (Removable Rigid Disk) system, which uses a removable

media, hard drives typically have permanently installed disks that are not

accessible from outside the PC case. Other devices have an external slot

for removable storage media.

External devices have a stand-alone drive housing and connect to a

computer’s USB port with a cable. USB (Universal Serial Bus) is a standard-

ized technology with data transfer rates up to 480 Mbs. As many as 127

devices can be connected to a single port with USB hubs.

External drives offer the advantage of portability because they can be

easily moved to other computers that support the technology. External

devices include hard disk, RRD, CD/DVD, diskette, tape, Zip, and Jaz

drives. Except for the hard disk drive, these drives have removable

media.

Ultra-portable devices include keychain, watch, mini drive, and mouse

storage to name just a few. These external devices are small and easy-to-

use, but currently more expensive than comparable storage devices that

are larger in size. Most ultra-portable devices, including the keychain and

mini drive, have storage media attached directly to a USB plug that is con-

nected to a USB port. The watch and mouse storage devices use a cable

with a USB plug to connect to a USB port. The watch has a short cable and

USB plug hidden in the band. The mouse storage device requires a longer

cable so that it can also function as a pointing device.

Storage device technologies determine the media, size, and portabil-

ity of a device. Magnetic technology uses a mechanical drive with tiny

electromagnetic heads for reading and writing data to media. The media

required with magnetic technology is a disk, usually made of aluminum or

Mylar®, coated with iron oxide. The disk is either encased in hard plastic

(floppy diskette and Zip) or several disks, called platters, are sealed in a

case (Jaz, RRD, and hard disk). A data signal sent through the heads in

the drive magnetize a bit of the media in one direction to store a 1 and in

the other direction to store a 0.

Optical technology uses a drive with a laser and an optoelectronic sen-

sor. The media required with optical technology is a compact disc made

of polycarbonate plastic. A CD-R (CD-Recordable) disc is used for stor-

ing files. CD-Rs are coated with a reflective organic compound and then

sealed with a plastic layer to protect the reflective layer from scratches.

The laser in the drive is focused on a bit of the CD-R to darken, or “burn,”

the organic compound to store a 1. The areas of the CD-R left unburned

are read as bits storing a 0.

Firewire

Using the IEEE 1394 standard,

a FireWire port allows devices

to quickly trans fer large

amounts of data (greater than

400Mbs). FireWire is often

used for digital video cameras

and sometimes external hard

drives because of the amount

of data associated with these

devices. FireWire devices can

be daisy-chained together,

which means one device

is connected to another’s

FireWire port and that device

is connected to another and so

on. FireWire also supports iso-

chronous mode for real-time

data transfer.

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Another application of optical technology is the DVD drive, which

uses a DVD-R disc, similar to a CD-R. The DVD-R (Digital Video Disc-

Recordable) can store much more data than a CD-R because of the preci-

sion used in manufacturing the drive and the DVD-R itself. Bits are much

smaller and stored much more closely together on the DVD-R.

Solid state technology allows for the smallest, most portable storage

devices because the technology requires no moving parts. The media is

Flash memory, which consists of a grid with two tiny transistors at each

cell. Each cell corresponds to a bit. Applying a charge to a cell stores a

0, while applying a stronger charge stores a 1. The grid of transistors is

encased in hard plastic and is very small. Some devices can store 2MB or

more within a package thinner and smaller than a quarter. Slightly larger

media can store gigabytes of data. Encased media is often directly attached

to a USB plug for use with a computer, or simply has conductive material

imprinted so the media can slide into a digital camera slot.

Magnetic technology allows for storage devices that range in capacity from

1.44MB (a floppy diskette) to many gigabytes (hard disk drives with many

platters). Optical technology includes CDs that can store about 700MB of

data, while DVDs can store at least 4GB of data. Solid-state devices store

from 64KB of data to many gigabytes.

Storage media can be very sensitive. Care should be taken to avoid

damaging files:

• Never attempt to open a case containing a disk.

• Keep magnetic media away from magnets.

• Handle CD/DVDs by the center hole or by the edges.

• Never bend CD/DVDs or other flexible media.

• Store CD/DVDs in a jewel case or sleeve to prevent scratches.

• Keep media away from moisture and extreme temperatures.

Intranet, Extranet, Internet

An intranet is a network that is used by a single organization, such as

a corporation or school, and is only accessible by authorized users. The

purpose of an intranet is to share information. However, a firewall is also

used to lock out unauthorized users. A firewall is a network security system

that prevents unauthorized network access.

An extranet extends an intranet by providing various levels of acces-

sibility to authorized members of the public. For example, a corporation

may extend their intranet to provide access to specific information, such

as their ordering system, to registered customers.

The largest and most widely accessed network is the Internet, a world-

wide network of computers that is not controlled by any one organization.

The Internet has had an undeniable impact on modern society because it

allows users worldwide to communicate in a matter of seconds.

Tera, Peta, Exa

As more and more data is

stored electronically, file sizes

become very large and require

storage devices with very large

capacities. TB (terabyte) is 2

bytes or 1 trillion bytes, pet-

abyte (PB) is 2

bytes or 1,024

terabytes, and EB (exabyte) is

bytes or 1,024 petabytes.

Devices with TB storage

capacities are gradually com-

ing into use, especially for

database files.

firewall

storage media care

History of the Internet

The Internet evolved from

ARPANET, a network cre-

ated in the late 1960s by the

Department of Defense’s

ARPA (Advanced Research

Projects Agency), and the

theory of open architecture

networking.

Storage Media

The capacity of storage media

varies. For example, a disk has

a storage capacity of 1.44 MB,

a CD has a storage capacity

of 650 MB, and a DVD has a

storage capacity of over 4GB.

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The Internet is actually numerous networks all linked together through

routers. A router is a device that connects different network technolo-

gies. Networks connected to routers use TCP/IP (Transmission Control

Protocol/Internet Protocol) software to communicate.

Computers on the Internet are either servers or clients. The client is sent

information from a server. The client/server structure of the Internet is

called interactive because the information accessed is a result of selections

made by the user. For example, a computer with just minimal software

for accessing the Internet is a client. The client user selecting options from

the Internet is receiving the information from a server, a computer with

additional software and files that is also connected to the Internet.

Telecommunications

Telecommunications is the transmitting and receiving of data. Data can be

in various forms including voice and video. Telecommunications requires

a modem or adapter and a line or cable. The speed of data transmission

(sending) and receipt (receiving) is measured in Kbps (thousands of bits

per second) or Mbps (millions of bits per second). Numerous telecommu-

nications options are available, which vary in speed and cost:

• A conventional modem uses standard telephone lines to convert

analog signals to digital data. A conventional modem is a 56 Kbps

modem, which transmits data at 28.8 Kbps and 36.6 Kbps, and

receives data at 56 Kbps. Home computers sometimes use a con-

ventional modem.

• A DSL (Digital Subscriber Line) modem uses standard telephone

lines with data transmission up to 640 Kbps. Data receipt is from

1.5 Mbps to 9 Mbps. A DSL (Asymmetric DSL) is the most common

form used.

• A cable modem transmits data through a coaxial cable television

network. Data transmission is from 2 Mbps to 10 Mbps and data

receipt is from 10 Mbps to 36 Mbps.

• Leased/Dedicated lines are used by many businesses and schools

for Internet access. They allow for a permanent connection to the

Internet that is always active. The cost of a leased line is usually a

fixed monthly fee. A T-1 carrier is a type of leased line that trans-

mits data at 1.544 Mbps.

• ISDN (Integrated Services Digital Network) is a digital telephone

network provided by a local phone company. ISDN is capable of

transmitting and receiving data at up to 64 Kbps. ISDN requires

the use of an ISDN terminal adapter instead of a modem.

TIP In a wireless network, a

router/wireless access point is

typically connected by a cable

to a cable or DSL modem.

TIP Access to the Internet

requires telecommunications

and the use of an Internet

Service Provider (ISP).

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Internet Services: Web, E-mail, and

Mailing Lists

Internet services include the World Wide Web, e-mail, and mailing lists.

The World Wide Web (WWW), also called the Web is the most widely used

Internet service. The Web can be used to search and access information

available on the Internet. A web browser application, such as Microsoft

Internet Explorer, provides a graphical interface to present information

in the form of a website:

A web page that is part of the New York Times website

Another widely used Internet service is e-mail or electronic mail, which

is the sending and receiving of messages and computer files over a com-

munications network, such as a LAN (Local Area Network) or the Internet.

E-mail can be received in a matter of seconds, even if the recipient is

located half way around the world.

An e-mail address is required in order to send and receive e-mail mes-

sages. E-mail addresses are provided when you sign up with an ISP or an

online service. A typical e-mail address is similar to:

E-mail software is also required for sending and receiving e-mail mes-

sages. Examples of e-mail software include Outlook, Outlook Express,

and Eudora. Browser-based e-mail only requires a web browser and is

available through sites such as Yahoo! and Hotmail.

World Wide Web

web browser

Blog

Blog is short for weblog and is

a type of website where users

can post entries in a journal

format.

Instant Messaging

Instant messaging is a com-

munication tool that allows

for real time or immediate text-

based communication.

Digital Signature

A digital signat ur e is a

code that is attached to an

electronic message to verify

the authenticity of a website

or e-mail message.

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Certain rules should be followed when composing e-mail messages

• Use manners. Include “please” and “thank you” and also properly

address people you do not know as Mr., Ms., Mrs., Dr., and so on.

• Be concise.

• Be professional, which includes using the proper spelling and

grammar.

• Re-read a message before it is sent. Always fill in the To box last to

avoid sending a message before it is complete.

E-mail messages are not private. An e-mail message goes through sev-

eral mail servers before it reaches the recipient, making it easily accessible

for others to read. Therefore, sending e-mail messages requires following

a certain etiquette:

• Send messages through your account only.

• Use appropriate subject matter and language.

• Be considerate of other people’s beliefs and opinions.

When sending e-mail at work or school, it is important to remember

that employers and school administrators have the right to read any e-mail

messages sent over the corporate or school network, as well as the right to

track online activity.

A mailing list server is a server that manages mailing lists for groups of

users. Two mailing list servers are Listserv and Majordomo. Often users

subscribe to mailing lists for discussion purposes. When a subscriber posts

a message to a mailing list server, every subscriber receives a copy of the

message. Subscribers are identified by a single name or e-mail address.

Finding Information on the Web and

Downloading Files

A search engine is a program that searches a database of web pages for

keywords and then lists hyperlinks to pages that contain those keywords.

Commonly used search engines include:

Yahoo! (www.yahoo.com)

Google (www.google.com)

MSN (www.msn.com)

AOL (www.aol.com)

Excite (www.excite.com)

Ask Jeeves (www.ask.com)

Overture (www.overture.com)

Lycos (www.lycos.com)

WebCrawler (www.webcrawler.com)

FAST Search (www.alltheweb.com)

About.com (www.about.com)

AltaVista (www.altavista.com)

Looksmart (www.looksmart.com)

Search Engines

A search engine usually works

by sending out an agent,

such as spider. A spider is an

application that gathers a list

of available web page docu-

ments and stores this list in a

database that users can search

by keywords.

When displaying information,

search engines often show

“Sponsored Sites Results” first.

These are sites that contain the

information being searched

for but have paid the search

engine to list their sites at the

top of the list.

E-mail Protocols

POP3 is an e-mail protocol

that connects to an e-mail

server to download messages

to a local computer.

IMAP is an e-mail protocol that

connects to an e-mail server

to read message headers and

then the user selects which

e-mail messages to download

to a local computer.

HTTP is used as an e-mail pro-

tocol when a web page is used

to access an e-mail account.

Spam

Along with personal and

business messages, most

people also receive a lot of

“junk e-mail” or spam. Most

e-mail sof tware includes

features to filter and block

messa ges f r o m s p e cif ic

senders.

Chapter 1 An Introduction to Computers 17

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A search engine can be queried to display specific web pages. Search criteria

can include single words or phrases that are then used by the engine to

determine a match. A match is a web page that contains the search criteria.

Surrounding phrases with quotation marks finds web pages that contain

the entire phrase. The more specific the search criteria, the better the

chance the information will be found.

Most searches yield far too many matches to be useful. Limiting the

number of matches to a reasonable number can usually be accomplished

by using Boolean logic in the search criteria:

• The + (plus sign) is used in search criteria to limit a search to only

Web pages that contain all of the specified words. For example, a

search for florida +hotel or florida hotel returns only links to pages

containing both words. AND can be used in place of + in most

search engines.

• OR can be used in most search engines to find Web pages that

contain any one of the words in the criteria. For example, the cri-

teria florida OR hotel returns links to pages containing either of

the words.

• The – (minus sign) is used to exclude unwanted Web pages. For

example, the search for shakespeare –play returns hyperlinks to

pages containing the word shakespeare, but eliminates pages that

also contain the word play. NOT can be used in place of – in most

search engines.

Some search engines provide a subject tree, or web directory, which is a

list of sites separated into categories. The term subject tree is used because

many of the categories “branch” off into subcategories. These subcategories

allow the user to narrow down the subject and display a list of appropriate

hyperlinks, which are at the lowest level of the tree.

Information on a website is sometimes in the form of a downloadable

file. Downloading is the process of copying a file from a website to the

user’s computer. For example, virus definitions can be downloaded from a

antivirus software company’s website and software updates can be down-

loaded from the software company’s website. When a file is downloaded,

the user specifies where the file should be saved on the local computer.

Files should only be downloaded from known, authentic websites since

downloadable files are often associated with viruses.

If information from a website is to be referenced or quoted in a report,

essay, or other document, a citation must be used to give credit to the

original author and allow the reader to locate the cited information. A

widely accepted form for citation is published by the Modern Language

Association (MLA) in its publication MLA Handbook for Writers of Research

Papers, Fourth Edition.

In general, a citation for material located at a website should look similar

to:

Author's Last Name, First Name MI. Site Title. Access date.

Organization name. <URL>.

A citation of a personal website could look similar to:

Rawlings, Julie. Home page. 23 Dec. 2006. <http://www.

lpdatafiles.com/jrawlings/index.htm>.

Boolean Logic

Boolean logic uses three

logical operators:

AND locates pages that

include both words

OR locates pages that include

one word or the other or both

NOT locates pages that

include the first word, but not

the second word

A boolean expression always

evaluates to TRUE or FALSE

with pages that match the

search condition evaluating to

TRUE.

MLA

TIP Just because a file is

available on a website for

download does not mean that

it is legal to download the file.

Downloading copyrighted

files that have not been made

freely available is a violation of

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A citation of an article in an online magazine could look similar to:

Schiffman, Paula. "Making Vinegar at Home." Vinegar

Monthly. 4 May 2006. <http://www.lpdatafiles.com/

vinegarassoc/journal.asp>.

A citation of a posting to a discussion list could look similar to:

Cruz, Anthony. "Are Orchestras Going Downhill?" online

posting. 10 Oct. 2006. Tuscon Annual Ballet Conf.

<http://www.lpdatafiles.com/tuscontoes/downhill.txt>.

Internet Privacy Issues

The growth of the Internet has caused additional concerns about

personal privacy. Searching for information on the Internet is not as

anonymous as it might seem.

The collection of data about consumers visiting a website is a marketing

technique known as online profiling. When a commercial website is visited,

information about the user may be collected using various methods such

as cookies or web beacons.

A cookie is a text file created by the server computer when a user enters

information into a website. The cookie file is then stored on the user’s

computer and accessed each time the user visits that website. Cookies

are often created when online purchases are made. Although cookies can

only store information that the user has selected or entered, their use has

raised concerns over privacy issues.

Web beacons, also called web bugs or pixel tags, are tiny, transparent

graphics located on web pages or in e-mail messages that are used in

combination with cookies to collect data about web page users or e-mail

senders. Usually the monitoring is done by an outside advertising company.

The information a web beacon collects includes the IP address of the

computer, the URL being visited, the time the web page was viewed, the

type of browser being used, and the cookie file.

Before providing a company with personal information through a

website, check the site’s privacy policy. A privacy policy is a legally binding

document that explains how any personal information will be used.

The Internet has opened up access to many files that were previously

inaccessible. To protect both the privacy of an individual and the accuracy

of data stored about individuals, several laws have been passed:

• The Electronic Communications Privacy Act of 1986 (ECPA)

makes it a crime to access electronic data without authorization.

It also prohibits unauthorized release of such data.

• The Electronic Freedom of Information Act of 1996 (E-FOIA)

requires federal government agencies to make certain agency

information available for public inspection and is designed to

improve public access to agency records by making more informa-

tion available online.

• The Children’s Online Privacy Protection Act of 1998 (COPPA)

requires commercial websites that collect personal information

from children under the age of 13 to obtain parental consent.

Spyware

Spy ware is sof tware that

uses the Internet to gather

personal information from an

unsuspecting user. Spyware

is unknowingly downloaded

and installed with another file,

such as freeware or shareware

programs.

TIP A website’s privacy policy

is typically found as a link at

the bottom of the home page

of a website.

NET Act

The NET (No Electronic Theft)

Act of 1997 closed a loophole

in the law which allowed copy-

righted material to be given

away on the Internet without

any legal penalty.

IP Address

An IP address is an identifier

for a computer or device on a

TCP/IP network.

Chapter 1 An Introduction to Computers 19

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• The Safety and Freedom through Encryption Act of 1999 (SAFE)

gives Americans the freedom to use any type of encryption to

protect their confidential information.

Other laws have been passed that may invade the privacy of some to

protect the safety of others. For example, the Provide Appropriate Tools

Required to Intercept and Obstruct Terrorism (PATRIOT) Act of 2001

gives law enforcement the ability to monitor individual’s e-mail and web

activity.

Internet Acceptable Use Policy

Internet content, unproductive use, and copyright have prompted many

schools and businesses to develop an Acceptable Use Policy or Internet

Use Agreement. Acceptable Use Policies typically contain rules similar

to:

• Use appropriate language.

• Do not reveal personal address or phone numbers.

• Do not access, upload, download, or distribute inappropriate

materials.

• Do not access another user’s account.

• Use of the network for private business is prohibited.

• Only administrator installed software may be used on the com-

puters. Adding, deleting, or modifying installed software is not

permitted.

The Social and Ethical Implications of

Computer Use

The society in which we live has been so profoundly affected by

computers that historians refer to the present time as the information age.

This is due to the our ability to store and manipulate large amounts of

information (data) using computers. As an information society, we must

consider both the social and ethical implications of our use of computers.

By ethical questions we mean asking what are the morally right and wrong

ways to use computers.

Ergonomics is the science that studies safe work environments. Many

health-related issues, such as carpal tunnel syndrome and computer vision

syndrome (CVS) are related to prolonged computer use.

Power and paper waste are environmental concerns associated with

computer use. Suggestions for eliminating these concerns include recycling

paper and printer toner cartridges and turning off monitors and printers

when not in use.

Employee monitoring is an issue associated with computers in the work-

place. It is legal for employers to install software programs that monitor

employee computer use. As well, e-mail messages can be read without

employee notification.

Encryption

Encryption is the process of

translating data into a code that

is not readable without the key

to the code. Encryption pre-

vents unauthorized access to

the data. Data that is encrypted

is referred to as cipher text.

Internet Filtering

Software

Many schools and organiza-

tions install Internet filtering

software to block offensive

material.

ergonomics

information age

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As discussed in a previous section in the chapter, the invasion of privacy

is a serious problem associated with computers. Because computers can

store vast amounts of data we must decide what information is proper to

store, what is improper, and who should have access to the information.

Every time you use a credit card, make a phone call, withdraw money,

reserve a flight, or register at school, a computer records the transaction.

These records can be used to learn a great deal about you—where you have

been, when you were there, and how much money was spent. Should this

information be available to everyone?

Computers are also used to store information about your credit rating,

which determines your ability to borrow money. If you want to buy a car

and finance it at a bank, the bank first checks your credit records on a

computer to determine if you have a good credit rating. If you purchase

the car and then apply for automobile insurance, another computer will

check to determine if you have traffic violations. How do you know if

the information being used is accurate? The laws listed below have been

passed to help ensure that the right to privacy is not infringed by the

improper use of data stored in computer files:

• The Fair Credit Reporting Act of 1970 gives individuals the right

to see information collected about them for use by credit, insur-

ance, and employment agencies. If a person is denied credit they

are allowed to see the files used to make the credit determination.

If any of the information is incorrect, the person has the right to

have it changed. The act also restricts who may access credit files

to only those with a court order or the written permission of the

individual whose credit is being checked.

• The Privacy Act of 1974 restricts the way in which personal data

can be used by federal agencies. Individuals must be permitted

access to information stored about them and may correct any infor-

mation that is incorrect. Agencies must insure both the security

and confidentiality of any sensitive information. Although this law

applies only to federal agencies, many states have adopted similar

laws.

• The Financial Privacy Act of 1978 requires that a government

authority have a subpoena, summons, or search warrant to access

an individual’s financial records. When such records are released,

the financial institution must notify the individual of who has had

access to them.

Protecting Computer Software and

Data

As society becomes more and more reliant on digital information,

issues among computer users. Copyright is protection of digital informa-

tion. Copyright infringement is the illegal use or reproduction of data

(text, pictures, music, video, and so on). Laws, such as the NET Act (No

Electronic Theft Act) of 1997, protect against copyright infringement. There

have been several well-known cases of high penalties for individuals guilty

of copyright infringement.

Identity Theft

Identity theft is a growing crime

where personal information is

stolen electronically in order

to make fraudulent purchases

or loans.

Chapter 1 An Introduction to Computers 21

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when copies are being used by individuals who have not paid for the

software. This practice is called piracy when illegal copies are distributed.

Developing, testing, marketing, and supporting software is an expensive

process. If the software developer is then denied rightful compensation,

the future development of all software is jeopardized. Therefore, it is

important to use only legally acquired copies of software, and to not make

illegal copies for others.

Malicious code comes in many forms and is delivered in many ways. A

virus, a Trojan horse, and an Internet worm are three forms of malicious

code. They can appear on a system through executable programs, scripts,

macros, e-mails, and some Internet connections. One devastating effect

of malicious code is the destruction of data.

A virus is a program or series of instructions that can replicate without

the user’s knowledge. Often a virus is triggered to run when given a cer-

tain signal. For example, a virus might check the computer’s clock and then

destroy data when a certain time is reached. A virus is easily duplicated

when the file is copied, which spreads it to other computers.

A Trojan horse program appears as something else, usually a program

that looks trustworthy. Running the program runs the malicious code

and damages files on the computer. A worm is a program that is able to

reproduce itself over a network. Worms are a threat because of the way

they replicate and use system resources, sometimes causing the system

to shut down.

Malicious code has become so widespread that software called antivirus

programs must be installed on computers and networks to detect and

remove the code before it can replicate or damage data. Precautions can

also be taken to prevent damage from malicious code:

• Update antivirus software. An antivirus program can only detect

the viruses, Trojan horses, and worms it is aware of. Antivirus

programs have a web link for updating the virus definitions on

the computer containing the antivirus program.

• Do not open e-mail attachments without scanning for malicious

code. One estimate states that 80% of virus infection is through

e-mail.

Newspapers have carried numerous reports of crackers, or hackers, gain-

ing access to large computer systems to perform acts of vandalism. This

malicious act is illegal and can cause expensive damage. The Electronic

Communications Privacy Act of 1986 specifically makes it a federal offense

to access electronic data without authorization. Networks usually include a

firewall, which is a combination of hardware and software, to help prevent

unauthorized access.

The willful destruction of computer data is no different than any other

vandalizing of property. Since the damage is done electronically the

result is often not as obvious as destroying physical property, but the

consequences are much the same. It is estimated that computer crimes

cost billions of dollars each year.

virus

Trojan horse

crackers, hackers

antivirus programs

TIP It is usually legal to make

one backup copy of a pur-

chased software program.

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Phishing is the act of sending an e-mail to a user falsely claiming to

be a legitimate business in an attempt to trick the user into revealing

personal information that could be used for crimes such as identity theft.

The Communications Privacy Act of 1986 specifically makes it a federal

offense to access electronic data without authorization. Networks usually

include a firewall, which is a combination of hardware and software, to

help prevent unauthorized access.

The Ethical Responsibilities of an IT

Professional

An IT (information technology) professional has responsibilities that

relate to system reliability. System reliability involves installing and updat-

ing appropriate software, keeping hardware working and up-to-date, and

maintaining databases and other forms of data. Governments, schools, and

employers rely on IT professionals to maintain their computer systems.

In addition to ensuring system reliability, an IT professional must take

responsibility for the ethical aspects of the career choice. For example,

IT professionals involved in creating software must ensure, as best he or

she can, the reliability of the computer software. This means the ethical

responsibility of the IT professional includes using the appropriate tools

and methods to test and evaluate programs before distribution. A special

cause for concern is the increased use of computers to control potentially

dangerous devices such as aircraft, nuclear reactors, or sensitive medical

equipment.

IT professionals must also consider the impact they have on computer

users. Web users for example often rely on data from websites providing

real-time information. The information displayed is determined with a

program written using a 4GL or other language that accesses a database.

The IT professionals involved in such a project have the ethical respon-

sibility to possibly millions of individuals for ensuring, as best they can,

accurate data retrieval.

As capable as computers have proven to be, we must be cautious when

allowing them to replace human beings in areas where judgement is cru-

cial. As intelligent beings, we can often detect that something out of the

ordinary has occurred which has not been previously anticipated and then

take appropriate actions. Computers will only do what they have been

programmed to do, even if it is to perform a dangerous act.

Chapter Summary

A desktop computer and its components are designed to fit on or under

a desk. Mobile computers include notebooks, tablets, handhelds, smart

phones, and wearables. A computer must run operating system (OS)

software in order to control processing and peripherals, run application

software, and control input and output, among other tasks.

phishing

IT Careers

The growth of computers,

the Internet, and the Web

have created many new job

opportunities in the IT field.

IT careers include data-entry

operator, systems analyst,

p r o gra m m e r, c o m p u t er

en gin e er, and t echnical

support technician.

Chapter 1 An Introduction to Computers 23

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A network is a combination of hardware and software that allows com-

puters to exchange data and share software and devices, such as printers.

Networks are classified by their size, architecture, topology, and protocol.

Network users should use netiquette.

A programming language is a set of words, codes, and symbols that

allows a programmer to communicate with the computer. Programming

languages can be classified as low-level and high-level languages. Low-

level programming languages include machine language and assembly

language. High-level programming languages have English-like

instructions and are easier to use than machine language. High-level

programming languages include Fortran, C, Basic, COBOL, and Pascal.

The electrical circuits on an IC have one of two states, off or on. Therefore,

the binary number system (base 2), which uses only two digits (0 and 1),

was adopted for use in computers. Our most familiar number system is the

decimal or base 10 system. The binary number system is a base 2 system

and the hexadecimal system is base 16. Every letter of an alphabet (Latin,

Japanese, Cherokee, and so on) and symbols of every culture (=, @, ½, and

so on) have been given a representation in a digital code called Unicode.

Computer memory, file sizes, and storage device capacities are measured

in bytes. In computers and electronics MB stands for megabytes, GB stands

for gigabytes, and K stands for kilobytes.

The binary representation of an integer number is usually stored in four

bytes of memory. Real numbers are numbers that contain decimal points

and the binary representation of a real number is usually 4 to 8 bytes of

memory.

A file is related data stored on a persistent media. A file is really just 1s

and 0s because it is stored in binary code. Computers are programmed to

translate bytes and words into symbols. File types are distinguished by

the extension that comes after the file name. Folders are used to organize

commonly related files.

Storage devices use a persistent media to maintain files. These devices,

which are also referred to as drives, mass storage, and auxiliary storage,

can be categorized as internal or external, as removable or permanent

media, and as magnetic, optical, or solid state technology.

An intranet is a network that is used by a single organization and is only

accessible by authorized users. A firewall is a network security system that

prevents unauthorized network access. An extranet extends an intranet

by providing various levels of accessibility to authorized members of the

public. The largest and most widely accessed network is the Internet. The

most widely used Internet service is the World Wide Web, also called the

Web. Other Internet service include e-mail and mailing lists.

Telecommunications is the transmitting and receiving of data.

Telecommunication options include a conventional modem, a DSL modem,

a cable modem, leased/dedicated lines, and ISDN.

A search engine is a program that searches a database of web pages for

keywords and then lists hyperlinks to pages that contain those keywords.

24 Chapter 1 An Introduction to Computers

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Search criteria is used by the search engine to determine a match. Limiting

the number of matches to a reasonable number can be accomplished using

Boolean logic in the search criteria. Some search engines also provide a

subject tree, or web directory.

Information found at a website should be evaluated for accuracy. There

are guidelines for citing electronic material on the Internet. The primary

purpose of a citation is to give credit to the original author and allow the

reader to locate the cited information.

The growth of the Internet has caused concerns about personal privacy.

Online profiling, cookies, and web bugs are all areas of concern. Before

providing personal information through a website, check the site’s pri-

vacy policy. To protect an individual’s privacy, several laws have been

passed. Concerns about Internet content, unproductive use, and copyright

have prompted many schools and businesses to develop an Internet Use

Agreement.

Historians refer to our present time as the information age. The poten-

tial for the use of computers to invade our right to privacy has prompted

legislation to protect individuals. Piracy is the illegal act of duplicating

software without permission. A virus is a computer file that erases data

and can cause considerable damage.

Working as an IT (information technology) professional includes taking

responsibility for the ethical aspects of a career choice. IT professionals

must also consider the impact they have on computer users.

Chapter 1 An Introduction to Computers 25

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Vocabulary

Address A unique binary representation of a location

in memory.

Address bus Carries memory addresses that indi-

cate data storage locations.

ALU (Arithmetic Logic Unit) The part of the CPU

that handles arithmetic and logic operations.

Antivirus program Software installed on computers

and networks to detect and remove viruses.

Applications software Program written to perform

a specific task.

Base unit Housing that contains the mother-

board, CD-RW/DVD drive, disk drive, and hard

disk drive.

Binary number system Number system used by

computers that uses only digits 0 and 1. Also called

base 2.

Bit (BInary digiT) A single 0 or 1 in binary code.

Bus A central network cable. Also a set of circuits

that connect the CPU to other components.

Bus topology A physical LAN topology that uses a

single central cable to attach each node directly.

Byte A group of 8 bits.

Cable modem A modem that transmits data through

a coaxial cable television network.

Cache High-speed memory used to store frequently

used data so that it can be quickly retrieved by an

application.

Client A computer that is sent information from a

server computer.

Client/server network A type of network that

consists of a group of computers, called clients con-

nected to a server computer.

Clock rate The speed at which a CPU can execute

instructions, measured in megahertz or gigahertz.

Compiler A program that converts an entire pro-

gram into machine code before the program is

executed.

Control bus Carries control signals.

Conventional modem A modem that uses stan-

dard telephone lines to convert analog signals to

digital data.

Cookie Text file created by the server computer

when a user enters information into a website.

tion without permission from the work’s author.

CPU (Central Processing Unit) Processes data and

controls the flow of data between the computer’s

other units. Also contains the ALU. Located on the

motherboard.

Cracker Person who accesses a computer system

without authorization.

Cross-platform connectivity The ability of one

type of PC to link to and share data with a different

type of PC.

Dedicated line See Leased line.

Device driver One type of utility program.

Downloading The process of copying a file from

a website to the user’s computer.

DSL (Digital Subscriber Line) modem A modem

that uses standard telephone phone lines. ADSL is

the most common form used.

E-mail (electronic mail) The sending and receiving

of messages and electronic files over a communica-

tions network such as a LAN or the Internet.

Environment A computer’s hardware and soft-

ware configuration. Also referred to as platform.

Environment types include desktop, multiuser, net-

work, handheld, distributed, multiprocessing, and

multitasking.

Ergonomics The science that studies safe work

environments.

Extension Added after a file name to distinguish

file types.

Extranet An extended intranet that provides vari-

ous levels of access to authorized members of the

public.

Expansion boards Circuit boards that connect to the

motherboard to add functionality to the computer.

File A collection of related data stored on a lasting

medium.

Firewall A network security system that prevents

unauthorized network access.

26 Chapter 1 An Introduction to Computers

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Folder Used to organize commonly related files.

Gigabytes (GB) Approximately one billion bytes.

Gigahertz (GHz) Billion of cycles per second.

Hacker see Cracker.

Handheld computer A mobile computing device.

Hardware The physical components of the computer,

such as the monitor and system unit.

Hexadecimal system Number system based on 16

digits. Also called base 16.

High-level programming languages Third

generation programming languages that have

English-like instructions.

Hub A communication device that joins communica-

tion lines at a central location on the network.

Information age Present time characterized

by increasing dependence on the computer’s

ability to store and manipulate large amounts of

information.

Input device Device used to enter data and instruc-

tions into the computer.

Integrated circuits (ICs) A silicon wafer with intri-

cate circuits etched into its surface and then coated

with a metallic oxide that fills in the etched circuit

patterns. Also called a chip.

Interactive Information accessed as a result of

selections made by the user.

Internet The largest and most widely accessed

network.

Interpreter A program that translates and

executes an instruction before moving on to the

next instruction in the program.

Intranet A network that is used by a single organi-

zation and only accessible by authorized users.

ISDN (Integrated Services Digital Network) A

digital telephone network provided by a local tele-

phone company.

IT (Information Technology) A term that

encompasses all aspects of computer-related

technology.

Kbps Thousands of bits per second.

Kilobytes (K) Approximately a thousand bytes.

LAN (Local Area Network) A network used to

connect devices within a small area.

Leased line A telecommunication option used

for a permanent connection to the Internet that is

always active.

Logical topology Refers to the way in which data

is passed between the nodes on a network.

Low-level programming languages First and

second generation programming languages including

machine language and assembly language.

Mailing list server A server that manages mailing

lists for groups of users.

Magnetic technology Storage device technology that

uses a mechanical drive with tiny electro-magnetic

heads for reading and writing data to media.

Match A web page that contains the search

criteria.

Mbps Millions of bits per second.

Megabytes (MB) Approximately one million

bytes.

Megahertz (MHz) Million of cycles per second.

Memory-resident A program that is always in

memory.

Minus sign (–) Used in search criteria to exclude

unwanted web pages.

Modern Language Association (MLA) Organization

that publishes standards used for citations.

Motherboard The main circuit board inside the

base unit.

Netiquette The etiquette that should be followed

when using a network.

Network A combination of software and hardware

that allows computers to exchange data and to share

software and devices, such as printers.

Net work architecture The structure of a

network.

Network interface card A circuit board that goes

into a computer or other device in a LAN.

Network operating system Software that allows

users and devices to communicate over a network.

Node A location on the network capable of processing

information, such as a computer or a printer.

Notebook A portable, lightweight computer.

Chapter 1 An Introduction to Computers 27

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Object-oriented programming (OOP) An approach

to programming where modules are created that can

be used over and over again.

Online profiling A marketing technique that

collects online data about consumers.

Operating system Software that allows the user

to communicate with the computer. Types include

multiuser, multiprocessing, multitasking, multi-

threading, or real time.

Optical technology Storage device technology

that uses a drive with a laser and optoelectronic

sensor.

Output device A device used to convey processed

data.

Overflow error An error that occurs when the num-

ber of bits that are needed to represent the integer

is greater than four bytes.

Over wr ites Updates an original file with

changes.

Peer-to-peer network A type of network that does

not have a server.

Peripheral device A device attached to a PC.

Phishing The act of sending an e-mail to a user

falsely claiming to be a legitimate business in an

attempt to trick the user into revealing personal

information that could be used for crimes such as

identity theft

Piracy Illegally copying or distributing software.

Plus sign (+) Used in search criteria to limit a search

to only those web pages containing two or more

specified words.

Port Used to attach a peripheral device to a

computer.

explains how any personal information will be

used.

Programming languages A set of words, codes, and

symbols that allows a programmer to communicate

with the computer.

RAM (Random Access Memory) Memory that

temporarily stores data and instructions. Also called

primary or main memory.

Real numbers Numbers that contain decimal

points.

Real time Occurs immediately.

Ring topology A physical LAN topology where each

node is connected to form a closed loop.

ROM (Read Only Memory) Memory that stores

data and is a permanent part of the computer.

Roundoff error An error that occurs when there

are not enough bits to hold the mantissa.

Router A device that connects different network

technologies.

Search criteria A single word or phrase that is used

by the search engine to match web pages.

Search engine A program that searches a database

of web pages for keywords and then lists hyperlinks

to pages that contain those keywords.

Secondary memory Any type of storage media.

Server A computer used to manage network func-

tions such as communication and data sharing.

Smartphone Cellular phone that is able to send and

receive e-mail messages and access the Internet.

Solid state technology Storage device technology

that requires no moving parts.

SRAM (Static Random Access Memory) High-

speed memory referred to as cache.

Star topology A physical LAN topology where

each node is attached to a hub.

Storage devices Devices that use persistent media

to maintain files. Also referred to as drives, mass

storage, and auxiliary storage.

Subject tree A list of sites separated into

categories.

Tablet PC A computer designed similar to a pad

of paper.

TCP/IP (Transmission Control Protocol/Internet

Protocol) Software used by networks connected

to routers to communicate.

Telecommunications The transmitting and receiv-

ing of data.

Topology The physical or logical arrangement of

the nodes on a network.

Transmission media The media that joins the nodes

on a network to enable communication.

Trojan horse Malicious code in the form of a program

that appears as something else, usually a program

that looks trustworthy.

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Ultra-portable devices Storage devices, such as

keychains, that are small and easy-to-use.

Unicode A digital code that uses a set of sixteen

1s and 0s to form a 16-bit binary code for each

symbol.

Utility program Program run by the operating

system to manage input and output, read and write

to memory, manage the processor, maintain system

security, and manage files and disks.

Virus A program that is designed to reproduce

itself by copying itself into other programs stored

on a computer without the user’s knowledge.

WAN (Wide Area Network) A network used to con-

nect computers over large geographical distances.

Wearable computer A mobile computing device

that is incorporated into clothing, eyewear, wrist-

wear, and other wearables.

Web See World Wide Web.

Web beacon A tiny, transparent graphic located on

a web page used to collect data about the web page

user. Also called a web bug or pixel tag.

Web browser Interprets an HTML document to

display a web page.

Web directory See Subject tree.

Wireless network A type of network that does not

require the use of cables.

Word Bits grouped in units of 16 to 64.

World Wide Web The most widely used Internet

service. Used to search and access information

available on the Internet.

Worm Program that is able to reproduce itself over

a network.

Chapter 1 An Introduction to Computers 29

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Review Questions

1. a) What is hardware?

b) What are input and output devices used

for?

c) What is a peripheral device?

2. List and describe five components found on the

motherboard.

3. Describe the flow of data between the compo-

nents of a computer, starting with input.

4. a) Describe one difference between operating

system software and applications software.

b) Describe three different types of operating

systems.

c) What does environment refer to?

5. What is a utility program? Give an example.

6. List four types of mobile computing devices.

7. What is a stylus used for?

8. Describe one type of wearable computer.

9. Why is cross-platform connectivity important

to many computer users?

10. a) What is the difference between low and high

level programming languages?

b) List three high-level programming

languages.

c) What is the difference between a compiler

and an interpreter?

d) List an advantage of using an object-oriented

programming language.

11. List four benefits of using a network.

12. a) What are the two common size classifica-

tions for networks?

b) What size classification is used to connect

devices over large geographical distances?

13. a) What is a network operating system?

b) What does a network environment refer

to?

14. Describe two common network architecture

models.

15. a) What does physical topology refer to?

b) What is a node?

c) Which topology uses a hub?

d) Which topology connects each node to form

a closed loop?

e) What is the difference between physical and

logical topology?

16. List three netiquette rules.

17. Explain why the binary number system was

adopted for use in computers.

18. a) What is the decimal equivalent of 111

b) What is the decimal equivalent of 2C

19. What is Unicode?

20. a) How many bytes of data can 512 MB of RAM

store?

b) How many bytes of data can a 40 GB hard

drive store?

21. What are bits grouped in units of 16 to 64

called?

22. When would an overflow error occur?

23. a) What are real numbers?

b) When would a roundoff error occur?

24. a) What is the difference between a text file and

a binary file?

b) Explain how an extension distinguishes file

types.

c) Why would organizing files into folders be

considered a good practice?

25. List three ways storage devices can be classified

and give an example of a storage device in each

category.

26. Describe three storage device technologies.

27. List four rules that should be followed to avoid

damaging files stored on disks or CD/DVDs.

28. a) What is the difference between an intranet

and an extranet?

b) Who controls the Internet?

30 Chapter 1 An Introduction to Computers

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29. List three telecommunications options.

30. a) If a business needed constant access to the

Internet, what type of connection line would

be a good choice? Why?

b) What does a cable modem use instead of

analog phone lines?

31. What is the most widely used Internet

service?

32. a) What is e-mail?

b) List one benefit of e-mail over standard

mail.

c). Write your e-mail address and label the parts

of the address.

d) What are the two requirements for sending

and receiving e-mail messages?

e) List one example of a browser-based e-mail

site.

33. a) Explain why sending an e-mail message

should be thought of the same as sending a

postcard.

b) List three examples of e-mail etiquette.

34. a) What is a search engine?

b) List three commonly used search engines.

c) Which search engine do you prefer to use,

and why?

d) What is search criteria?

e) What is a match?

35. Write search criteria to locate web pages that

contain the following information:

a) restaurants in Los Angeles

b) art museums in Boston

c) auto repair jobs in Montreal, Canada

d) mosquitoes and bees, but not ants

e) the English author Jane Austen

f) the phrase to each his own

g) George Washington and John Adams, but

not Thomas Jefferson

h) travel to Ireland, but not Dublin

36. List a search engine that provides a subject

tree.

37. a) What is downloading?

b) Why should files only be downloaded from

authentic sites?

38. a) List four questions to answer when evaluat-

ing a website source.

b) Why is it necessary to cite sources?

c) On August 2, 2006 you accessed a posting on

the Clewiston Kite Surfing discussion list at

http://www.lpdatafiles.com/kitesurf/color.txt.

The posting was made by Tara Perez on the

topic of kite colors. Write a citation for a

research paper that quotes Tara’s posting.

39. What is online profiling?

40. What is a cookie?

41. a) What is a web beacon?

b) Who usually monitors the information

collected by web beacons?

42. Locate a website’s privacy policy and document

its contents.

43. Name and briefly describe one law that helps

protect the privacy of an individual.

44. a) List three reasons why many schools have

developed an Acceptable Use Policy.

b) List an example of a rule that typically

appears on an Acceptable Use Policy.

45. What can you do if you are turned down for

credit at a bank and believe that the data used

to deny credit is inaccurate?

46. a) What is necessary for a federal government

authority to access an individual’s financial

records?

b) What must a financial institution do after

releasing an individual’s records?

47. a) What is copyright infringement?

b) Why is computer piracy such a concern to

software developers?

c) What is a computer virus?

d) Describe phishing.

48. What ethical responsibilities does an IT

professional have?

Chapter 1 An Introduction to Computers 31

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True/False

49. Determine if each of the following are true or

false. If false, explain why.

a) A computer must have an operating system

installed before application software can be

installed.

b) FireWire and USB are types of ports.

c) A peer-to-peer network has a server.

d) A LAN’s logical topology is always the same

as its physical topology.

e) The hexadecimal system is a base 2 system.

f) Computer memory is measured in bytes.

g) The most widely accessed network is the

Internet.

h) A conventional modem transmits data faster

than a cable modem.

i) E-mail messages are private.

j) Information found at a website is always

accurate.

k) The present time is referred to as the

industrial age.

l) Ergonomics is the science that studies safe

work environments.

m) A virus is a harmless computer game.

32 Chapter 1 An Introduction to Computers

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Exercises

Exercise 1 ——————————————————————————

In this exercise you will research your classroom computer network by answering a series of

questions:

a) Is your computer network a LAN or a WAN?

b) List one device that is shared on the network.

c) Locate the cable that plugs into the network interface card on your workstation.

d) What type of physical topology is used?

e) What type of transmission media is used?

f) What network protocol is used?

g) What operating system is used?

h) Describe your workstation’s environment.

i) What telecommunication option is used?

j) Does the school have an intranet?

k) List four rules on the school’s Internet Use Agreement.

Exercise 2 ——————————————————————————

In this exercise you will assess the input and output devices you have access to.

a) List the input devices accessible on the classroom network.

b) List the output devices accessible on the classroom network. List advantages and dis-

advantages associated with each accessible output device.

Exercise 3 ——————————————————————————

In this exercise you will organize your existing files. You may need to refer to the appropriate operating

system chapter on www.lpdatafiles.com to complete this exercise.

a) Examine the files you currently have saved on your computer. Use the appropriate

operating system command to rename any files that do not have descriptive names.

b) Use the appropriate operating system commands to organize your existing files into

appropriate folders.

Chapter 1 An Introduction to Computers 33

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Exercise 4 ——————————————————————————

A good friend has been diagnosed with Carpal Tunnel Syndrome and would like you to find out as

much as you can about the injury and possible treatments.

a) Conduct a search on the Internet using at least two search engines to find three web

pages that have information about Carpal Tunnel Syndrome.

b) Write a brief description of the injury.

c) In a second paragraph, write about possible treatments for the injury.

d) Write a citation for each source.

Exercise 5 ——————————————————————————

Expand on the information presented in this chapter by researching one of the following topics:

• Network Protocols

• Operating Systems

• The History of the Internet

• Evolution of Programming Languages

• Identity Theft

a) Use the Internet, magazines, and books to find at least three sources of information.

b) Write a two page report that summarizes your research.

c) Write a citation for each source.

Exercise 6 ——————————————————————————

In this exercise you will research and compare the advantages and cost of obtaining Internet access

through three different telecommunication options.

a) Use the Internet and newspapers to find information about Internet service providers

(ISPs).

b) Compare the costs and the advantages of at least three different telecommunication

options.

c) Write a one paragraph conclusion that explains what telecommunication option would

be the best choice.

d) Write a citation for each source.

34 Chapter 1 An Introduction to Computers

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Exercise 7 ——————————————————————————

In this exercise you will further research emerging technologies and find real-life examples of how

these technologies have impacted individuals and businesses.

a) Use the Internet, magazines, and books to learn more about at least three emerging

technologies. Look specifically for information on how these emerging technologies

impact individuals and businesses. For example, speech recognition technology greatly

impacts those individuals who must rely on voice input rather than keyboard input

for a PC.

b) Write a two-page report that summarizes the impact of and lists several functions of

the emerging technologies you have researched.

c) Write a citation for each source.

Exercise 8 ——————————————————————————

Many computer viruses have been associated with e-mail attachments.

a) Conduct a search on the Internet to find information about a virus associated with an

e-mail attachments.

b) Write a one-paragraph description of the virus. Include details, such as the damage

caused by the virus and steps necessary to remove the virus.

c) Write a citation for each source.

Exercise 9 ——————————————————————————

You have decided to investigate computer programming as a possible career path.

a) Conduct a search on the Internet using at least two search engines to find three appro-

priate bachelor degree programs.

b) List each program location (college name), the number of credits required to finish the

degree, and the tuition cost per credit or per course.

Exercise 10 ——————————————————————————

In this exercise you will investigate mailing lists.

a) Join an appropriate computer-related mailing list.

b) Participate on the mailing list as a learner.

c) Contribute to the mailing list content.

Chapter 2 Applets and Web Programming 35

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This chapter discusses Web programming by introducing HTML and

JavaScript. Java applets are also introduced.

The World Wide Web

The most widely used Internet service is the World Wide Web (WWW),

also called the Web. The Web is used to search and access information avail-

able on the Internet. A web browser application, such as Internet Explorer

provides a graphic interface to present information from a website. A

website consists of a series of related web pages. For example, a CNN web

page looks similar to:

A web page displayed in a web browser

Most web pages are created using HTML (HyperText Markup Language)

and other code. HTML is a markup language that is well suited for the

Web because it supports hypertext and multimedia. Hypertext is a database

Browsers

Commonly used web browser

applications include Internet

Explorer, Netscape, Opera,

Firefox, Amaya, and Safari.

Chapter 2

Applets and Web Programming

hypertext

web browser application

website

HTML

36 Chapter 2 Applets and Web Programming

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system where objects, such as text and images, can be linked. Multimedia

includes images, video, audio, and Java applets, which can be embedded

in an HTML document.

Millions of people all over the world are able to view and author web

content because the World Wide Web Consortium (W3C) continuously

develops standards for the Web. These standards include HTML standards

to ensure that HTML documents display similarly in different browsers

and across different platforms. They have also developed Web accessibility

standards for those with disabilities.

HTML

HTML uses a set of codes, called tags, to “mark up” plain text so that

a browser application, such as Internet Explorer, knows how to interpret

the text. A tag is comprised of an element inside angle brackets (<>). For

example, <title> is called the title tag, where title is the element. Tags

affect the text they surround, and are usually paired to indicate the start

and end of an instruction. A slash (/) before the element indicates the end

of an instruction, such as </title>.

A web page with one line of text will be displayed when the HTML

document below is opened in a browser:

<html>

<head>

<title>An example HTML document</title>

</head>

<body>

<p>Hello world!</p>

</body>

</html>

Text marked up with <title> and </title> is displayed in the title bar of

the browser window. The text Hello world! is marked to be displayed as

a paragraph (<p> and </p>) in the body of the browser window (<body>

and </body>). When viewed in Internet Explorer, the HTML tags are inter-

preted sequentially and the document appears similar to:

A web browser is used to access and view HTML documents that have

been published to a web server. The web browser first interprets the URL

to identify the location of the of the page on the Web and then interprets

the HTML document to display a web page in the browser window. HTML

documents saved on a local computer can also be viewed in a browser.

TIP HTML is not a case

sensitive language.

TIP A tag should not have any

spaces between the opening

bracket and the element or

slash.

Tim Berners-Lee

1955 –

Tim Berners- Lee is cred-

ited with creating the World

Wide Web. Berners-Lee now

heads a non-profit group,

the W3C (World Wide Web

Consortium), which sets tech-

nical standards for the Web.

Internet Explorer

To view an HTML document

saved on a local computer in

Internet Explorer, select File

j Open. Next, select Browse

to navigate to the location

where the HTML document

is saved.

TIP A web server is a com-

puter that communicates

with a web browser over the

Internet using HTTP.

multimedia

Chapter 2 Applets and Web Programming 37

sample

Validating HTML

HTML documents can be

validated to ensure they are

meeting W3C standards at the

http://validator.w3.org

website.

In order to validate an HTML

document, a DTD (docu-

ment definition tag) must be

included as the first line of an

HTML document. For exam-

ple, to check to see if an HTML

document meets HTML 4.01

standards, include the tag:

<!DOCTYPE HTML PUBLIC "-

//W3C//DTD HTML 4.01// EN"

"http://www.w3.org/TR/

hmtl4/stict.dtd">

TIP To help make an HTML

document easier to under-

stand, place document tags

on separate lines, except the

title tags, and use blank lines to

separate sections of HTML.

Creating an HTML Document

HTML documents are plain text ﬁles and can be created using any text

editor, such as Notepad, or by using a word processor. In general, the

structure of an HTML document should be similar to:

















An HTML document contains pairs of tags

The html, head, title, and body tags are called document tags:

• The <html> tag tells the browser that the file contains HyperText

Markup Language.

• The <head> tag defines the section that contains information about

the document, including its title. This section will not be displayed

as part of the document content.

• The <title> tag marks the document title. The title section

must be within the head section. The document title should be

descriptive and meaningful because it is displayed in the title bar

of the browser’s window and is also used when the user adds the

document to the browser’s Favorites list.

• The <body> tag defines the body section, which contains the doc-

ument’s content. All content must be enclosed in the appropriate

tags. For example, on the previous page, the content is marked as

a paragraph.

HTML documents are free-form, which means that spaces and blank lines

generally have no effect on how the document is interpreted. Therefore,

the document:

<html><head><title>An example HTML document</title>

</head>

<body> <p>Hello world!</p></body></html>

Poorly structured HTML document

displays exactly the same as the HTML document on the previous page.

However, editing a poorly structured document can be time-consuming

and error-prone.

An HTML document is saved with a lowercase, descriptive ﬁle name.

The ﬁle name should not contain any spaces and the .htm extension needs

to be added. If using a word processor to save the ﬁle, be sure to save the

ﬁle in TXT format.

TIP In Internet Explorer,

the HTML associated with a

displayed web page can be

viewed by selecting View j

Source.

saving an HTML document

38 Chapter 2 Applets and Web Programming

sample

Review: hello_world.htm

Create a properly structured HTML document that displays “My name is Name. Hello world!”, replacing

Name with your name. Include the title “First HTML Document”. View the HTML document in a browser.

Review: Computer Viruses Website – part 1 of 6

Create a properly structured HTML document that displays the text “Computer Viruses.” Include the title

“Computer Viruses”. Save the document as computer _ virus.htm and view the HTML document in a

browser.

JavaScript

Scripts are used to add dynamic content to an HTML document and

consist of a list of commands that execute without user interaction. Scripts

are written in a scripting language, such as JavaScript. JavaScript is a

scripting language that is interpreted by a browser’s built-in JavaScript

engine.

In an HTML document, JavaScript code is written as a script block

between <script> and </script> tags. Scripts are typically found in

the head section, but can be placed anywhere in an HTML document.

Displaying a message in an alert dialog box is one form of dynamic content

that can be added to an HTML document using a script:

<head>

<title>JavaScript Greeting</title>

// Display a greeting

alert("Hello World!");

</script>

</head>

• The type attribute in the script tag specifies which scripting

language is used to define the script.

• // is used to add a single line comment that explains the script.

• alert() displays an alert dialog box with the specified text

message.

• A semicolon is used to end each JavaScript statement.

The script above is interpreted when the HTLM document is loaded:

TI P J av a S cri p t is ca s e

sensitive.

Java vs JavaScript

JavaScript is similar to the Java

programming language, but it

is a separate language.

JavaScript Files

Scripts can also be written as a

separate JavaScript file, which

is saved with a .js extension,

and then referenced in the

script tag.

Chapter 2 Applets and Web Programming 39

sample

JavaScript can also be used to prompt the user for information:

<head>

<title>JavaScript User Name</title>

//initialize a variable with a null value

var name = null;

// Ask user for their name

name = prompt("Please enter your first name", " ");

//Greet the user

alert("Welcome " + name);

</script>

</head>

• A variable called name is initialized to represent the user’s name.

• prompt() displays the specified message in a prompt dialog box.

The empty string, " ", after the message indicates the prompt box

is to be blank when the dialog box is first displayed. When the user

enters their name, it is assigned it to the variable name.

• The text message and variable are joined by a +.

The script above generates output similar to:

Review: welcome.htm

Create an HTML document that contains a script block that prompts the user for their full name and then

displays the message “Welcome to our site Full Name”, replacing Full Name with the user’s name, in an alert

dialog box.

Review: Computer Viruses Website – part 2 of 6

Modify computer _ virus.htm to include a script block that prompts the user for their first name when the

page loads and then displays “Ready to Learn About Computer Viruses Name?”, replacing Name with the

user’s name, in an alert dialog box.

TIP JavaScript terminology

is similar to Java terminology

which is explained throughout

the text.

40 Chapter 2 Applets and Web Programming

sample

Using Scripts to Enhance a Website

Static websites can be enhanced by the dynamic nature of scripts. For

example, JavaScript can be used to define the default message that is dis-

played in the status bar of the browser window:

// Display a status bar message

window.defaultStatus="Hello World";

</script>

The script above is interpreted when the HTML document is loaded, and

displays a message in the status bar of the browser window:

Note that priority is given to system messages, such as when a page is

JavaScript can also be used to display the current date and time on a

web page:

<head>

<title>JavaScript Current Date</title>

// Display the current date

var now = new Date();

document.write(now);

</script>

</head>

• A new date object called now is created. Objects are discussed in

chapter 4.

• document.write is used to display output on the web page:

Web applications are often programmed to display differently depend-

ing on the user’s browser, platform, and whether Java is enabled. These

settings can be detected using JavaScript:

<head>

<title>JavaScript Setting Detector</title>

// Detect the browser

var browser = navigator.appName;

// Detect the platform

var platform = navigator.platform;

//Detect Java enabled

var JavaCheck = navigator.javaEnabled();

alert(browser +" \n" + platform + " \n" + "Java is enabled: "

+ JavaCheck);

</script>

</head>

• navigator.appName detects the browser name.

• navigator.platform detects the operating system.

TIP The current date and time

is accessed from the operating

system clock on the user’s

computer.

Chapter 2 Applets and Web Programming 41

sample

• navigator.javaEnabled() detects whether Java is enabled and

returns a value of true or false.

• \n creates a new line.

The script will generate output similar to:

Review: Computer Viruses Website – part 3 of 6

Modify computer _ virus.htm to display “Computer Viruses” in the status bar of the browser window and

to display the current time and date on the first line of the web page.

Review: System Check – part 1 of 2

Create an HTML document that detects the browser, platform, and whether the browser is Java enabled.

Display the output in an alert dialog box.

Java Applets

A Java applet is a small Java application that is embedded in an HTML

document and run in a browser window. When a browser interprets a

document that contains a Java applet, the program files are downloaded

onto the user’s machine and then the browser’s Java interpreter runs the

applet. Java applets are well suited for the Web because they are able to

run on different hardware and across different platforms. Applets are

secure because they do not have the ability to read or write to files on a

user’s computer.

Numerous applets can be downloaded from the Web and embedded in

an HTML document to add dynamic content. Applets take various forms,

such as animated banners, stock ticker tapes, photo cubes, and animated

video clips. Original applets can also be created.

Creating Java Applets

An applet is created in a Java compiler, such as JCreator. The Java code for

the applet is saved with a .java extension and then compiled to convert the

Java code to bytecode. The bytecode is saved with a .class extension.

TIP This section provides

a brief overview on writing

Java applets. You may want to

revisit this section after becom-

ing more familiar with the Java

programming language.

Java Enabled

Users can enable and disable

Java in their web browser’s

Internet options settings.

TIP Visit lpdatafiles.com for

specific information about dif-

ferent Java compilers.

42 Chapter 2 Applets and Web Programming

sample

The code below is for a basic applet that paints the message “My first

Java applet” at a specific screen location:

* Example _ Applet.java

import java.awt.*;

import java.applet.*;

public class Example _ Applet extends Applet {

String message;

public void init() {

message="My first Java applet";

}

public void paint(Graphics g) {

g.setColor(Color.blue);

g.drawString(message, 50, 60 );

}

• The two import statements indicate which Java packages are

used.

• A class is used to define an applet and extend the Applet class.

Applets are always an extension of the Applet class.

• The init() method is used to initialize variables to starting values.

The variable message is assigned the text string, “My first Java

applet”.

• The paint() method is used to paint text, shapes, and graphics onto

the screen. In this example, the paint() method defines a Graphics

object named g.

• The setColor() method sets the text color.

• The drawString() method draws the message on the screen at the

specified coordinates.

Sun’s Java Software Development Kit (SDK) includes a tool called an

appletviewer, which can be used to interpret, execute, and test an applet.

When executed, the example applet above will appear similar to:

TIP Packages, classes, and

methods are explained in

Chapter 3.

Coordinates

A picture painted on the

screen is made up of series

of pixels (picture elements.)

Each pixel maps to a screen

location. Screen locations are

represented using (x,y) values.

The top-left corner has the

coordinates (0,0) with the x-

axis running horizontal and the

y-axis running vertical.

TIP The example applet uses

the Applet class, which is part

of the java.applet package,

and the Graphic s cla ss,

which is part of the java.awt

package.

Chapter 2 Applets and Web Programming 43

sample

Drawing Shapes and Adding Color

Original applets can be created to draw colorful images. The applet

below illustrates how shapes can be drawn and filled and how the back-

ground and foreground colors are set:

* Drawing Shapes and Changing Color Example

import java.awt.*;

import java.applet.*;

public class Shapes _ Color extends Applet {

public void paint(Graphics g) {

setBackground (Color.darkGray);

g.setColor(Color.pink);

g.drawRect(50, 50, 40, 40);

g.setColor(Color.blue);

g.fillRect(100, 100, 150, 150);

g.setColor(Color.green);

g.drawLine(20, 20, 300, 20);

g.setColor(Color.red);

g.fillOval(250, 250, 50, 50);

}

When executed, the applet looks similar to:

The different shapes require specified coordinates. For example:

• drawLine (x1, y1, x2, y2) Paints a line from coordinates (x1,

y1) to (x2, y2).

• drawOval (x, y, width, height) Paints an oval with the upper

left corner at position (x, y) with the specified width and height.

• drawRect (x, y, width, height) Paints a rectangle with the

upper left corner at position (x, y) with the specified width and

height.

Predefined Colors

Predefined colors include

black , blue, c yan, gray,

darkGray, lightGray, green,

magenta, orange, pink, red,

white, and yellow.

44 Chapter 2 Applets and Web Programming

sample

• drawArc (x, y, width, height, startAngle, arcAngle) Paints

an arc with the upper left corner at position (x, y) with the specified

width, height, starting angle, and arc angle.

Review: Hot Air Balloon

This review requires a Java compiler. Experiment with drawing shapes and adding color by

creating an applet that paints a picture of a hot air balloon on the screen. Compile the applet

and view it in the appletviewer.

Placing an Applet in an HTML

Document

An applet is embedded in an HTML document within the <applet>

and </applet> tags. The tags can surround an alternative text message

that will be displayed if the applet cannot run in the browser:

<html>

<head>

<title>Embedding an Applet</title>

</head>

<body>

You are unable to view the applet.

</applet>

</body>

The <applet> tag has three required attributes:

• code=“name” specifies the name of the applets to run

• width=“value” specifies the width for the applet display in pixels

• height=“value” specifies the height for the applet display in

pixels

Applet Parameters

Parameters allow users to specify custom values to use in a Java applet. In

an HTML document, parameter information is specified in a <param> tag,

which requires two attributes, name and value. For example, the HTML

document below specifies a specific image file, scenery.gif, to use in the

applet.

<body>

You are unable to view the applet.

</applet>

</body>

TIP Parameters typically need

to be specified for applets

downloaded from the Web.

Accessibility

In response to t he ADA

(Americans with Disabilities

Act), enacted in 1990, the

W3C has developed guidelines

called the Web Accessibility

Initiative (WAI). These guide-

lines call for alternative text to

be provided for any content on

a web page that is not text.

<object> Tag

The <object> tag allows for

multimedia resources, such as

video and audio, to be embed-

ded in an HTML document.

When interpreting an <object>

tag, the browser determines if

another application, such as

the Windows media player, is

needed to display the object.

The <object> tag can also be

used to embed a media player

console in an HTML docu-

ment using Microsoft ActiveX

controls.

Chapter 2 Applets and Web Programming 45

sample

Review: System Check – part 2 of 2

An applet available at the Sun Microsystems website, http://java.sun.com, is an analog clock.

Modify the body section of the System Check HTML document as follows, which embeds

the JavaClock.class applet data file:

</applet>

Save the modified System Check HTML document in the classes folder in the CLOCK website included in

the data files for this text.

HTML Tags

In addition to applets and scripts, a web page can contain text. For

example, consider the following web page:

The HTML for the web page is shown below. The body section of the

HTML document includes the content and tags that format the content:

<body>

<h1>Computer Viruses</h1>

<hr>

<p>A computer virus is a program that is loaded onto the computer

without the user's knowledge. Computer viruses have varying

effects, such as:</p>

HTML 4

The current version of HTML is

HTML 4. HTML 4 is supported

by newer browsers.

46 Chapter 2 Applets and Web Programming

sample

<ul>

<li>displaying annoying messages</li>

<li>causing programs to run incorrectly</li>

<li>erasing the contents of the hard drive</li>

</ul>

<p>In order to protect against viruses:</p>

<ol>

<li>install an antivirus program</li>

<li>update antivirus definitions on a regular basis</li>

</ol>

<h4>Report by Student Name</h4>

</body>

There are six levels of headings, which are represented with tags <h1>

through <h6>. Heading tags are used to emphasize enclosed text. Each

heading level has specific formatting associated with it, which includes

font size, bold text, and space above and below the heading. Heading 1 has

the largest font size and is used to represent the most important informa-

tion. Heading 6 has the smallest font size.

The <hr> tag places a horizontal rule (line) across the width of the

browser window. This feature is used to divide the text in the browser

window into sections for easier reading. The horizontal rule tag does not

need to be paired.

HTML tags may also contain attributes. An attribute is placed in the start

tag and set to a value that modifies the element. For example, the hori-

zontal rule width attribute specifies the width of the line in the browser

window as a percentage, <hr width="50%">. Other attributes of the <hr>

tag include:

• size=“value” specifies the thickness of the rule in pixels.

• align=“value” specifies the rule alignment. The default alignment

is center.

Text enclosed by <p> and </p> is a paragraph. Lines of paragraph text

are automatically wrapped by the browser, and a blank line is added after

each paragraph. To move a line of text within a paragraph to the next line,

a break tag <br> is used. A break tag does not need to be paired.

Comments are text used to explain and clarify HTML to the reader of an

HTML document. They do not appear in a browser window. Comments

start with an angle bracket, followed by an exclamation mark and two

hyphens. At the end of the comment are two more hyphens and an ending

bracket, .

Lists are used to organize information. Bulleted and numbered are

two types of lists that can be created in an HTML document. A bulleted

list, also called an unordered list, is used when each item is equally impor-

tant. A numbered list, also called an ordered list, is used to show priority of

importance.

Bulleted list tags include:

• <ul> </ul> defines the start and end of a bulleted list

• <li> </li> defines the start and end of an item

attribute

comments

lists

Browser Preferences

The formatting associated with

heading tags varies between

browsers and is dependent

on the preferences set by the

user.

paragraphs

Chapter 2 Applets and Web Programming 47

sample

Numbered list tags include:

• <ol> </ol> defines the start and end of a numbered list

• <li> </li> defines the start and end of a list item

Review: Computer Viruses Website – part 4 of 6

Modify the body section of computer _ virus.htm to include the content and tags shown on the two previous

pages. View the HTML document in a browser.

Hyperlinks, Tables, and Images

The display of an HTML document can be further enhanced with

hyperlinks, tables, and images. Tables are used to arrange data in an HTML

document. Note the virus table:

The HTML for the web page is shown below:

<html>

<head>

<title>Antivirus Program</title>

</head>

<body>

<h2>Checking for Viruses</h2>

<p>A computer can be checked for <a href="computer _ virus.

htm">viruses</a> using an antivirus program. An antivirus pro-

gram is a utility that scans a hard disk for viruses. If a virus

is located, it will be removed by the antivirus program.</p>

<h2>Example Virus Threats </h2>

48 Chapter 2 Applets and Web Programming

sample

<th>Virus</th>

<th>Threat </th>

<tr><td>Worm MyDoom.p</td>

<tr><td>Worm Blueworm.D</td>

<tr><td>Worm Bagle.AI</td>

<td>Medium</td> </tr>

</table>

<h5>Report by: Student Name</h5>

</body>

</html>

The anchor tag (<a>) is used in an HTML document to mark text that is

a link. The href attribute is set in the tag to the name of the linked docu-

ment. For example, <a href="digicam.htm">digital cameras</a>.

A hyperlink, also called a link, is text displayed in a browser window

that can be clicked to display a different HTML document in the browser

window. Hyperlinks are what make a hypertext system, such as the Web

work. Hyperlinks are typically displayed as blue, underlined text in the

browser window. Countless documents can all be linked, allowing the

user to go from topic to topic, or browse HTML documents.

A table requires several tags for formatting:

• <table> </table> creates a table.

• <th> </th> creates a table header, which is a cell with bold, centered

text.

• <tr> </tr> defines the start and end of a table row.

• <td> </td> defines the start and end of a table data cell.

The <table> tag attributes include:

• border=“value” specifies the thickness of the cell border where

value is in pixels.

• cellpadding=“value” sets the amount of space between table cells

where value is a number.

• width=“value” specifies the width of a table where value is a num-

ber in pixels or a percentage of the document’s width.

The display of an HTML document can also be enhanced with images.

The <img src="file name"> tag inserts an image where file name is the

file name of the graphic. Image files added to an HTML document should

be GIF, JPG, or PNG format. The image tag does not need to be paired.

Attributes of the <img> tag include:

• border=“value” specifies the size of the border around the image

where value is a number in pixels.

• alt=“value” specifies alternate text for the graphic where value is

the alternative text.

• height=“value” specifies the height of the image in pixels.

• width=“value” specifies the width of the image in pixels.

TIP Visited hyperlinks are

typically displayed as purple,

underlined text in the browser

window.

GIF, JPG, PNG

GIF (Graphics Interchange

Format) format is limited to

256 colors and best used for

clip art or logos, JPG (Joint

Photographic Expert Group)

format supports millions of

colors and is best used for

photographs. PNG (Portable

Network Graphic) format is a

newer format only support by

recent brower versions.

TIP Tables can also be used to

control the layout of an HTML

document by placing content

in table cells and setting the

border attribute to 0.

Chapter 2 Applets and Web Programming 49

sample

Review: Computer Viruses Website – part 5 of 6

Modify computer _ virus.htm to make the text “antivirus program” a hyperlink to a document named

antivirus.htm. Create the antivirus.htm document using the content and formatting shown in the HTML

document in the “Hyperlinks, Tables, and Images” section. Note that the first paragraph links “viruses” to

computer _ virus.htm. The VIRUS.gif image file is a data file for this text. Test the hyperlinks in a browser

window.

Style Sheets

A style sheet is used to define the type, paragraph, and page formats

for an HTML document. Style sheets give HTML documents a consistent

appearance because they override the browser settings that interpret how

tags are displayed:

A style sheet can be embedded or linked. An embedded style sheet is

defined within <style type="text/css"> and </style> tags in the head

section of the HTML document. The embedded style sheet for the web

page above appears as:

h1 {color: #FF0000; text-align: center}

p {font-family: Georgia, "Times New Roman", Times, serif; font-

size: 16 px; line-height: 18 px}

ul {font-family: Georgia, "Times New Roman", Times, serif;font-

size: 14 px; line-height: 18 px}

ol {font-family: Georgia, "Times New Roman", Times, serif;font-

size: 14 px; line-height: 18 px}

h4 {text-align : right}

</style>

embedded style sheet

50 Chapter 2 Applets and Web Programming

sample

A linked style sheet is a separate file that is saved with a .css extension and

applied using <link rel="stylesheet" href "style.css" type="text/

css">, where style.css is the name of the style sheet.

Style sheets can include rules and classes, a linked style sheet can con-

tain only rules. A rule modifies an HTML element and is comprised of a

selector and declarations. The selector is the HTML element being redefined

and the declarations are the formats to be applied. For example:

p { font-family: Georgia, "Times New Roman", Times, serif;

font-size: 16px;}

Style Sheet Rule

The rule above will automatically display paragraphs in 16 px Georgia.

The font-family property can also be specified as generic font, such as

serif, sans serif, or monospace and the font-size may be defined in points,

pixels, inches, or centimeters (pt, px, in, cm).

A class is a set of declarations that can be applied to different tags. Class

names begin with a dot (.). For example:

.para _ with _ space {

font-family: Georgia, "Times New Roman", Times, serif;

font-size: 14px;

line-height: 28px;

}

Style Sheet Class

The class above can be applied to individual paragraphs to format the

paragraph in 14px Georgia with a line-height of 28 px. For example:

<p class="para _ with _ space">Spyware is software that collects

information without the user’s knowledge. The information is

usually for advertising purposes.</p>

Text and background colors in an HTML document are specified using

hexadecimal numbers. Hexadecimal is a base-16 numbering system that

consists of the numbers 0 through 9 and the letters A through F. Color

constants and corresponding hexadecimal values include:

Black (#000000) Silver (#C0C0C0)

Gray (#808080) White (#FFFFFF)

Maroon (#800000) Red (#FF0000)

Purple (#800080) Fuchsia (#FF00FF)

Green (#008000) Lime (#00FF00)

Olive (#808000) Yellow (#FFFF00)

Navy (#000080) Blue (#0000FF)

Teal (#008080) Aqua (#00FFFF)

To change the background and text color of an HTML document, the

HTML body element is modified in a style sheet rule:

body { background-color : #000000; color : #FFFFFF }

hexadecimal

class

linked style sheet

text and background color

Font Family

Declarations

Font-family d eclaratio ns

indicate the first font that a

browser should display, and

then alternate fonts if the first

is not installed on the user’s

computer.

Chapter 2 Applets and Web Programming 51

sample

To change the text color of a selected tag, the appropriate HTML element

is modified in a style sheet rule. For example:

h1 {color : #0000FF }

HTML content is left aligned by default. To change the alignment of an

entire HTML document, the HTML body element is modified in a style

sheet rule:

body { text-align : center }

To change the alignment of certain parts of a document, modify the

appropriate HTML element. For example, the Heading 1 tag is modified

in a style sheet rule to be right aligned:

h1 {text-align : right }

Review: Computer Viruses Website – part 6 of 6

Modify computer _ virus.htm to include an embedded style sheet with rules to format Heading 1 style in

a red color, center aligned and Heading 4 style as right aligned. Also include rules to format paragraphs in

Georgia, Times New Roman, Times, serif font-family in a font size of 16 pixels and a line height of 18 pixels

and unordered, and ordered list tags in Georgia, Times New Roman, Times, serif font-family in a font size

of 14 pixels and a line height of 18 pixels. Add an appropriate comment to the document.

Create a linked style sheet with the rules to format Heading 1 style in a navy color and Heading 4 style as

right aligned. Link the style sheet to antivirus.htm. View the documents in a browser.

Chapter Summary

Most web pages are created using HTML (HyperText Markup Language)

and other code. HTML is a markup language that is well suited for the Web

because it supports hypertext and multimedia. HTML uses a set of codes,

called tags, to “mark up” plain text so that a browser application, such as

Internet Explorer, knows how to display the text in a browser window.

Scripts are used to add dynamic content to an HTML document.

JavaScript is a scripting language that is interpreted by a browser’s built-

in JavaScript engine. In an HTML document, JavaScript code is written as

a script block between <script> and </script> tags.

A Java applet is a small Java application that is embedded in an HTML

document within the <applet> and </applet> tags and run in a browser

window. Applets can be downloaded from the Web and embedded in an

HTML document to add dynamic content. Original applets can also be

created. Parameters allow users to specify custom values to use in a Java

applet. In an HTML document, parameter information is specified in a

<param> tag.

text alignment

52 Chapter 2 Applets and Web Programming

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The <html>, <head>, <title>, and <body> tags are called document tags.

Other HTML tags introduced in this chapter include:

• the paragraph tag, <p>

• the break tag, <br>

• the heading tags, <h1> through <h6>

• the horizontal rule tag, <hr>

• the unordered list tag, <ul>

• the ordered list tag, <ol>

• the table tag, <table>

• the image tag, <img>

• the anchor tag, <a>

• the comment tag,

• the style sheet tag, <style>

Tags may also contain attributes. An attribute is placed in the start tag and

set to a value that modifies the element.

Chapter 2 Applets and Web Programming 53

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Vocabulary

Attribute Used to modify the features of an element

in an HTML tag.

Bulleted list A list that is used when each item is

equally important:

Class A set of declarations that can be applied to

different tags.

Comment Text used to explain and clarify HTML

for a reader.

Declarations The formats to be applied in a style

sheet rule.

Document tags The html, head, title, and body

tags.

Element The part of an HTML tag placed inside

angle brackets (<>). For example, <title> is called

the title tag, where title is the element.

Embedded style sheet A style sheet defined with

HTML document.

Free-form Spaces and blank lines generally have

no effect on how the document is interpreted. The

format of an HTML document.

Hexadecimal A base-16 numbering system that

consists of the numbers 0 through 9 and the letters

A through F.

HTML (HyperText Markup Language) A set of tags

that are used to “mark up” plain text so that a browser

application knows how to display the text.

Hyperlink Text that can be clicked to display another

HTML document. Also called a link.

Hypertext A database system where objects, such

as text and images, can be linked.

Java applet A small Java application that is

embedded in an HTML document and run in a

browser window.

JavaScript A scripting language that is interpreted

by a browser’s built-in JavaScript engine.

Link see hyperlink.

Linked style sheet A style sheet saved as a sepa-

rate file with a .css extension and applied using a

<link> tag.

Multimedia Images, video, audio, and Java applets

embedded in an HTML document.

Numbered list A list that is used to show a priority

of importance.

Ordered list see Numbered list.

Parameters Used to specify custom values to use

in a Java applet.

Rule A line in a browser window for dividing

content.

Scripts Used to add dynamic content to an HTML

document. Scripts are written in a scripting language,

such as JavaScript.

Selector The HTML element being redefined in a

style sheet rule.

Style sheet Used to define the type, paragraph, and

page formats for an HTML document.

Tables Used to arrange data in an HTML

document.

Tag Comprised of an element inside angle brackets

that is used to “mark up” plain text so that a browser

application knows how to display the text.

Unordered list see Bulleted list.

Web Tool used to search and access information

available on the Internet.

Web browser application Provides a graphic

interface to present information in the form of a

website.

Website Series of related web pages.

54 Chapter 2 Applets and Web Programming

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HTML Tags

<a> The anchor tag. Links text to another HTML

document. Attributes include href.

<applet> The applet tag. Embeds an applet in an

HTML document.

<br> The break tag. Moves a line of text within a

paragraph to the next line.

A comment tag. Explains and

clarifies HTML to the reader.

<h1> through <h6> The heading tags. Emphasizes

text.

<head> The head tag. Indicates information about

the document, including its title.

<hr> The horizontal rule tag. Displays a line in the

browser window. Attributes include width, align,

and size.

<html> The HTML tag. Indicates that the file contains

HTML.

<img> The image tag. Inserts an image.

<li> The list item tag. Defines the start and end

of an item.

<ol> The ordered list tag. Defines the start and end

of a numbered list.

<p> The paragraph tag. Formats the content.

Attributes include align.

<table> The table tag. Creates a table.

<title> The title tag. Displays the document title

in the title bar of the browser window. Must be in

the head section of an HTML document.

<ul> The unordered list tag. Defines the start and

end of a bulleted list.

Chapter 2 Applets and Web Programming 55

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Critical Thinking

1. a) What is the most widely used Internet

service?

b) List two examples of web browsers.

2. a) What is used to create most web pages?

b) Why is HTML well suited for the Web?

c) Why is it important for the W3C to develop

Web standards?

3. Why is the order of HTML tags and content

important in an HTML document?

4. a) List the four document tags.

b) Why is it important to properly structure an

HTML document when HTML is a free-form

language?

c) What rules are followed when saving an

HTML document?

5. a) Where are scripts placed in an HTML docu-

ment?

b) How can scripts enhance a website?

c) Write a script to display “Good-bye” in an

alert dialog box.

d) Write a script to display “Today’s News” in

the status bar of the browser window.

6. a) What is a Java applet?

b) How is a Java applet interpreted by a web

browser?

c) List two reasons why Java applets are well

suited for the Web?

7. The following HTML document has seven

errors. What are they?

<html>

<body>

<title>Operating Systems</title>

</body>

<head>

<!--adds a horizontal rule>>

<p>Every computer must have an operat-

ing system. Types of operating systems

include:</p>

<ul>

<li>Windows<li>

<li>Linux</li>

</ul>

</head>

</html>

8. a) What does a style sheet define?

b) Why are style sheets used?

c) What is the difference between an embedded

and a linked style sheet?

9. What element is modified to change the back-

ground color or alignment of a web page?

True/False

10. Determine if each of the following are true or

false. If false, explain why.

a) A website consists of a series of web pages.

b) Hypertext is a database system.

c) An HTML document must be published to

a web server in order to be viewed in a web

browser.

d) Spaces and blank lines generally have no

effect on how an HTML document is inter-

preted.

e) HTML documents are saved with a TXT

extension.

f) Scripts must be placed in the head section of

an HTML document.

g) JavaScript is used to add dynamic content to

an HTML document.

h) Java applets are interpreted on web servers.

i) Java applets can only run on a Windows

platform.

j) Java applets have the ability to write files on

a user’s computer.

k) Java applets have to be compiled.

l) The anchor tag is used to create a

hyperlink.

m) A rule modifies an HTML element.

56 Chapter 2 Applets and Web Programming

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Exercises

Exercise 1 ——————————————— tourist_attractions.htm

Research tourist attractions in a particular city by using the Internet, magazines, and books and then

create an HTML document that lists tourist attractions for a particular city. The HTML document

should include:

• a comment with your name

• an appropriate title

• the city name in Heading 1 format

• “Tourist Attractions” in Heading 2 format

• a horizontal rule

• at least five tourist attractions, each displayed in a bulleted list

• a style sheet with at least three rules

• a script

Exercise 2 ————————————————— sports_report.htm

Create an HTML document that documents recent school sports related news. The HTML document

should include:

• a comment with your name

• appropriate titles formatted with heading tags

• a horizontal rule

• at least three news stories

• an image

• a style sheet with at least three rules

• a script

Exercise 3 ————————————————————— applet.htm

Create an “Applet Help” HTML document that documents the steps to create an original applet or

download an applet and embed the applet in an HTML document. Display an example of an original

applet or a downloaded applet from http://java.sun.com/openstudio/index.html on the HTML

document.

Chapter 2 Applets and Web Programming 57

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Exercise 4 —————————————— electronic_portfolio.htm

A portfolio is a collection of work that clearly illustrates effort, progress, and achievement of knowledge

and skills. An electronic portfolio stores and presents portfolio content in a digital format such as a

website. Create linked HTML documents that presents your contact information, academic history,

work and volunteer experience, and accomplishments.

Exercise 5 ——————————————— computer_history.htm

Research the history of computers by using the Internet, magazines, and books and then collaborate in

small groups to create linked HTML documents that outline key events in computer history by decade.

Describe at least five key events for the 1970s, 1980s, 1990s, and 2000s. Use a style sheet to format the

HTML documents.

Exercise 6 ———————————————— html_reference.htm

Create an “HTML Reference” document that lists HTML tags, describes the tag, and provides corre-

sponding examples. Research and include at least three HTML tags not covered in this chapter. The

www.w3c.org website documents HTML tags.

Exercise 7 ——————————————————— copyright.htm

Research copyright laws and issues as they pertain to digital information. Present your research in the

form of at least two linked HTML documents. Include an additional linked HTML document to cite

the sources used using an established method, such as MLA or APA style.

Exercise 8 ——————————————— technology_report.htm

Create an HTML document that reviews a recently released software application or hardware device.

List the product specifications and target market for the product. Include your opinion on whether you

think the product will be successful or useful.

Exercise 9 ——————————————————— interview.htm

Interview a local web programmer about software, tools, and knowledge they feel are important when

creating websites. Document your interview. In small groups, share your interview documentation.

58 Chapter 2 Applets and Web Programming

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Chapter 3 Introducing Java 59

sample

ava, developed by Sun Microsystems, is a widely used high-level

programming language. One reason for its wide-spread use is the ability

to create platform-independent applications. This chapter introduces Java,

OOP terminology, code conventions, and program design.

Why Program in Java?

Object-oriented programming (OOP) evolved out of the need to develop

complex programs in a systematic, modular approach. The OOP approach

allows programmers to create modules that can be used over and over

again in a variety of programs. These modules group related data and

instructions for performing actions on that data. Properly designed, these

modules encapsulate data to hide implementation details, are versatile

enough to be extended through inheritance, and give the programmer

options through polymorphism. Encapsulation, inheritance, and polymorphism

are features of every object-oriented language, including Java.

In addition to being object-oriented, the Java language can be used to

create platform-independent applications. Platform-independent applications

can be run on any computer regardless of operating system or hardware

configuration. These features of Java have allowed programmers to cre-

ate programs for the masses—similar to the way the Gutenburg press

revolutionized the printing process, making printed materials available

to the masses.

Objects, Classes, and Packages

Object-oriented program development involves selecting objects to

perform the tasks outlined in a program specification. An object consists

of related data and the instructions for performing actions on that data.

The design for an object is called a class. A class defines the type of data

and actions that will be associated with an object of that class, but not the

actual data for an individual object. Classes are required to create objects.

Many objects of the same class may be needed in an application.

Chapter 3

Introducing Java

The Gutenburg Press

About 1450, Johann Gutenburg

designed a system that used

cast metal letters and a printing

press where each of the

letters could be easily loaded

and then inked to make an

impression on paper. The key

to the Gutenburg press was

the reusable metal type that

could be reorganized over and

over again to inexpensively

create books and other printed

materials. The impact on

society was immeasureable as

people of every social standing

became literate.

Program Specification

A program specification is a

definition or outline of what

a program is expected to

do. In industry, a program

specification can serve as

a co nt rac t be t ween t he

programmer and the client.

60 Chapter 3 Introducing Java

sample

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





A class can be used to create many objects—each object

will have the same type of data and possible actions, but

each object maintains its own set of data.

A package, sometimes called a library, is a group of related classes. For

example, classes related to a particular task, such as input and output, can

be grouped together in a package. A media package containing a DVD

class and a CD class can be illustrated as:

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

A package contains related classes.

An application is also contained in a package. It contains a controlling

class and can contain other classes as well:







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



An application is contained in a package.

Packages are importable, which means an application can use existing

classes from another package.

TIP Reusability is a term asso-

ciated with object-oriented

programming.

TIP Applications use, or

import, packages to define

objects.

package, library

Chapter 3 Introducing Java 61

sample

A Java Application

A Java application is a package with at least one class that contains a

main() method. The following Greeting application is a simple, yet com-

plete Java program:

* Greeting.java

* A first Java application.

* A Student

* Course

* Date

package firstApplication;

/**

* The Greeting class displays a greeting.

public class Greeting { //start class definition

public static void main(String[] args) {

System.out.println("Hello, world!");

}

} //end class definition

Greeting generates output similar to:

A program consists of a set of instructions called statements. A semi-

colon is required to indicate the end of a statement. Related statements

are enclosed by curly braces ({ }) to begin and end the instructions. The

statements in the Greeting application are:

• package firstApplication declares a package name. If a package

name is not declared, then the application is given the package

name Default by the compiler. Simple applications often do not

have package statements.

• public class Greeting is a class declaration. The class is available

to anyone (public) and is named Greeting. The Greeting class does

not define any data or actions for objects. However, it contains the

main() method making it the application’s controlling class. The

controlling class is a program’s starting point.

• public static void main(String[] args) defines the main() method.

A method is a named set of statements that perform a single, well-

defined task. The main() method is placed in the controlling class.

Its statements are automatically run when the program is executed.

The statement in this main() method uses the println() method to

display “Hello, world!” to the system output (the screen).

In addition to statements, programs contain comments, which provide

information about the program to the reader of the code. Comments have

no affect on the program, but they allow a reader of the program to quickly

understand the purpose and logic behind segments of code. Because

complex applications are often developed and maintained by more than

one programer, properly commented code allows for easier modifications

and can decrease the number of mistakes.

method

comments

statements

File Organization

Application development

requires careful organization.

Typically, the folder for an

application is given the same

name as the package name,

and the application name is

the same as the controlling

class name.

controlling class

TIP The static void in the

main() method means that it is

a method of the class and does

not generate a value.

62 Chapter 3 Introducing Java

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Java programs can contain three types of comments:

• /* */ are used to enclose single or multiline comments. These

comments are appropriate at the beginning of a program to describe

the application and where necessary to clarify a segment of code.

• // are used for adding a comment to the end of a statement or to

create a single line comment. The // is also useful for debugging

a program, which will be discussed in a later chapter.

• /** */ are used for documentation. The javadoc tool copies

these comments into a separate HTML document to create an

instructional manual or external documentation. Documentation

comments are appropriate for describing a class or method.

Multiline comments that describe a program, class, or method are some-

times referred to as a comment block. Tips throughout the text will provide

additional pointers about commenting code.

Executing a Java Application

Java code typed by a programmer is called source code. For source code

to execute, or run, it must be translated to code the computer understands

in a process called compiling. Many Java compilers provide an environ-

ment for entering the source code as well as for compiling and running

an application. Source code files have the extension .java, while compiled

files have the extension .class.

Compiled Java source code is called bytecode. Executing a Java applica-

tion means that its bytecode is interpreted with a Java Virtual Machine

(Java VM). The interpreter runs each bytecode instruction as it is read.

The Java VM can reside on any computer, regardless of operating system

environment, making Java applications extremely portable, reliable, and

platform-independent.

Although bytecode is versatile for porting applications to several dif-

ferent environments, programs compiled to machine code run faster.

Machine code is comprised of just 1s and 0s and is different depending on

the computer platform. A just-in-time compiler (JIT) converts bytecode to

machine code before it is executed with the Java VM.

A program containing syntax errors will not compile. A syntax error

occurs in a statement that violates the rules of Java. For example, all Java

statements must end with a semicolon. A statement without a semicolon

generates a syntax error when the program is compiled, preventing the

compiler from generating bytecode for the application.

Review: Greeting

Create a Greeting application similar to the one shown in the “A Java Application” section. Refer to online

materials at www.lpdatafiles.com for guidance with your Java compiler. Your instructor may also have spe-

cific information regarding your compiler. The goal of this review is to write the source code for a simple

application and then compile and run the code.

Platform-Dependent

Programming languages such

as C++ and Visual Basic

.NET are compiled directly to

machine language. Although

faster, these programs must be

recompiled for every platform

that will run the application.

TIP The main() method does

not typically have a comment

block.

Virtual Machine

Virtual means not real. A

virtual machine is therefore

conceptual, not made of

hardware and other physical

components.

TIP Visit lpdatafiles.com for

specific information about dif-

ferent Java compilers.

Chapter 3 Introducing Java 63

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Displaying Output

An output stream sends data to an output device. To process data for the

output stream, Java provides the System class with methods for display-

ing output. For displaying data to the standard output stream, which is

typically the computer screen, use System.out. out contains print() and

println() methods. The difference between these methods is how they

control output. The print() method displays data and leaves the insertion

point at the end of the output, while println() moves the insertion point to

the next line after displaying output. The following application uses both

methods:

/**

* Displays a welcome message.

public class MulticulturalGreeting {

public static void main(String[] args) {

System.out.print("Hello");

System.out.print("Buenos Dias");

System.out.println("Bonjour");

System.out.println("How do you greet another?");

}

The print() and println() methods require arguments. An argument is data

passed to a method for processing. In this case, the print() and println()

arguments are strings. A string is a set of characters, which are enclosed

by quotation marks.

MulticulturalGreeting produces output similar to:

An escape sequence is a backslash (\) followed by a symbol that together

represent a character. Escape sequences are used to display special char-

acters. Common escape sequences include:

\n newline

\t tab (8 spaces)

\\ backslash

\" double quotation mark

The modified MulticulturalGreeting illustrates the use of escape

sequences:

/**

* Displays a welcome message.

public class MulticulturalGreeting {

public static void main(String[] args) {

System.out.print("Hello\t");

System.out.print("Buenos Dias\t");

System.out.println("Bonjour");

System.out.println("How do you greet another?");

}

escape sequence

output stream

print() println()

argument

string

TIP The System class is in the

java.lang package.

64 Chapter 3 Introducing Java

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Review: AboutMe – part 1 of 2

Create an AboutMe application that displays your first name and last initial, your instructor‘s name, and

your school name on three separate lines. Below the personal information, display a phrase that encourages

your school team. For example, “Go Bears!” Be sure the phrase is displayed with quotation marks.

Formatting Output

The format() method can be used in place of the print() or println()

methods to control the way output is displayed. The format() method

arguments include a format string and an argument list. The format

string contains specifiers that indicate how the corresponding strings in

the argument list should be displayed. The following code demonstrates

the format() method:

System.out.format("%-10s %8s %8s", "Team", "Wins", "Losses\n");

System.out.format("%-10s %8s %8s", "Jaguars", "10", "5\n");

System.out.format("%-10s %8s %8s", "Cheetahs", "14", "1\n");

System.out.format("%-10s %8s %8s", "Panthers", "8", "7\n");

System.out.format("%-10s %8s %8s", "Penguins", "4", "11\n");

When executed, the statements display:

A format string specifier takes the form:

%[alignment][width]s

% indicates the start of a specifier

[alignment] skip for right alignment.

Include a minus sign (–) for left alignment

[width] the number of characters to use for output

s indicates that the corresponding argument is a string

If [width] is greater than the number of characters in the corresponding

string argument, then spaces pad the output. A string longer than [width]

characters is displayed, but any strings to the right are moved over.

Text may also be included within the format string. For example, the

statement:

System.out.format("The final game score: %-8s %8s", "10", "5");

displays:

Numeric Output

The NumberFormat class,

discussed in Chapter 4, can

also be used to format numeric

data.

TIP The format() method is

new to Java 5 and requires

JDK 5.

Chapter 3 Introducing Java 65

sample

Review: AboutMe – part 2 of 2

Modify the AboutMe application to include your class schedule, the days of the week that your class meets,

and the start and end time of each class. Include code to properly align the data into three columns with the

weekdays left aligned and the class start and end times right-aligned.

Code Conventions

Code conventions are a set of guidelines for writing an application. These

guidelines provide details about commenting, rules for naming methods,

classes, and packages, and statement formatting. Just as comments inform

a reader about a segment of code, a program that follows specific code

conventions is easier to read and understand.

A company or organization that employs programmers will typically

adhere to specific code conventions. A programmer familiar with the

code conventions will more quickly become familiar with code written

by another programmer in the company. Code conventions can make

modifying and maintaining code faster, easier, and less expensive. Because

of these benefits, organizations often not only encourage the use of code

conventions, but require it.

The code conventions introduced in this chapter are:

• An introductory comment should begin a program. This comment

should include information such as your name, class name, the

date, and a brief statement about the program.

• Package names should begin with a lowercase letter and then an

uppercase letter should begin each word within the name. Package

names may not contain spaces.

• Class names should be nouns and begin with an uppercase letter

and an uppercase letter should begin each word within the name.

Class names may not contain spaces.

• A comment block should be included before each class and

method. A comment block is not typically placed before the main()

method.

• Comments should not reiterate what is clear from the code.

• Statements in a method should be indented.

• An open curly brace ({) should be placed on the same line as

the class or method declaration, and the closing curly brace (})

should be on a separate line and aligned with the class or method

declaration.

TIP Code conventions are

important. About 80% of the

lifetime cost of a piece of soft-

ware goes to maintenance.

Rarely is software maintained

for its whole life by the original

author.

66 Chapter 3 Introducing Java

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Algorithm Design

Programs are created to solve problems. However, problems of any

complexity require outlining, or designing, a solution before typing any

source code. One method of design is called an algorithm. An algorithm is

a set of steps that outline how to solve a problem.

Algorithms can be created in several ways. Often more than one

approach is implemented. Steps written out in plain English is one

approach. Pseudocode is a mix of English and program code, and is useful

for refining a plain English algorithm. Flowcharts use symbols and text to

give a visual representation of a solution.

A description of the problem to be solved is used in developing an

algorithm. For example, a program specification may state “The Triangle

application displays a right triangle made up of the asterisk (*) symbol. The

triangle should be 4 asterisks high by 4 asterisks wide.” Triangle appears

to be a very simple application. From the description, we conclude that

Triangle should display an image of a right triangle.

The next step after analyzing the problem is to produce the algorithm. In

most cases, use more than one method to generate the algorithm to ensure

that the solution to the problem is accurate. The following illustrates the

Triangle program in both plain English steps and a flowchart:

The Triangle algorithm in plain English:

1. Print an asterisk to the screen.

2. Print two asterisks to the screen.

3. Print an asterisk followed by a space and an asterisk to the

screen.

4. Print four asterisks to the screen.

The Triangle flowchart:





















pseudocode

flowcharts

Chapter 3 Introducing Java 67

sample

Each flowchart symbol has a different meaning. The indicates start

or end. The shape indicates input/ouput. Other flowchart symbols

will be introduced throughout the text as new concepts are covered.

Chapter Summary

This chapter introduced Java, which is an object-oriented program-

ming language. OOP languages evolved out of the need to better develop

complex programs. In addition to being object-oriented, Java is platform

independent. Platform-independent applications can run on any computer,

regardless of the operating system or hardware configuration.

Object-oriented languages use classes to define objects. A class defines

the type of data and actions associated with an object, but not the actual

data for an object. A package groups related classes.

A Java application is a package with at least one class. Statements in an

application provide instructions. Methods are a named set of statements

that perform a single, well-defined task. Comments in an application

provide details about the code to the reader. Comments can be single or

multiline and can also be extracted for documentation.

The code typed by a programmer is called source code. The source code

is translated to bytecode with a compiler. Program execution occurs when

the bytecode is interpreted with a Java Virtual Machine (Java VM). The

Java VM can reside on any computer. A just-in-time (JIT) compiler converts

bytecode to machine code before execution by the Java VM. Although

less portable, machine code is faster. If a program contains errors, it will

not compile. One type of error is the syntax error, which results when a

statement violates the rules of Java.

Program output is through the output stream. The standard output

stream is typically the computer screen and requires the System.out meth-

ods print() and println(). These methods require a string argument.

Escape sequences are used to display special characters. Output can be

formatted with the format() method.

Code conventions are a set of guidelines for writing an application. The

code conventions introduced in this chapter are:

• An introductory comment should begin a program. This comment

should include information such as your name, class name, the

date, and a brief statement about the program.

• Package names should begin with a lowercase letter and then an

uppercase letter should begin each word within the name. Package

names may not contain spaces.

• Class names should be nouns and begin with an uppercase letter

and then an uppercase letter should begin each word within the

name. Class names may not contain spaces.

• A comment block should be included before each class and

method. A comment block is not typically placed before the main()

method.

68 Chapter 3 Introducing Java

sample

• Comments should not reiterate what is clear from the code.

• Statements in a method should be indented.

• An open curly brace ({) should be placed on the same line as

the class or method declaration, and the closing curly brace (})

should be on a separate line and aligned with the class or method

declaration.

Programs are created to solve problems. However, problems of any

complexity require outlining, or designing, a solution before typing any

source code. One method of design is called an algorithm. An algorithm

can be implemented through steps written in plain English, steps written

in a mixture of code and English called pseudocode, or steps presented

visually with a flowchart.

Chapter 3 Introducing Java 69

sample

Vocabulary

Algorithm A set of steps that outline how to solve

a problem.

Argu ment Data passed to a method for

processing.

Bytecode Compiled Java source code.

Class The description of an object.

Code conventions A set of guidelines for writing

an application.

Comment Text that provides information to the

reader of program code.

Comment block Multiline comments that describe

a program, class, or method.

Compiling The process where source code is con-

verted to code the computer understands.

Controlling class The class in an application that

contains the main() method.

Encapsulation An object-oriented language

feature.

Escape Sequence A backslash followed by a symbol

that together represent a character.

Execute To run a program.

Flowchart A visual representation of an

algorithm.

Importable Package code that can be used by an

application.

Inheritance An object-oriented language feature.

Interpreter Software that runs each bytecode

instruction of a compiled Java program.

Java application A package with a controlling class

and possibly other classes.

Java Virtual Machine (Java VM) The Java bytecode

interpreter.

Just-in-time compiler (JIT) Software that converts

bytecode to specific machine code.

Library see Package.

Machine code The most basic computer language,

which is comprised of just 1s and 0s.

Method A named set of statements that perform

a single, well-defined task. A method is always a

member of a class.

Object A named entity that consists of related

data and instructions for performing actions on

that data.

Object-oriented pr ogramming (OOP) A

systematic, modular approach to developing complex

programs.

OOP see Object-oriented programming.

Output Stream Sends data to an output device,

typically the computer screen.

Package A group of related classes. Also called a

library.

Platform-independent application A program that

can be run on any computer regardless of operating

system or hardware configuration.

Polymorphism An object-oriented language

feature.

Pseudocode An algorithm written in a mix of

English and program code.

Run see Execute.

Source code The code typed by a programmer.

Statement An instruction in a program.

String A set of characters.

Syntax error A statement that violates the rules

of Java.

70 Chapter 3 Introducing Java

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Java

/* */ Used to enclose single or multiline

comments.

/ * * */ Used to enclose documentation

comments.

// Used to begin a single line comment.

{ } Used to begin and end a set of related

statements.

; Required at the end of each program statement.

\\ Escape sequence for displaying a backslash.

\" Escape sequence for displaying a double quota-

tion mark.

\n Escape sequence for displaying a newline.

\t Escape sequence for displaying a tab.

class Used to declare a class.

format() Method that displays more precisely for-

matted output to the screen.

java.lang.System The class that contains the out

member.

main() The method in the controlling class that

is automatically executed when a Java application

is run.

out The java.lang.System member that represents

the standard output stream.

package Statement used to declare a package.

print() Method that displays output to the

screen.

println() Method that displays output to the

screen and then moves the insertion point to the

next line.

public An access modifier that declares a class or

method as available to any code.

static A declaration used for class methods.

void Indicates a method will not return a value.

Chapter 3 Introducing Java 71

sample

Critical Thinking

1. a) List three features of every object-oriented

programming language.

b) Explain, in your own words, what you think

the meaning is of each of the three features

listed in part (a).

2. Draw a sketch that shows the relationship, and/

or hierarchy, of object, class, and package for the

package File, class FileReader, and the object

fileInput.

3. Write an appropriate comment block for the

beginning of a program to describe an applica-

tion that is intended to calculate test averages.

4. Write an appropriate comment for describ-

ing a class that displays the average of a set of

scores.

5. Write a statement that declares a package with

the name gradeCalculator.

6. Write a statement that declares a class named

AverageScore that is available to any code.

7. Explain the difference between source code and

bytecode.

8. Describe machine code.

9. Explain the difference between a Java compiler

and the Java VM.

10. What is the advantage of compiling Java source

code using a JIT?

11. The following application has seven syntax

errors. What are they?

* Test.java

* What's wrong application.

* Student Name

package testMyKnowledge;

/**

* The Test class should display a string,

public class Test {

private static int main(string[] args) {

System.out.println("Testing...)

}

12. Explain the difference between the print() and

println() methods.

13. Explain the advantages of using the format()

method in place of the print()and println()

methods.

14. There are five places in which the application

below does not follow the code conventions

outlined in this chapter. Where are they?

* getGreeting.java

* What's wrong application.

* Student Name

package notSoGood;

/**

* Good Morning is displayed.

public class getGreeting {

public static void main(String[] args) {

//Output Good Morning to the screen

System.out.println("Good Morning");

} }

15. Explain the similarities and differences between

pseudocode and a flowchart.

True/False

16. Determine if each of the following are true or

false. If false, explain why.

a) Java applications can run only on the

Windows platform.

b) Statements must end with a semicolon.

c) Comments have no effect on program

execution.

d) The main() method is placed in the

controlling class.

e) Related statements are enclosed with brackets

([]).

f) A file containing only source code can be

executed on a computer.

g) Compiled source code is called machine

code.

h) A program containing syntax errors will

compile.

i) An algorithm is a set of steps that outline

how to solve a problem.

j) Pseudocode cannot be used to implement an

algorithm.

72 Chapter 3 Introducing Java

sample

Exercises

Exercise 1 ————————————————————— BingoCard

Create a BingoCard application that displays a traditional bingo card with five columns of five unique

numbers. The column labels are B, I, N, G, and O. Column B contains numbers ranging from 1 through

15, column I has numbers ranging from 16 through 30, column N has four numbers ranging from 31

through 45 and a Free Space in the middle of the column, column G has numbers ranging from 46

through 60, and column O has numbers ranging from 61 through 75. The application output should

look similar to:

Exercise 2 —————————————————————BingoRules

Create a BingoRules application that displays the rules for playing bingo. Place each rule on a separate

line and place a blank line between rules. The application output should look similar to:

Exercise 3 ————————————————————— Rectangle

Create a Rectangle application that displays a rectangle of asterisks (*). The rectangle should be 15

asterisks wide and 7 asterisks high. The application output should look similar to:

Chapter 3 Introducing Java 73

sample

Exercise 4 —————————————— RockPaperScissorsRules

Create a RockPaperScissorsRules application that displays the rules for playing Rock Paper Scissors.

Place each rule on a separate line and place a blank line between rules. The application output should

look similar to:

Exercise 5 —————————————————— TicTacToeBoard

Create a TicTacToeBoard application that displays a tic-tac-toe board with an X in the center. The appli-

cation output should look similar to:

Exercise 6 —————————————————— TicTacToeRules

Create a TicTacToeRules application that displays the rules for playing tic-tac-toe. Place each rule on a

separate line and place a blank line between rules. The application output should look similar to:

74 Chapter 3 Introducing Java

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Exercise 7 ——————————————————————— Smile

Create a Smile application that displays a smiling face made of keyboard characters. The application

output should look similar to:

Exercise 8 —————————————————— JavaTerminology

Create a JavaTerminology application that displays at least five words from the vocabulary list in this

chapter and the corresponding definition. Place each word on a separate line followed by the definition.

Place a blank line between entries. The application output should look similar to:

Exercise 9 ————————————————— FlowchartSymbols

Create a FlowchartSymbols application that illustrates the two flowchart symbols that were introduced

in this chapter. The application output should look similar to:

Chapter 3 Introducing Java 75

sample

Exercise 10 —————————————— CompilerDocumentation

Create a CompilerDocumentation application that creates compiler-specific documentation for the

compiler you will be using in your class.

a) Add the compiler name to the right of “Compiler” and then explain how to create a new

project, enter source code, compile, and run a Java application using a format similar

to:

b) Explore the compiler’s help features. Add documentation that explains how to use

the compiler’s Help features.

Exercise 11 —————————————————— BinaryNumbers

As discussed in Chapter 1, computers are digital and they recognize two states: on and off. Therefore, the

binary number system (base 2), which uses only two digits (0 and 1), was adopted for use in computers.

Our most familiar number system is the decimal, or base 10, system. It uses ten digits: 0 through 9.

a) Create a BinaryNumbers application that illustrates the binary numbers 1 through

20 and their decimal equivalents. Refer to chapter 1 for the conversion formula or if

you have the Windows operating system, use the Microsoft Calculator in the Start j

All Programs j Accessories menu to convert the numbers. In the Microsoft Calculator,

select View j Scientific and then enter the number and select Bin to convert the decimal

(Dec) number:

76 Chapter 3 Introducing Java

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The application output should look similar to:

b) The hexadecimal, or base 16, system is based on 16 digits: 0 through 9, and the letters

A through F representing 10 through 15 respectively. Modify the BinaryNumbers

application to include a Hexadecimal column that contains the corresponding

hexadecimal numbers.

Exercise 12 —————————————— ProgrammingLanguages

a) Create a ProgrammingLanguages application that displays information about object-

oriented programming languages. The application output should look similar to:

b) Use books and the Internet to research other object-oriented programming languages

and add three additional object-oriented programming languages to the list.

Chapter 4 Variables and Constants 77

sample

Variables and constants are two important concepts explained in this

chapter. Using primitive and abstract data types to declare variables is

covered. User input, numeric expressions, and assignment operators are

also discussed.

Declaring Variables

A variable is a name for a value stored in memory. Variables are used in

programs so that values can be represented with meaningful names. For

example, when a variable named length is used in a program, it is clear

that its value is a distance. Variables should be used to represent values

because they make code easier to read, understand, and modify.

A variable must be declared before it is used. A declaration takes the

form:

The declaration includes two parts. The first is the data type, which

determines the type of data the variable will store. The second part of a

declaration is the variable name, called the identifier. For example, in the

declaration

int length;

int is the data type and length is the identifier. An int stores an integer

value, which is a positive or negative whole number. When an integer

variable is declared it stores the value 0.

An identifier must begin with a letter and contain only letters, numbers,

and some special characters. Typically variable identifiers begin with a

lowercase letter. Any word after the first in a variable identifier should

begin with an uppercase letter. For example, rectangleLength. This code

convention allows variables to be easily recognized.

Multiple variables with the same data type can be declared in a single

statement, similar to:

int length, width;

Grouping variables together in a single statement is good programming

style when the variables represent related items. Declarations should not

be grouped together in the same statement just because the variables are

all the same type.

Chapter 4

Variables and Constants

data type

declaration

identifier

78 Chapter 4 Variables and Constants

sample

Using Variables

Applications typically contain many variables, as in RectangleArea:

/**

* Calculates and displays the area of a rectangle

public class RectangleArea {

public static void main(String[] args) {

int length = 10; //longer side of rectangle

int width = 2; //shorter side of rectangle

int area; //calculated area of rectangle

area = length * width;

System.out.println("Area of rectangle: " + area);

}

RectangleArea produces output similar to:

Variable declarations should be grouped at the beginning of a method.

A blank line after the declarations makes it easy to determine where the

declarations end.

The value of a variable is changed through assignment. An assignment

statement is formed with the variable name on the left side of an equal

sign and the value it is to receive on the right side of the equal sign. The

equal sign (=) is an operator that indicates that the variable on the left is to

receive the value on the right. The value on the right can be a literal, which

is any actual value. It could also be another variable or an expression. For

example, area was assigned the value of the length multiplied by the width

(length * width). Note that the * symbol indicates multiplication.

An assignment statement can be part of a variable declaration. In addition

to being declared, the variable is initialized. For example, in RectangleArea,

variables length and width were assigned values when declared.

A System.out.println() statement can be used to output the value of

a variable. Variable identifiers are not enclosed by quotation marks. To

append, or concatenate, the value of a variable to a string, the + operator

is used. The + operator converts the value of the variable to a string and

then concatenates the strings before output.

It is important to realize that a variable can store only one value at any

one time. For example, after the following statements execute

int x;

x = 5;

x = 10;

the value of x is 10 because this was the last value assigned to x.









assignment

concatenation

equal sign

literal

initialize

Chapter 4 Variables and Constants 79

sample

Review: RectanglePerimeter

Create a RectanglePerimeter application that calculates and displays the perimeter of a rectangle with width

4 and length 13. The perimeter of a rectangle is calculated as 2w + 2l. Use variables as appropriate.

Primitive Data Types

The int data type is called a primitive data type. A variable that is

defined with a primitive data type stores a single piece of data. Java supports

several primitive data types, including:

Type Bytes Data Range

int 4 a positive or negative integer from –2,147,483,648

to 2,147,483,647

double 8 a positive or negative number that may contain

a decimal portion in the range –1.7E+308 to

1.7E+308

char 2 a single character

boolean true or false

An int variable uses 4 bytes of memory to store its value and is used

for representing whole numbers.

Values that are represented by the double data type are sometimes

referred to as floating point, meaning that the values contain numbers after

the decimal point. Because of the many digits that are possible in a double,

a variable of this type uses 8 bytes of memory.

A char variable requires 2 bytes of memory because Java uses the 16-

bit Unicode character encoding. Assignment to a char variable requires

enclosing a single character in single quotation marks, as in 'a'.

Variables that are type boolean can have only one of two values—true

or false. Boolean variables are particularly useful for representing yes/no

or on/off values.

When choosing a data type, it is important to choose the most appropri-

ate type for the quantity being represented. If a value could possibly have

a decimal portion, then double is the best choice. If a variable will represent

only whole numbers, then int is the best choice even though double will

work. Using the most appropriate data types for variables has two benefits.

First, both the compiler and the reader will understand the possible values

for a variable. Second, the compiler allocates the appropriate memory for

the variable.

Review: Distance – part 1 of 2

Create a Distance application that calculates and displays the total distance of a race with three segments.

The first segment is 12.2 km, the second is 10.6 km, and the third is 5.8 km. Use variables of the appropriate

type.

String Data

Strings are comprised of a set

of characters and therefore

cannot be represented by a

primitive data type. The String

class in the java.lang package

is used to create string vari-

ables. Strings are discussed in

more detail in Chapter 6.

TIP Java also supports the

byte, short, long, and float

primitive data types.

floating point

choosing data types

TIP Primitive data types are

also called built-in data types.

80 Chapter 4 Variables and Constants

sample

Abstract Data Types

In addition to primitive data types, a variable can be declared using an

abstract data type. One kind of abstract data type is the class. Many classes

are provided in Java, and many more classes will be created throughout

this text. Each class defines not just a single piece of data like a primitive

data type, but a set of data along with methods for performing actions on

that data.

A variable declared with a class is called an object. The variable itself

actually stores a reference to the area in memory where the object’s data

and methods are stored:









Creating a new object is called instantiation. In addition to declaring a

variable to refer to the object, the object must be created and initialized

in a statement that takes the form:

<class> <variable name> = new <class>(<arguments>);

The new operator allocates memory for the object and returns a reference

to the object. <arguments> are used to initialize the data for the object.

The code below creates a new object using a class named Circle:

Circle spot = new Circle(4); //spot with radius 4

In this statement, the variable spot refers to a Circle object that has been

initialized with a radius of 4.

To access a member of a class, such as a method, use the object name

followed by a dot (.) and then the member name. For example, the code

below executes method members getRadius() and area():

Circle spot = new Circle(4);

System.out.println("Radius of spot is " + spot.getRadius());

System.out.println("Area of spot is " + spot.area());

These statements produce output similar to:

The Circle class will be developed later in this text.

Java Packages

Java includes numerous packages as part of the Java Runtime

Environment (JRE). These packages contain general use classes, utility

classes, or special purpose classes. The most fundamental package is

java.lang with classes that define the language itself. Other packages such

as java.util have classes for reading input and generating random numbers.

These packages will be explained and used throughout this text.

object

instantiation

Package

Documentation

Pack age docume ntation

typically summarizes the

package classes and the data

and methods available in those

classes. Code examples that

use the classes may also be

included in the documentation.

Docu me nt at ion for Java

packages are available online

at www.sun.com.

Chapter 4 Variables and Constants 81

sample

Packages follow a certain naming convention. Java packages start with

java followed by a dot (.) and then the package name. Companies and

other organizations will often name a package with the organization name

followed by a dot and then the package name.

The import statement is used to make the members of a package acces-

sible to an application. To make a single class from a package accessible,

a statement similar to the following is used:

import java.util.Scanner;

The class name starts with an uppercase letter, following the appropriate

naming convention for class names. If several classes in a package are to

be accessible, then a statement that imports the entire package may be

used:

import java.util.*;

The asterisk (*) indicates that all members of the util package are to be

accessible. import statements must appear after a package statement and

before any class definitions. Java applications automatically import the

entire java.lang package.

Obtaining a Value from the User

An application is more flexible when values can be read from an input

stream. An input stream is the sequence of characters received from an

input device, such as a keyboard. For example, as a user types data, the

data goes into the input stream. To process data in the input stream, Java

includes the Scanner class with methods for reading integers, floating

point numbers, and strings.

A program that obtains a value from the user must instantiate a Scanner

object that is initialized with an input stream. For data typed from a

keyboard, initialize the object with System.in because it represents the

standard input stream.

Scanner class methods include:

Class Scanner (java.util.Scanner)

Methods

next() returns a string from the input stream.

nextLine() returns the string up to the end of line character

from the input stream.

nextInt() returns the int read from the input stream.

nextDouble() returns the d ou b l e read from the input

stream.

nextBoolean() returns the boolea n read from the input

stream.

close() closes the input stream.

The next() method is used for reading a string that does not contain

spaces. For example, “apple”. Attempting to read the string “apple pie”

generates a run-time exception called InputMismatchException. An

exception is an error affecting program execution. Exceptions are discussed

later in this chapter.

TIP The Scanner class is new

to Java 5.

input stream

Scanner

TIP Companies sometimes

use their reversed Internet

domain in package names. For

example, com.mycompany.util

names a package with utility

classes.

import

exception

java.lang

82 Chapter 4 Variables and Constants

sample

When reading in a combination of numeric and string data, the next()

method should be used for reading string data after reading numeric data.

Using the nextLine() method is ineffective. It reads the end-of-line charac-

ter left by the numeric data entry, essentially reading an empty string. If a

string with multiple words is expected from the user, the nextLine() can

be used to read in the end-of-line character and then another nextLine()

used to read the string.

The RectangleArea2 class below instantiates a Scanner object and reads

values typed by the user:

import java.util.Scanner;

/**

* Calculates and displays the area of a rectangle

* based on the width and length entered by the user.

public class RectangleArea2 {

public static void main(String[] args) {

int length; //longer side of rectangle

int width; //shorter side of rectangle

int area; //calculated area of rectangle

Scanner input = new Scanner(System.in);

System.out.print("Enter the length: ");

length = input.nextInt();

System.out.print("Enter the width: ");

width = input.nextInt();

input.close();

area = length * width;

System.out.println("Area of rectangle: " + area);

}

Note that the import statement appears above the class. RectangleArea2

produces output similar to the following when values 6 and 2 are typed

by the user:

In the RectangleArea2 code, a Scanner object is declared, instantiated,

and initialized in the statement Scanner input = new Scanner(System.in).

The calls to the nextInt() method are used to obtain the values typed by

the user. When a call to nextInt() occurs, the application waits until the

user types a value and presses enter before the next statement is executed.

The application also includes prompts that tell the user what kind of input

is expected. For example, System.out.print("Enter the length: ") prompts

the user for a length value. When a Scanner object is no longer needed, it

should be closed with the close() method.

Review: Distance – part 2 of 2

Modify the Distance application to first prompt the user for the distance of each race segment and then

prompt the user for the runner’s name. The application should then display the runner’s name and total

distance to run.

prompt

reading numbers and strings

Chapter 4 Variables and Constants 83

sample

Numeric Expressions

Java includes built-in arithmetic operators for addition (+), subtrac-

tion (-), multiplication (*), division (/), and modulus division (%). These

operators are for use with primitive data and can be used to form numeric

expressions. A numeric expression contains at least one operand, which is

a value or primitive variable, and may contain operators. For example,

the numeric expression 6 + 5 contains two operands and one operator.

Numeric expressions can be used in assignment statements, as in the

statement area = length * width.

The / division operator performs differently depending on the data

type of the operands. When both operands are type int, the / operator

performs integer division. Integer division truncates the decimal portion

of the quotient to result in an integer:

Real division returns the entire quotient, including the decimal portion,

and is performed when one or both operators are type double.

Modulus division returns the remainder resulting from division. The %

operator truncates the operands, if necessary, to return an integer:

Modulus division is useful for retrieving digits of a number.

The statements below demonstrate the division operators:

int num1 = 5;

int num2 = 3;

int result;

double doubleNum1 = 5;

double doubleNum2 = 3;

double doubleResult;

result = num1 / num2;

System.out.println("num1 / num2: " + result);

doubleResult = doubleNum1 / doubleNum2;

System.out.println("doubleNum1 / doubleNum2: "

+ doubleResult);

doubleResult = num1 / doubleNum2;

System.out.println("num1 / doubleNum2: " + doubleResult);

result = num1 % num2;

System.out.println("num1 % num2: " + result);

doubleResult = doubleNum1 % doubleNum2;

System.out.println("doubleNum1 % doubleNum2: "

+ double Result);

Object Operators

Objects typically cannot be

manipulated with the built-in

arithmetic operators. A class

usually defines methods that

are used to perform operations

on objects.

Integer division

modulus division

84 Chapter 4 Variables and Constants

sample

Executing the statements on the previous page produces the output:

Java evaluates an expression using a specific order of operations based

on operator precedence. Operator precedence is the level assigned to an

operator. Multiplication and division (including modulus division) have

the highest precedence, followed by addition and subtraction. Two opera-

tors of the same precedence are evaluated in order from left to right.

The order of operations can be changed by including parentheses in a

numeric expression. The operations within parentheses are evaluated first.

For example, the expression 6 + 4 * 2 – 1 evaluates to 13, and the expression

(6 + 4) * (2 – 1) evaluates to 10. It is also considered good programming

style to include parentheses when there is any possibility of ambiguity or

question about the expression.

Review: Digits

Create a Digits application that prompts the user for a two-digit number and then displays the ones-place

and tens-place digits.

Type Casting

Type casting converts a number of one type to a number of a different,

but compatible type. For example, a double can be cast as an int, as in the

statements:

int i = 2;

double d = 3.7;

int x;

x = i * (int)d //d is explicitly cast; x is assigned 2x3

Type casting is necessary in this case because one of the operands in the

expression has less precision than the variable that will store the result.

Explicit casting also makes it clear that the programmer intended for the

calculation result to be an int.

Casting a double to an int truncates, or removes, the decimal portion of

the number, as in the statements above. When decreasing the precision of a

number, it is better to round the number. A number with a decimal portion

greater than or equal to 0.5 should be rounded up to the next integer, and

a number with a decimal portion less than 0.5 should be rounded down.

For example, rounding 3.7 results in 4.

operator precedence

truncate

TIP Truncation is always

toward 0.

order of operations

Chapter 4 Variables and Constants 85

sample

Rounding can be simulated when casting a double to an int by adding

0.5 to the number before casting, as in the statement:

x = i * (int)(d + 0.5) //x is assigned 2x4

If casting a negative number, then 0.5 should be subtracted from the

number before casting.

Casting is useful when real division with integers is preferred. The fol-

lowing statements demonstrate the difference between integer division

and real division with integers:

int i = 5;

int j = 2;

double result;

result = i / j; //integer division; result=2

result = (double)i / (double)j; //real division; result=2.5

Java will implicitly type cast operands in a mixed expression to match

the precision of the variable storing the result, as in the statements:

int i = 2;

double d = 3.7;

double y;

y = i * d //i is implicitly cast; y is assigned 2.0x3.7

Although explicit type casting is not necessary in this case, it is better

programming style to include casts. Casting makes a programmer’s inten-

tions clear and may make bugs easier to find. Therefore, the statements

above should be written as:

int i = 2;

double d = 3.7;

double y;

y = (double)i * d //better code; y is assigned 2.0x3.7

Review: GradeAvg – part 1 of 2

Create a GradeAvg application that prompts the user for five grades and then displays the average of the

grades. Assume the grades are integer values (for example, 89, 97, and so on). Real division should be per-

formed when calculating the average.

Review: TempConverter

Create a TempConverter application that converts a Fahrenheit temperature to the corresponding Celsius

temperature. The formula for converting Fahrenheit to Celsius is C = 5/9(F – 32). The application should

prompt the user for the Fahrenheit temperature. Be sure to carefully form the expression. Parentheses will

be needed to specify the order of operations.

rounding

real division

86 Chapter 4 Variables and Constants

sample

Formatting Numeric Output

The NumberFormat class, which is part of the java.text package, is used to

create objects that format numbers. NumberFormat objects return a string

that contains a formatted number. The formatting of the number depends

on which NumberFormat object is used. The NumberFormatExample

application creates four different NumberFormat objects:

import java.text.NumberFormat;

public class NumberFormatExample {

public static void main(String[] args) {

double dollars = 21.5;

int num = 1234;

double numWithDecimal = 2.0 / 3.0;

double sale = .15;

NumberFormat money = NumberFormat.getCurrencyInstance();

NumberFormat number = NumberFormat.getIntegerInstance();

NumberFormat decimal = NumberFormat.getNumberInstance();

NumberFormat percent = NumberFormat.getPercentInstance();

System.out.println(money.format(dollars));

System.out.println(number.format(num));

System.out.println(decimal.format(numWithDecimal));

System.out.println(percent.format(sale));

}

When executed, the application produces the following output:

Assignment Operators

In an assignment statement, the expression on the right side of the equal

sign (=) is evaluated first and then that value is given to the variable on

the left. Because the expression on the right is evaluated before an assign-

ment is made, it is possible to use the current value of the variable in the

expression itself. For example:

numPlayers = 12; //numPlayers is assigned 12

numPlayers = numPlayers + 2; //numPlayers is now 14

Changing the value of a variable based on its current value is often done

in programming. Therefore, in addition to the = assignment operator, Java

recognizes the +=, -=, *=, /=, and %= assignment operators. These operators

perform an operation before making an assignment. For example, the

previous assignment statement can be rewritten as:

numPlayers += 2; //numPlayers is now 14

The -=, *=, /=, and %= operators work similarly, as in the statements:

numPlayers -= 3; //same as: numPlayers = numPlayers - 3

numCopies *= 5; //same as: numCopies = numCopies * 5

total /= 2; //same as: total = total / 2

remainder %= 6; //same as: remainder = remainder % 6

java.text

The DecimalFormat

Class

The DecimalFormat class

offers additional options for

formatting numbers to a spec-

ified decimal place. Refer to

Java online documentation for

more information.

The format() Method

The format() method, discussed

in Chapter 3, can also be used

to format numeric values. A

specifier can take the form:

%[alignment][width][.decimal]f

where [.decimal] indicates

the number of decimal places

and f indicates a floating point

number. For an integer, the

specifier takes the form:

%[alignment][width]d

Chapter 4 Variables and Constants 87

sample

Review: GradeAvg – part 2 of 2

Modify the GradeAvg application to use the += operator to sum the grades as they are entered by the user.

Format the average grade to display as a percentage.

Using Named Constants

A constant is a name for a memory location that stores a value that cannot

be changed from its initial assignment. Constants, like variables, are used

in programs so that values can be represented with meaningful names. A

constant declaration is a variable declared final and takes the form:

final <type> <identifier>

The declaration begins with final, which indicates that the value will

not change, followed by the type of data the constant will store and the

constant identifier. For example, the following declaration represents „:

final double PI = 3.14;

double declares a numeric value possibly containing a decimal portion.

Constant identifiers are typically all uppercase, and may include under-

score (_) characters to separate words. For example, MAX _ PRICE.

The following class uses a constant in the main() method:

/**

* Calculates and displays the area of a circle

public class CircleArea {

public static void main(String[] args) {

final double PI = 3.14;

double radius = 5; //radius of circle

double area;

area = PI * radius * radius;

System.out.println("Area of circle: " + area);

}

CircleArea produces output similar to:

A constant can be assigned a value only once. Trying to change the

value of a constant after the initial assignment generates an error. Constant

declarations should be grouped at the beginning of a method before any

variable declarations.

When should a named

constant be used?

Named constants should be

used wherever they can add

clarity to code. However, there

are some values that should

not be replaced with named

constants. For example, in an

expression that calculates the

area of a triangle (½bh), the

value 0.5 is best used instead

of a named constant because

the value does not have an

obvious name.

88 Chapter 4 Variables and Constants

sample

Identifiers and Keywords

Identifiers in Java must begin with a letter and may contain letters,

numbers, and some special symbols. Periods and spaces are not allowed.

Identifiers are also case sensitive, which means that an uppercase letter is

different from the same letter in lowercase. For example, identifiers Count

and count are viewed by Java as two different identifiers.

The Java language contains keywords, which have special meaning to

the Java compiler and therefore cannot be used for a variable or constant

identifier. The Java keywords are:

abstract double int strictfp

boolean else interface super

break extends long switch

byte final native synchronized

case finally new this

catch float package throw

char for private throws

class goto protected transient

const if public try

continue implements return void

default import short volatile

do instanceof static while

Although not keywords, true, false, and null are reserved and not for

use as identifiers.

Review: CircleCircumference – part 1 of 2

Create a CircleCircumference application that calculates and displays the circumference of a circle. The

application should prompt the user for the value of the radius. The circumference of a circle is calculated as

2„r. Use variables and constants as appropriate.

Programming Errors

There are many types of errors that can occur in a program. Some errors

are found by the compiler. Others occur at run time. A program that has

been carefully designed will have fewer errors. Code reuse can also lead to

fewer errors because packages that have been carefully tested and properly

documented produce cleaner and more robust code.

Errors that violate the rules of Java are called syntax errors. For example,

forgetting a semicolon at the end of a statement generates a syntax error.

Syntax errors are found by the compiler. An application with syntax errors

will not run because it will not compile.

syntax error

case sensitivity

Chapter 4 Variables and Constants 89

sample

A logic error, also called a semantic error, is more difficult to detect. Logic

errors occur in statements that are syntactically correct, but produce unde-

sired or unexpected results, as in the following example:

int length;

int area;

length = 3.2; //3 is actually assigned

area = length * length; //expected value is 10.24

The statements assign the value 9 to area rather than the expected 10.24.

Although, it is possible that the programmer intended for the value to be

truncated, it is more likely that variables length and area were supposed

to be declared as double.

Logic errors must be found by the programmer through testing and by

carefully examining the source code. Accurate and careful commenting,

proper indentation, and descriptive identifiers can help in finding and

preventing logic errors.

Errors that are not detected by the compiler may generate a run-time

error. A run-time error, also called an exception, halts program execution

at the statement that cannot be executed. For example, although the state-

ments below are syntactically correct, they will generate a run-time error

because division by 0 is undefined:

int totalScores = 40;

int totalTests = 0;

double avgScore;

avgScores = totalScores / totalTests;

This code generates an ArithmeticException exception.

Exceptions can also be generated when user input is not as expected. For

example, the application run below generates an InputMismatchException

exception because the user typed a string when a numeric was

expected:

The program only had code to handle numeric user input. When a letter,

rather than a number was typed, an exception was “thrown.” Writing code

to handle exceptions is discussed in Chapter 12.

run-time error, exception

logic error, semantic error

ArithmeticException

InputMismatchException

90 Chapter 4 Variables and Constants

sample

Chapter 4 Case Study

This and all subsequent chapters end with a case study. Case studies are

used to learn problem-solving techniques. Each case study will include a

description, program specification, code design, program implementation,

and a discussion about testing and debugging.

In this case study, a Birthday game will be created. The BirthdayGame

guesses a player’s birthday by having the player perform mathematics

with the month and day of their birthday. The number computed by the

player is then entered and the program displays the month and day of the

player’s birthday.

BirthdayGame Specification

BirthdayGame is played with one player. The player is given directions

for computing a number that uses the player’s birth month and birth day

in the calculations:

1. Determine your birth month (January=1, February=2, and so

on).

2. Multiply that number by 5.

3. Add 6 to that number.

4. Multiply the number by 4.

5. Add 9 to the number.

6. Multiply that number by 5.

7. Add your birth day to the number (10 if born on the 10th and so

on).

BirthdayGame prompts the player for the calculated number and then

displays the player’s birthday. To determine the player’s birthday, 165 is

subtracted from the number entered by the player. This number is then

divided by 100. The decimal portion of the quotient represents the birth

month. The remainder of the division is the birth day.

The BirthdayGame interface should consist of steps that tell the user

how to calculate the number that needs to be entered. The player should

then be prompted for their number. Finally, the application displays the

player’s birthday.

A sketch of a program run:





















Chapter 4 Variables and Constants 91

sample

An algorithm in plain English for BirthdayGame:

1. Display the directions for the player to calculate the number.

2. Prompt the player for the calculated number.

3. Subtract 165 from the number.

4. Use integer division to divide the number by 100. Store the

quotient as the birth month.

5. Use modulus division to divide the number by 100. Store the

remainder as the birth day.

6. Display a message containing the player’s birthday.

The BirthdayGame flowchart:





























TIP The flowchart

object represents a process.

92 Chapter 4 Variables and Constants

sample

BirthdayGame Code Design

The code design describes how to accomplish the specification. Included

in the code design are a description of the input, output, data generated,

and additional flowcharts, algorithms, and pseudocode.

The input for BirthdayGame is a number calculated by the user. An

integer variable to store the user’s input will be needed.

The output for BirthdayGame is a message with the user’s birthday.

Data generated by BirthdayGame is the birth month and the birth day.

Integer variables to store the birth month and birth day will be needed.

Based on the algorithm and flowchart, the code design for the

BirthdayGame application will include statements for input and output.

Calculations will require both integer and modulus division. A pseudo-

code algorithm for BirthdayGame follows:

Display directions (7 steps)

Prompt the user for the calculated number

playerNum -= 165

birthMonth = playerNum / 100

birthDay = playerNum % 100

Display player's birthday

BirthdayGame Implementation

Based on the code design, the BirthdayGame implementation follows:

* BirthdayGame.java

import java.util.Scanner;

/**

* Plays a birthday guessing game with one player.

public class BirthdayGame {

public static void main(String[] args) {

int playerNum;

int birthMonth, birthDay;

Scanner input = new Scanner(System.in);

/* Give the player directions for calculating the number */

System.out.println("Using paper and pencil, perform the following

calculations:\n");

System.out.println("1. Determine your birth month (January=1, February=2

and so on).");

System.out.println("2. Multiply that number by 5.");

System.out.println("3. Add 6 to that number.");

System.out.println("4. Multiply the number by 4.");

System.out.println("5. Add 9 to the number.");

System.out.println("6. Multiply that number by 5.");

System.out.println("7. Add your birth day to the number (10 if the 10th

and so on).\n");

Chapter 4 Variables and Constants 93

sample

System.out.print("Enter your number: ");

playerNum = input.nextInt();

input.close();

/* Calculate birth day and month and display result. */

playerNum -= 165;

birthMonth = playerNum / 100;

birthDay = playerNum % 100;

System.out.println("Your birthday is " + birthMonth + "/" + birthDay);

}

A run of BirthdayGame looks similar to:

BirthdayGame Testing and Debugging

This case study performs minimal calculations and the algorithm is simple

and straight forward. Simply testing it with your birthday is one method

of verifying results.

Chapter Summary

Variables and constants are used in programs so that values can be

represented with meaningful names. Variables and constants should be

used because they make code easier to read, understand, and modify.

Both variables and constants are created with a declaration statement.

A variable declaration includes the data type and identifier. A constant

declaration also includes the keyword final. Identifiers are case sensitive

and cannot be the same as a Java keyword. The value of a variable can be

changed throughout program execution with assignment statements. The

value of a constant cannot be changed from its initial assignment.

A primitive data type stores a single piece of data and can include int,

double, char, and boolean. Abstract data types include classes. Each class

defines not just a single piece of data like a primitive data type, but a set

of data along with methods for performing actions on that data. Variables

declared with an abstract data type are called objects. An object declara-

tion is called instantiation. An object is instantiated with the keyword

new.

Data can be read from the user at run time by using the Scanner class.

This class processes data from the input stream. Objects that read data

from the keyboard are initialized with System.in. When obtaining data

from the user, a prompt should be included so that the user knows what

information is expected.

94 Chapter 4 Variables and Constants

sample

Java includes many packages. Package members are accessible with

an import statement. The Scanner class is in the java.util package. The

NumberFormat class is in the java.text class. The NumberFormat class is

used for formatting numbers.

Java includes built-in operators that are used to form numeric expres-

sions. Arithmetic operators include +, -, *, /, and %. The / operator performs

integer division when both operands are type int, and real division when

at least one operand is a double. Modulus division is performed with the

% operator. An expression is evaluated according to operator precedence.

The order of operations can be changed with parentheses. Assignment

operators include +=, -=, *=, /=, and %=. Each of these operators perform

an operation before making an assignment.

Type casting converts a number of one type to a number of a different

type. Casting is useful when real division with integers is preferred. A

double can be rounded by first adding 0.5 before casting to an int.

Programming errors occur for many reasons. A syntax error violates

the rules of Java. A logic error is also called a semantic error and is more

difficult to detect because statements are syntactically correct, but produce

unexpected results. A run-time error is also called an exception. An excep-

tion halts program execution.

Code conventions introduced in this chapter are:

• Variable identifiers begin with a lowercase letter and any word

after the first within the identifier should begin with an uppercase

letter.

• Constant identifiers are all uppercase. Multiple words in an identi-

fier can be separated with an underscore (_) character.

• Variable and constant declarations should be grouped at the begin-

ning of a method.

• Each line of a program should contain only one statement.

Chapter 4 Variables and Constants 95

sample

Vocabulary

Abstract data type A class. A data type that can

store data and methods.

ArithmeticException exception An exception

thrown when division by 0 occurs.

Assignment statement A statement that gives the

variable or constant on the left of an assignment

operator the value of the expression on the right

side of the assignment operator.

Case sensitive An uppercase letter is different

from the same letter in lowercase.

Class see Abstract data type.

Concatenate To join two or more strings to form

one larger string.

Constant A name for a memory location that stores

a value than cannot be changed from its initial

assignment.

Data type The kind of information a variable

stores.

Declaration A statement that creates a variable or

constant.

Equal sign (=) An assignment operator that indicates

the variable or constant on the left is to receive the

value of the expression on the right.

Exception see Run-time error.

Floating point Values that are represented by the

double data type. Values that contain numbers after

the decimal point.

Identifier A name for a variable or constant. An

identifier must begin with a letter and can include

any number of letters, numbers, and some special

characters.

Initialize To assign a variable a value in a declara-

tion statement.

InputMismatchException exception An exception

thrown when user input is not as expected.

Input stream The sequence of characters received

from an input device.

Instantiation To create a new object.

Integer division Division that truncates the decimal

portion.

Keyword A word that has special meaning to the

Java compiler and therefore cannot be used as a

variable or constant identifier.

Literal An actual value.

Logic error An error caused by a statement that is

syntactically correct, but produces unexpected or

undesired results. Also called a semantic error.

Modulus division Division that returns the

remainder.

Numeric expression At least one operand and

possibly one or more operators that evaluate to a

single value.

Object A variable declared with a class.

Operator precedence The level assigned to an

operator so that a specific order of operations is

maintained.

Primitive data type A data type that can store only

a single piece of data. Primitive data types are also

called built-in data types.

Prompt A string that informs the user of the kind

of data expected to be typed.

Run-time error An error affecting program execu-

tion. Also called an exception.

Semantic error see Logic error.

Syntax error An error caused by a statement that

violates the rules of Java.

Truncate Removing the decimal portion of a number

when casting a double to an int.

Type casting Converting a number from one type

to a different type.

Variable A name for a memory location that stores

a value.

96 Chapter 4 Variables and Constants

sample

Java

+ Operator used for concatenating strings.

+ The arithmetic addition operator.

- The arithmetic subtraction operator.

* The arithmetic multiplication operator.

/ The arithmetic division operator.

% The arithmetic modulus division operator.

() Used to change the order of operations in an

expression. Also used for type casting.

= An assignment operator that gives the variable

on the left the value on the right.

+= An assignment operator that adds the value on

the right to the variable on the left and then assigns

that value to the variable on the left.

-= An assignment operator that subtracts the value

on the right from the variable on the left and then

assigns that value to the variable on the left.

*= An assignment operator that multiplies the value

on the right by the value of the variable on the left and

then assigns that value to the variable on the left.

/= An assignment operator that divides the value of

the variable on the left by the value on the right and

then assigns that value to the variable on the left.

%= An assignment operator that divides the value

of the variable on the left by the value on the right

and then assigns the remainder of that division to

the variable on the left.

boolean A data type that represents true or false.

c h a r A data type that represents a single

character.

double A data type that represents positive or

negative floating point numbers.

final Keyword used to declare an identifier a

constant.

import Statement used to make a package or classes

from a package accessible to an application.

in The java.lang.System member that represents

the standard input stream.

int A data type that represents positive or negative

integers.

java.lang The most fundamental Java package. It

contains classes that define the Java language.

java.text A Java package with the NumberFormat

class for formatting numbers.

java.util A Java package with the Scanner class for

reading input.

new An operator that allocates memory for an

object.

NumberFormat A java.text class with methods for

formatting numbers.

Scanner A java.util class with methods for reading

input from the user.

System.in The input stream for reading from the

keyboard.

Chapter 4 Variables and Constants 97

sample

Critical Thinking

1. a) List four legal identifier names.

b) List four illegal identifier names and explain

why each is illegal.

2. a) In two statements, declare a variable named

numBeads and assign it the value 5.

b) In one statement, declare a variable named

numBeads and assign it the value 5.

3. a) What is the final value of yourNumber after

the last statement executes?

int myNumber = 5;

int yourNumber = 4;

myNumber = yourNumber * 2;

yourNumber = myNumber + 5;

b) What is the final value of yourNumber after

the last statement executes?

int myNumber;

int yourNumber = 4;

myNumber = yourNumber + 7;

yourNumber = myNumber;

4. Determine the appropriate data type for each

of the following values:

a) the number of basketballs in a department

store.

b) the price of a basketball.

c) the number of players on a basketball

team.

d) the average age of the players on a basketball

team.

e) whether a basketball player has received a

jersey or not.

f) the first initial of a basketball player’s first

name.

5. a) What is the difference between a primitive

data type and an abstract data type?

b) What is the difference between a class and

an object?

6. Assume a class named Team defines a sports

team.

a) Methods define the actions in a class and

typically include action words in their name.

For example, getTeamName is a method

name that returns the name of the team. List

three more possible method names for the

Team class.

b) List three possible object names of type

Team.

7. The java.util package contains a class named

R a n do m. Write a statement that makes the

Random class accessible to an application.

8. What is the value of each of the following

expressions?

a) 5 + 7 – 3

b) 10 * 2 – 3

c) 10 * (2 – 3)

d) 8 – 3 * 2

e) 10 / 5 * 4

f) 10 / 2 + 3

g) 6 % 3 + 4

h) 12 % 5 * 3

i) 12 % (5 * 3)

9. What is the result of the following expression

when x is 2005? When x is 1776? When x is 39?

(x/10)%10

10. Write each equation as a valid Java expression:

a) (geometry)

b) (business)

c) (geometry)

d) (geometry)

e) (algebra)

f) (physics)

g) (business)

11. Using the following declarations, rewrite the

statements to include the appropriate type cast-

ing, rounding where necessary. If type casting

is not necessary, explain why:

int j = 5;

double k = 1.6;

int y;

double z;

a) y = j * k;

b) z = j * k;

98 Chapter 4 Variables and Constants

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c) z = k * k;

d) j = k;

e) k = j;

f) y = j + 3;

12. Compare the way the / and % operators perform

to the effects of type casting.

13. Rewrite the statements below using the appro-

priate assignment operator:

a) total = total + 10;

b) numStones = numStones - 1;

c) days = days % 24;

d) price = price * 1.2;

14. Determine if each of the following are better

represented by a variable or a constant and then

write declarations using appropriate data types

and descriptive identifiers:

a) the number of votes received by an election

candidate

b) the percentage of votes won by a candidate

c) the first, middle, and last initials of an elec-

tion candidate

d) the year of the election

15. Determine if each of the following segments of

code contain a syntax error, logic error, or run-

time error. Explain.

a) duble salary;

b) int numHats

c) length == 12;

d) int test1 = 90;

int test2 = 85;

double avg;

avg = test1 + test2 / 2;

e) double x = 12;

double y = 0;

double z;

z = x / y;

f) double payCheck = 120.00;

NumberFormat money =

NumberFormat.getPercentInstance();

System.out.println(money.format(payCheck);

True/False

16. Determine if each of the following are true or

false. If false, explain why.

a) An identifier can contain spaces.

b) Data of type double is sometimes referred to

as floating point.

c) An abstract data type is also called a primi-

tive data type.

d) Values typed by the user cannot be used in

an application.

e) The Scanner class is part of a Java package.

f) The + operator has higher precedence than

the – operator.

g) The – operator has lower precedence than

the % operator.

h) byte is a keyword.

i) The identifiers apple and Apple are consid-

ered the same in Java.

j) Errors that violate the rules of Java are called

semantic errors.

Chapter 4 Variables and Constants 99

sample

Exercises

Exercise 1 ————————————————————ObjectHeight

The height of an object at any given time dropped from a starting height of 100 meters is given by the

equation h=100–4.9*t2 where t is the time in seconds. Create an ObjectHeight application that prompts

the user for a time less than 4.5 seconds and then displays the height of the object at that time. The

application output should look similar to:

Exercise 2 ————————————————————— PizzaCost

The cost of making a pizza at a local shop is as follows:

• Labor cost is $0.75 per pizza, regardless of size

• Rent cost is $1.00 per pizza, regardless of size

• Materials is $0.05*diameter*diameter (diameter is measured in inches)

Create a PizzaCost application that prompts the user for the size of a pizza and then displays the cost

of making the pizza. The application output should look similar to:

Exercise 3 ————————————————— CollegeCalculator

In small groups brainstorm all the expenses involved in attending a college or university (rent, tuti-

tion, books, etc) and possible offset costs (scholarships, etc). Create a CollegeCalculator application that

prompts the user for the amount of each expense and offset cost. If the cost is not applicable the user

should enter a value of 0. Add the expenses and subtract the offset costs to determine how much money

an individual will need for their school year. College websites can be used as a guide to determine

relevant and appropriate expenses.

Exercise 4 ö —————————————————— JavaTerminology

Modify the JavaTerminology application created in Chapter 3, Exercise 8 to include five words from

the vocabulary list in this chapter and the corresponding definition. Place each word on a separate line

followed by the definition. Place a blank line between entries.

100 Chapter 4 Variables and Constants

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Exercise 5 —————————————————————— Energy

Einstein’s famous formula, e=mc2, gives the amount of energy released by the complete conversion of

matter of mass m into energy e. If m represents the mass in kilograms and c represents the speed of

light in meters per second (3.0 ∗ 10

m/s), then the result is in the energy units Joules. It takes 360000

Joules to light a 100-watt light bulb for an hour. Create an Energy application that prompts the user for

a mass in kilograms and then displays the energy and the number of light bulbs that could be powered.

The application output should look similar to:

Exercise 6 —————————————————————— Change

Create a Change application that prompts the user for an amount less than $1.00 and then displays

the minimum number of coins necessary to make the change. The change can be made up of quarters,

dimes, nickels, and pennies. The application output should look similar to:

Exercise 7 ö —————————————————————— Digits

Modify the Digits application created in a review earlier in this chapter to show the hundreds-place

digit of a three digit number. The application output should look similar to:

Exercise 8 ———————————————————— DivAndMod

Create a DivAndMod application that prompts the user for two integers and then displays the result of

integer and modulus division in either order. The application output should look similar to:

Chapter 4 Variables and Constants 101

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Exercise 9 —————————————————— TimeConversion

Create a TimeConversion application that prompts the user for a time in minutes and then displays

the time in hours and minutes. Be sure to consider times whether the number of minutes left over is

less than 10. For example, 184 minutes in hour:minute format is 3:04 (Hint: use the modulus operator).

The application output should look similar to:

Exercise 10 ——————————————————————— Sleep

Create a Sleep application that calculates the number of hours of your life that you have spent sleeping.

Assume that you sleep 8 hours each night. To simplify the problem, assume that there are 30 days in

each month and 365 days in each year. The application output should look similar to:

Exercise 11 ——————————————————————— Order

A fast food restaurant charges $1.69 for burgers, $1.09 for fries, and $0.99 for sodas.

a) Create an Order application that prompts the employee for the number of burgers, fries,

and sodas and then displays the total, the tax (6.5%), and the final cost. The application

output should look similar to:

b) Modify Order to prompt the employee for the amount tendered and then display the

change due. Application output should look similar to:

102 Chapter 4 Variables and Constants

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Exercise 12 —————————————————————— Project

Create a Project application to help analyze the time taken for a Java project. The application should

prompt you for the time spent designing, coding, debugging, and testing, and then displays a table

showing the percentage of time taken for each part. The application output should look similar to:

Exercise 13 ————————————————————— Spending

Create a Spending application to help examine the spending patterns of a user. The application should

prompt the user for the amount spent last month on food, clothing, entertainment, and rent, and then

displays a table showing the percentage of expenditures in each category. The application output should

look similar to:

Exercise 14 ————————————————— CollegeCalculator

In small groups brainstorm all the expenses involved in attending a college or university (rent, tuition,

books, etc) and possible offset costs (scholarships, etc). Create a CollegeCalculator application that

prompts the user for the amount of each expense and offset cost. If the cost is not applicable the user

should enter a value of 0. Add the expenses and subtract the offset costs to determine how much money

an individual will need for their school year. College websites can be used as a guide to determine

relevant and appropriate expenses.

Chapter 4 Variables and Constants 103

sample

Exercise 15 ——————————————————— SimpleInterest

There are two kinds of interest: simple and compound. With simple interest, the amount of the deposit

remains the same, and the amount of interest is paid at the end of a time interval. For example, if $1,000

is deposited for 7 years at an interest rate of 6% per year, $60 will be deposited at the end of each year,

for a total of $1,420 after 7 years.

a) The value of the amount after the term is calculated using the formula:

Amount = Principal * (1 + years * interest rate)

Create a SimpleInterest application that prompts the user for the principal, number of

years, and the interest rate (as a fraction) and then calculates the amount of interest.

The application should display output similar to:

b) The formula in part (a) can be adjusted to calculate what principal will need to be

invested in order to have a certain amount of money after a specified term and interest

rate:

Principal = Amount / (1 + years * interest rate).

Modify SimpleInterest to prompt the user for the desired amount, number of years,

and interest rate and then calculate the principal that will need to be invested.

Exercise 16 —————————————————————— Election

The results of a primary election between two candidates in three states are:

Awbrey Martinez

New York 314159 271860

New Jersey 89008 121032

Connecticut 213451 231034

Write a program that prompts the user for the election results, and then displays output similar to:

104 Chapter 4 Variables and Constants

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Chapter 5 Conditional Control Structures 105

sample

Statements that branch to perform one action or another depending on

a condition are used to give an application decision-making capabilities.

This chapter focuses on the if and switch conditional control structures.

The if Statement

The if statement is a conditional control structure, also called a decision

structure, which executes a set of statements when a condition is true.

Conditional control structures are used to change program flow. The if

statement takes the form:

if (<condition>) {

}

For example, in the following if statement, guess == 7 is the condition, and

there is one statement that will be executed when this condition is true:

if (guess == SECRET _ NUM) {

System.out.println("You guessed it!");

}

The == relational operator determines if the value of guess is equal to the

value of SECRET _ NUM. If equal, the println() statement executes. If not, then

program flow continues to the next statement after the closing brace of

the if statement.

The condition of an if statement is a Boolean expression, which evaluates

to either true or false. Relational operators can be used to form Boolean

expressions. There are six relational operators:

Operator Meaning

== equal

< less than

<= less than or equal

> greater than

>= greater than or equal

!= not equal

Chapter 5

Conditional Control Structures

TIP Using = instead of == in

an if statement condition gen-

erates an error.

conditional control structure

Boolean expression

relational operators

Comparing Objects

Because objects point to a

location in memory, rather

than directly storing a value,

they cannot be compared using

built-in relational operators. A

class defines methods that are

used to compare objects.

106 Chapter 5 Conditional Control Structures

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A boolean variable may also be used as the condition of an if statement

because its value is true or false. For example, in the following statements,

the message is displayed:

boolean gameOver = true;

if (gameOver) {

System.out.println("Thanks for playing!");

}

Roundoff Error

The condition of an if statement should never make an equality com-

parison between floating point numbers because of the possibility of

roundoff error. A roundoff error occurs when a floating point number

cannot be exactly represented in binary notation by the computer. For

example, the decimal number 0.8 is a repeating decimal in binary form

(0.1100110011…). Since there are only a finite number of bits in memory that

can be used to represent a number, a repeating decimal must be rounded

off, preventing an exact representation.

For example, consider the following statements:

if ((4.80 * 100 - 480) == 0) {

System.out.println("Zero.");

}

The condition seems to evaluate to true. However, the number 4.80 cannot

be exactly represented in binary. Therefore, when 4.80 is multiplied by 100

the result is slightly different from 480. This difference is due to roundoff

error. In this case, subtracting 480 from 4.80 * 100 results in a very small

number that is not equal to 0 (–1.77635683940025E-14). The following state-

ments are one way to take into consideration possible roundoff error:

final double VERY _ SMALL _ VALUE = 0.000001

if ((4.80 * 100 - 480) < sngVERY _ SMALL _ VALUE) {

System.out.println("Zero.");

}

Review: SurfsUp – part 1 of 3

Create a SurfsUp application that prompts the user for the wave height and then displays “Great day for

surfing!” when the waves are 6 feet and over.

The if-else Statement

The if statement can include an optional else clause that is executed

when the if condition evaluates to false. The if-else statement takes the

following form:

if (<condition>) {

} else {

}

Chapter 5 Conditional Control Structures 107

sample

For example, in the following if-else statement, different messages are

displayed for correct and incorrect guesses:

if (guess == SECRET _ NUM) {

System.out.println("You guessed it!");

} else {

System.out.println("Try again.");

}

The indentation and organization of the if-else is important for read-

ability. The structure shown is a code convention that clearly indicates the

actions for a true condition and the actions for a false condition.

Review: SurfsUp – part 2 of 3

Modify the SurfsUp application to display “Great day for surfing!” when the waves are 6 feet or over and

“Go body boarding!” when the waves are less than 6 feet.

Review: CircleCircumference – part 2 of 2

Modify the CircleCircumference application from Chapter 4 so that the message “Negative radii are illegal.”

is displayed if a negative number is entered by the user for the radius value. Otherwise the application should

calculate and display the circumference of the circle.

Nested Statements

An if-else statement can contain another if-else or if statement.

Statements placed within the same type of statements are called nested.

For example, the nested if-else gives a hint when the user does not guess

the correct number:

if (guess == SECRET _ NUM) { //correct

System.out.println("You guessed it!");

} else {

if (guess < SECRET _ NUM) { //too low

System.out.println("Too low.");

} else { //too high

System.out.println("Too high.");

}

Carefully indenting the statements makes it clear which are nested.

Review: Stages

Create a Stages application that prompts the user for an age. For an age over 18, adult is displayed. For an age

less than or equal to 18, toddler is displayed when the age is less than or equal to 5, child when the age is less

than or equal to 10, preteen when the age is less than or equal to 12, and teen when the age is over 12.

108 Chapter 5 Conditional Control Structures

sample

The if-else if Statement

The if-else if statement is used to decide among three or more actions

and takes the form:

if (<condition>) {

} else if (<condition>) {

} else {

}

There can be multiple else if clauses, and the last else clause is optional.

For example, there are three possible decisions in the if-else if statement

below:

if (guess == SECRET _ NUM) { //correct

System.out.println("You guessed it!");

} else if (guess < SECRET _ NUM) { //too low

System.out.println("Too low.");

} else { //too high

System.out.println("Too high.");

}

The logic used in developing an if-else if statement is important. For

example, when testing a range of numbers, if conditions must be properly

ordered because statements are executed for the first true condition only

and then program flow continues to the next statement after the if-else

if.

When choosing between nested if-else statements and a single if-else

if statement, the if-else if allows only one branch to execute and the

conditions show a clear sequence. In general, the if-else if statement is

easier to read and understand.

Review: SurfsUp – part 3 of 3

Modify the SurfsUp application to display “Great day for surfing!” when the waves are 6 feet or over, “Go

body boarding!” when the waves are between 3 and 6 feet, ”Go for a swim.” when the waves are from 0 to

3 feet, and “Whoa! What kind of surf is that?” otherwise.

Review: Discriminant

In mathematics, the quantity b

– 4ac is called the “discriminant.” Create a Discriminant application that

prompts the user for the values of a, b, and c an then displays “No roots” if the discriminant is negative,

“One root” is the discriminant is zero, and “Two roots” if the discriminant is positive. Application output

should look similar to:

Commenting Complex

Decision Structures

Decision structures with many

branches can quickly become

difficult to understand. Brief

inline comments can make

code much more readable.

This is especially important

for the last branch of a deci-

sion structure, which usually

does not include an explicit

condition.

Chapter 5 Conditional Control Structures 109

sample

The switch Statement

The switch statement is a conditional control structure that uses the

result of an expression to determine which statements to execute. The

switch statement is sometimes preferable to the if-else if statement

because code may be easier to read. The switch statement takes the form:

switch (<integer expression>) {

case x:

<statement>;

break;

...

default:

<statements>;

break;

}

The expression must evaluate to an integer. There can be multiple case

clauses. The break statement is necessary to move program control to the

next statement after the switch statement. The default code is optional and

is executed when none of the previous cases are met. For example, when

score is 5, the case 5 statement executes and then program control moves

to the next statement after the switch (skipping the case 10 statement):

switch (score) {

case 0: System.out.println("Better luck next time."); break;

case 5: System.out.println("Pretty good."); break;

case 10: System.out.println("Great!"); break;

}

If the break statement is not included in a case clause, execution continues

on to the next statement within the switch statement. This can be useful

when the same set of statements applies to more than one situation:

switch (score) {

case 0: System.out.println("Better luck next time."); break;

case 1:

case 2:

case 3:

case 4:

case 5: System.out.println("Pretty good."); break;

case 6:

case 7:

case 8:

case 9:

case 10: System.out.println("Great!"); break;

}

In this statement, “Pretty good.” is displayed when the score is 1, 2, 3, 4,

or 5. Scores 6 though 10 display “Great”.

case

break

110 Chapter 5 Conditional Control Structures

sample

Review: Hurricane

The Saffir-Simpson Hurricane Scale provides a rating (a category) depending on the current intensity of a

hurricane. Create a Hurricane application that displays the wind speed for the hurricane category entered

by the user. Display the speed in miles per hour (mph), knots (kts), and kilometers per hour (km/hr). Refer

to the Saffir-Simpson Hurricane Scale below for wind speeds:

Category 1: 74-95 mph or 64-82 kt or 119-153 km/hr

Category 2: 96-110 mph or 83-95 kt or 154-177 km/hr

Category 3: 111-130 mph or 96-113 kt or 178-209 km/hr

Category 4: 131-155 mph or 114-135 kt or 210-249 km/hr

Category 5: greater than 155 mph or 135 kt or 249 km/hr

Generating Random Numbers

Games, simulators, screen savers, and many other types of applications

make use of random numbers. A widely used method for generating ran-

dom numbers is called the Linear Congruential Method. This method uses

a formula to generate a sequence of numbers. Although the numbers in

the sequence vary and for most applications can be considered random,

the sequence will at some point repeat. Therefore, random numbers in a

computer application are referred to as pseudorandom (like random).

Java includes the Random class in the java.util package for generating

random numbers. This class uses the Linear Congruential Method. Some

of the Random class methods include:

Class Random (java.util.Random)

Methods

nextInt() returns the next random integer in the random

number generator’s sequence.

nextInt(int n) returns the next random integer between 0

(inclusive) and n in the random number gener-

ator’s sequence.

nextDouble() returns the next random double between 0.0

and 1.0 in the random number generator’s

sequence.

The RandomNumberDemo class below instantiates a Random object and

displays the first five numbers between 0 and 100 in its sequence:

public class RandomNumberDemo {

public static void main(String[] args) {

Random r = new Random();

System.out.println("First number: " + r.nextInt(100));

System.out.println("Second number: " + r.nextInt(100));

System.out.println("Third number: " + r.nextInt(100));

System.out.println("Fourth number: " + r.nextInt(100));

System.out.println("Fifth number: " + r.nextInt(100));

}

Linear Congruential Method

pseudorandom

Random class

Chapter 5 Conditional Control Structures 111

sample

RandomNumberDemo produces output similar to the following:

To generate a random number in a range with a minimum value greater

than 0, the following formula is used:

r.nextInt(highNum - lowNum + 1) + lowNum

A similar formula can be used to generate random doubles in a range:

(highNum - lowNum + 1) * r.nextDouble() + lowNum

The Linear Congruential Method requires a seed, which is a starting

value, for calculating a sequence of numbers. Java automatically gener-

ates this seed when a new Random object is instantiated. However, if a

seed value is specified, the same sequence of “random” numbers will be

generated each time the program is run. This can be useful for debugging.

After the program has been tested, remove the seed so that the sequence of

generated numbers vary each time the application runs. For example, the

code below specifies a seed. Two runs of the application are displayed:

public class RandomNumberDemo {

public static void main(String[] args) {

Random r = new Random(10);

System.out.println("First number: " + r.nextInt(100));

System.out.println("Second number: " + r.nextInt(100));

System.out.println("Third number: " + r.nextInt(100));

System.out.println("Fourth number: " + r.nextInt(100));

System.out.println("Fifth number: " + r.nextInt(100));

}

first run: second run:

Two runs of RandomNumberDemo using the same seed.

Note that both runs generate the same sequence of

numbers.

Review: RandomNum

Create a RandomNum application that prompts the user for two numbers. The first number is a minimum

value and the second is a maximum value. RandomNum then displays an integer between the min and max

values entered by the user.

random numbers in a range

seed

112 Chapter 5 Conditional Control Structures

sample

Compound Boolean Expressions

Conditions with complex criteria are formed using the && and ||

operators. The && operator is called the logical And. It is used to form an

expression that evaluates to true only when both operands are also true.

The || operator is called the logical Or. An expression formed with this

operator evaluates to true when either operand is true. For example, the

following statement tests for invalid guesses:

if (guess < 1 || guess > 50) { //invalid guess

System.out.println("Invalid guess.");

} else if (guess == SECRET _ NUM) { //correct guess

System.out.println("You guessed it!");

}

When a guess is either less than 1 or greater than 50, “Invalid guess.”

is displayed. Note that the expression also evaluates to true when both

operands are true. The condition in the if statement is called a compound

Boolean expression because more than one Boolean expression determines

whether the condition is true or false.

How a compound Boolean expression evaluates with && and || operators

can be shown with truth tables. A truth table shows the possible outcomes

of compound Boolean expressions:

And Or

Exp1 Exp2 Result Exp1 Exp2 Result

True True True True True True

True False False True False True

False True False False True True

False False False False False False

As another example, consider an application that computes a discount

depending on the item and quantity purchased:

if (itemNum == 873 && quantity > 50) { //more than 50 of 873

discount = 1; //$1 discount

}

This if statement executes the discount = 1 statement if item number is

873 and quantity is greater than 50.

A third operator is !. The ! operator is called the logical Not. An expres-

sion including ! is evaluated according to the following truth table:

Not

Exp Result

True False

False True

For example, the following statements display a message when the item

number is not 873:

if (!itemNum == 873) { //any item EXCEPT 873

System.out.println("No discount given.");

}

TIP The | key is located above

the Enter key on most standard

keyboards.

&& and ||

truth table

logical And

logical Or

Chapter 5 Conditional Control Structures 113

sample

Java uses short-circuit evaluation for determining the result of a com-

pound Boolean expression that includes && or ||. In short-circuit evaluation,

the left operand is evaluated first. If the result of the entire expression can

be determined by the value of the left operand, then no other operands will

be evaluated. For example, the expression x < 0 || x > 5 evaluates to true

if x is less than 0 regardless of the value of x > 5. Therefore, when x is less

then 0, the second operand will not be evaluated. As another example, the

expression x > 5 && x < 20 evaluates to false if x is less than or equal to

5 regardless of the value of x < 20. Therefore, when x is less than or equal

to 5, the second operand will not be evaluated.

In the order of operations, ! is evaluated before &&. || is evaluated last.

For example, the expression !5 < 6 || 2 > 4 && 3 < 6 evaluates to false

because !5 < 6 is performed first, then 2 > 4 && 3 < 6, and then False ||

False. Use parentheses to change operator precedence and to make code

More on Concatenation

As introduced in Chapter 4,

concatenation appends one

string to another. When the

+ operator is used to join a

string and a numeric, the com-

piler first converts any non-

String data to a String object

before joining the strings. The

String class also contains the

concat() method for joining

two strings.

Chapter 6 Loop Structures and Strings 139

sample

/* display middle three characters */

threeLetters = phrase.substring(mid - 1, mid + 2);

System.out.println("Middle three characters are: "

+ threeLetters);

}

Note that the String objects (phrase, threeLetters) can be declared in the

same way primitives are declared—the data type followed by the vari-

able name. With the String class, the following two statements perform

the same task:

String alpha = new String("abc"); //these assignments are

String alpha = "abc"; //efffectively the same

The MiddleThree application produces output similar to:

A string is said to be immutable because it cannot be changed. Methods

that manipulate the original string, for example toLowerCase(), create

a new string in memory because the original string cannot be changed.

Assigning a new string to a String object simply changes the object refer-

ence to point to the new string in memory. For example, the following code

generates a new string. Assigning the string to the text object changes the

object’s reference:

String text;

text = "heLlO";

text = text.toLowerCase();

System.out.println(text);

The code produces the output:

Until a String object is assigned a value, it refers to null. Calling a method

from a null String object generates the exception NullPointerException.

Review: AccountSetup

Create an AccountSetup application that prompts the user for a user name and a password. The application

should prompt the user until a password with at least eight characters is entered. The user name and pass-

word should be converted to all lowercase letters and then an appropriate message displayed. Application

output should look similar to:







immutable

NullPointerException

null

140 Chapter 6 Loop Structures and Strings

sample

Comparing Strings

Strings are compared when determining equality or alphabetical order.

In chapter 5, relational operators, including == and >, were used to compare

primitive types. When objects need to be compared, methods from their

class are used. Some of the String class methods for comparing strings

include:

Class String (java.lang.String)

Methods

equals(String str)

returns true when the string is the same as str.

Returns false otherwise.

equalsIgnoreCase(String str)

same as equals() except that uppercase and

lowercase differences between the strings are

ignored.

compareTo(String str)

returns 0 when str is the same as the string, a

negative integer is returned when str comes

alphabetically after the string, and a positive

integer is returned when str comes alphabeti-

cally before the string. Note that uppercase and

lowercase letters are considered different.

compareToIgnoreCase(String str)

same as compareTo() except that uppercase and

lowercase differences between the strings are

ignored.

indexOf(String str)

returns the integer corresponding to the

location of the first occurrence of str in the

string. Otherwise –1 is returned.

lastIndexOf(String str)

returns the integer corresponding to the

location of the last occurrence of str in the

string. Otherwise –1 is returned.

startsWith(String str)

returns true when the string begins with str.

Returns false otherwise.

endsWith(String str)

returns true when the string ends with str.

Returns false otherwise.

The AlphaOrder class compares two strings and then displays them in

alphabetical order:

public class AlphaOrder {

public static void main(String[] args) {

String word1, word2;

Scanner input = new Scanner (System.in);

Unicode

The Unicode Standard is

a 16-bit encoding system

that assigns a value for

each character and symbol

of every language. Java

uses this standard when

defining strings, and

String class methods use

the character values when

comparing strings.

Chapter 6 Loop Structures and Strings 141

sample

System.out.print("Enter a word: ");

word1 = input.nextLine();

System.out.print("Enter a second word: ");

word2 = input.nextLine();

input.close();

if (word1.compareToIgnoreCase(word2) == 0) {

System.out.println("Words are equal.");

} else if (word1.compareToIgnoreCase(word2) < 0) {

System.out.println("In alphabetical order: " + word1

+ " " + word2);

} else {

System.out.println("In alphabetical order: " + word2

+ " " + word1);

}

AlphaOrder produces output similar to the following:

Review: FormalGreeting

Create a FormalGreeting application that prompts the user for his or her name, including title. The applica-

tion should display “Hello, sir.” if the string starts with Mr., “Hello, ma’am.” if the string starts with Ms., Mrs.,

or Miss, and “Hello, name.” otherwise where name is the user’s name.

Chapter 6 Case Study

In this case study, a word guessing game will be created. The word

guessing game allows the player to guess the letters of a secret word. At

the start of the game, the player is shown only how many letters the word

contains through a set of dashes. When a letter matching one in the word

is guessed, it replaces the appropriate dash. Play continues until the entire

word is guessed letter-by-letter or when the player chooses to guess the

entire word.

WordGuess Specification

WordGuess is played between the computer and a single player. The

secret word is BRAIN. At the start of the game, six dashes are displayed

(––––––), one for each letter of the word. The player is repeatedly prompted

for a letter guess. When a letter matching one in the word is guessed, the

letter replaces the corresponding dash. Letters may be entered as upper-

case or lowercase. However, only uppercase letters should be displayed. If

the player enters an exclamation point (!), the player is prompted to guess

the word. At that point the player either wins (a correct guess) or loses

(an incorrect guess). Alternatively, the player can continue to guess letters

until the entire word is revealed. The games ends by showing the player

the total number of guesses.

142 Chapter 6 Loop Structures and Strings

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The WordGuess interface should display a row of dashes, one dash for

each letter in the word. Prompts should be used to get letter guesses from

the player. As corresponding letters are guessed, the letter is displayed

instead of the dash. At the end of the game, the user should be shown the

word along with the number of guesses.

The WordGuess output sketch:



























The WordGuess algorithm:

1. Display a row of dashes to represent the word.

2. Prompt the user for a letter guess.

3. If the letter guessed is part of the word, then display that letter in

place of the corresponding dash.

4. Repeat steps 2 and 3 until all the letters have been guessed or an

exclamation point has been entered by the user.

5. If an exclamation point has been entered, prompt the user to guess

the entire word.

6. If the player correctly guesses the entire word or all the letters have

been guessed, then display a message indicating that the player

has won, otherwise the message should indicate that the player

has lost.

7. Display the secret word and the number of guesses.

Chapter 6 Loop Structures and Strings 143

sample

The WordGuess flowchart:































































144 Chapter 6 Loop Structures and Strings

sample

WordGuess Code Design

The input for WordGuess are letters typed by the user. A String vari-

able to store the player’s letter guess will be needed. The player may also

choose to guess the entire word, so another String variable to store a word

guess will be needed.

The output for WordGuess is the secret word displayed as dashes and

then redisplayed whenever a dash should be replaced by a letter, a prompt

for the user’s guess, a message indicating a win or loss, and a message

indicating the secret word and the number of guesses made.

Data generated by WordGuess is a count of the number of guesses made

by the user. A counter variable to store the number of guesses will be

needed. Other data used in this application can be represented by String

constants to represent the secret word (SECRET_WORD) and to use as a

loop sentinel (FLAG). A String variable will also be needed to “build” a

new string that contains any correctly guessed letters.

Based on the algorithm and flowchart, the code design for the WordGuess

application will include a loop structure to compare the user’s input to

the letters in the secret word. The best loop structure will be a do-while

because under any condition the loop statements should iterate at least

once. It also unknown how many times the loop statements should iter-

ate, so a type of while statement, not a for statement, should be used. This

comparison will be done with an if statement. A pseudocode algorithm

for WordGuess follows:

Generate and display a set of dashes that represent the word

update guesses counter

Prompt user for a letter

Convert to all uppercase

Determine if letter is in word

if letter is in word

Create new string that contains the guessed letter

while (all letters haven't been guessed and user hasn't chosen

to guess the entire word)

if (! has been entered)

get a word guess from player

convert word to all uppercase

if (word guessed equals secret word OR all the letters have

been guessed)

display message that player has won

else

display message that player has lost

Display secret word

Display number of guesses

WordGuess Implementation

Based on the code design, the WordGuess implementation follows:

* WordGuess.java

import java.util.Scanner;

Chapter 6 Loop Structures and Strings 145

sample

/**

* Plays a word guessing game with one player.

public class WordGuess {

public static void main(String[] args) {

final String SECRET _ WORD = "BRAIN";

final String FLAG = "!";

String wordSoFar = "", updatedWord = "";

String letterGuess, wordGuess = "";

int numGuesses = 0;

Scanner input = new Scanner(System.in);

/* begin game */

System.out.println("WordGuess game.\n");

for (int i = 0; i < SECRET _ WORD.length(); i++) {

wordSoFar += "-"; //word as dashes

}

System.out.println(wordSoFar + "\n"); //display dashes

/* allow player to make guesses */

do {

System.out.print("Enter a letter (" + FLAG + " to guess entire word): ");

letterGuess = input.nextLine();

letterGuess = letterGuess.toUpperCase();

/* increment number of guesses */

numGuesses += 1;

/* player correctly guessed a letter--extract string in wordSoFar

* up to the letter guessed and then append guessed letter to that

* string Next, extract rest of wordSoFar and append after the guessed

* letter

if (SECRET _ WORD.indexOf(letterGuess) >= 0) {

updatedWord = wordSoFar.substring(0, SECRET _ WORD.indexOf(letterGuess));

updatedWord += letterGuess;

updatedWord += wordSoFar.substring(SECRET _ WORD.indexOf(letterGuess)+1,

wordSoFar.length());

wordSoFar = updatedWord;

}

/* display guessed letter instead of dash */

System.out.println(wordSoFar + "\n");

} while (!letterGuess.equals(FLAG) && !wordSoFar.equals(SECRET _ WORD));

/* finish game and display message and number of guesses */

if (letterGuess.equals(FLAG)) {

System.out.println("What is your guess? ");

wordGuess = input.nextLine();

wordGuess = wordGuess.toUpperCase();

}

if (wordGuess.equals(SECRET _ WORD) || wordSoFar.equals(SECRET _ WORD)) {

System.out.println("You won!");

} else {

System.out.println("Sorry. You lose.");

}

System.out.println("The secret word is " + SECRET _ WORD);

System.out.println("You made " + numGuesses + " guesses.");

}

146 Chapter 6 Loop Structures and Strings

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A run of WordGuess looks similar to:

WordGuess Testing and Debugging

This case study should test all possible guess combinations. For example,

the player may enter an exclamation point on the first guess. Testing

should also include incorrect word guesses.

Review: WordGuess

Modify the WordGuess Chapter 6 Case Study to display a score at the end of each game. The player should

start with 100 points and have 10 points taken off for each guess. The score should be updated and displayed

as the game is played. Display a player loses message if the score gets down to 0.

Chapter Summary

This chapter introduced loop structures and the String class. The while

statement and do-while statement are loop structures that iterate a set of

statements repeatedly based on a condition. The difference between the

loops is when the condition is evaluated. The while statement evaluates

the condition before any iterations are performed. The do-while does not

evaluate the condition until after the first iteration.

Chapter 6 Loop Structures and Strings 147

sample

Some syntax errors and logic errors can lead to an infinite loop, which

executes forever causing the application to just hang. A logic error can also

cause an overflow, which occurs when there are not enough bits to store

a number.

Counters are used for keeping track of loop iterations and are used

in applications that keep track of the number of guesses or the number

of values entered. An accumulator is increased by varying amounts.

Accumulators are often used to sum values. Both counters and accumula-

tors should be initialized when they are declared.

A flag, also called a sentinel, is used to signify that a loop should stop

iterating. Flags are usually a constant that is declared in the application,

but may also be determined by prompting the user for a value.

The for statement is another loop structure. This loop structure executes

a set of statements a fixed number of times. A loop control variable is used

to determine loop iterations and can be declared in the for statement itself.

When a variable is declared in a statement, its scope is limited to the open-

ing and closing curly braces of that statement. The increment operator (++)

and decrement operator (--) are used to increase or decrease the value of

a for loop control variable.

Debugging techniques include using a debugger, often included with

a compiler, and a variable trace, which is a manual technique. Debuggers

have the advantage of being able to display the actual value of a variable

as it changes. Other techniques include adding println statements before

and after variable assignment. Commenting out statements can also locate

an error through process of elimination.

The String class is used to declare string variables. It contains numerous

methods for determining the length of a string, converting a string to low-

ercase or uppercase characters, extracting substrings, and for comparing

strings. A string is immutable, which means it cannot be changed from

its original value. However, a String object can be assigned a new string

in memory. The characters of a string have an index value, with the first

character at index 0.

Code conventions introduced in this chapter are :

• The statements of an while statement should be indented.

• The statements of a do-while statement should be indented.

• The statements of a for statement should be indented.

• Declare variables so that their scope is limited to where they are

needed.

• Changes to a loop control variable should occur in the increment

portion of the loop only, and the loop should end only when the

condition is false.

148 Chapter 6 Loop Structures and Strings

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Vocabulary

Accumulator A variable that is incremented by

varying amounts.

Breakpoint A statement selected where execution

will be suspended.

Counter A variable that is incremented by a fixed

value.

Debugger A tool included with some compilers

for debugging.

Debugging The process of getting an application

to work correctly.

Decrement operator The -- operator, which

decreases the value of a variable by 1.

Flag see Sentinel.

Immutable Unable to change.

Increment operator The ++ operator, which increases

the value of a variable by 1.

Index The position of a character in a string.

Infinite loop A loop that continues forever.

Iteration The execution of a loop.

Loop control variable A counter that is used to

control the number of for loop iterations.

Loop structure A statement that executes a set of

statements repeatedly based on a condition.

NullPointerException exception An excep-

tion thrown when operations on a null String are

attempted.

Overflow A condition that occurs when a number

is too large to be stored in a specified number of

bits.

Sentinel A constant that stores a value that is used

to signify that a loop should stop iterating. Also

called a flag.

Scope The set of statements that can access a declared

variable.

Variable trace A table listing the values of vari-

ables at the points of assignment. Used for manually

debugging an application.

Java

++ The increment operator.

-- The decrement operator.

do-while A loop structure that executes a set of

statements over and over again based on a condition,

which is evaluated after an iteration.

for A loop structure that executes a set of statements

a fixed number of times.

while A loop structure that executes a set of state-

ments over and over again based on a condition,

which is evaluated before any iterations.

String A java.lang class with methods for manipu-

lating and comparing strings.

Chapter 6 Loop Structures and Strings 149

sample

Critical Thinking

1. What is the purpose of a loop structure?

2. Explain the difference between a while statement

and a do-while statement.

3. An input validation loop is a loop that checks

user input for valid data. If valid data is not

entered, the loop iterates until valid data is

entered. In which review of this chapter did

you write code for an input validation loop?

4. a) What is an infinite loop?

b) List two types of errors that can lead to an

infinite loop.

c) What is meant by overflow?

5. How many times will the do -wh i le loop

execute?

int x = 0;

do {

x = x + 2;

while (x < 120);

6. What initial value of x would make the loop

infinite?

do {

x = x + 3;

while (x < 120);

7. Compare and contrast counters and accumula-

tors. List two uses for each.

8. Write a for statement that sums the integers

from 3 to 10, inclusive.

9. List two factors that should be considered when

determining which loop structure to choose.

10. a) List two methods for debugging an

application.

b) Which method listed in part (a) would be

best for debugging an application that gen-

erates random numbers that are used for

determining the condition of an if state-

ment? Why?

11. Consider the following assignment:

String x = "my string.";

Determine the value returned by each of the

following methods:

a) x.length()

b) x.substring(0, 3)

c) x.toLowerCase()

d) x.toUpperCase

e) x.trim()

12. Consider the following statements:

String x = "lots of words.";

String y = "Lots of Words.";

String z = "Two words.";

Determine the value returned by each of the

following methods:

a) x.equals(y)

b) x.equalsIgnoreCase(y)

c) x.compareTo(z)

d) x.compareToIgnoreCase(y)

e) x.compareToIgnoreCase(z)

f) x.IndexOf("or")

g) x.lastIndexOf("o")

h) z.startsWith("Tw")

i) x.endsWith("ds")

13. a) Write an algorithm to count the number of

words in a sentence.

b) Write an algorithm to count the number of

letters in a sentence.

True/False

14. Determine if each of the following are true or

false. If false, explain why.

a) A while statement iterates once before evalu-

ating the condition.

b) A counter is incremented by a constant

amount.

c) An accumulator signifies that a loop should

stop iterating.

d) Sentinel values must always be the value

–1.

e) A variable declared in a for statement can be

used again anywhere in the program code.

f) String variables are primitive data types.

g) The first character of a string has index

position 1.

h) Strings are compared using relational opera-

tors such as >.

i) The String class includes a method for deter-

mining the location of a substring within a

string.

150 Chapter 6 Loop Structures and Strings

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Exercises

Exercise 1 ——————————————————— PrimeNumber

a) A prime number is an integer greater than 1 that is evenly divisible by only 1 and

itself. For example, 2, 3, 5, and 7 are prime numbers, but 4, 6, 8, and 9 are not. Create

a PrimeNumber application that prompts the user for a number and then displays a

message indicating whether the number is prime or not. Hint: The % operator can be

used to determine if one number is evenly divisible by another.

b) Modify the application to prompt the user for two numbers and then display the prime

numbers between those numbers.

Exercise 2 ————————————————————PrimeFactors

The Fundamental Theorem of Arithmetic states that every positive integer is the product of a set of

prime numbers. This set is called the prime factors. For example, the prime factors for 140 are 2, 2, 5,

and 7 (2*2*5*7 = 140). Create a PrimeFactors application that prompts the user for a positive integer

and then displays that integer’s prime factors. Use the following pseudocode when implementing the

PrimeFactors code:

Initialize a counter to 2

while the counter is less than or equal to the number

if the counter divides the number evenly

display the counter

divide the number by the counter to get a new number

else increment counter by 1

Exercise 3 —————————————————————Investment

Create an Investment application that calculates how many years it will take for a $2,500 investment

to be worth at least $5,000 if compounded annually at 7.5%

Exercise 4 ö ———————————————————— CarRecall

Modify the CarRecall application created in Chapter 5 Exercise 4 to allow the user to input as many

model numbers as needed. Use 0 as a sentinel to end user input. The application output should look

similar to:

Chapter 6 Loop Structures and Strings 151

sample

Exercise 5 ——————————————————— DigitsDisplay

Create a DigitsDisplay application that prompts the user for a non-negative integer and then displays

each digit on a separate line. Application output should look similar to:

Exercise 6 ————————————————————— DigitsSum

Create a DigitsSum application that prompts the user for a non-negative integer and then displays the

sum of the digits. Application output should look similar to:

Exercise 7 ————————————————————— CubesSum

a) Create a CubesSum application that prompts the user for a non-negative integer and

then displays the sum of the cubes of the digits. Application output should look similar

to:

b) Modify the application to determine what integers of two, three, and four digits are

equal to the sum of the cubes of their digits.

Exercise 8 ö ————————————————— GuessingGame

The GuessingGame application created in Chapter 5 Exercise 8 would be more fun if users could make

as many guesses as necessary to guess the secret number. Modify the GuessingGame application as

follows:

a) Modify the algorithm to allow for as many guesses as needed.

b) Modify the flowchart based on the algorithm modifications.

c) Modify the GuessingGame code. Application output should look similar to:

152 Chapter 6 Loop Structures and Strings

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d) A binary search is a divide-and-conquer technique for efficiently searching a list of

numbers that are sorted from lowest to highest. A strategy that incorporates the binary

search technique can be used by the Guessing Game player when making guesses

about the secret number:

1. Guess the number halfway between the lowest and highest numbers.

2. If the number guessed matches the secret number, then the player wins.

3. If the number guessed is too high, then take the number guessed minus one and

make this the highest number and go back to Step 1.

4. If the number guessed is too low, then take the number guessed plus one and make

this the lowest number and go back to Step 1.

For example, assuming 15 is the random number generated in the Guessing Game

application, the game would play out as follows when the player uses a divide-and-

conquer technique:

Current Low Current High Player Types Message Displayed

1 50 26 (i.e., (1+50)/2=25.5) Too high.

1 25 13 (i.e., (1+25)/2=13) Too low.

14 25 20 (i.e., (14+25)/2=19.5) Too high.

14 19 16 (i.e., (14+19)/2=16.5) Too high.

14 15 14 (i.e., (14+15)/2=14.5) Too low.

15 15 15 (i.e., (15+15)/2=15) You guessed it!

In another program run, assuming the random number generated is 20, the game

would play out as follows using the same divide-and-conquer technique:

Current Low Current High Player Types Message Displayed

1 50 26 (i.e., (1+50)/2=25.5) Too high.

1 25 13 (i.e., (1+25)/2=13) Too low.

14 25 20 (i.e., (14+25)/2=19.5) You guessed it!

When this approach is taken, it has been proven that a player will not be required

to make more than Log

n guesses, in this case Log

50, or at most 6 guesses. Try this

technique yourself. Explain in your own words why this works. Would this strategy

be possible if hints were not given after each guess?

Exercise 9 ———————————————————— PowersTable

Create a PowersTable application that displays a table of of powers similar to:

Chapter 6 Loop Structures and Strings 153

sample

Exercise 10 ——————————————————————— GCD

Create a GCD application that prompts the user for two non-negative integers and then displays the

greatest common divisor (GCD) of the two numbers. The GCD is the largest integer that divides into

both numbers evenly. An algorithm for finding the GCD is called Euclid’s Algorithm. Use the follow-

ing pseudocode when implementing the GCD code:

while (num2 > 0) {

temp = num1 % num2;

num1 = num2;

num2 = temp;

}

Application output should look similar to:

Exercise 11 ——————————————— ElapsedTimeCalculator

What comes 13 hours after 4 o’clock? Create an ElaspsedTimeCalculator application that prompts the

user for a starting hour, whether it is am or pm, and the number of elapsed hours. The application then

displays the time after that many hours have passed. Application output should look similar to:

Exercise 12 ————————————————————— Necklace

An interesting problem in number theory is sometimes called the “necklace problem.” This problem

begins with two single-digit numbers. The next number is obtained by adding the first two numbers

together and saving only the ones digit. This process is repeated until the “necklace” closes by return-

ing to the original two numbers. For example, if the starting two numbers are 1 and 8, twelve steps are

required to close the necklace: 1 8 9 7 6 3 9 2 1 3 4 7 1 8

Create a Necklace application that prompts the user for two single-digit integers and then displays the

sequence and the number of steps taken. The application output should look similar to:

154 Chapter 6 Loop Structures and Strings

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Exercise 13 ————————————————————— Hailstone

An interesting (yet unsolved) question in mathematics is called “hailstone numbers.” This series is

produced by taking an initial integer, and if the number is even, dividing it by 2. If the number is

odd, multiply it by 3 and add 1. This process is then repeated. For example, an initial number of 10

produces:

10, 5, 16, 8, 4, 2, 1, 4, 2, 1 …

An initial value of 23 produces:

23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1 …

Note that both numbers eventually reach the 4, 2, 1, 4, 2, 1 … cycle. Create two applications (Hailstone1

and Hailstone2) that answer the following questions for initial values of 1 to 200:

a) Do all integers from 1 to 200 eventually reach this cycle?

b) What is the maximum number of iterations to reach the cycle and which starting

number produces this maximum?

Exercise 14 ————————————————————— DiceRolls

Create a DiceRolls application that displays five rolls of two dice where each die is numbered from 1

to 6. The application should also show the total of each roll:

Exercise 15 ——————————————————————— Chaos

“Chaos theory” is a subfield of mathematics which relies heavily on the computer. A simple chaos

experiment is:

Start with any real number x between 0 and 1. Generate a new number using the

“logistic equation:”

x = 2*x(1 - x)

Display this new x and repeat the process 50 times.

a) Create a Chaos application that prompts the user for a starting value and then performs

this experiment. Make a prediction about what happens for different starting values.

b) Modify the application so that the 2 in the logistic equation can be replaced with a

value specified by the user in the range 2 to 4, but the starting value of x is always 0.5.

Note any interesting behavior.

Chapter 6 Loop Structures and Strings 155

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Exercise 16 ————————————————————RandomWalk

In the “random walk” problem, a person is placed at the center of a 7 meter long bridge. Each step the

person moves 1 meter either forward or backward at random.

Create a RandomWalk application that determines how many steps the person will walk before taking

a step off the bridge. Have the application average 50 trials, and display the average and the greatest

number of steps. (Hint: Generate a random number between 0 and 1, with 0 meaning to go forward

and 1 meaning to go backward.)

Exercise 17 ————————————————————— Password

Create a Password application that stores a secret password of your choice. The Password application

should prompt the user for the password and then display “Welcome” if the correct password is typed.

If after three tries the correct password has not been entered, the message “Access denied.” should be

displayed. Application output should look similar to:

Exercise 18 —————————————————————Monogram

Create a Monogram application that prompts the user for his or her first name, middle name, and last

name and then displays a monogram with the first and middle initials in lowercase and the last initial

in uppercase. Application output should look similar to:

Exercise 19 ——————————————————— RemoveString

Create a RemoveString application that prompts the user for a sentence and a string. The application

should then remove every occurrence of the string from the sentence. The application should look

similar to:

156 Chapter 6 Loop Structures and Strings

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Exercise 20 ————————————————————CountVowels

Create a CountVowels application that prompts the user for a string and then displays a count of the

number of vowels in the string. Application output should look similar to:

Exercise 21 ————————————————— GroupAssignment

Create a GroupAssignment application that prompts the user for his or her name and then displays a

group assignment. The group assignment depends on the first letter of the student’s last name. Last

names beginning with A through I are assigned to Group 1, J through S are assigned to Group 2, T

through Z are assigned to Group 3. Application output should look similar to:

Chapter 7 Methods 157

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Object-oriented programs use classes with methods to perform

tasks. A program often performs several tasks, each with its own level of

complexity. To manage these tasks, they are broken down into methods.

This chapter discusses top-down program development and writing and

documenting methods.

Program Development Using Methods

The solution to a task can be developed by breaking the task down into

smaller subtasks. These subtasks can then be reduced to yet simpler tasks.

This process can be continued until the original task is broken down into

units that each describe a specific goal. As the task is broken down into

smaller subtasks and then further into units, more detail for achieving the

specific goal is added. This problem-solving approach describes a software

development process called top-down development.

In top-down development, the first level of subtasks translates into the

main() method. Levels of tasks below main() are developed into a series

of additional methods. Using methods to define tasks is called procedural

abstraction. For example, consider the following program specification:

TempConverter allows the user to convert a temperature from

either Fahrenheit to Celsius or Celsius to Fahrenheit.

The algorithm for this application breaks the program specification down

into the first level of subtasks:

1. Determine the type of conversion to be done.

2. Convert the temperature using the appropriate formula.

Step 2 can then be broken down into another level of subtasks:

2a. Prompt the user for a Celsius temperature.

Convert the temperature to Fahrenheit using the formula:

F=9/5C + 32.

Display the temperature.

2b. Prompt the user for a Fahrenheit temperature.

Convert the temperature to Celsius using the formula:

C=5/9(F – 32).

Display the temperature.

Chapter 7

Methods

top-down development

procedural abstraction

TIP Top-down development

is also called top-down design

or step-wise refinement.

158 Chapter 7 Methods

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Top-down development and procedural abstraction were used to break

the program specification down into levels of subtasks, as shown on the

previous page. Outlining the levels of subtasks in pseudocode defines a

main() method and two other methods:

main()

Prompt the user for the conversion type.

Execute the appropriate method to convert the temperature.

fahrenheitToCelsius()

Prompt the user for a temperature in degrees Fahrenheit

Convert the temperature to degrees Celsius

Display the temperature

celsiusToFahrenheit()

Prompt the user for a temperature in degrees Celsius

Convert the temperature to degrees Fahrenheit

Display the temperature

The TempConverter application implements the pseudocode above:

import java.util.Scanner;

public class TempConverter {

public static void fahrenheitToCelsius() {

double fTemp, cTemp;

Scanner input = new Scanner(System.in);

System.out.print("Enter a Fahrenheit temperature: ");

fTemp = input.nextDouble();

input.close();

cTemp = (double)5/(double)9*(fTemp - 32);

System.out.println("The Celsius temperature is " + cTemp);

}

public static void celsiusToFahrenheit() {

double cTemp, fTemp;

Scanner input = new Scanner(System.in);

System.out.print("Enter a Celsius temperature: ");

cTemp = input.nextDouble();

input.close();

fTemp = (double)9/(double)5*cTemp + 32;

System.out.pri ntln("T he Fa hrenheit temperatu re is "

+ fTemp);

}

public static void main(String[] args) {

int choice;

Scanner input = new Scanner(System.in);

/* Prompt user for type of conversion */

System.out.println("1. Fahrenheit to Celsius conversion.");

System.out.println("2. Celsius to Fahrenheit conversion.");

System.out.print("Enter your choice: ");

choice = input.nextInt();

if (choice == 1) {

fahrenheitToCelsius();

} else {

celsiusToFahrenheit();

}

input.close();

}

TIP Methods must be part of

a class.

Chapter 7 Methods 159

sample

The TempConverter controlling class contains two methods as well

as a main() method. The methods are executed when they are called. A

method call consists of the method name followed by parentheses. The if

statement in the main() method on the previous page contains two method

calls, fahrenheitToCelsius() and celsiusToFahrenheit().

TempConverter produces output similar to:

In this run of the application, the user entered 1 and therefore the

fahrenheitToCelsius() method was called.

Writing Methods

A method consists of a declaration and a body. The method declaration

includes access level, return type, name, and parameters, if any. The method

body contains the statements that implement the method. A method takes

the form:

<access _ level> <return _ type> <name>(<parameters>) {

}

For example, consider the fahrenheitToCelsius() method from the

TempConverter application:

public static void fahrenheitToCelsius() {

double fTemp, cTemp;

Scanner input = new Scanner(System.in);

System.out.print("Enter a Fahrenheit temperature: ");

fTemp = input.nextDouble();

input.close();

cTemp = (double)5/(double)9*(fTemp - 32);

System.out.println("The Celsius temperature is " + cTemp);

}

The method above is a class method with access level public, return

type void, name fahrenheitToCelsius, and no parameters. The access level

of a method determines if other classes can call the method. The keyword

public is an access modifier. A public method can be called by any other

method. The access level of a method can also be thought of as its visibility.

Access levels are discussed further in Chapter 8.

The keyword static declares the method a class method. A class method

can be called from the class itself. Methods that are not class methods must

be called from an instantiated object of that class.

The return type void means that the method will not return a value,

and parameters are specified when a method needs values to perform its

task. The body of the method starts with the first opening brace ({) and

ends with the closing brace (}).

method declaration

method body

access level

class method

call

access modifier

void

visibility

160 Chapter 7 Methods

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Method names should indicate an action. Verbs make good method

names. A method name should also begin with a lowercase letter and

then an uppercase letter should begin each word within the name. Method

names may not contain spaces.

Methods can also have their own set of variables, constants, and objects.

Variable, constant, and object declarations in the body of a method have

a scope that extends from the declaration to the end of the method

body. These variables, constants, and objects are said to be local to the

method because their scope is limited to that method. For example, the

fahrenheitToCelsius() method contains local variables fTemp and cTemp and

a local object named input.

Review: TimeConverter

Create a TimeConverter application that allows the user to choose among converting hours to minutes, days

to hours, minutes to hours, or hours to days. Use methods as appropriate.

Method Parameters

A method declaration can include method parameters, which accept values

from the method call. The data passed to the method can then be used

inside the method to perform its task. For example, the drawBar() method

includes an int parameter named length:

public static void drawBar(int length) {

for (int i = 0; i < length; i++) {

System.out.print("*");

}

System.out.println();

}

Data is given, or passed, to a method by enclosing the data in parentheses

in the method call. The value or variable passed to a method is called the

argument. For example, the RightTriangle application makes six calls to

drawBar(). Each call passes a different variable argument:

public class RightTriangle {

public static void drawBar(int length) {

for (int i = 1; i <= length; i++) {

System.out.print("*");

}

System.out.println();

}

public static void main(String[] args) {

/* draw a right triangle with base size 6 */

for (int i = 1; i <= 6; i++) {

drawBar(i);

}

local scope

TIP The terms “parameter”

and “argument” are often used

synonymously.

naming conventions

passing data

argument

TIP The term “formal parame-

ter” is sometimes used to refer

to a parameter in the method

declaration, and the term

“actual parameter” is used to

refer to the argument being

passed to the method.

Chapter 7 Methods 161

sample

The RightTriangle application produces the output:

In Java, arguments are passed by value, which means that the data stored

in an argument is passed. An argument that is a primitive data type gives

the method a copy of its value. An argument that is an object gives the

method a copy of its reference that points to methods for changing object

data. Therefore, a method can change the data stored in an object because

it has access to the object’s methods, but it cannot change the data stored

in a primitive variable because the method does not have access to the

actual location of the primitive data.

When a method declaration includes more than one parameter, the

parameters are separated by commas. For example, a modified drawBar()

has an int parameter for the length of the bar and a String parameter for

the character to use to draw the bar:

public static void drawBar(int length, String mark) {

for (int i = 1; i <= length; i++) {

System.out.print(mark);

}

System.out.println();

}

A call to the modified drawBar() method includes two arguments sepa-

rated by commas:

drawBar(6, "$");

This call produces the following output:

The order of the arguments in a method call is important because the

first argument corresponds to the first parameter in the method declara-

tion, the second argument corresponds to the second parameter, and so

on. Note that argument names do not necessarily match parameter names.

Descriptive variable names should be used throughout a program without

regard to matching parameter names in a method declaration.

Review: SpanishNumbers

Create a SpanishNumbers application that displays numbers 1 through 10 in Spanish. A method with an int

parameter should display the Spanish word for the number passed. A loop structure in the main() method

should be used to call the method ten times. The Spanish word equivalents for numbers 1 through 10 are:

1 uno 6 seis

2 dos 7 siete

3 tres 8 ocho

4 cuatro 9 nueve

5 cinco 10 diez

pass by value

multiple parameters

TIP Passing an argument of a

type that is not expected by a

method generates the exception

IllegalArgumentException.

162 Chapter 7 Methods

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Review: DisplayBox – part 1 of 2

Create a DisplayBox application that prompts the user for a height and width and then displays a box of that

size. The DisplayBox application should include a method named drawBox() that has two parameters and

makes calls to the drawBar() method.

Method Overloading

The method declaration is used by the compiler to determine which

method to execute. Therefore, method names do not have to be unique

as long as the parameters are different for methods with the same name.

Method overloading is when more than one method of the same name is

included in a class. For example, the following application contains two

drawBar() methods:

public class MethodOverloadingExample {

public static void drawBar(int length) {

for (int i = 1; i <= length; i++) {

System.out.print("*");

}

System.out.println();

}

public static void drawBar(int length, String mark) {

for (int i = 1; i <= length; i++) {

System.out.print(mark);

}

System.out.println();

}

public static void main(String[] args) {

drawBar(10);

drawBar(5, "@");

}

The MethodOverloading application produces the output:

Note that the first call in main() executes the drawBar() method containing

only one parameter. The second call executes the drawBar() method that

contains two parameters. The compiler uses the types, order, and number

of parameters to determine which method to execute.

Chapter 7 Methods 163

sample

Review: DisplayBox – part 2 of 2

Modify the DrawBox application to ask the user if a specific character should be used for the display. For

example, the prompt could be “Do you want to enter a character to use to display the box? (enter y for yes):”

If the user types y, then prompt the user for the character. Otherwise, the default character should be used.

The modified application should contain overloaded drawBox() and drawBar() methods.

The return Statement

A method can return a value. For example, the cubeOf() method returns

the cube of its parameter:

public static double cubeOf(double x) {

double xCubed;

xCubed = x * x * x;

return(xCubed);

}

The return statement is used to send a value back to the calling statement.

A return statement can return only one value.

A method that returns a value must include the return type in the

method declaration. For example, the cubeOf() method declaration

declares a return type double. Return types can be primitive types, such

as int, double, and boolean, or abstract types, such as the String class. The

return type void is used when there will be no return value. A method

declared as void does not contain a return statement.

A method that returns a value is called from a statement that will

make use of the returned value, such as an expression or an assignment

statement. For example, the following application calls cubeOf() from an

assignment statement:

public class CubeCalculator {

public static double cubeOf(double x) {

double xCubed;

xCubed = x * x * x;

return(xCubed);

}

public static void main(String[] args) {

double num = 2.0;

double cube;

cube = cubeOf(num);

System.out.println(cube);

}

The CubeCalculator application produces the following output:

TIP The return t ypes of

methods cannot be used to

distinguish one method from

another for overloading.

164 Chapter 7 Methods

sample

Review: Exponentiation

Create an Exponentiation application that prompts the user for two numbers and then displays the first num-

ber raised to the power of the second number. The application should include a method named powerOf()

that returns its first parameter raised to the power of its second parameter.

Documenting Methods

Methods should be carefully commented so that a reader of the program

understands what task the method is performing and what data, if any,

will be returned by the method. Method documentation is in the form of

documentation comments (/** */) that appear just above the method

declaration. For example, the drawBar() method with documentation:

/**

* Print a bar of asterisks across the screen.

* pre: length > 0

* post: Bar drawn of length characters, insertion

* point moved to next line.

public static void drawBar(int length) {

for (int i = 0; i < length; i++) {

System.out.print("*");

}

System.out.println();

}

The assumptions, or initial requirements, of a method are stated in the

documentation in a section called the precondition, or just pre. Note that

the pre for drawBar() states that length must be greater than 0, but not that

length must be an int. Information that the compiler will verify, such as

data types, should not be stated in method documentation.

The postcondition section of the documentation, or post, states what must

be true after the method has been executed. However, the post should not

state how the method accomplished its task.

A method may not have a precondition, but every method must

have a postcondition. For example, below is the cubeOf() method with

documentation:

/**

* Calculates the cube of a number.

* pre: none

* post: x cubed returned

public static double cubeOf(double x) {

double xCubed;

xCubed = x * x * x;

return(xCubed);

}

precondition

postcondition

Chapter 7 Methods 165

sample

To summarize, the guidelines for writing pre and post conditions are:

• The precondition states what must be true at the beginning of a

method for the method to work properly.

• The postcondition states what must be true after the method has

executed if the method has worked properly.

• Preconditions and postconditions should not state facts that the

compiler will verify. They should also not refer to variables or

information outside the method.

• The postcondition should not state how the method accomplished

its task.

Review

Modify each of the Reviews in this chapter so that the methods are properly documented.

Chapter 7 Case Study

This case study will focus on top-down development and procedural

abstraction. Testing and debugging methods in isolation will also be

demonstrated.

An application for generating a letter grade based on a numeric grade

will be created. The GradeConverter application allows the user to enter

a numeric grade and then a letter grade is displayed. The user may then

choose to enter another grade or quit.

GradeConverter Specification

The GradeConverter application prompts the user for a numeric grade in

the range 0 to 100 or a –1 to end the application. When a valid numeric

grade is entered, the corresponding letter grade is then displayed. Grades

from 90 to 100 are an A, grades from 80 to 89 are a B, grades from 70 to 79

are a C, grades from 60 to 69 are a D, and grades below 60 are an F. After

displaying the corresponding letter grade, the user is prompted to enter

another letter grade or can choose to quit the application.

The GradeConverter interface should include a prompt asking for the

numeric grade. The prompt should give the option of quitting the appli-

cation. After displaying the letter grade, the user should be prompted to

enter another numeric grade or quit the application.

The GradeConverter output sketch:











166 Chapter 7 Methods

sample

The GradeConverter algorithm:

1. Prompt the user for a number.

2. Determine the letter grade that corresponds to the entered

numeric grade and display the result.

3. Repeat steps 1 and 2 until the user chooses to quit.

The GradeConverter flowchart:













GradeConverter Code Design

Using the top-down development approach, the algorithm is further

refined:

Step 1 of the algorithm can be broken down further:

1a. Display a prompt that gives the user the option to quit.

Check that the number entered is valid. It should correspond to

either a sentinel value that indicates the user wants to quit or a

number in the range 0 through 100.

Step 2 of the algorithm can be broken down further:

2a. Determine if the numeric grade is between 90 to 100, 80 to 89, 70

to 79, 60 to 69, or 0 to 59.

Assign the letter A to a grade from 90 to 100, a letter B to a grade

from 80 to 89, the letter C to a grade from 70 to 79, the letter D to

a grade from 60 to 69, and the letter F to a grade from 0 to 59.

Chapter 7 Methods 167

sample

Using the flowchart, algorithm, and procedural abstraction, the pseudo-

code for the GradeConverter application can be created. The code will

include a loop structure to get the user’s input and two additional methods.

One method will determine if the input is valid and another determines

which letter corresponds to the numeric grade:

main()

Prompt the user for a number

while (number != -1) {

if (isValidNumber(number)) {

getLetterGrade(number)

Display message with letter grade

}

Prompt the user for a number

}

isValidNumber(userNum, maxNum, minNum)

if (minNum <= userNum <= maxNum) {

return (true);

} else {

return(false);

}

getLetterGrade(numericGrade)

if (numericGrade < 60) {

return ("F");

} else if (numericGrade < 70) {

return ("D");

} else if (numericGrade < 80) {

return ("C");

} else if (numericGrade < 90) {

return ("B");

} else {

return ("A");

}

GradeConverter Implementation

Testing methods in isolation is important to ensure that the program

as a whole will run without error. When testing a method, statements in

main() should call the method using test data. The main() method should

not call any other method or perform any other task except test the current

method.

Rather than writing code for the entire application at once, one method

at a time will be added and then tested. When testing the methods is com-

plete, the main() method will be rewritten to implement the GradeConverter

pseudocode.

168 Chapter 7 Methods

sample

The isValidNumber() method is the first method written and tested:

public class GradeConverter {

/**

* Determines if a numeric entry is valid.

* pre: none

* post: true return if minNum <= userNum <= maxNum;

* false returned otherwise

public static boolean isValidNumber(int userNum, int minNum, int maxNum) {

if (minNum <= userNum && userNum <= maxNum) {

return(true);

} else {

return(false);

}

public static void main(String[] args) {

final int minValue = 0;

final int maxValue = 100;

int numericGrade;

numericGrade = 0;

if (isValidNumber(numericGrade, minValue, maxValue)) {

System.out.println(numericGrade + " is valid.");

} else {

System.out.println(numericGrade + " is NOT valid.");

}

numericGrade = 100;

if (isValidNumber(numericGrade, minValue, maxValue)) {

System.out.println(numericGrade + " is valid.");

} else {

System.out.println(numericGrade + " is NOT valid.");

}

numericGrade = -1;

if (isValidNumber(numericGrade, minValue, maxValue)) {

System.out.println(numericGrade + " is valid.");

} else {

System.out.println(numericGrade + " is NOT valid.");

}

numericGrade = 101;

if (isValidNumber(numericGrade, minValue, maxValue)) {

System.out.println(numericGrade + " is valid.");

} else {

System.out.println(numericGrade + " is NOT valid.");

}

The statements in main() test the isValidNumber() method with data

that includes boundary values. A boundary value is data that is just inside

or just outside the range of valid values. For example, the value 100 lies just

inside the high end of the range of valid grades. Testing the method with

this data verifies that the <= operator was used rather than the < operator.

The GradeConverter application produces the following output:

boundary value

Chapter 7 Methods 169

sample

Next, the getLetterGrade() method is added and the main() statements

are changed to test that method:

public class GradeConverter {

/**

* Determines if a numeric entry is valid.

* pre: none

* post: true has been returned if minNum <= userNum <= maxNum;

* false has been returned otherwise

public static boolean isValidNumber(int userNum, int minNum, int maxNum) {

if (minNum <= userNum && userNum <= maxNum) {

return(true);

} else {

return(false);

}

/**

* Determines the letter grade that corresponds to the numeric grade.

* pre: 0 <= numGrade <= 100

* post: The letter grade A, B, C, D, or F has been returned.

public static String getLetterGrade(int numGrade) {

if (numGrade < 60) {

return("F");

} else if (numGrade < 70){

return("D");

} else if (numGrade < 80) {

return("C");

} else if (numGrade < 90) {

return("B");

} else {

return("A");

}

public static void main(String[] args) {

int numericGrade;

numericGrade = 90;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 89;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 80;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 79;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 70;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 69;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 60;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

numericGrade = 59;

System.out.println(numericGrade + " is " + getLetterGrade(numericGrade));

}

170 Chapter 7 Methods

sample

Boundary values for getLetterGrade() are tested with statements in

main(). Running GradeConverter displays the output:

After verifying that the methods are working as expected, the final

GradeConverter application can be completed:

* GradeConverter.java

import java.util.Scanner;

/**

* Display the letter grade that corresponds to the numeric

* grade entered by the user.

public class GradeConverter {

/**

* Determines if a numeric entry is valid.

* pre: none

* post: true has been returned if minNum <= userNum <= maxNum;

* false has been returned otherwise

public static boolean isValidNumber(int userNum, int minNum, int maxNum) {

if (minNum <= userNum && userNum <= maxNum) {

return(true);

} else {

return(false);

}

/**

* Determines the letter grade that corresponds to the numeric grade.

* pre: 0 <= numGrade <= 100

* post: The letter grade A, B, C, D, or F has been returned.

public static String getLetterGrade(int numGrade) {

if (numGrade < 60) {

return("F");

} else if (numGrade < 70){

return("D");

} else if (numGrade < 80) {

return("C");

} else if (numGrade < 90) {

return("B");

} else {

return("A");

}

Chapter 7 Methods 171

sample

public static void main(String[] args) {

final int FLAG = -1;

final int minValue = 0;

final int maxValue = 100;

int numericGrade;

String letterGrade;

Scanner input = new Scanner(System.in);

System.out.print("Enter a numeric grade (-1 to quit): ");

numericGrade = input.nextInt();

while (numericGrade != FLAG) {

if (isValidNumber(numericGrade, minValue, maxValue)) {

letterGrade = getLetterGrade(numericGrade);

System.out.println("The grade " + numericGrade + " is a(n) " +

letterGrade + ".");

} else {

System.out.println("Grade entered is not valid.");

}

System.out.print("Enter a numeric grade (-1 to quit): ");

numericGrade = input.nextInt();

}

The GradeConverter application produces output similar to:

GradeConverter Testing and Debugging

Testing done at this point should test the logic in main() because the

other methods have already been verified. The logic in main() is simple.

Therefore, testing need only include verifying that the loop control vari-

able is working as expected, the user is able to enter grades as expected,

and that letter grades are returned for values entered by the user in the

range 0 though 100.

Review: GradeConverter

Modify the GradeConverter Case Study to display an A+ for a grade of 100, a B+ for a grade of 89, a C+ for

a grade of 79, and a D+ for a grade of 69.

Chapter Summary

This chapter introduced a new level of software development that

included writing methods to perform tasks. In the software development

process, top-down development is a problem-solving approach that breaks a

task down into smaller subtasks and then further into units. Implementing

these tasks with methods is called procedural abstraction.

172 Chapter 7 Methods

sample

Methods are executed in a statement by including the method name

followed by parentheses. A statement that executes a method is said to

call the method. When a method requires data to perform its tasks, the

data is included inside the parentheses in the method call. A method that

returns data must be called from an assignment statement or from inside

an expression.

A method includes a declaration and a body. The method declaration

includes the access level, return type, if any, method name, and param-

eters for receiving data, if necessary. The access level of a method can

be declared public, which means that the method can be called from a

statement in any other method. The keyword public is called an access

modifier. A method declaration that includes the keyword static is a class

method, which can be called from the class itself.

The return type of a method declares what type of value will be given

back to the calling statement. The return type void indicates that the

method will not return a value at all. Return types can be primitive types,

such as int and double, or abstract data types, such as String. Methods that

return a value must include a return statement in the method body.

A method can have multiple parameters. Arguments in a method call

must be passed to a method in the same order as the parameter declara-

tions. Methods with the same name, but with different parameters are

said to be overloaded. The compiler determines which method to call by

the types, order, and number of parameters in overloaded methods.

Primitive arguments are passed by value, which means that the data

stored in the argument is passed, not a reference to the argument loca-

tion. A method can only use the argument values in the task it performs.

A method cannot change the data stored in an argument.

The body of a method can include variable, constant, and object decla-

rations. These declarations are said to be local because they have a scope

that extends just from the declaration to the end of the method body.

Careful documentation is important for the reader of a program to

understand a method. Method documentation is enclosed by /** */ and

includes a brief description of the method, a precondition, and a postcon-

dition. Every method must have a postcondition, but not every method

requires a precondition.

Code conventions introduced in this chapter are:

• Method names should indicate an action and begin with a lower-

case letter and then an uppercase letter should begin each word

within the name.

• Method documentation should be enclosed in /** */ comment

blocks.

• Method documentation should include a brief description of the

task the method performs, a precondition, and a postcondition.

Chapter 7 Methods 173

sample

Vocabulary

Access level The part of a method declaration that

determines if the method can be called by other

classes.

Access modifier A keyword in the declaration

of a method that determines the access level of a

method.

Argument The value or variable passed to a

method.

Call A statement that contains a method name

followed by parentheses.

Boundary value A value that lies just inside or just

outside the range of valid values.

Class method A method that can be called from

the class itself.

Local Variables, constants, and objects that are

declared within a method and therefore have a scope

limited to that method.

Method body The statements that implement a

method.

Method declaration The first line of a method,

which contains the method name, access level, return

type, and parameters, if any.

Method overloading Writing more than one method

of the same name in a class.

Method parameters The part of a method declara-

tion that accepts values from the method call.

Pass Giving data to a method by enclosing the data

in parentheses in the method call.

Pass by value Passing the value of an argument to a

method. The type of data passed depends on whether

the argument is a primitive or an object.

Precondition The part of a method’s documentation

that states the assumptions, or initial requirements,

of the method. Also called pre.

Procedural abstraction Breaking a task down into

methods.

Postcondition The part of a method’s documenta-

tion that states what must be true after the method

has been executed. Also called post.

Top-down development A problem-solving

approach where a task is broken down into subtasks

and then the subtasks are reduced to yet simpler

tasks.

Visibility The access level of a method.

Java

/** */ Used to enclose documentation comments

for a method.

public An access modifier used in the declaration

of a method to indicate that the method is visible

to any other class.

static A keyword used in the declaration of a method

to indicate that the method is a class method.

void A keyword used in the declaration of a method to

indicate that the method will not return a value.

return Statement used to send a value from a method

back to the calling statement.

174 Chapter 7 Methods

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Critical Thinking

1. Use top-down development and procedural

abstraction to write pseudocode for the follow-

ing specification:

The Pizza application allows the user to

choose to display the instructions for mak-

ing a pizza in either English or Spanish.

2. Explain the difference between method declara-

tion and method body.

3. What type of keyword is used to change the

access level of a method?

4. What is another word used for describing the

access level of a method?

5. Explain the scope of each of the variables in the

code below:

public class ScopeExample {

public static void main(String[] args) {

int var1;

for (int var2 = 0; var2 < 5; var2++) {

method1();

}

public static void method1() {

int var3;

for (int var4 = 0; var4 < 2; var4++) {

var3 += 1;

}

6. Write a method declaration for each of the fol-

lowing descriptions:

a) A class method named getVowels that can be

called by any other method, requires a String

parameter, and returns an integer value.

b) A class method named extractDigit that can

be called by any other method, requires an

integer parameter, and returns an integer

value.

c) A class method named insertString that can

be called by any other method, requires a

String parameter and an integer parameter,

and returns a String parameter.

7. a) How does the compiler distinguish one

method from another?

b) Can two methods in the same class have the

same name? Explain.

8. a) What is the return statement used for?

b) How many values can a return statement

send back to the calling statement?

c) How is the declaration of a method return-

ing a value different from the declaration of

a method that does not return a value?

9. Find and explain the error in the code below:

public class MethodCallExample {

public static void main(String[] args) {

int num;

doSomething();

num = doSomething();

}

public static int doSomething() {

return(5);

}

10. a) What type of comments should be used for

describing a method?

b) What three things should the comments for

a method describe?

True/False

11. Determine if each of the following are true or

false. If false, explain why.

a) Breaking a task down into methods is called

procedural abstraction.

b) A method call consists of the method decla-

ration in an assignment statement.

c) A void method must return a value.

d) An access modifier declares the return type

of a method.

e) The keyword static declares a method is a

class method.

f) Method parameters are enclosed by braces

({}).

g) Local variables can be used by any method

in a class.

h) The value of an argument passed to a method

can be changed in an assignment statement

in the method.

i) Method overloading means that an applica-

tion contains more than 10 methods.

j) The return statement is used to send a value

back to the calling statement.

k) The precondition of a method states the data

types of the method’s parameters.

l) The postcondition of a method describes the

way the method accomplishes its task.

Chapter 7 Methods 175

sample

Exercises

Exercise 1 ——————————————————————— House

Create a House application that calls methods addRoof(), addBase(), and addWalk() to display the

following:

Exercise 2 ————————————————— MetricConversion

The following formulas can be used to convert English units of measurements to metric units:

inches * 2.54 = centimeters

feet * 30 = centimeters

yards * 0.91 = meters

miles * 1.6 = kilometers

Create a MetricConversion application that displays a menu of conversion choices and then prompts

the user to choose a conversion. Conversion choices should include inches to centimeters, feet to cen-

timeters, yards to meters, miles to kilometers, and vice versa. The application should include separate

methods for doing each of the conversions. Application output should look similar to:

Exercise 3 ö —————————————————— PrimeNumber

Modify the PrimeNumber application created in Chapter 6 Exercise 1 to include a method named

isPrime(). The isPrime() method should require one parameter and return a Boolean value.

176 Chapter 7 Methods

sample

Exercise 4 ———————————————————— IsoTriangle

Create an IsoTriangle application that prompts the user for the size of an isosceles triangle and then

displays the triangle with that many lines. The IsoTriangle application code should include:

• the drawBar() method from the chapter.

• An addSpaces() method which “prints” spaces.

Application output should look similar to:

Exercise 5 ————————————————————— AddCoins

Create an AddCoins application that prompts the user for the number of pennies, nickels, dimes,

and quarters, and then displays their total dollar amount. The AddCoins application should include

a getDollarAmount() method that has four int parameters corresponding to the number of pennies,

nickels, dimes, and quarters, and returns a String that corresponds to the dollar value of the coins.

Note that the String returned should include the currency sign ($). Application output should look

similar to:

Exercise 6 ————————————————— PythagoreanTriple

Create a PythagoreanTriple application that displays all pythagorean triples with values of A and B

less than 100. A pythagorean triple is a set of three integers that make the equation a

+ b

= c

true.

The application should include a PerfectSquare() method that uses the solution from the PerfectSquare

review in Chapter 6. (Hint: You will need to generate all possible combinations of A and B and display

just those that work.)

Chapter 7 Methods 177

sample

Exercise 7 ———————————————————PerfectIntegers

Create a PerfectIntegers application that displays all perfect integers up to 100. A perfect integer is a

number which is equal to the sum of all its factors except itself. For example, 6 is a perfect number

because 1 + 2 + 3 = 6. The application should include a boolean method isPerfect().

Exercise 8 ————————————————————————HiLo

a) In the Hi-Lo game, the player begins with a score of 1000. The player is prompted for the

number of points to risk and a second prompt asks the player to choose either High or

Low. The player’s choice of either High or Low is compared to random number between

1 and 13, inclusive. If the number is between 1 and 6 inclusive, then it is considered

“low”. A number between 8 and 13 inclusive is “high”. The number 7 is neither high

nor low, and the player loses the points at risk. If the player had guessed correctly,

the points at risk are doubled and added to the total points. For a wrong choice, the

player loses the points at risk. Create a HiLo application based on this specification.

Application output should look similar to:

b) Modify the application to allow the player to continue until there are 0 points left. At

the end of the game, display the number of guesses the user took before running out

of points.

178 Chapter 7 Methods

sample

Exercise 9 ———————————————————————— Nim

The game of Nim starts with a random number of stones between 15 and 30. Two players alternate

turns and on each turn may take either 1, 2, or 3 stones from the pile. The player forced to take the last

stone loses. Create a Nim application that allows the user to play against the computer. In this version

of the game, the application generates the number of stones to begin with, the number of stones the

computer takes, and the user goes first. The Nim application code should:

• prevent the user and the computer from taking an illegal number of stones. For

example, neither should be allowed to take three stones when there are only 1 or 2

left.

• include an isValidEntry() method to check user input.

• include a drawStones() method that generates a random number from 1 to 3 for the

number of stones the computer draws.

• include separate methods to handle the user’s turn and the computer’s turn.

Application output should look similar to that shown on the next page:

Exercise 10 ö ————————————————— GuessingGame

The GuessingGame application modified in Chapter 6 Exercise 8 should include a separate method for

displaying a hint to the user. Modify the GuessingGame application as follows:

a) Modify the algorithm to include a call to a method named giveHint(), which displays

a hint, but does not return a value.

b) Modify the flowchart based on the algorithm modifications.

c) Modify the GuessingGame code. Application output should look similar to:

Chapter 8 Classes and Object-Oriented Development 179

sample

ava applications use objects to perform tasks. Objects are defined

with classes. This chapter explains how to design and write a class. The

Object class and inheritance are introduced. Object-oriented development,

encapsulation, and reusability are also discussed.

What is an Object?

In object-oriented programming, an object stores data and can perform

actions and provide communication. The state of an object refers to the

data it stores. The behavior of an object is defined by the action and com-

munication it provides.

Objects often model, or simulate, real-world things. For example, con-

sider a circle shape. To create a Circle object modeled after the circle shape,

we analyze the state and behavior of the shape. A circle is defined by its

radius, so this will make up the state of the object. A circle shape doesn’t

do much in the way of actions, but a Circle object could change its radius,

calculate its area, and tell us what its radius is. These actions will make

up the behavior of a Circle object.

An object is an instance of a class. A class is a data type that defines vari-

ables for the state of an object and methods for an object’s behavior. Good

programming style dictates that the state of an object can only be changed

through its behavior. For example, to change the radius of a Circle object,

a method for changing the radius variable must be called. Protecting an

object’s data is called encapsulation. Encapsulation is also called information

hiding because the object hides certain data from code outside the class.

For example, a Circle object declared in client code can be visualized as:







Chapter 8

Classes and Object-Oriented

Development

state

behavior

TIP A class is an abstract data

type, which was discussed in

Chapter 4.

encapsulation

information hiding

180 Chapter 8 Classes and Object-Oriented Development

sample

Client code refers to an application that uses one or more classes. The

client can access the methods of the class, but cannot directly access the

data defined in the class. This reinforces that the state of an object can

only be changed through its behavior.

TestCircle is client code. It uses the Circle class:

public class TestCircle {

public static void main(String[] args) {

Circle spot = new Circle();

spot.setRadius(5);

System.out.println("Circle radius:" + spot.getRadius());

System.out.println("Circle area: " + spot.area());

}

In the TestCircle application, a Circle object named spot is instantiated.

The object spot uses behavior setRadius() to change the state of the object,

making the radius of the circle 5. Two other behaviors are implemented

to produce the application output:

Designing and Writing a Class

Designing a class requires choosing the data the object will store and

determining the actions and communication the object will provide. The

design should include variable names and method names along with a

description of the method and any required parameters. For example, the

Circle class design appears similar to:









 





 

A class is written in a separate file and consists of a declaration and

a body. The class declaration includes the access level, the keyword class,

and the class name. The class body contains variables, constructors, and

methods. Constructors are used to initialize variables in a class. Variables

and methods are called the members of a class. A class takes the form:

<access _ level> class <name> {

}

Functional

Decomposition

The process of creating clearly

defined functions, or behavior,

for a class is sometimes called

functional decomposition. A

well-written class has been

functionally decomposed into

a set of methods that cannot

be simplified further.

class declaration, body

member

constructor

client code

TIP In Java, the controlling

class is the client code.

Chapter 8 Classes and Object-Oriented Development 181

sample

The Circle class code is based on the design on the previous page:

/**

* Circle class.

public class Circle {

private static final double PI = 3.14;

private double radius;

/**

* constructor

* pre: none

* post: A Circle object created. Radius initialized to 1.

public Circle() {

radius = 1; //default radius

}

/**

* Changes the radius of the circle.

* pre: none

* post: Radius has been changed.

public void setRadius(double newRadius) {

radius = newRadius;

}

/**

* Calculates the area of the circle.

* pre: none

* post: The area of the circle has been returned.

public double area() {

double circleArea;

circleArea = PI * radius * radius;

return(circleArea);

}

/**

* Returns the radius of the circle.

* pre: none

* post: The radius of the circle has been returned.

public double getRadius() {

return(radius);

}

The Circle class has access level public which means that it is visible

to other classes and can be used to instantiate objects in those classes.

The class name is Circle. A class name should be a noun, begin with an

uppercase letter, and each word within the name should also begin with

an uppercase letter. Class names may not contain spaces.

The body of a class starts with an opening brace ({) and ends with a

closing brace (}). Member variables are declared after the opening brace,

and outside of any methods. Variable declarations in the body of a class

have a local scope that extends from the opening brace of the class body

to the closing. Note that the Circle class also has a member variable that

is a constant.

naming conventions

Organizing Files

Each class is written in a

separate file. The client code

and the classes it uses are then

compiled together as part of a

project.

Interface

The public methods of a class

define the interface of an

object. The interface is how

client code can interact with

an object.

182 Chapter 8 Classes and Object-Oriented Development

sample

The visibility of a member variable is controlled with an access modifier.

Declaring a variable as private makes it visible to the class, but not to

client code. This encapsulates the data and provides information hiding.

For example, the Circle class contains a private variable radius that can be

used by any of the methods of the class, but cannot be directly accessed

by statements in the client code where the Circle object was created.

A constructor is automatically called when an object is created. The con-

structor is where variables are initialized. Variables that are not initialized

may contain data that could generate a run-time error when a method of

the class is executed.

The methods in a class are accessor methods, modifier methods, or

helper methods. Accessor methods are called to determine the value of

a variable. For example, in the Circle class, getRadius() is an accessor

method. It returns the value of the variable radius. A modifier method is

called to change the value of a variable. In the Circle class, setRadius() is a

modifier method. It assigns a value passed in a parameter to the variable

radius. Accessor and modifier methods have access level public so that

they may be called from the class where the Circle object was created.

Helper methods are called from within a class by other methods. They

are used to help complete a task and have access level private. The Circle

class does not contain helper methods.

An application that includes Circle objects can include statements that

call the public methods, but statements that refer to the private members

will generate a compiler error.

Review: Circle – part 1 of 4

Modify the Circle class to include a member method named circumference. The circumference() method

should return the circumference of the circle (2πr). Test the class with the following client code:

public static void main(String[] args) {

Circle spot = new Circle();

spot.setRadius(3);

System.out.println("Circle radius: " + spot.getRadius());

System.out.println("Circle circumference: " + spot.circumference());

}

Review: Coin – part 1 of 2

Create a Coin class that includes a variable faceUp that stores either a 0 for heads up or 1 for tails up, an

accessor method named showFace() that returns a 0 if the coin is heads up or a 1 if the coin is tails up, and a

modifier method named flipCoin() that assigns a random integer between 0 and 1, inclusive, to the variable

faceUp. Test the class with the following client code:

public static void main(String[] args) {

Coin nickel = new Coin();

if (nickel.flipCoin() == 0) {

System.out.println("Heads up!");

} else {

System.out.println("Tails up!");

}

helper method

accessor method

modifier method

TIP Access modifiers and

visibility were introduced in

Chapter 7.

Chapter 8 Classes and Object-Oriented Development 183

sample

Writing Constructors

The constructor of a class is automatically executed when an object

is instantiated. Once an object is instantiated, the method members of

the class can be called in any order. Unexpected results may occur if an

accessor method is called before a member variable has been set to a valid

value. To prevent this, variables should be initialized in the constructor.

A constructor takes the form:

public <class name>(<parameters>) {

}

The constructor of a class does not have a return type and always has the

same name as the class. When a constructor contains parameters, they

are separated by commas.

Constructors can be overloaded to provide more options for instantiat-

ing an object. For example, if the radius of the circle object is known when

the Circle object is created, it would be more efficient to assign the value

to radius when the object is created:

Circle spot = new Circle(5);

A constructor can be added to the Circle class to handle creating an object

with a parameter that contains the circle radius:

/**

* Circle class.

public class Circle {

private static final double PI = 3.14;

private double radius;

/**

* constructor

* pre: none

* post: A Circle object created. Radius initialized to 1.

public Circle() {

radius = 1; //default radius

}

/**

* constructor

* pre: none

* post: A Circle object created with radius r.

public Circle(double r) {

radius = r;

}

…rest of Circle class

When a class contains more than one constructor, the compiler uses

the number and types of parameters to determine which constructor to

execute.

overloading constructors

184 Chapter 8 Classes and Object-Oriented Development

sample

Review: Circle – part 2 of 4

Modify the Circle class to include an overloaded constructor that accepts the radius of the Circle object, as

shown in the previous section.

Review: Rectangle – part 1 of 5

Design and then create a Rectangle class that has overloaded constructors. The first constructor requires no

parameters. The second has two parameters, one for length and a second for width. Member variables store

the length and width of the rectangle, and member methods assign and retrieve the length and width and

return the area and perimeter of the rectangle. Test the class by writing appropriate client code.

Instance and Class Members

Each object, or instance, of a class has its own copy of variables called

instance variables. For example, the Circle class contains the instance

variable radius. A class may also contain class variables. A class variable is

declared with the keyword static and only one copy is maintained for all

objects to refer to. For example, the Circle class contains the class variable

PI. Note that because PI is a constant, it also includes the keyword final:

/**

* Circle class.

public class Circle {

private static final double PI = 3.14; //class constant

private double radius; //instance variable

…rest of Circle class

In the statements below, two Circle objects are instantiated. Each

instance has its own copy of the instance variable radius, but both objects

refer to the same copy of the class constant PI:





Methods can be either instance methods or class methods. Accessor

and modifier methods are instance methods because they change the state

of an object. They must be called from an instance of a class. Chapter 7

introduced class methods that are declared with the keyword static. Class

methods can be called from the class itself, rather than an object of the

class, to perform a task. For example, consider the Circle class with the

following class method added:

/**

* Displays the formula for the area of a circle.

* pre: none

* post: The formula for area of a circle has been displayed.

public static void displayAreaFormula() {

System.out.println("The formula for the area of a

circle is a=Pi*r*r");

}

instance variable

class variable

instance methods

class methods

Chapter 8 Classes and Object-Oriented Development 185

sample

The following client code calls the displayAreaFormula() class

method:

public class TestCircle {

public static void main(String[] args) {

Circle spot = new Circle(5);

System.out.println("Circle radius:" + spot.getRadius());

System.out.println("Circle area: " + spot.area());

Circle.displayAreaFormula();

}

The class method is called from the class itself (Circle) rather than an object

of the class. The TestCircle application displays the following output:

To summarize the differences between instance and class members:

• instance variables are created each time an object is declared.

• class variables and constants are created once for the class and then

objects of the class refer to this copy.

• instance methods can only be called from an object of the class.

• class methods can be called from the class itself.

Review: Circle – part 3 of 4

Modify the Circle class to include a class method named displayAreaFormula, as shown in the previous sec-

tion. Modify existing client code to test the new method.

Review: Rectangle – part 2 of 5

Modify the Rectangle class to include a class method named displayAreaFormula. Modify existing client code

to test the new method.

The Object Class

The Object class is the superclass of all other classes. Classes, such as

Circle and String, are subclasses of Object:











TIP Class methods cannot be

used to change the value of an

instance variable.

superclass

subclass

186 Chapter 8 Classes and Object-Oriented Development

sample

Subclasses inherit, or receive, the methods of its superclass. The Object

class includes methods for comparing objects and representing an object

as a string:

Class Object (java.lang.Object)

Method

equals(Object obj)

returns true if obj is equal to the object.

toString() returns a String that represents the object.

A subclass typically contains its own version of the equals() and toString()

superclass methods to better suit the object of the subclass. For example,

two Circle objects are equal when they both have the same radius, and two

String objects are equal when they consist of the same set of characters.

When a subclass redefines a superclass method, the subclass method

is said to override the superclass method. The Circle class should con-

tain an equals() method that compares the state of the object to another

Circle object and a toString() method that returns a String describing the

object:

/**

* Determines if the object is equal to another

* Circle object.

* pre: c is a Circle object.

* post: true has been returned if the objects have

* the same radii. false has been returned otherwise.

public boolean equals(Object c) {

Circle testObj = (Circle)c;

if (testObj.getRadius() == radius) {

return(true);

} else {

return(false);

}

/**

* Returns a String that represents the Circle object.

* pre: none

* post: A string representing the Circle object has

* been returned.

public String toString() {

String circleString;

circleString = "Circle has radius " + radius;

return(circleString);

}

The equals() method requires an Object parameter. In the body of the

method, the obj parameter must be cast as the appropriate type, in this

case Circle, and then assigned to an object of the appropriate type. If an

Object variable is cast with an incompatible class, then the exception

ClassCastException will be generated. To convert an object to its superclass

Object, no class casting is required.

inherit

override

TIP If a subclass does not over-

ride the equals() and toString()

methods, then the Object class

methods are used.

object casting

equals() vs. ==

Objects compared using the

== operator are equal only if

they refer to the same object.

The == operator compares the

references of the objects, not

the data stored by the objects

as the equals() methods does.

ClassCastException

Chapter 8 Classes and Object-Oriented Development 187

sample

The code below creates two Circle objects, compares them, and displays

information about the objects. An object’s toString() method is invoked

when an object is passed to the println() method:

public static void main(String[] args) {

Circle spot1 = new Circle(3);

Circle spot2 = new Circle(4);

if (spot1.equals(spot2)) {

System.out.println("Objects are equal.");

} else {

System.out.println("Objects are not equal.");

}

System.out.println(spot1);

System.out.println(spot2);

}

The code above displays the output:

Review: Circle – part 4 of 4

Modify the Circle class to override the equals() and toString() methods, as shown in the previous section.

Modify existing client code to test the new methods.

Review: Rectangle – part 3 of 5

Modify the Rectangle class to override the equals() and toString() methods. Two rectangles are equal when

they both have the same length and width. Modify the existing client code to test the new method.

Review: Coin – part 2 of 2

Modify the Coin class to override the toString() method so that it indicates whether the coin is face up or face

down. For example, “The coin is face up.” Modify existing client code to test the new method.

Classes Using Classes

A class may contain member variables that are class data types. Complex

data can be easily represented in this way. A class that contains class

member variables demonstrates a has-a relationship. The class “has a” class.

For example, a class with a String member variable demonstrates a has-a

relationship.

The Bank program specification on the next page is best implemented

with two classes. One class (Account) has a member variable (Customer)

for representing the customers that hold the accounts:

A bank maintains accounts where account holders can deposit

money and withdraw money. The account holders are customers

with a first and last name and complete address.

println()

has-a relationship

TIP The concatenation opera-

tor + also invokes the toString()

method of an object.

188 Chapter 8 Classes and Object-Oriented Development

sample

A model of Bank includes an Account object that stores customer data

and a current balance. Account methods should return a balance, perform

deposits, and perform withdrawals. If an Account object is passed to the

println() method, customer data and their balance should be displayed.

The designs for the Bank classes are:







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





















The Bank client code uses the class designs and looks similar to:

import java.util.Scanner;

import java.text.NumberFormat;

public class Bank {

public static void main(String[] args) {

Account munozAccount = new Account(250, "Maria", "Munoz", "110 Glades Road",

"Mytown", "FL", "33445");

Scanner input = new Scanner(System.in);

double data;

NumberFormat money = NumberFormat.getCurrencyInstance();

System.out.println(munozAccount);

System.out.print("Enter deposit amount: ");

data = input.nextDouble();

munozAccount.deposit(data);

System.out.println("Balance is: " + money.format(munozAccount.getBalance()));

System.out.print("Enter withdrawal amount: ");

data = input.nextDouble();

munozAccount.withdrawal(data);

System.out.println("Balance is: " + money.format(munozAccount.getBalance()));

}

Nested Classes and

Inner Classes

A nested class is a class

defined in another class as

a member of that class. The

member class has access to

other data members, just as

other members of the class. A

nested class is also called an

inner class, unless it is declared

static.

Chapter 8 Classes and Object-Oriented Development 189

sample

The Account class is implemented below:

import java.text.NumberFormat;

public class Account {

private double balance;

private Customer cust;

/**

* constructor

* pre: none

* post: An account created. Balance and

* customer data initialized with parameters.

public Account(double bal, String fName, String lName,

String str, String city, String st, String zip) {

balance = bal;

cust = new Customer(fName, lName, str, city, st, zip);

}

/**

* Returns the current balance.

* pre: none

* post: The account balance has been returned.

public double getBalance() {

return(balance);

}

/**

* A deposit is made to the account.

* pre: none

* post: The balance has been increased by the amount of the deposit.

public void deposit(double amt) {

balance += amt;

}

/**

* A withdrawal is made from the account if there is enough money.

* pre: none

* post: The balance has been decreased by the amount withdrawn.

public void withdrawal(double amt) {

if (amt <= balance) {

balance -= amt;

} else {

System.out.println("Not enough money in account.");

}

this

The keyword t h is can be

used to distinguish between

a parameter and a member

variable. For example, it can

be convenient to use the

same name for both a method

parameter and a member

variable in a class, in which

case, the member variable is

preceded by this. If in the

Account class, the constructor

used double balance as a

parameter, then the statement

in the body must be written as:

this.balance = balance;

190 Chapter 8 Classes and Object-Oriented Development

sample

/**

* Returns a String that represents the Account object.

* pre: none

* post: A string representing the Account object has

* been returned.

public String toString() {

String accountString;

NumberFormat money = NumberFormat.getCurrencyInstance();

accountString = cust.toString();

accountString += "Current balance is " + money.format(balance);

return(accountString);

}

The Customer class is implemented below:

public class Customer {

private String firstName, lastName, street, city,

state, zip;

/**

* constructor

* pre: none

* post: A Customer object has been created.

* Customer data has been initialized with parameters.

public Customer(String fName, String lName, String str,

String c, String s, String z) {

firstName = fName;

lastName = lName;

street = str;

city = c;

state = s;

zip = z;

}

/**

* Returns a String that represents the Customer object.

* pre: none

* post: A string representing the Account object has

* been returned.

public String toString() {

String custString;

custString = firstName + " " + lastName + "\n";

custString += street + "\n";

custString += city + ", " + state + " " + zip + "\n";

return(custString);

}

Chapter 8 Classes and Object-Oriented Development 191

sample

Running the Bank application produces output similar to:

Review: Bank

Modify the Customer class to include changeStreet(), changeCity(), changeState(), and changeZip() methods.

Modify the Account class to include a changeAddress() method that has street, city, state, and zip parameters.

Modify the Bank application to test the changeAddress() method.

Object-Oriented Development

Object-oriented programming requires that the solution to a task be

implemented as a system of objects. In this system, objects communicate

with other objects to provide a solution to the task. This approach to creat-

ing software is called object-oriented development.

In object-oriented development, the programmer reads the specification

and selects objects to model the specification. Some of these objects will

require new classes designed and written by the programmer. Other

objects can be created from existing classes previously written by the

programmer or by other programmers. For example, the JRE contains

numerous classes for use in a Java application. Reusability is an important

feature of object-oriented programming because it reduces development

time and decreases the likelihood of bugs.

To demonstrate object-oriented development, consider the following

Carnival program specification:

A carnival has many games that are similar in nature. These games

allow the player three tries, and the player who is successful all

three times is a winner. For example, the Balloon Dart Toss game

allows the player to throw three darts at a wall of balloons. If each

dart pops a balloon, then the player is a winner. The Ring Toss and

Break A Plate games work similarly.

reusability

TIP The JRE was first discussed

in Chapter 4.

192 Chapter 8 Classes and Object-Oriented Development

sample

designing objects

Every player gets a prize. There are winning prizes and consolation

prizes. The Balloon Dart Toss prizes are tiger plush and sticker. The

Ring Toss prizes are bear key chain and pencil, and the Break A

Plate prizes are pig plush and plastic dinosaur. The Balloon Dart

Toss and Ring Toss games are $2 to play. The Break A Plate game

costs $1.50.

The player comes to the carnival with some spending money and

can play games until the money runs out. The player also holds

onto all the prizes won.

The Carnival application should produce output similar to the

following when Shonda has $5 spending money and Luis has $3:













In the first step of object-oriented development, objects are selected to

model the specification. In this case, the carnival can be modeled with

game booth objects and player objects. A game booth object should store

data about the cost of playing the game, the winning prize, and the con-

solation prize. Game booth methods should start the game and give the

cost to play. A player object should store data about the spending money

of the player and the prizes won. Player methods should play the game

and show the list of prizes won.

The designs for the Carnival classes are:

























selecting objects for the

model

Chapter 8 Classes and Object-Oriented Development 193

sample

The Carnival client code uses the class designs and looks similar to:

GameBooth balloonDartToss = new GameBooth(2,"tiger plush", "sticker");

GameBooth ringToss = new GameBooth(2,"bear keychain", "pencil");

GameBooth breakAPlate = new GameBooth(1.5, "pig plush", "plastic dinosaur");

Player shonda = new Player(5); //$5 spending money

Player luis = new Player(3); //$3 spending money

System.out.print("Shonda goes to Balloon Dart Toss. ");

System.out.println(shonda.play(balloonDartToss));

System.out.print("Luis goes to Ring Toss. ");

System.out.println(luis.play(ringToss));

System.out.print("Shonda goes to Ring Toss. ");

System.out.println(shonda.play(ringToss));

System.out.print("Luis goes to Break A Plate. ");

System.out.println(luis.play(breakAPlate));

System.out.println("Shonda won: " + shonda.showPrizes());

System.out.println("Luis won: " + luis.showPrizes());

Note how simple the application appears. All the work is being done by

the objects, rather than with individual statements in the main() method.

The Carnival application, like other object-oriented applications, is modular.

It uses components that are separately written and maintained.

Another aspect of object-oriented development is that objects send

information to other objects to perform a task. When information is passed

from one object to another, the object is said to be passing a message. For

example, in the pseudocode above, the Player objects are passed a message

that includes the cost of game and the prize the player won.

The GameBooth class is implemented below. Note that in the start()

method, the player’s throws are simulated with random numbers. The

player is said to win if three ones are generated:

import java.util.Random;

public class GameBooth {

private double cost;

private String firstPrize, consolationPrize;

/**

* constructor

* pre: none

* post: A GameBooth object created.

* The cost and prizes are set.

public GameBooth(double charge, String p1, String p2) {

cost = charge;

firstPrize = p1;

consolationPrize = p2;

}

modular

message

client code

implementing the classes

194 Chapter 8 Classes and Object-Oriented Development

sample

/**

* Game is played and prize awarded.

* pre: none

* post: Player had three tries. Player successful all

* three times received the first prize. A consolation

* prize has been awarded otherwise.

public String start() {

int toss;

int successes = 0;

Random rand = new Random();

/* play game */

for (int i = 0; i < 3; i++) { //player gets three tries

toss = rand.nextInt(2);

if (toss == 1) {

successes += 1; //1 is a successful toss

}

/* award prize */

if (successes == 3) {

return(firstPrize);

} else {

return(consolationPrize);

}

/**

* Returns the cost to play the game.

* pre: none

* post: Cost of the game has been returned.

public double getCost() {

return(cost);

}

The Player class is implemented below:

public class Player {

private double spendingMoney;

private String prizesWon;

/**

* constructor

* pre: none

* post: A Player object created. Spending money given to

* player. The prizes won set to none.

public Player(double money) {

spendingMoney = money;

prizesWon = "";

}

Chapter 8 Classes and Object-Oriented Development 195

sample

/**

* Player pays for and then plays a game.

* pre: none

* post: Player's spending money decreased by cost of game.

* The player has a new prize added to existing prizes.

public String play(GameBooth game) {

String newPrize;

if (game.getCost() > spendingMoney) {

return("Sorry, not enough money to play.");

} else {

spendingMoney -= game.getCost(); //pay for game

newPrize = game.start(); //play game

prizesWon = newPrize + ", " + prizesWon;

return("prize won: " + newPrize);

}

/**

* Returns the list of prizes won.

* pre: none

* post: The list of prizes has been returned.

public String showPrizes() {

return(prizesWon);

}

Running the Carnival application produces output similar to:

Although the classes may look long, once written they are available for

many different implementations of a Carnival or another application that

involves games.

Review: Carnival

Modify the Player class to override the toString() method. When a Player object is passed to the println()

method, a message should display how much money the player has left and the prizes won so far.

Modify the GameBooth class to keep track of the number of prizes awarded. There should be separate

totals for the first prizes awarded and the consolation prizes awarded. Add a method to the GameBooth

class named prizesAwarded() that displays the number of first prizes and the number of consolation prizes

given away.

Modify the Carnival client code to pass the Player objects to println() in the last two statements, and in

separate statements, display how many prizes were given away by each booth.

196 Chapter 8 Classes and Object-Oriented Development

sample

Chapter 8 Case Study

In this case study, a Rock Paper Scissors game will be created using

object-oriented development. Rock Paper Scissors is a popular game played

between two individuals for decision making or just for competitive fun.

The rules of the game are Rock dulls Scissors (Rock wins), Scissors cuts

Paper (Scissors wins), and Paper covers Rock (Paper wins). The two players

make a “throw” at the same time. The hand signals thrown by the players

are then compared to the rules of the game to determine the winner. In

the computerized version, the user plays against the computer.

RPS2 Specification

The computerized version of the Rock Paper Scissors game is played

by one user that “throws” either rock, paper, or scissors. The game then

randomly selects either rock, paper, or scissors for the computer’s “throw”

and the winner is determined by comparing the two choices. Rock wins

over scissors, scissors wins over paper, and rock wins over scissors. The

player can initially choose to play multiple rounds. At the end of the

rounds, an overall winner is declared.

The RPS2 interface should show the result of each round and the overall

winner. The RPS2 output sketch:































The RPS2 algorithm:

1. Prompt the player for the number of rounds.

2. For each round:

Prompt for the player’s throw.

Generate the computer’s throw.

Announce the winner of the round.

3. Announce an overall winner.

TIP An RPS application was

also developed for the Chapter

5 Case Study.

Chapter 8 Classes and Object-Oriented Development 197

sample

RPS2 Code Design

The RPS2 application can be modeled with a player object and a game

object. The player object should store the player’s throw (either rock,

paper, or scissors) and contain methods that make and return the player’s

throw. The game object should store the computer’s throw, the number

of computer wins, and the number of player wins and contain methods

that make and return the computer’s throw, determine the winner of each

round, and determine an overall winner.

The designs for the RPS2 classes are:























  

  



Based on the algorithm and the class designs, the RPS2 code design will

include two objects and a loop. The pseudocode for the RPS2 client code

follows:

declare game object

declare player object

prompt player for number of rounds

for (i = 0; i < rounds; i++) {

prompt player for throw

player.makeThrow(playerThrow);

gameObject.makeThrow();

gameObject.announceWinner(playerObject.getThrow);

}

gameObject.bigWinner

198 Chapter 8 Classes and Object-Oriented Development

sample

RPS2 Implementation

The RPS2 implementation involves creating three files. One file contains

the client code and the other two files are the classes.

The RPS2Player class is implemented below:

/**

* models the player in a game of RPS

public class RPSPlayer {

private int playerThrow; //ROCK=1, PAPER=2, SCISSORS=3

/**

* constructor

* pre: none

* post: RPSPlayer object created. The player is given a

* default throw.

public RPSPlayer() {

playerThrow = 1; //default throw

}

/**

* Sets the player's throw.

* pre: newThrow is the integer 1, 2, or 3.

* post: Player's throw has been made.

public void makeThrow(int newThrow){

playerThrow = newThrow;

}

/**

* Returns the player's throw.

* pre: none

* post: Player's throw has been returned.

public int getThrow() {

return(playerThrow);

}

Chapter 8 Classes and Object-Oriented Development 199

sample

The RPSGame class is implemented below:

/**

* Models a game of RPS

import java.util.Random;

public class RPSGame {

public static final int ROCK = 1, PAPER = 2, SCISSORS = 3;

private int compThrow;

private int playerWins = 0, computerWins = 0;

/**

* constructor

* pre: none

* post: RPSGame object created. Computer throw generated.

public RPSGame() {

Random rand = new Random();

compThrow = rand.nextInt(3) + 1; //random int between 1 and 3

playerWins = 0;

computerWins = 0;

}

/**

* Computer's throw is generated (ROCK, PAPER, or SCISSORS)

* pre: none

* post: Computer's throw has been made.

public void makeCompThrow(){

Random rand = new Random();

compThrow = rand.nextInt(3) + 1; //random int between 1 and 3

}

/**

* Returns the computer's throw.

* pre: none

* post: Computer's throw has been returned.

public int getCompThrow() {

return(compThrow);

}

/**

* Determines the winner of the round.

* pre: playerThrow is the integer 1, 2, or 3.

* post: Displays a message indicating throws. Compares player's

* throw to computer's throw and displays a message indicating

* the winner.

public void announceWinner(int playerThrow) {

/* Inform player of throws */

System.out.print("You throw ");

switch (playerThrow) {

case ROCK: System.out.println("ROCK."); break;

case PAPER: System.out.println("PAPER."); break;

case SCISSORS: System.out.println("SCISSORS."); break;

}

200 Chapter 8 Classes and Object-Oriented Development

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System.out.print("Computer throws ");

switch (compThrow) {

case ROCK: System.out.println("ROCK."); break;

case PAPER: System.out.println("PAPER."); break;

case SCISSORS: System.out.println("SCISSORS."); break;

}

/* Determine and annouce winner */

if (playerThrow == ROCK && compThrow == ROCK) {

System.out.println("It's a draw!");

} else if (playerThrow == ROCK && compThrow == PAPER) {

System.out.println("Computer wins!");

computerWins += 1;

} else if (playerThrow == ROCK && compThrow == SCISSORS) {

System.out.println("You win!");

playerWins += 1;

}

if (playerThrow == PAPER && compThrow == ROCK) {

System.out.println("You win!");

playerWins += 1;

} else if (playerThrow == PAPER && compThrow == PAPER) {

System.out.println("It's a draw!");

} else if (playerThrow == PAPER && compThrow == SCISSORS) {

System.out.println("Computer wins!");

computerWins +=1;

}

if (playerThrow == SCISSORS && compThrow == ROCK) {

System.out.println("Computer wins!");

computerWins += 1;

} else if (playerThrow == SCISSORS && compThrow == PAPER) {

System.out.println("You win!");

playerWins += 1;

} else if (playerThrow == SCISSORS && compThrow == SCISSORS) {

System.out.println("It's a draw!");

}

/**

* Displays the overall winner.

* pre: none

* post: Computer and player wins compared and

* an overall winner announced.

public void bigWinner() {

if (computerWins > playerWins){

System.out.println("Computer wins!");

} else if (playerWins > computerWins){

System.out.println("You win!");

} else {

System.out.println("It's a draw!");

}

Chapter 8 Classes and Object-Oriented Development 201

sample

The RPS2 client code follows:

* RPS2.java

import java.util.Scanner;

/**

* Computer plays Rock Paper Scissors against one player.

public class RPS2 {

public static void main(String[] args) {

RPSGame rps = new RPSGame();

RPSPlayer rpsOpponent = new RPSPlayer();

int rounds;

int playerThrow;

Scanner input = new Scanner(System.in);

/* play RPS */

System.out.print("How many rounds? ");

rounds = input.nextInt();

for (int i = 0; i < rounds; i++) {

System.out.print("Enter your throw (ROCK=1,

PAPER=2, SCISSORS=3): ");

playerThrow = input.nextInt();

rpsOpponent.makeThrow(playerThrow);

rps.makeCompThrow();

rps.announceWinner(rpsOpponent.getThrow());

}

rps.bigWinner();

}

Note how concise the client code is. The RPS2 application uses objects

to perform all the work.

Although the classes may look long, once written they are available

for many different implementations of the RPS game. Client code can be

written to use the classes in many different ways. For example, multiple

players and games can be instantiated for tournaments.

RPS2 Testing and Debugging

When a new class is written, client code should be written to test the

class. For the RPSGame class, client code should test all the possible throw

combinations, similar to the testing discussed in the Chapter 5 Case

Study.

202 Chapter 8 Classes and Object-Oriented Development

sample

Review: RPS2 – part 1 of 2

Modify the RPSPlayer class to include a playerName variable and methods named assignName and getName. The

assignName() method has a String parameter name that is assigned to playerName. The getName() method

returns the value of playerName. Modify the announceWinner() and bigWinner() methods in the RPSGame

class to include a String parameter name that is the player’s name. Change the messages displayed in the

announceWinner() and bigWinner() methods to include the player’s name rather than the word “You”.

Modifying the two classes should produce output similar to the sketch below:

































Review: RPS2 – part 2 of 2

Modify the RPS2 client code to perform error checking on the player’s input. Have the client code verify that

the user has entered a 1, 2, or 3 for a throw before passing the entered value to the makeThrow() method.

Chapter Summary

This chapter introduced writing and designing classes. Classes are the

data types of objects. An object has a state (data) and behavior (actions and

communication in the form of methods). An important aspect of object-

oriented programming is encapsulation, also called information hiding.

In OOP, classes are written to encasulate, or hide, data from outside code.

Client code is code that uses one or more classes.

A class includes a class declaration, variables, constructors, and meth-

ods. The class declaration includes the access level, the keyword class, and

a name. Variables and methods are the members of a class. Variables are

the data members and should be declared private. Accessor and modifier

methods are declared public, while helper methods are declared private.

Constructors are used to initialize variables and can be overloaded so that

objects can be declared with vaying numbers of parameters.

Chapter 8 Classes and Object-Oriented Development 203

sample

The variables and methods of a class are either instance or class mem-

bers. Instance members are copied for each instance of a class. Only one

copy of a class member exists for the class. Every object of a class refers to

the same class member. The keyword static is used for a class member

declaration. Class methods can be called from the class itself. An object

of the class can call either instance or class members.

Every class is a subclass of the Object class. The Object class could also

be called the superclass of all other classes. The equals() and toString()

methods in the Object class are inherited by all other classes. In most cases,

these methods should be redefined in subclasses.

An object that contains an object is said to demonstrate a has-a relation-

ship. Any class that contains a String data member demonstrates a has-a

relationship.

Object-oriented development requires the solution to a task be imple-

mented as a system of objects. In this system, objects pass messages back

and forth to provide a solution to the task.

This chapter discussed several important aspects of the object-oriented

paradigm, including encapsulation, reusability, and modularity.

The code convention introduced in this chapter is:

• Class names should be a noun, begin with an uppercase letter, and

each word within the name should also begin with an uppercase

letter.

204 Chapter 8 Classes and Object-Oriented Development

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Vocabulary

Accessor method A method of a class that is used to

determine the value of a variable member. Accessor

methods have access level public.

Behavior The action and communication an object

provides.

Class A data type that defines variables for the state

of an object and methods for an object’s behavior.

Class body The variables, constructors, and methods

that implement a class.

ClassCastException An exception thrown when an

object variable is cast with an incompatible class.

Class declaration The first line of a class, which

contains the access level, the keyword class, and

the class name.

Class method A method of a class that can be called

from the class itself. It cannot change the state of an

object. Class methods include the keyword static.

Class variable A variable of a class that exists as

one copy that all instances of a class refer to. Class

variables include the keyword static.

Client code An application that uses one or more

classes.

Constructor The part of a class that is used to

initialize the variable members of a class.

Encapsulation Protecting an object’s data from

code outside the class.

Has-a relationship The relationship demonstrated

by a class that contains another class.

Helper method A method of a class that is used

by other methods in a class to help complete a task.

Helper methods have access level private.

Information hiding Also called encapsulation.

Inherit To receive the methods of a superclass.

Instance An object of a class.

Instance method A method of a class that changes

the state of a class. It must be called from an instance

of the class.

Instance variable A variable of a class that is copied

for each instance of the class.

Member A variable or method of a class.

Message Information passed from one object to

another.

Modifier method A method of a class that is used

to change the value of a variable member. Modifier

methods have access level public.

Modular An application that uses components that

are separately written and maintained.

Object An instance of a class. An object stores

data and can perform actions and provide

communication.

Object casting To cast an object as the appropriate

class.

Object-oriented development The solution to a task

that is implemented as a system of objects.

Override To redefine a method from a superclass

in a subclass.

Reusability A feature of object-oriented program-

ming that reduces development time and decreases

the likelihood of bugs.

State The data an object stores.

Subclass A class below another class in a class

hierarchy. A class that inherits another class.

Superclass The upper-most class in a class hierarchy.

A class that has subclasses.

Visibility The access level of a method.

Chapter 8 Classes and Object-Oriented Development 205

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Java

class The keyword used to declare a class.

public An access modifier used in the declaration

of a class to indicate that the class is visible to client

code. Also used in the declaration of class methods to

indicate that the method is visible to client code.

static The keyword used in the declaration of a

variable or method in a class to indicate that the

member is a class method.

private A keyword used in the declaration of class

members when those members should be visible to

the class but not to client code.

206 Chapter 8 Classes and Object-Oriented Development

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Critical Thinking

1. Which members of the Circle class are

encapsulated?

2. What name must the constructor of a class

have?

3. Explain the difference between the private and

public access modifiers.

4. Consider the following code. Is the last state-

ment valid or invalid? Explain.

Circle dot = new Circle(2);

dot.radius = 5;

5. Use the following class to answer the questions

below:

public class Roo {

private int x;

public Roo {

x = 1;

}

public void setX(int z) {

x = z;

}

public int getX() {

return(x);

}

public int calculate() {

x = x * factor();

return(x);

}

private int factor() {

return(0.12);

}

a) What is the name of the class?

b) What is the name of the data member?

c) List the accessor method.

d) List the modifier method.

e) List the helper method.

f) What is the name of the constructor?

g) How many method members are there?

6. What is the difference between a class and an

object?

7. Imagine a band festival where there are many

bands playing—the TwoToos, the EggRolls, and

Goop. Each band can TuneUp, PlayMusic, and

TakeABow. A set list can be read or created. If

this was simulated in an object-oriented pro-

gram, what would appropriate names be for:

a) the class

b) the objects

c) a data member

d) the method members

8. Assume a class for a sports team named

Team.

a) List three possible object names.

b) List three possible method members.

c) List three possible data members.

9. Use the following class data member definitions

to answer the questions below:

public class Moo {

private double y;

private static int x;

private static final z;

…

a) Which data member is a constant?

b) Which data members are variables?

c) Which data member(s) are instance

members?

d) Which data member(s) are class members?

10. Explain the difference between calling an

instance method member and a class method

member.

11. Compare and contrast overriding methods to

overloading methods.

12. The Customer class in the Bank application also

demonstrates a has-a relationship. Explain.

13. How can reusing code decrease the likelihood

of bugs in an application?

14. Explain what is meant by passing a message.

Chapter 8 Classes and Object-Oriented Development 207

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True/False

15. Determine if each of the following are true or

false. If false, explain why.

a) The state of an object is described by its

methods.

b) The behavior of an object is described by its

variables.

c) An instance of a class is called an object.

d) Client code is an application that uses a

class.

e) Encapsulation means that all the variables

in a class are available to client code.

f) A constructor is a member of a class.

g) A variable that is visible to a class, but not

to client code is declared with the keyword

private.

h) An accessor method is called to change the

value of a data member.

i) A modifier method returns the value of a

data member.

j) A constructor of a class is automatically

called when an object of the class is instan-

tiated.

k) A class can contain multiple constructors.

l) An instance variable is copied for each

instance of a class.

m) A class variable is declared with the key-

word public.

n) A class method must be called from an object

of the class.

o) A class constant is declared with only the

keyword final.

p) The Object class is a subclass of all other

classes.

q) The toString() method can be redefined in

subclasses.

r) Object-oriented development requires that

only one object be used in an application.

208 Chapter 8 Classes and Object-Oriented Development

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Exercises

Exercise 1 ————————————————————— MySavings

Create a MySavings application that displays a menu of choices for entering pennies, nickels, dimes, and

quarters into a piggy bank and then prompts the user to make a selection. The MySavings application

should include a PiggyBank object that can add coins to the piggy bank, remove coins, and return the

total amount in the bank. Application output should look similar to:

Exercise 2 ——————————————————— DigitExtractor

Create a DigitExtractor application that prompts the user for an integer and then displays the ones,

tens, and hundreds digit of the number. The DigitExtractor application should include a Num object

that can return the ones digit, tens digit, hundreds digit, and the whole number. Application output

should look similar to:

Chapter 8 Classes and Object-Oriented Development 209

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Exercise 3 ———————————————————— LunchOrder

Create a LunchOrder application that prompts the user for the number of hamburgers, salads, french

fries, and sodas and then displays the total for the order. The LunchOrder application should include

a Food object with a constructor that accepts the price, fat, carbs, and fiber for an item. Food methods

should return the price of the item and return the fat, carbohydrates, and fiber. Use the chart below for

food prices and nutrition information:

Item Price Fat(g) Carbohydrates(g) Fiber(g)

hamburger $1.85 9 33 1

salad $2.00 1 11 5

french fries $1.30 11 36 4

soda $0.95 0 38 0

Application output should look similar to:

210 Chapter 8 Classes and Object-Oriented Development

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Exercise 4 ——————————————————— DiceRollGame

In the Dice Roll game, the player begins with a score of 1000. The player is prompted for the number

of points to risk and a second prompt asks the player to choose either high or low. The player rolls

two dice and the outcome is compared to the player’s choice of high or low. If the dice total is between

2 and 6 inclusive, then it is considered “low”. A total between 8 and 12 inclusive is “high”. A total of

7 is neither high nor low, and the player loses the points at risk. If the player had called correctly, the

points at risk are doubled and added to the total points. For a wrong call, the player loses the points at

risk. Create a DiceRollGame application that uses a DRPlayer object based on this specification. The

DRPlayer object should have two Die member variables that represent the dice. The Die class should

use a random number generator to determine the outcome in a roll() method. Application output

should look similar to:

Exercise 5 ——————————————————————— Nim2

The game of Nim starts with a random number of stones between 15 and 30. Two players alternate

turns and on each turn may take either 1, 2, or 3 stones from the pile. The player forced to take the last

stone loses. Use object-oriented development to create a Nim2 application that allows the user to play

Nim against the computer. The Nim2 application and its objects should:

• Generate the number of stones to begin with.

• Allow the player to go first.

• Use a random number generator to determine the number of stones the computer

takes.

• Prevent the player and the computer from taking an illegal number of stones. For

example, neither should be allowed to take three stones when there are only 1 or 2

left.

Chapter 8 Classes and Object-Oriented Development 211

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Exercise 6 ————————————————————— GameOf21

In the Game of 21, a player is dealt two cards from a deck of playing cards and then optionally given

a third card. The player closest to 21 points without going over is the winner. Use object-oriented

development to create a Game of 21 application that allows the user to play the Game of 21 against the

computer. The Game of 21 application and its objects should:

• Deal a card from a deck of playing cards by generating a random number between 1

and 13. A 1 corresponds to an Ace, numbers 2 through 10 correspond to those cards,

and 11 through 13 correspond to Jack, Queen, and King. The Jack, Queen, and King

have a value of 10 in the Game of 21. An Ace can have a value of either 1 or 11.

• Allow the player to stay with two cards or be given a third card.

• Announce the winner.

• Play rounds until the player says to stop.

Exercise 7 —————————————————————— Bowling

In bowling, a ball is rolled down a lane, also called an alley, at a set of ten pins. A game consists of a

bowler bowling for ten frames, where each frame consists of two chances (throws) to knock over all ten

pins. Bowling centers often use computers to electronically keep scores for bowlers. Use object-oriented

development to create a Bowling application that simulates a simplified game of bowling. The Bowling

application and its objects should:

• Allow a bowler to bowl ten frames. Each frame consists of two throws, unless a strike

is thrown.

• Award 20 points to the bowler when all ten pins are knocked over on the first throw

of a frame.

• Award 15 points to the bowler when all ten pins are knocked over within the two

throws of a frame.

• Award one point for each pin knocked over in the two throws of a frame when all

ten pins are not knocked over.

• If there is more than one bowler in a game, then the bowlers take turns until each

has bowled ten frames.

• Use a random number generator to determine how many pins a bowler has knocked

over with each throw.

• Display an updated score after each frame.

212 Chapter 8 Classes and Object-Oriented Development

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Exercise 8 ——————————————————————— Adder

The Adder game prompts a player for the answer to an addition problem. The Adder game cre-

ates a problem from two randomly selected integers between 0 and 20. Adder allows the player

three tries to enter a correct answer. If the correct answer is entered on the first try, the player is

awarded 5 points. If the correct answer is entered on the second try, 3 points are awarded. The

correct answer on the third try earns 1 point. If after three tries, the correct answer is still not

entered, the player receives no points and the correct answer is displayed. The game continues until

999 is entered as an answer. At the end of the game, Adder displays the player’s score. Application

output should look similar to:

Chapter 9 Inheritance and Polymorphism 213

sample

bject-oriented programming is based on a paradigm in which objects

are used to model a specification. Objects are created from classes, which

provide encapsulation. Inheritance extends a class and provides a means

of polymorphism. This chapter discusses inheritance and polymorphism.

Abstract classes and interfaces are also discussed.

Extending a Class

Often times there is an existing class that provides a basis for an object

that models a specification. However, the existing class may need addi-

tional methods or different implementations of existing methods to more

closely represent the object for the model. For example, consider a disk,

which has circular shape. It is similar to a circle. However, a disk is three-

dimensional and also has a thickness. Rather than create a whole new class

to represent a disk, a class named Disk could extend the Circle class.

Making one class an extension of another involves inheritance. Inheritance

allows a class to define a specialized type of an already existing class. In

this case, a disk is a solid circle with a thickness. Classes that are derived

from existing classes demonstrate an is-a relationship. A class “is a” type

of another class. In this case, a disk is a circle with a thickness.

A class can have many levels of inheritance. For example, consider the

following class hierarchy:







The Puck class inherits the Disk class, which inherits the Circle class. The

Circle class is the superclass of Disk. Disk is the subclass of Circle and the

superclass of Puck. Puck is the subclass of Disk.

Chapter 9

Inheritance and Polymorphism

inheritance

TIP The Object class is the

superclass of all other classes.

is-a relationship

214 Chapter 9 Inheritance and Polymorphism

sample

Implementing a Subclass

A class that inherits another class includes the keyword extends in the

class declaration and takes the form:

public class <name> extends <class _ name> {

}

Designing a subclass requires selecting the superclass, or base class,

and then defining any additional variable and method members for the

subclass. In many cases, existing methods in the base class will also be

overridden by new definitions in the subclass, also called the derived class.

For example, the Disk class design appears similar to:

















The Disk class implementation, based on the design above, is:

/**

* Disk class.

public class Disk extends Circle {

private double thickness;

/**

* constructor

* pre: none

* post: A Disk object has been created with radius r

* and thickness t.

public Disk(double r, double t) {

super(r);

thickness = t;

}

/**

* Changes the thickness of the disk.

* pre: none

* post: Thickness has been changed.

public void setThickness(double newThickness) {

thickness = newThickness;

}

extends

base class

derived class

Chapter 9 Inheritance and Polymorphism 215

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/**

* Returns the thickness of the disk.

* pre: none

* post: The thickness of the disk has been returned.

public double getThickness() {

return(thickness);

}

/**

* Returns the volume of the disk.

* pre: none

* post: The volume of the disk has been returned.

public double volume() {

double v;

v = super.area() * thickness;

return(v);

}

/**

* Determines if the object is equal to another

* Disk object.

* pre: d is a Disk object.

* post: true has been returned if objects have the same

* radii and thickness. false has been returned otherwise.

public boolean equals(Object d) {

Disk testObj = (Disk)d;

if (testObj.getRadius() == super.getRadius()

&& testObj.getThickness() == thickness) {

return(true);

} else {

return(false);

}

/**

* Returns a String that represents the Disk object.

* pre: none

* post: A string representing the Disk object has

* been returned.

public String toString() {

String diskString;

diskString = "The disk has radius " + super.getRadius()

+ " and thickness " + thickness + ".";

return(diskString);

}

In a subclass, the keyword super is used to access methods of the

base class. For example, the statement super(r) calls the constructor of

the superclass, Circle, and passes an argument for setting the radius

value. Members that are declared private are not accessible to derived

classes. Therefore, accessor methods are used to get inherited member

variable values. For example, the equals() method in the Disk class calls

getRadius().

super

TIP The equals() and toString()

methods override the methods

by the same name in the Circle

class.

visibility

216 Chapter 9 Inheritance and Polymorphism

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Inherited methods are called directly from an object, just as any method

of the class is called. Whether a method is original to the Disk class or

inherited from the Circle class is transparent to client code, as demonstrated

in the TestDisk application:

public class TestDisk {

public static void main(String[] args) {

Disk saucer = new Disk(10, 0.02);

System.out.println("Disk radius: " + saucer.getRadius());

System.out.println("Disk surface area: " + saucer.area());

System.out.println("Disk volume: " + saucer.volume());

Disk plate1 = new Disk(12, 0.05);

Disk plate2 = new Disk(12, 0.07);

if (plate1.equals(plate2)) {

System.out.println("Objects are equal.");

} else {

System.out.println("Objects are not equal.");

}

System.out.println(plate1);

System.out.println(plate2);

}

The TestDisk application displays the following output:

Review: Puck – part 1 of 2

Create a Puck class that inherits the Disk class. The Puck class should include member variables weight,

standard, and youth. The standard and youth variables should be boolean variables that are set to either true

or false depending on the weight of the puck. A standard puck weighs between 5 and 5.5 ounces. A youth

puck weighs between 4 and 4.5 ounces. Official hockey pucks, regardless of weight, are one inch-thick with a

three-inch diameter. The Puck class should also contain member methods getWeight(), getDivision(), which

returns a string stating whether the puck is standard or youth, and equals() and toString(), which overrride

the same methods in the Disk class. The Puck constructor should require an argument for weight. Be sure

that the constructor initializes other variables to appropriate values as necessary.

Create a Hockey application that tests the Puck class.

Chapter 9 Inheritance and Polymorphism 217

sample

Polymorphism

Polymorphism is an OOP property in which objects have the ability to

assume different types. In object-oriented programming, polymorphism

is based on inheritance. Because a subclass is derived from a superclass,

a superclass object can reference an object of the subclass. For example,

the following statements are valid because Disk inherits Circle:

Circle wafer;

Disk cookie = new Disk(2, 0.5);

wafer = cookie; //wafer now references cookie

The wafer object, declared a Circle, is polymorphic, as demonstrated in

the statement wafer = cookie where wafer assumes the form of cookie, a

Disk object.

Polymorphism is further demonstrated when the referenced object

determines which method to execute. This is possible when a subclass

overrides a superclass method. In this case, the Disk class has overridden

the equals() and toString() methods. Because of this, the following state-

ment executes the Disk toString() method even though wafer was declared

a Circle object:

/* displays: The disk has radius 2.0 and thickness 0.5. */

System.out.println(wafer);

To further demonstrate polymorphism, the Music application will

be developed in this section. The Music application allows the user to

assemble a small band. The user can assign a band member either vocals

(voice) or a woodwind instrument (piccolo or clarinet). The user can then

select to hear either a solo, duet, or trio performance from this band.

The Instrument class, its subclasses, and the Performance class are

used to model the objects for the Music application. The diagram below

illustrates the client code and classes for the Music application. Note the

hierarchy of the Instrument class and its subclasses:





















218 Chapter 9 Inheritance and Polymorphism

sample

The Music client code is shown below:

* Music.java

import java.util.Scanner;

public class Music {

/* Returns a selected instrument.

* pre: none

* post: An instrument object has been returned.

public static Instrument assignInstrument() {

String instrumentChoice;

Scanner input = new Scanner(System.in);

System.out.println("Select an instrument for the

band member. ");

System.out.print("Vocals, Piccolo, or Clarinet: ");

instrumentChoice = input.nextLine();

System.out.print("Enter the band member's name: ");

name = input.nextLine();

if (instrumentChoice.equalsIgnoreCase("V")) {

return(new Vocal(name));

} else if (instrumentChoice.equalsIgnoreCase("P")) {

return(new Piccolo(name));

} else { //default to clarinet

return(new Clarinet(name));

}

public static void main(String[] args) {

Performance band;

Instrument bandMember1, bandMember2, bandMember3;

Scanner input = new Scanner(System.in);

String performanceChoice;

/* assign instruments */

bandMember1 = assignInstrument();

bandMember2 = assignInstrument();

bandMember3 = assignInstrument();

System.out.println(bandMember1 + " " + bandMember2 + " "

+ bandMember3 + "\n");

System.out.print("Would you like to hear a Solo, a Duet,

a Trio, or Leave? ");

performanceChoice = input.nextLine();

while (!performanceChoice.equalsIgnoreCase("L")) {

if (performanceChoice.equalsIgnoreCase("S")) {

band = new Performance(bandMember1);

} else if (performanceChoice.equalsIgnoreCase("D")) {

band = new Performance(bandMember1, bandMember2);

} else { //default to trio

band = new Performance(bandMember1, bandMember2,

bandMember3);

}

band.begin();

System.out.print("\nWould you like to hear a Solo,

a Duet, a Trio, or Leave? ");;

performanceChoice = input.nextLine();

}

Chapter 9 Inheritance and Polymorphism 219

sample

The assignInstrument() method declares an Instrument return type, but

the individual return statements return Vocal, Piccola, and Clarinet types.

The Instrument object returned by the method is polymorphic, changing

to whichever subclass is actually returned.

The Music application produces output similar to:

The Music application allows the user numerous combinations for select-

ing a band and hearing performances. The code for such an application

would be more complicated and less flexible without the object-oriented

principles of inheritance and polymorphism. Music is versatile because it

takes advantage of inheritance and polymorphism.

The documentation for the Instrument, Vocal, Woodwind, Piccolo,

and Clarinet classes is below. Note that the makeSound() method in the

Instrument class is a method that must be implemented (written) in a sub-

class. This is discussed further in the next section. The code for the classes

is also shown in the next section where abstract classes are discussed.

Class Instrument

Constructor/Methods

Instrument(String name)

creates an instrument object with musician

name.

getMusician() returns a string that is the musician’s name.

makeSound() an abstract method that should return a String

representing the instrument’s sound.

220 Chapter 9 Inheritance and Polymorphism

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Class Vocal (inherits Instrument)

Constructor/Methods

Vocal(String name)

creates a singer object with singer name.

makeSound() returns the String LaLaLa.

toString() returns a String that represents the singer.

Class Woodwind (inherits Instrument)

Constructor/Method

Woodwind(String name)

creates a woodwind instrument object with

musician name.

makeSound() returns the String toot.

Class Piccolo (inherits Woodwind)

Constructor/Methods

Piccolo(String name)

creates a piccoloist object with musician name.

makeSound() returns the String peep.

toString() returns a String that represents the object.

Class Clarinet (inherits Woodwind)

Constructor/Methods

Clarinet(String name)

creates a clarinetist object with musician name.

makeSound() returns the String squawk.

toString() returns a String that represents the object.

The Performance class creates an arrangement of Instrument objects.

The constructors require Instrument arguments, but polymorphism

enables objects of Instructor subclasses to be passed:

/**

* Performance class.

public class Performance {

private String arrangement;

private Instrument solo;

private Instrument duet _ 1, duet _ 2;

private Instrument trio _ 1, trio _ 2, trio _ 3;

/**

* constructor

* pre: none

* post: A soloist has been selected.

public Performance(Instrument s) {

solo = s;

arrangement = solo.makeSound();

}

Chapter 9 Inheritance and Polymorphism 221

sample

/**

* constructor

* pre: none

* post: The members of a duet have been selected.

public Performance(Instrument d1, Instrument d2) {

duet _ 1 = d1;

duet _ 2 = d2;

arrangement = duet _ 1.makeSound() + duet _ 2.makeSound();

}

/**

* constructor

* pre: none

* post: The members of a trio have been selected.

public Performance(Instrument t1, Instrument t2,

Instrument t3) {

trio _ 1 = t1;

trio _ 2 = t2;

trio _ 3 = t3;

arrangement = trio _ 1.makeSound() + trio _ 2.makeSound()

+ trio _ 3.makeSound();

}

/**

* Begins the performance.

* pre: none

* post: The performance has been played.

public void begin() {

System.out.println(arrangement);

}

/**

* Returns a String that represents the performers.

* pre: none

* post: A string representing the performers has

* been returned.

public String toString() {

String program = "The performance includes ";

program += arrangement;

return(program);

}

Review: Music – part 1 of 2

Modify the Music application to allow the user to select a quartet (four band members) in addition to the

other performances. Changes to the Performance class will also be required to provide the option of creat-

ing a quartet.

222 Chapter 9 Inheritance and Polymorphism

sample

Abstract Classes

An abstract class models an abstract concept. For example, a musical

instrument is an abstract concept. An instrument is something that can

be played, but there is no such thing an “instrument” instrument. There

are however, flutes, piccolos, drums, and cymbals.

Abstract classes cannot be instantiated because they should not repre-

sent objects. They instead describe the more general details and actions

of a type of object. For example, the Instrument class describes the very

basics of an instrument—it can make a sound. The Woodwind class is also

an abtract class because it describes a group of instruments. It includes a

general sound that woodwind instruments make.

Abstract classes are declared with the keyword abstract in the class

declaraction. They are intended to be inherited. The public members of

the abstract class are visible to derived objects. However, an abstract class

can also contain an abstract method. An abstract method is declared with

the keyword abstract and contains a method declaration, but no body.

The abstract class must be implemented in its subclass.

The Instrument class is an abstract class with an abstract method. The

makeSound() method must be implemented in an Instrument subclass:

/**

* Instrument class.

abstract class Instrument {

String musician;

/**

* constructor

* pre: none

* post: A musician has been assigned to the instrument.

public Instrument(String name) {

musician = name;

}

/**

* Returns the name of the musician

* pre: none

* post: The name of the musician playing the instrument

* has been returned.

public String getMusician() {

return(musician);

}

/**

* Should return the sound of the instrument.

* pre: none

* post: The sound made by the instrument is returned.

abstract String makeSound();

}

The Vocal class is a subclass of Instrument. It provides the body for the

makeSound() method:

abstract method

abstract

Chapter 9 Inheritance and Polymorphism 223

sample

/**

* Vocal class.

public class Vocal extends Instrument {

/**

* constructor

* pre: none

* post: A singer has been created.

public Vocal(String singerName) {

super(singerName);

}

/**

* Returns the sound of the instrument.

* pre: none

* post: The sound made by the singer.

public String makeSound() {

return("LaLaLa");

}

/**

* Returns a String that represents the instrument.

* pre: none

* post: A string representing the singer.

public String toString() {

return(super.getMusician() + " sings " + makeSound() + ".");

}

The Woodwind class is also an Instrument subclass. It too implements

the makeSound() method. However, Woodwind describes a group of

instruments so it has also been declared abstract:

/**

* Woodwind class.

abstract class Woodwind extends Instrument {

/**

* constructor

* pre: none

* post: A woodwind instrument has been created.

public Woodwind(String player) {

super(player);

}

/**

* Returns the sound of the instrument.

* pre: none

* post: The sound made by the instrument is returned.

public String makeSound() {

return("toot");

}

224 Chapter 9 Inheritance and Polymorphism

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The Piccolo class is a subclass of Woodwind. It overrides the makeSound()

method:

/**

* Piccolo class.

public class Piccolo extends Woodwind {

/**

* constructor

* pre: none

* post: A piccolo has been created.

public Piccolo(String piccoloist) {

super(piccoloist);

}

/**

* Returns the sound of the instrument.

* pre: none

* post: The sound made by the instrument is returned.

public String makeSound() {

return("peep");

}

/**

* Returns a String that represents the instrument.

* pre: none

* post: A string representing the instrument has

* been returned.

public String toString() {

return(super.getMusician() + " plays " + makeSound() + ".");

}

The Clarinet class is also a Woodwind subclass. It too overrides the

makeSound() method:

/**

* Clarinet class.

public class Clarinet extends Woodwind {

/**

* constructor

* pre: none

* post: A clarinet has been created.

public Clarinet(String clarinetist) {

super(clarinetist);

}

/**

* Returns the sound of the instrument.

* pre: none

* post: The sound made by the instrument is returned.

public String makeSound() {

return("squawk");

}

Chapter 9 Inheritance and Polymorphism 225

sample

/**

* Returns a String that represents the instrument.

* pre: none

* post: A string representing the instrument has

* been returned.

public String toString() {

return(super.getMusician() + " plays " + makeSound() + ".");

}

Through inheritance and abstraction, a hierarchy of classes can be cre-

ated that begin with a general abstraction and lead to a specific object.

Review: Music – part 2 of 2

Modify the Music application to allow the user to select a cymbal or drum in addition to the other instru-

ments for the band members. The Music application changes will require that Percussion, Cymbal, and Drum

classes be created. The Percussion class should be an abstract class that inherits the Instrument class. The

Cymbal and Drum classes should inherit the Percussion class.

Interfaces

An interface is a class with method declarations that have no implemen-

tations. Although an interface may seem similar to an abstract class, it is

very different. An interface cannot be inherited. It may only be imple-

mented in a class. An interface can add behavior to a class, but it does not

provide a hierarchy for the class.

An interface takes the form:

<access _ level> interface <name> {

<return _ type> <method _ name> (<method _ param>);

…additional methods

}

The methods defined in an interface are by default public and abstract.

Therefore, the methods in an interface are only declarations followed by

a semicolon.

The Comparable interface is part of the java.lang package. It contains

one method:

Interface Comparable (java.lang.Comparable)

Method

compareTo(Object obj)

returns 0 when obj is the same as the object,

a negative integer is returned when obj is

less than the object, and a positive integer is

returned when obj is greater than the object.

When an interface is implemented in a class, the class must implement

each method defined in the interface. In this case, the Comparable interface

contains just one method. The Circle class shown on the next page has

been modified to implement the Comparable interface.

Comparable interface

226 Chapter 9 Inheritance and Polymorphism

sample

/**

* Circle class.

public class Circle implements Comparable {

private static final double PI = 3.14;

private double radius;

/**

* constructor

* pre: none

* post: A Circle object created. Radius initialized to 1.

public Circle() {

radius = 1; //default radius

}

…getRadius(), setRadius(), and other Circle class methods

/**

* Determines if object c is smaller, the same,

* or larger than this Circle object.

* pre: c is a Circle object

* post: -1 has been returned if c is larger than

* this Circle, 0 has been returned if they are the

* same size, and 1 has been returned if c is smaller

* then this Circle.

public int compareTo(Object c) {

Circle testCircle = (Circle)c;

if (radius < testCircle.getRadius()) {

return(-1);

} else if (radius == testCircle.getRadius()) {

return(0);

} else {

return(1);

}

The TestCircle client code tests the compareTo() method:

/**

* The Circle class is tested.

public class TestCircle {

public static void main(String[] args) {

Circle spot1 = new Circle(3);

Circle spot2 = new Circle(4);

if (spot1.compareTo(spot2) == 0) {

System.out.println("Objects are equal.");

} else if (spot1.compareTo(spot2) < 0) {

System.out.println("spot1 is smaller than spot2.");

} else {

System.out.println("spot1 is larger than spot2.");

}

System.out.println(spot1);

System.out.println(spot2);

}

Chapter 9 Inheritance and Polymorphism 227

sample

The TestCircle application produces the output:

A class can implement multiple interfaces. When more than one inter-

face is implemented, the interface names are separated by commas in the

class declaration.

Review: Disk

Modify the Disk class to implement the Comparable interface. Two disks are equal when they have the same

thickness and same radius. Modify the existing client code to test the new method.

Review: Puck – part 2 of 2

Modify the Puck class to implement the Comparable interface. Two pucks are the equal when they have the

same weight. Modify the existing client code to test the new method.

Review: Rectangle – part 4 of 4

Modify the Rectangle class to implement the Comparable interface. Two rectangles are the equal when they

have the same width and height. Modify the existing client code to test the new method.

Review: Rectangle – part 4 of 5

Create an interface named ComparableArea that contains one method named compareToArea(). This method

should return 0 when the object has the same area as another object, –1 should be returned when the object

has an area less than another object, and 1 returned otherwise.

Modify the Rectangle class to implement the ComparableArea interface as well as the Comparable interface

implemented in the previous review. Modify the existing client code to test the new method.

Chapter 9 Case Study

In this case study, a sales center application will be created. The sales

center has three employees, which include a manager and two associates.

The manager earns a salary and the associates are paid by the hour. The

owner of the sales center wants a computer application to display employee

information and calculate payroll.

multiple interfaces

228 Chapter 9 Inheritance and Polymorphism

sample

SalesCenter Specification

The SalesCenter application stores information about three employees.

There is one manager (Diego Martin, salary $55,000), and two associates

(Kylie Walter earning $18.50 per hour and Michael Rose earning $16.75

per hour). SalesCenter should be able to display the name and title for

a specified employee. Additionally, the SalesCenter application should

calculate and display the pay for a specified employee based on the pay

argument entered by the user. The pay argument should correlate to hours

worked if the pay for an associate is to be calculated. The pay argument

for a manager should correlate to the number of weeks the manager is to

be paid for.

The SalesCenter interface should provide a menu of options. Depending

on the option selected, additional input may be needed. The SalesCenter

output sketch:

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

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















The SalesCenter algorithm:

1. Display a menu of options.

2. Prompt the user for a menu choice.

3. If the user has not selected to quit, prompt the user to specify

employee 1, 2, or 3.

4. Perform the action requested by the user.

5. Repeat steps 1 through 4 until the user has selected the option to

quit.

Chapter 9 Inheritance and Polymorphism 229

sample

SalesCenter Code Design

The SalesCenter application can be modeled with objects for a man-

ager and two associates. The manager and associate objects are both

employee objects. Therefore, an Employee abstract class should be used

for subclasses Manager and Associate. The Employee class should define

an emplyee’s first and last name and include an abstract class for calcu-

lating pay. A manager’s pay is based on a pay period specified in weeks.

Associates are paid by the hour. The abstract pay() method in Employee

will have different implementations in Manager and Associate.

The SalesCenter class designs are:











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

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





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

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











230 Chapter 9 Inheritance and Polymorphism

sample

Based on the algorithm and the class designs, the SalesCenter code

design will include a loop. The pseudocode for the SalesCenter client code

follows:

import java.util.Scanner;

import java.text.NumberFormat;

public class SalesCenter {

payEmployee(emp, payArg) {

System.out.println(emp);

pay = emp.pay(payArg);

System.out.println(pay);

}

public static void main(String[] args) {

Manager emp1 = new Manager("Diego","Martin", 55000);

Associate emp2 = new Associate("Kylie", "Walter", 18.50);

Associate emp3 = new Associate("Michael", "Rose", 16.75);

Employee emp = emp1; //default employee choice

/* display menu of choices */

do {

prompt user for employee/pay/quit

get user choice;

if (not quit) {

prompt user for employee number 1, 2, or 3

get empNum

switch (empNum) {

case 1: emp = emp1; break;

case 2: emp = emp2; break;

case 3: emp = emp3; break;

}

if (choice == employee) {

display employee name and title;

} else if (choice == pay) {

prompt user for hours or pay period;

payEmployee(emp, payArg);

}

} while (not quit);

}

SalesCenter Implementation

The SalesCenter implementation involves creating four files. Three files

are the classes and one file is the client code.

Chapter 9 Inheritance and Polymorphism 231

sample

The Employee class is implemented below:

/**

* Employee class.

abstract class Employee {

String firstName, lastName;

/**

* constructor

* pre: none

* post: An employee has been created.

public Employee(String fName, String lName) {

firstName = fName;

lastName = lName;

}

/**

* Returns the employee name.

* pre: none

* post: The employee name has been returned.

public String toString() {

return(firstName + " " + lastName);

}

/**

* Returns the employee pay.

* pre: none

* post: The employee pay has been returned.

abstract double pay(double period);

}

The Manager class is implemented below:

/**

* Manager class.

class Manager extends Employee {

double yearlySalary;

/**

* constructor

* pre: none

* post: A manager has been created.

public Manager(String fName, String lName, double sal) {

super(fName, lName);

yearlySalary = sal;

}

/**

* Returns the manager salary.

* pre: none

* post: The manager salary has been returned.

public double getSalary() {

return(yearlySalary);

}

232 Chapter 9 Inheritance and Polymorphism

sample

/**

* Returns the manager pay for a specified period.

* pre: none

* post: The manager pay for the specified period

* has been returned.

public double pay(double weeks) {

double payEarned;

payEarned = (yearlySalary / 52) * weeks;

return(payEarned);

}

/**

* Returns the employee name and title.

* pre: none

* post: The employee name and title has been returned.

public String toString() {

return(super.toString() + ", manager");

}

The Associate class is implemented below:

/**

* Associate class.

class Associate extends Employee {

double hourlyPayRate;

/**

* constructor

* pre: none

* post: An associate has been created.

public Associate(String fName, String lName, double rate) {

super(fName, lName);

hourlyPayRate = rate;

}

/**

* Returns the associate pay rate.

* pre: none

* post: The associate pay rate has been returned.

public double getRate() {

return(hourlyPayRate);

}

/**

* Returns the associate pay for the hours worked.

* pre: none

* post: The associate pay for the hours worked

* has been returned.

public double pay(double hours) {

double payEarned;

payEarned = hourlyPayRate * hours;

return(payEarned);

}

Chapter 9 Inheritance and Polymorphism 233

sample

/**

* Returns the employee name and title.

* pre: none

* post: The employee name and title has been returned.

public String toString() {

return(super.toString() + ", associate");

}

The SalesCenter client code is implemented below:

import java.util.Scanner;

import java.text.NumberFormat;

public class SalesCenter {

/**

* Displays employee name and pay.

* pre: none

* post: Employee name and pay has been displayed

public static void payEmployee(Employee emp, double payArg) {

NumberFormat money = NumberFormat.getCurrencyInstance();

double pay;

System.out.println(emp);

pay = emp.pay(payArg);

System.out.println(money.format(pay));

}

public static void main(String[] args) {

Manager emp1 = new Manager("Diego","Martin", 55000);

Associate emp2 = new Associate("Kylie", "Walter", 18.50);

Associate emp3 = new Associate("Michael", "Rose", 16.75);

Scanner input = new Scanner(System.in);

String action;

int empNum;

double payArg;

Employee emp = emp1; //set to default emp1

do {

System.out.println("\nEmployee\\Pay\\Quit");

System.out.print("Enter choice: ");

action = input.next();

if (!action.equalsIgnoreCase("Q")) {

System.out.print("Enter employee number (1, 2, or 3):");

empNum = input.nextInt();

switch (empNum) {

case 1: emp = emp1; break;

case 2: emp = emp2; break;

case 3: emp = emp3; break;

}

if (action.equalsIgnoreCase("E")) {

System.out.println(emp);

} else if (action.equalsIgnoreCase("P")) {

System.out.print("Enter the hours for associate or

pay period for manager: ");

payArg = input.nextDouble();

payEmployee(emp, payArg);

}

} while (!action.equalsIgnoreCase("Q"));

}

234 Chapter 9 Inheritance and Polymorphism

sample

The SalesCenter application generates output similar to:

SalesCenter Testing and Debugging

Client code should first be written to test each class. Testing should be

done for the client code.

Review: SalesCenter

Modify the SalesCenter application to compensate associates when they have worked more than 40 hours.

Associates should be paid their hourly wage when 40 or fewer hours are worked. However, associates earn

time and a half for hours over 40. For example, an associate paid $10 per hour will earn $300 for 30 hours of

work. However, an associate working 42 hours will earn $400 + $30, or $430. The overtime pay is calculated

as (hours over 40) * (1.5 * base hourly rate).

Chapter Summary

This chapter discussed inheritance and polymorphism, two key aspects

of object-oriented programming. Inheritance allows classes to be derived

from existing classes. By extending an existing class, there is less devel-

opment and debugging necessary. A class derived from an existing class

demonstrates an is-a relationship.

A superclass is also called a base class, and a subclass is called a derived

class. The keyword extends is used to create a derived class from a base

class. The keyword super is used to access members of a base class from

the derived class.

Polymorphism is the ability of an object to assume different types. In

OOP, polymorphism is based on inheritance. An object can assume the

type of any of its subclasses.

Abstract classes model abstract concepts. They cannot be instantiated

because they should not represent objects. An abstract class is intended

to be inherited.

Chapter 9 Inheritance and Polymorphism 235

sample

Abstract classes may or may not contain abstract methods. An abstract

method is a method declaration with no implementation. If a class con-

tains one or more abstract methods, it must be declared abstract. Abstract

methods must be implemented in a class that inherits the abstract class.

An interface is a class that contains only abstract methods. An interface

can be implemented by a class, but it is not inherited. A class that imple-

ments an interface must implement each method in the interface. The

Comparable interface is part of the java.lang package and is used to add

a compareTo() method to classes that implement the interface.

236 Chapter 9 Inheritance and Polymorphism

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Vocabulary

Abstract class A class that models an abstract

concept. A class that contains one or more abstract

methods must be declared abstract.

Abstract method A method that has been declared,

but not implemented. Abstract methods appear in

abstract classes. They are implemented in a subclass

that inherits the abstract class.

Base class A superclass.

Derived class A subclass.

Inheritance The OOP property in which a class

can define a specialized type of an already exist-

ing class.

Interface A class with abstract methods. An inter-

face cannot be inherited, but it can be implemented

by any number of classes.

Is-a relationship The relationship demonstrated

by a class derived from an existing class.

Polymorphism The OOP property in which objects

have the ability to assume different types.

Java

abstract The keyword used for declaring a class

or a method as abstract.

Comparable A java.lang interface with the

compareTo() method that can be implemented in

classes to provide a means for an object to be com-

pared to another object of the same type.

extends The keyword used in a class declaration to

inherit another class.

interface The keyword used in a class declaration

to declare it an interface.

super The keyword used to call a superclass con-

structor or method.

Chapter 9 Inheritance and Polymorphism 237

sample

Critical Thinking

1. Explain the difference between a has-a and is-a

relationship among classes.

2. If a base class has a public method go() and a

derived class has a public method stop(), which

methods will be available to an object of the

derived class?

3. Compare and contrast implementing an abstract

method to overriding a method.

4. Compare and contrast an abstract class to an

interface.

5. List the method(s) contained in the Comparable

interface.

6. Use the following classes to answer the questions

below:

interface Wo {

public int doThat();

}

public class Bo {

private int x;

public Bo(int z) {

x = z;

}

public int doThis() {

return(2);

}

public int doNow() {

return(15);

}

public class Roo extends Bo implements Wo {

public Roo {

super(1);

}

public int doThis() {

return(10);

}

private int doThat() {

return(20);

}

a) What type of method is doThat() in Wo?

b) What is Wo?

c) Why is doThat() implemented in Roo?

d) List the methods available to a Roo object.

e) How does the implementation of doThis() in

Roo affect the implementation of doThis() in

Bo?

f) What action does the statement super(1) in

Roo perform?

g) Can the doThis() method in Bo be called

from a Roo object? If so, how?

h) Can a method in Roo call the doThis()

method in Bo? If so, how?

True/False

7. Determine if each of the following are true or

false. If false, explain why.

a) Inheritance allows a class to define a special-

ized type of an already existing class.

b) Classes that are derived from existing classes

demonstrate a has-a relationship.

c) A class can have only one level of

inheritance.

d) A class that inherits another class includes

the keyword i n her ita nc e in the class

declaration.

e) When implementing a subclass, existing

methods i n t he base c lass ca n be

overridden.

f) Members of a base class that are declared

private are accessible to derived classes.

g) Inherited methods are called directly from

an object.

h) Polymorphism is an OOP property in which

objects have the ability to assume different

types.

i) Abstract classes can be instantiated.

j) An abstract class must be implemented in its

subclass.

k) An abstract method contains a method

declaration and a body.

l) Inheritance and abstraction allow a hierarchy

of classes to be created.

m) An interface can be inherited.

n) An interface can add behavior to a class.

o) The methods defined in an interface are pri-

vate by default.

p) The Comparable interface contains three

methods.

238 Chapter 9 Inheritance and Polymorphism

sample

Exercises

Exercise 1 —————————————— UEmployee, Faculty, Staff

Create a UEmployee class that contains member variables for the university employee name and salary.

The UEmployee class should contain member methods for returning the employee name and salary.

Create Faculty and Staff classes that inherit the UEmployee class. The Faculty class should include

members for storing and returning the department name. The Staff class should include members for

storing and returning the job title.

Exercise 2 ———————— Account, PersonalAcct, BusinessAcct

Create PersonalAcct and BusinessAcct classes that inherit the Account class presented in Chapter 8.

A personal account requires a minimum balance of $100. If the balance falls below this amount, then

$2.00 is charged (withdrawn) to the account. A business account requires a minimum balance of $500,

otherwise the account is charged $10. Create client code to test the classes.

Exercise 3 ———————————— Vehicle, Car, Truck, Minivan

Create a Vehicle class that is an abstract class defining the general details and actions associated with

a vehicle. Create Car, Truck, and Minivan classes that inherit the Vehicle class. The Car, Truck, and

Minivan classes should include additional members specific to the type of vehicle being represented.

Create client code to test the classes.

Chapter 10 Arrays 239

sample

Arrays are used to implement many different kinds of algorithms.

This chapter explains how to create and use arrays. Searching arrays, two-

dimensional arrays, and the ArrayList class are also discussed. Arrays of

characters and Unicode are explained.

Declaring Arrays

An array is a structure that can store many of the same kind of data

together at once. For example, an array can store 20 integers, another

array can store 50 doubles, and a third array can store 100 objects, such as

Strings. Arrays are an important and useful programming concept because

they allow a collection of related values to be stored together with a single

descriptive name.

An array has a fixed length and can contain only as many data items

as its length allows:







   

   

An array element is one of the data items in an array. For example, in the

array of Strings above, Roxy is an element. Each element has an index value,

with 0 being the index of the first item, 1 the index of the second item,

and so on. In the array above, Roxy is the fourth element in the array and

has the index value 3.

An array must be declared and then space allocated for the elements of

the array. The statements for declaring an array and allocating space for

its elements take the form:

<type>[] <name>; //declare array

<name> = new <type>[<num>]; //allocate space for elements

The declaration includes the type followed by brackets ([]) to indicate an

array. The array name can be any valid identifier. The new operator allocates

space for the number of elements indicated in brackets. The statements on

the next page declare an array and then prompt the user for the number

of elements:

Chapter 10

Arrays

array element

index

declaring and allocating

space for an array

TIP The [] bracket s are

operators used for declaring

and creating arrays and for

accessing array elements.

240 Chapter 10 Arrays

sample

Scanner input = new Scanner(System.in);

int numFriends;

String[] friends; //declare array

System.out.print("How many friends? ");

numfriends = input.nextInt();

friends = new String[numFriends]; //allocate space

If the size of the array is known when the application is written, then

the array can be created and space allocated for elements in one statement,

similar to:

String[] friends = new String[5]; //5 friends

When space has been allocated for the elements of an array, the array is

initialized to the default values for that element type. For example, each

element of an int array is automatically initialized to 0. An array of objects,

such as a String array, contains null for each element.

A third way to create an array is to initialize it in the declaration.

Initializing an array means that a value is given for each element. In this

case, the length of the array is determined by the number of elements

between the curly braces:

String[] friends = {"Kermit", "Lucille", "Sammy", "Roxy", "Myah"};

Using Arrays

An array element is accessed by including its index in brackets after

the array name. For example, the following statement displays the third

element:

System.out.println(friends[2]); //displays Sammy

An array element is changed through assignment. For example, the

assignment statement below changes the third element to “Sunshine”:

friends[2] = "Sunshine";

A run-time error is generated when an invalid index is used. For exam-

ple, the exception ArrayIndexOutOfBoundsException is thrown when the

following statement tries to execute:

friends[5] = "Wilbur"; //ERROR! Generates an exception.

The Array structure includes the length attribute, which can be used at

run time to determine the length of an array:

numElements = friends.length; //5

A for statement is often used to access the elements of an array because

the loop control variable can be used as the array index. Accessing each

element of an array is called traversing an array. For example, the following

statement displays each element of the friends array:

for (int i = 0; i < friends.length; i++) {

System.out.println(friends[i]);

}

Note that the loop iterates from 0 to one less than the length of the array

because length is a count of the elements, not the greatest index value.

changing an element

accessing an element

initial array values

ArrayIndexOutOfBounds

TIP length is a property, not

a method. Therefore, paren-

theses should not follow its

name.

declaring and initializing

TIP An array is an immutable

data structure, which cannot

be changed from its original

size.

traversing

Chapter 10 Arrays 241

sample

Java also provides a type of for loop just for traversing an array.

Sometimes referred to as a for-each statement, the following statement

displays each element in the array:

for (String element : friends) {

System.out.println(element);

}

The statement above displays the names in the array one after the other.

Using a for-each loop to traverse an array does not require a loop con-

trol variable. This type of for statement helps prevent the exception

ArrayIndexOutOfBoundsException.

Although convenient at times, the modified for statement above cannot

be used in situations where the array index value is needed. One example,

is when the elements of an array are to be accessed in reverse order.

Review: StudentRoster

Create a StudentRoster application that prompts the user for the number of students in the class and then

prompts the user for each student’s name and stores the names in an array. After all the names have been

entered, the application should display the title ”Student Roster” and then list the names in the array.

Review: Squares

Create a Squares application that stores the square of an element’s index in an integer array of 5 elements.

For example, the third element, which has index 2, should store 4. The application should then display the

value of each element in the array.

Review: Reverse

Create a Reverse application that stores the number corresponding to the the element’s index in an integer

array of 10 elements. For example, the second element, which has index 1, should store 1. The application

should then display the title “Countdown” and then list numbers stored in the array in reverse order.

Array Parameters

A method declaration can include array parameters. The array passed

to a method can be either an entire array or an element of the array. The

method below includes an array parameter. A second parameter, an int

parameter, corresponds to an element of the array:

public static void tryChanging(int[] numbers, int aNum) {

numbers[1] = 123;

aNum = 456;

}

Note that the data type followed by brackets indicates an array parameter,

similar to an array declaration.

for-each statement

TIP The for-each is new to

Java 5 and requires JDK 5.

242 Chapter 10 Arrays

sample

The statements below call the tryChanging() method shown on the

int[] myNums = {5, 8, 3};

System.out.println(myNums[1] + " " + myNums[0]);

tryChanging(myNums, myNums[0]);

System.out.println(myNums[1] + " " + myNums[0]);

The statements produce the output:

An array is a reference data type similar to a class. Therefore, passing a

whole array to a method passes the reference to the elements, allowing the

method to access an element of the array and change its value. However,

because the elements of the array are a primitve data type, passing a single

element passes only the data stored, not a reference to the data location.

Arrays with Meaningful Indexes

Many algorithms make use of the index value of an array element for

simplifying the storage and retrievel of data. For example, a testScores

array with 101 elements indexed from 0 to 100 could store a count of all the

scores of 90 in the element with index 90, the count of scores 82 in element

82, and so on.

The DiceRolls application counts the frequency of dice roll outcomes.

A roll is simulated by generating two random numbers between 1 and

6. The outcome of each roll is then used to increment the counter in the

element at the index corresponding to the outcome. For example, if a 4 is

rolled, then the value at index 4 is incremented:

import java.util.Scanner;

import java.util.Random;

public class DiceRolls {

public static void main(String[] args) {

int[] outcomes = new int[13];

Scanner input = new Scanner(System.in);

int numRolls;

Random rand = new Random();

int outcome;

/* prompt user for number of rolls */

System.out.print("How many rolls? ");

numRolls = input.nextInt();

/* roll dice and add to outcomes */

for (int roll = 0; roll < numRolls; roll++) {

outcome = (rand.nextInt(6) + 1) + (rand.nextInt(6) + 1);

outcomes[outcome] += 1;

}

/* show counts of outcomes */

for (int i = 2; i <= 12; i++) {

System.out.println(i + ": " + outcomes[i]);

}

Chapter 10 Arrays 243

sample

The DiceRolls application displays output similar to:

In the DiceRolls application, the outcomes ranged from 2 through 12

making it possible to store counters at array indexes directly correspond-

ing to the outcomes. However, this approach for a range of years 1900

through 2000 would require an array of 2001 elements with only the last

100 elements in use. For ranges such as these, the solution is to store coun-

ters at offset array indexes. For example, for an outcome of 1900, a counter

at index 0 would be incremented. for an outcome of 1901, a counter at index

1 would be incremented, and so on.

To determine the array size when offset array indexes will be used,

subtract the low value from the high and add 1:

int[] counts;

counts = new int[HIGH - LOW + 1];

The following statement increments a counter stored at an offset index:

counts[value - LOW] += 1;

Review: DiceRolls – part 1 of 2

Modify the DiceRolls application to roll three dice.

Review: DiceRolls – part 2 of 2

The DiceRolls application is not written generically. The application has “hard-coded” data, including the

maximum random number in the nextInt() method and the initial and final values for i in the show counts

for loop. Modify the DiceRolls application to prompt the user for the number of sides on each die, the num-

ber of dice to be rolled, and the number of rolls to make. For example, a ten-sided die will show a number

between a 1 and a 10 on a roll. Rolling three ten-sided dice has the possible outcomes of 3 through 30.

Review: NumberCounts

Create a NumberCounts application that prompts the user for a number and then counts the occurences of

each digit in that number.

offset array indexes

244 Chapter 10 Arrays

sample

Characters and Arrays

Although strings are comprised of characters, a String object cannot

be manipulated as a set of characters. However, the string stored in a

String object can be converted to a char array. Additionally, an individual

character of the String object can be converted to a char. The String class

methods for working with the characters in a string include:

Class String (java.lang.String)

Method

charAt(int index)

returns a char value that corresponds to the

letter at position index.

toCharArray() returns the String object converted to a char

array.

The value returned by the charAt() method is a char data type. A char

data type represents a single character, such as a letter or symbol. The

toCharArray() method converts each character in the string to a char and

then assigns it to the appropriate element in an existing char array.

Letters of every alphabet and symbols of every culture have been given a

representation in a digital code called Unicode. Unicode uses a set of sixteen

1s and 0s to form a sixteen-bit binary code for each symbol. For example,

the uppercase letter V is Unicode 00000000 01010110, which translates to

the base 10 number 86. Lowercase v has a separate code that translates to

the base 10 number 118.

When a letter is assigned to a char variable, the variable actually stores

the Unicode representation of the letter. Uppercase letters from A to Z have

values from 65 through 90. Lowercase letters from a to z have values from

97 through 122. Because char is a primitive data type, char values can be

compared with relational operators, as the code below demonstrates:

char letter1, letter2;

letter1 = 'a';

letter2 = 'A'

if (letter1 > letter2) {

System.out.println("greater than") //greater than displayed

} else {

System.out.println("less than")

}

The CountLetters application counts the frequency of letters in a string.

Each letter in the string is first converted to uppercase and then the coun-

ter at the appropriate index is incremented. Since uppercase letters have a

range from 65 to 90 in Unicode, offset array indexes are used to determine

which element to update:

import java.util.Scanner;

public class CountLetters {

public static void main(String[] args) {

final int LOW = 'A'; //smallest possible value

final int HIGH = 'Z'; //highest possible value

int[] letterCounts = new int[HIGH - LOW + 1];

Scanner input = new Scanner(System.in);

String word;

char[] wordLetters;

int offset; //array index

charAt()

toCharArray()

Unicode

TIP Refer to the appendix

in this text for more Unicode

symbols and their values.

TIP Assignment to a char vari-

able requires single quotation

marks around the character.

TIP The char data type was

introduced in Chapter 4.

Chapter 10 Arrays 245

sample

/* prompt user for a word */

System.out.print("Enter a word: ");

word = input.nextLine();

/* convert word to char array and count letter occurrences */

word = word.toUpperCase();

wordLetters = word.toCharArray();

for (int letter = 0; letter < wordLetters.length; letter++) {

offset = wordLetters[letter] - LOW;

letterCounts[offset] += 1;

}

/* show letter occurrences */

for (int i = LOW; i <= HIGH; i++) {

System.out.println((char)i + ": " + letterCounts[i - LOW]);

}

Note the statements for creating a char array from a String object. First,

the char array wordLetters was declared. Later, wordLetters was initialized

using the toCharArray() method in the statement:

wordLetters = word.toCharArray();

The number of characters in the string determined the number of array

elements.

Type casting was used in the last statement of the CountLetters applica-

tion ((char)i) to produce labels for the contents of the array. Casting the

int to a char produces the Unicode equivalent character for that number.

The CountLetters application produces output similar to:

type casting

246 Chapter 10 Arrays

sample

Review: CountLetters

The CountLetters application is limited to counting letters in a single word. Modify the CountLetters

application to count the letters in an entire phrase, which contains spaces. Care must be taken to ignore the

spaces and any other nonalphabetic character found in the phrase. Be sure to change comments and vari-

able names appropriately so that the reader of the application code understands that the letters in a phrase

are counted.

Review: NameBackwards

Create a NameBackwards application that prompts the user for his or her name and then displays the name

backwards.

Searching an Array

There are many ways to search an array for a specific value. The sim-

pliest searching algorithm is called linear search and works by proceeding

from one array element to the next until the specified value is found or

until the entire array has been searched. The Search class below contains

a linear() method that returns the index of a specified int element. If the

element is not found, then -1 is returned:

public class Search {

/**

* Returns the index of the element numToFind.

* -1 returned if element not found.

* pre: none

* post: index of numToFind has been returned. -1 has been

* returned if element not found.

public static int linear(int[] array, int numToFind) {

int index = 0;

while ((array[index] != numToFind) &&

(index < array.length - 1)) {

index += 1;

}

if (array[index] == numToFind) {

return(index);

} else {

return(-1);

}

The condition of the while statement checks all but the last element of

the array, unless the search element is found earlier. If the while statement

completes without finding the element, the index value has been incre-

mented to the last index of the array The if statement then checks the last

element of the array.

linear search

Algorithm Analysis

Algorithm analysis includes

measuring how efficiently an

algorithm performs its task.

A linear search sequentially

checks each element of an array

for a specified element. For an

array with n objects, finding an

element could take as many as

n checks. This measure can be

written as O(n). This notation

is called Big Oh notation and

is a theoretical measure of an

algorithm’s efficiency.

Chapter 10 Arrays 247

sample

The application below uses the linear() method to find an element in

the array:

import java.util.Scanner;

import java.util.Random;

public class FindNum {

public static void main(String[] args) {

final int MAX = 20;

int[] numArray = new int[MAX];

Random rand = new Random();

Scanner input = new Scanner(System.in);

int num, location;

/* fill array with random numbers */

for (int i = 0; i < numArray.length;i ++) {

numArray[i] = rand.nextInt(MAX);

}

/* prompt user for a number to search for */

System.out.print("Enter a number between 0 and " + MAX

+ ": ");

num = input.nextInt();

/* Search for number and notify user of num location */

location = Search.linear(numArray, num);

if (location == -1) {

System.out.println("Sorry, number not found in array.");

} else {

System.out.println("First occurrence is element "

+ location);

}

The FindNum application output looks similar to:

Review: FindName

Add a static method to the Search class that performs a linear search on a String array. The linear() method

should overload the existing method, have parameters for accepting a String array and a String variable,

and return an int indicating the position of the String. Create a FindName application that uses the Search

class. FindName should prompt the user for names to fill an array and then prompt the user for the name

to find.

Two-Dimensional Arrays

An array with two dimensions can be used to represent data that cor-

responds to a grid. For example, a checkerboard, the streets in a city, and

seats in a theater can all be represented with a grid. A tic-tac-toe board

represented in a two-dimensional array can be visualized as shown on

the next page.

248 Chapter 10 Arrays

sample











A two-dimensional array with three rows (0, 1, and 2) and

three columns (0, 1, and 2) represents a tic-tac-toe board

A two-dimensional array must be declared and then space allocated

for the elements of the array in statements that take the form:

<type>[][] <name>;

<name> = new <type>[<num>][<num>];

The declaration includes the type followed by two sets of brackets ([][]).

The array name can be any valid identifier. The new operator allocates space

for the number of elements indicated in brackets. For example, a tic-tac-toe

board could be created with the statement:

String[][] tttBoard = new String[3][3];

The length property can be used to determine the number of rows and

columns in a two-dimensional array with two separate statements:

rows = tttBoard.length;

cols = tttBoard[0].length;

Note that the number of columns is determined by checking the length

of the first row.

An element of a two-dimensional array is accessed by including the

indexes of the row and column in brackets after the array name. For

example, the following statement assigns the element in the second row,

third column the letter "X":

tttBoard[1][2] = "X";

Nested for statements are often used to access the elements of a two-

dimensional array because one loop counter indicates the row and the

second counter indicates the column. For example, the following state-

ments display the contents of a two-dimensional array:

for(int row = 0; row < tttBoard.length; row++) {

for (int col = 0; col < tttBoard[0].length; col++) {

System.out.print(tttBoard[row][col]);

}

System.out.println();

}

A method that requires a two-dimensional array parameter includes

the array data type followed by two sets of brackets ([][]).

The TicTacToe application allows two players to play a computerized

game of tic-tac-toe. The TTT class performs most of the work with private

methods. The client code simply instantiates a TTT object and then calls

the TTT object’s play() method. The client code implementation is shown

first and then the TTT class implementation:

declaration

accessing elements

nested for statements

length

array parameter

Chapter 10 Arrays 249

sample

/**

* Tic-tac-toe is played.

public class TicTacToe {

public static void main(String[] args) {

TTT TTTGame = new TTT();

TTTGame.play();

}

/**

* TTT class.

import java.util.Scanner;

public class TTT {

private String[][] tttBoard;

private String player1, player2;

/**

* constructor

* pre: none

* post: tttBoard has been initialized.

* player1 is X and player2 is O.

public TTT() {

player1 = "X";

player2 = "O";

tttBoard = new String[3][3];

for(int row = 0; row < tttBoard.length; row++) {

for (int col = 0; col < tttBoard[0].length; col++) {

tttBoard[row][col] = " ";

}

/**

* Plays a game of tic-tac-toe with two users,

* keeping track of player (X or O) turns.

* player1 goes first.

* pre: none

* post: A game of tic-tac-toe has been played.

public void play() {

String currPlayer = player1;

int movesMade = 0;

do {

displayBoard();

makeMove(currPlayer);

movesMade += 1;

if (currPlayer == player1){

currPlayer = player2;

} else {

currPlayer = player1;

}

} while (movesMade <= 9 && winner() == " ");

displayBoard();

System.out.println("Winner is " + winner());

}

250 Chapter 10 Arrays

sample

/**

* Displays the board.

* pre: none

* post: The tic-tac-toe board has been displayed.

private void displayBoard() {

for(int row = 0; row < tttBoard.length; row++) {

for (int col = 0; col < tttBoard[0].length; col++) {

System.out.print("[" + tttBoard[row][col] + "]");

}

System.out.println();

}

/**

* Prompt user for a move until a valid move has been made.

* pre: none

* post: A mark has been made in an empty tic-tac-toe

* board square.

private void makeMove(String player) {

Scanner input = new Scanner(System.in);

boolean validMove = false;

int row, col;

do {

System.out.print("Enter row number (0, 1, 2): ");

row = input.nextInt();

System.out.print("Enter column number (0, 1, 2): ");

col = input.nextInt();

if ((row >= 0 && row < tttBoard.length &&

col >= 0 && col < tttBoard[0].length) &&

tttBoard[row][col].equals(" ")) {

tttBoard[row][col] = player;

validMove = true;

} else {

System.out.println("Invalid move. Try again.");

}

} while (!validMove);

}

/**

* Determine winner. Return " " if no winner.

* pre: none

* post: X, O, or " " has been returned as the winner.

private String winner() {

/* test rows */

for (int row = 0; row < tttBoard.length; row++) {

if (tttBoard[row][0].equals(tttBoard[row][1]) &&

tttBoard[row][1].equals(tttBoard[row][2]) &&

!(tttBoard[row][0].equals(" "))) {

return(tttBoard[row][0]);

}

Chapter 10 Arrays 251

sample

/* test columns */

for (int col = 0; col < tttBoard[0].length; col++) {

if (tttBoard[0][col].equals(tttBoard[1][col]) &&

tttBoard[1][col].equals(tttBoard[2][col]) &&

!(tttBoard[0][col].equals(" "))) {

return(tttBoard[0][col]);

}

/* test diagonal */

if (tttBoard[0][0].equals(tttBoard[1][1]) &&

tttBoard[1][1].equals(tttBoard[2][2]) &&

!(tttBoard[0][0].equals(" "))) {

return(tttBoard[0][0]);

}

/* test other diagonal */

if (tttBoard[0][2].equals(tttBoard[1][1]) &&

tttBoard[1][1].equals(tttBoard[2][0]) &&

!(tttBoard[0][2].equals(" "))) {

return(tttBoard[0][2]);

}

return(" ");

}

The TicTacToe application displays output similar to:

252 Chapter 10 Arrays

sample

The ArrayList Class

A collection is a group of related objects, or elements, that are stored

together as a single unit. An array is an example of a collection. Java also

contains a collections framework, which provides classes for implementing

collections. One such class is the ArrayList class, which includes methods

for adding and deleting elements and finding an element.

Class ArrayList (java.util.ArrayList)

Method

add(int index, Object element)

inserts element at index position of the array.

Existing elements are shifted to the next posi-

tion up in the array.

add(Object element)

adds element to the end of the array.

get(int index)

returns the element at index position in the

array.

indexOf(Object obj)

returns the index of the first element matching

obj using the equals() method of the object’s

class to determine equality between the ele-

ment and the object.

remove(int index)

removes the element at index position in the

array.

set(int index, Object element)

replaces the element at index position with

element.

size() returns the number of elements in the array.

The ArrayList class implements a dynamic array. A dynamic array var-

ies in size during run time and is used in applications where the size

of an array may need to grow or shrink. An ArrayList object shifts ele-

ments up one position when a new element is added at a specific index.

Elements added to the end of the ArrayList do not move existing elements.

Removing an element from an ArrayList also shifts elements as necessary

to close the gap left by the removed element.

When using an ArrayList object, it is important to understand that only

objects, not primitive types, can be stored. Because the indexOf() method

compares its object parameter to each element of the array, it is important

that the object’s class has an appropriately overridden equals() method.

collection

collections framework

dynamic array

equals()

Data Structure Analysis

Data structure analysis includes

measuring the efficiency of a

data structure’s operations. For

example, adding an object to

the end of an ArrayList data

structure requires a single

operation, which can be writ-

ten as O(1). However, adding

an object to the beginning of

the array requires all the exist-

ing objects first be moved up

one position. For an array with

n objects, adding an object to

the front of the array requires n

operations, which can be writ-

ten as O(n). This is a much less

efficient operation.

TIP The ArrayList class is a

data structure. Data struc-

tures are discussed further in

Chapter 14.

Chapter 10 Arrays 253

sample

The following application creates an ArrayList object, adds elements,

removes an element, and then displays the remaining elements:

import java.util.ArrayList;

public class TestArrayList {

public static void main(String[] args) {

ArrayList myStrings = new ArrayList();

myStrings.add("Kermit");

myStrings.add("Lucille");

myStrings.add("Sammy");

myStrings.add("Roxy");

myStrings.add("Myah");

myStrings.remove(3);

for (Object name : myStrings) {

System.out.println(name);

}

The ArrayList declaration does not require an array size. An ArrayList

object grows and shrinks automatically as elements are added and

removed. The for-each statement traverses the ArrayList. An ArrayList

converts elements to their superclass Object, which is why name is type

Object, rather than String.

The TestArrayList application displays the output:

Wrapper Classes

Primitive data types cannot be directly stored in an ArrayList because

the elements in an ArrayList must be objects. The Integer and Double

classes, provided with Java, are used to “wrap” primitive values in an

object. The Integer and Double wrapper classes include the methods for

comparing objects and for returning the value stored by the object as a

primitive:

Class Integer (java.lang.Integer)

Method

compareTo(Integer intObject)

returns 0 when the Integer object value is the

same as intObject. A negative int is returned

when the Integer object is less than intObject,

and a positive int is returned when the Integer

object is greater than intObject.

intValue() returns the int value of the Integer object.

TIP Java also includes the

Character, Boolean, Byte,

Short, Long, and Float wrap-

per classes.

TIP The for-each statement

is not a safe structure for find-

ing and removing elements

from an ArrayList.

254 Chapter 10 Arrays

sample

Class Double (java.lang.Double)

Method

compareTo(Double doubleObject)

returns 0 when the Double object value is the

same as doubleObject. A negative int is returned

when the Double object is less than doubleObject,

and a positive int is returned when the Double

object is greater than doubleObject.

doubleValue() returns the double value of the Double object.

The Integer and Double wrapper classes are in the java.lang package.

Therefore applications do not require an import statement to use the

wrapper classes.

The DataArrayList application creates an ArrayList of Integer values,

compares the values, and then sums the elements:

import java.util.ArrayList;

public class DataArrayList {

public static void main(String[] args) {

ArrayList numbers = new ArrayList();

Integer element, element1, element2;

int sum = 0;

numbers.add(new Integer(5));

numbers.add(new Integer(2));

/* compare values */

element1 = (Integer)numbers.get(0);

element2 = (Integer)numbers.get(1);

if (element1.compareTo(element2) == 0) {

System.out.println("The elements have the same value.");

} else if (element1.compareTo(element2) < 0) {

System.out.println("element1 value is less than element2.");

} else {

System.out.println("element1 value is greater than element2.");

}

/* sum values */

for (Object num : numbers) {

element = (Integer)num;

sum += element.intValue();

}

System.out.println("Sum of the elements is: " + sum);

}

In the first numbers.add() statement above, the new operator allocates

memory and returns a reference to the Integer object that stores the value

5. A second statement performs the same type of action to add another

Integer object to the ArrayList.

The values stored in the elements are compared using the compareTo()

method. Note that the elements are first assigned to Integer objects

element1 and element2. The assignment statement must appropriately cast

the retrieved values because an ArrayList casts elements to their superclass

Object.

Finally, the for-each statement traverses the ArrayList elements and

sums their values. The (Integer) cast is again required to convert the

retrieved value num for assignment to element. The int value of each Integer

object is then used to update sum.

object casting

TIP The Integer and Double

cla s s e s i m p l e m e nt t h e

Comparable interface, intro-

duced in Chapter 9.

Generic Collection

Classes

ArrayList items can be declared

when the ArrayList is created.

For example:

ArrayList<Integer> numbers

= new ArrayList<Integer>;

designates the ArrayList as

a list of Integers. This allows

the ArrayList get() method to

be used without casting. For

example:

e l e m e n t 1 = n u m b e r s .

get(0);

returns an Integer object with-

out the need to cast.

Chapter 10 Arrays 255

sample

The DataArrayList displays the output:

Review: HighestGrade

Create a HighestGrade application that prompts the user for five grades between 0 and 100 points and stores

the grades in an ArrayList. HighestGrade then traverses the grades to determine the highest grade and then

displays the grade along with an appropriate message.

Chapter 10 Case Study

In this case study, a bank application will be created. A bank can open

new accounts, modify existing accounts, and close accounts. An account

has a number associated with it, and transactions, such as deposits and

withdrawals, require the account number.

LocalBank Specification

The LocalBank application allows accounts to be opened, modified,

and closed. Each account has a unique account number, which is required

for all transactions. Transactions include deposits and withdrawals. An

account balance can also be checked.

The LocalBank interface should provide a menu of options. Depending

on the option selected, additional input may be needed. When a transac-

tion is performed, updated account information should be displayed. The

LocalBank output sketch:

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









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



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







TIP A Bank application was

also developed in Chapter 8.

256 Chapter 10 Arrays

sample

The LocalBank algorithm:

1. Display a menu of options.

2. Prompt the user for a menu choice.

3. For all options except the option to add an account, prompt the

user for an account number.

4. Perform the action requested by the user on the account with the

number entered. If the user requested to create a new account, then

add an account and display the new account’s number.

5. Repeat steps 1 through 4 until the user has selected the option to

quit.

LocalBank Code Design

The LocalBank application can be modeled with a Bank object, Account

objects, and Customer objects. The Bank object should store the accounts,

add and remove accounts, and perform transactions that also display

updated account information. A transaction requires finding the correct

account. The Account objects should store the current balance, make

deposits, make withdrawals, and return the current balance and account

ID. An Account object must also have an equals() method for the Bank

object to use when finding an account. The Customer objects should store

the account holder’s name. The Bank object will display account infor-

mation, therefore, the Account and Customer objects will override the

toString() methods.

The LocalBank class designs are:

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

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

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

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



Chapter 10 Arrays 257

sample





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

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The Account and Customer class designs are similar to the classes devel-

oped in Chapter 8. In the real world, the existing classes would probably

be reused for the LocalBank application. The modularity of OOP makes

programming more efficient and less error-prone. For this case study,

simplified classes will be developed and used for the application.

Based on the algorithm and the class designs, the LocalBank code

design will include a loop. The pseudocode for the LocalBank client code

follows:

Bank easySave = new Bank();

do {

prompt user for transaction type

if (add account) {

easySave.addAccount();

} else if (not Quit) {

prompt user for account ID;

if (deposit) {

prompt user for deposit amount

easySave.transaction(make deposit, acctID, amt);

} else if (withdrawal) {

prompt user for withdrawal amount

easySave.transaction(make withdrawal, acctID, amt);

} else if (check balance) {

easySave.checkBalance(acctID);

} else if (remove account) {

easySave.deleteAccount(acctID);

}

} while (not quit);

258 Chapter 10 Arrays

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LocalBank Implementation

The LocalBank implementation involves creating four files. Three files

are the classes and one file is the client code.

The Bank class is implemented below:

/**

* Bank class.

import java.util.ArrayList;

import java.util.Scanner;

public class Bank {

private ArrayList accounts;

/**

* constructor

* pre: none

* post: accounts has been initialized.

public Bank() {

accounts = new ArrayList();

}

/**

* Adds a new account to the bank accounts.

* pre: none

* post: An account has been added to the bank's accounts.

public void addAccount() {

Account newAcct;

double bal;

String fName, lName;

Scanner input = new Scanner(System.in);

System.out.print("First name: ");

fName = input.nextLine();

System.out.print("Last name: ");

lName = input.nextLine();

System.out.print("Beginning balance: ");

bal = input.nextDouble();

newAcct = new Account(bal, fName, lName); //create acct object

accounts.add(newAcct); //add account to bank accounts

System.out.println("Account created. Account ID is: " + newAcct.getID());

}

/**

* Deletes an existing account.

* pre: none

* post: An existing account has been deleted.

public void deleteAccount(String acctID) {

int acctIndex;

Account acctToMatch;

Chapter 10 Arrays 259

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acctToMatch = new Account(acctID);

acctIndex = accounts.indexOf(acctToMatch); //retrieve location of account

if (acctIndex > -1) {

accounts.remove(acctIndex); //remove account

System.out.println("Account removed.");

} else {

System.out.println("Account does not exist.");

}

/**

* Performs a transaction on an existing account. A transCode of 1 is for deposits

* and a transCode of 2 is for withdrawals.

* pre: transCode is 1 or 2.

* post: A transaction has occurred for an existing account.

public void transaction(int transCode, String acctID, double amt) {

int acctIndex;

Account acctToMatch, acct;

acctToMatch = new Account(acctID);

acctIndex = accounts.indexOf(acctToMatch); //retrieve location of account

if (acctIndex > -1) {

acct = (Account)accounts.get(acctIndex); //retrieve object to modify

if (transCode == 1) {

acct.deposit(amt);

accounts.set(acctIndex, acct); //replace object with updated object

System.out.println(acct);

} else if (transCode == 2) {

acct.withdrawal(amt);

accounts.set(acctIndex, acct); //replace object with updated object

System.out.println(acct);

}

} else {

System.out.println("Account does not exist.");

}

/**

* Displays the account information, including the current balance,

* for an existing account.

* pre: none

* post: Account information, including balance, has been displayed.

public void checkBalance(String acctID) {

int acctIndex;

Account acctToMatch, acct;

acctToMatch = new Account(acctID);

acctIndex = accounts.indexOf(acctToMatch); //retrieve location of account

if (acctIndex > -1) {

acct = (Account)accounts.get(acctIndex); //retrieve object to display

System.out.println(acct);

} else {

System.out.println("Account does not exist.");

}

In the deleteAccount() and transaction() methods, a new Account object

is created for the purposes of finding the account to delete or modify. The

new Account object is instantiated with just the acctID and then this object

is passed to the indexOf() method of the ArrayList class. The indexOf()

260 Chapter 10 Arrays

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method searches the ArrayList and automatically invokes the equals()

method of the Account class to determine equality. The Account class is

implemented below. Note that the equals() method requires only that the

account numbers of two object match to be considered equal:

/**

* Account class.

import java.text.NumberFormat;

public class Account {

private double balance;

private Customer cust;

private String acctID;

/**

* constructor

* pre: none

* post: An account has been created. Balance and

* customer data has been initialized with parameters.

public Account(double bal, String fName, String lName) {

balance = bal;

cust = new Customer(fName, lName);

acctID = fName.substring(0,1) + lName;

}

/**

* constructor

* pre: none

* post: An empty account has been created with the specified account ID.

public Account(String ID) {

balance = 0;

cust = new Customer("", "");

acctID = ID;

}

/**

* Returns the account ID.

* pre: none

* post: The account ID has been returned.

public String getID() {

return(acctID);

}

/**

* Returns the current balance.

* pre: none

* post: The account balance has been returned.

public double getBalance() {

return(balance);

}

Chapter 10 Arrays 261

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/**

* A deposit is made to the account.

* pre: none

* post: The balance has been increased by the amount of the deposit.

public void deposit(double amt) {

balance += amt;

}

/**

* A withdrawal is made from the account if there is enough money.

* pre: none

* post: The balance has been decreased by the amount withdrawn.

public void withdrawal(double amt) {

if (amt <= balance) {

balance -= amt;

} else {

System.out.println("Not enough money in account.");

}

/**

* Returns a true when objects have matching account IDs.

* pre: none

* post: true has been returned when the objects are equal,

* false returned otherwise.

public boolean equals(Object acct) {

Account testAcct = (Account)acct;

if (acctID.equals(testAcct.acctID)) {

return(true);

} else {

return(false);

}

/**

* Returns a String that represents the Account object.

* pre: none

* post: A string representing the Account object has been returned.

public String toString() {

String accountString;

NumberFormat money = NumberFormat.getCurrencyInstance();

accountString = acctID + "\n";

accountString += cust.toString();

accountString += "Current balance is " + money.format(balance);

return(accountString);

}

The Account class has two constructors. The second constructor is used

in the deleteAccount() and transaction() methods of the Bank class for the

purposes of finding the index of the account matching the given account

ID.

262 Chapter 10 Arrays

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The Customer class is implemented below:

/**

* Customer class.

public class Customer {

private String firstName, lastName;

/**

* constructor

* pre: none

* post: A Customer object has been created.

* Customer data has been initialized with parameters.

public Customer(String fName, String lName) {

firstName = fName;

lastName = lName;

}

/**

* Returns a String that represents the Customer object.

* pre: none

* post: A string representing the Customer object has

* been returned.

public String toString() {

String custString;

custString = firstName() + " " + lastName() + "\n";

return(custString);

}

The LocalBank client code is implemented below:

/**

* A bank where accounts can be opened or closed and customers can

* make transactions.

import java.util.Scanner;

public class LocalBank {

public static void main(String[] args) {

Bank easySave = new Bank();

Scanner input = new Scanner(System.in);

String action, acctID;

Double amt;

/* display menu of choices */

do {

System.out.println("\nDeposit\\Withdrawal\\Check balance");

System.out.println("Add an account\\Remove an account");

System.out.println("Quit\n");

System.out.print("Enter choice: ");

action = input.next();

Chapter 10 Arrays 263

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if (action.equalsIgnoreCase("A")) {

easySave.addAccount();

} else if (!action.equalsIgnoreCase("Q")) {

System.out.print("Enter account ID: ");

acctID = input.next();

if (action.equalsIgnoreCase("D")) {

System.out.print("Enter deposit amount: ");

amt = input.nextDouble();

easySave.transaction(1, acctID, amt);

} else if (action.equalsIgnoreCase("W")) {

System.out.print("Enter withdrawal amount: ");

amt = input.nextDouble();

easySave.transaction(2, acctID, amt);

} else if (action.equalsIgnoreCase("C")) {

easySave.checkBalance(acctID);

} else if (action.equalsIgnoreCase("R")) {

easySave.deleteAccount(acctID);

}

} while (!action.equalsIgnoreCase("Q"));

}

Running the LocalBank application displays output similar to:

It was possible to create the LocalBank application with fewer classes.

However, by breaking the application into discrete objects, it will be

easier to later extend the classes to enhace the client code. For example,

an account can easily be extended to include an account holder’s address

by modifying, or extending, the Customer class. Then, only the first con-

structor of the Account class will need to be modifed to handle additional

parameters for creating a Customer object.

264 Chapter 10 Arrays

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LocalBank Testing and Debugging

When a new class is written, client code should be written to test the

class. Testing should be done first for each class and then for the client

code.

Review: LocalBank

Modify the Bank class to prompt the user for a full address (street, city, state, and zip) when an account is

opened. Modify the Customer class to include street, city, state, and zip variable members and changeStreet(),

changeCity(), changeState(), and changeZip() method members. Modify the Account class to include a

changeAddress() method member. Modify the Bank class to include a modifyAccount() method member

that requires a parameter for the account ID. modifyAccount() should prompt the user for the new street,

city, state, and zip for the account, find the account with the matching account ID, and then overwrite the

existing account object with the object containing the updated information.

Chapter Summary

This chapter discussed arrays as a structure for storing many of the

same kind of data together at once. A data item stored by an array is called

an element. An element has an index value and is accessed by using the

index inside of [] brackets along with the array name. A for statement and

the for-each statement can be used to access all the elements of an array.

Accessing the elements of an array is called traversing the array. When

the index of an element is needed, the for statement should be used.

An array can be passed to a method as a parameter and is a reference

data type. Passing a single element passes the data stored, not a reference

to the data location.

Many algorithms make use of the index value of an array element for

simplifying the storage and retrieval of data. Offset array indexes are

used when a range should be shifted to correlate to a lower range of index

values.

A String can be converted to an array of characters so that individual

characters can be maipulated. Unicode is the standard for numeric repre-

sentation of every letter and symbol in use.

The linear search is an algorithm for searching an array where each ele-

ment is checked one after the other until the desired element is found.

Two-dimensional arrays represent data that corresponds to a grid. The

number of rows in an existing two-dimensional array corresponds to the

length of the array. The number of columns corresponds to the length of

the first row. Elements in a two-dimensional array are accessed by using

a double bracket ([][]) along with the array name.

The ArrayList class is used for storing a collection of objects. Methods

are used for accessing and retrieving elements and for determining the

number of elements in the collection. An ArrayList object is a dynamic

array, which can vary in size at run time. Because an ArrayList can store

only objects, wrapper classes are used to represent primitive types that

are to be stored in an ArrayList.

Chapter 10 Arrays 265

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Vocabulary

Array A structure that can store many of the same

kind of data together at once.

ArrayOutOfBoundsException An exception

thrown when an invalid array index is used.

Collection A group of related elements that are

stored together as a single unit.

Collections framework Classes for implementing

collections.

Dynamic array An array that varies in size at run

time.

Element A data item in an array.

Index The value associated with an element in an

array. Index values begin at 0 and count up.

Linear search An algorithm for searching an array

in which each element of the array is checked one

after the other.

Java

[] The operators for accessing an array element.

ArrayList A java.util class with methods for imple-

menting a dynamic array.

Double A java.lang class for wrapping double values

in an object.

for A statement that can be used to traverse an array.

In one form, it is referred to as a for-each statement

and does not use a counter variable.

Integer A java.lang class for wrapping int values

in an object.

new Operator that allocates space for the elements

in an array.

String A java.lang class with methods for convert-

ing a string to a set of characters or for inspecting

individual characters of a string.

Traversing Iterating through element of an array.

Unicode The sixteen-bit digital code used to

represent every letter and symbol.

Wrapper class A class that wraps primitive values

in an object.

266 Chapter 10 Arrays

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Critical Thinking

1. What index value does the third element of an

array have?

2. Write the declaration for an array named

quantities that stores 20 integers.

3. Write a declaration for an array named heights

storing the numbers 1.65, 2.15, and 4.95.

4. Write a for-each statement that displays the inte-

ger values stored in an array named grades.

5. a) Write an algorithm for inserting data into an

array so that existing data is moved up one

position to make room for the new data.

b) Write an algorithm for deleting data from an

array so that existing data is moved to close

the gap made by the deleted data.

6. How does passing an entire array to a method

differ from passing a single element of the

array?

7. Why are offset array indexes required in some

cases.

8. What output is displayed by the statements

below?

String name = "Elaine";

System.out.println(name.charAt(3));

9. Compare and contrast an array to an ArrayList

by describing the differences between the two

for:

a) accessing an element.

b) adding an element.

c) deleting an element.

d) assigning a new value to an element.

e) determining the size of the collection.

10. Give an example of when a dynamic array might

be a better structure choice over an array.

11. How does the ArrayList indexOf() method

determine equality between the object passed

to the method and an element in the array?

12. How can the values of wrapper class objects be

compared?

True/False

13. Determine if each of the following are true or

false. If false, explain why.

a) All data in an array has the same data

type.

b) Index values always begin at 0.

c) The statement int[] empNums = new int[10]

declares an array with 10 elements.

d) In the statement int[] empNums = new int[10],

the elements are automatically initialized to

e) An entire array can be passed to a method.

f) The method toCharArray() converts a String

object to a char array.

g) A linear search never searches an entire

array.

h) The statement int[][] grid = new int[4][4]

declares a total of eight elements.

i) In Unicode, uppercase letters have higher

base 10 number values than lowercase

letters.

j) The size of an array can change during the

execution of a program.

k) The ArrayList class implements a dynamic

array.

l) Primitive data types can be stored directly

in an ArrayList.

Chapter 10 Arrays 267

sample

Exercises

Exercise 1 —————————————————— EvensAndOdds

Create an EvensAndOdds application that generates 25 random integers between 0 and 99 and then

displays all the evens on one line and all the odds on the next line. Application output should look

similar to:

Exercise 2 —————————————————— GeneratedNums

Create a GeneratedNums application that generates the number to store in an array element by sum-

ming its index and the individual digits of the index. For example, the element with index 17 should

store 25 (17 + 1 + 7 = 25) and the element with index 2 should store 4 (2 + 0 + 2 = 4). GeneratedNums

should use an array with 101 elements and then display the value at each element. Application output

should look similar to:

Exercise 3 ———————————————————— RandomStats

Create a RandomStats application that generates 500 random numbers between 0 and 9 and then dis-

plays the number of occurrences of each number. Application output should look similar to:

268 Chapter 10 Arrays

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Exercise 4 —————————————————————— Analysis

A program that analyzes a set of numbers can be very useful. Create an Analysis application that

prompts the user for numbers in the range 1 through 50, terminated by a sentinel, and then performs

the following analysis on the numbers:

• Determine the average number

• Determine the maximum number

• Determine the range (maximum – minimum)

• Determine the median (the number that occurs the most often)

• Displays a bar graph called a histogram that shows the numbers in each five-unit

range (1–5, 6–10, 11-15, etc.). The histogram may look similar to:

Exercise 5 ———————————————————— Mastermind

The game of Mastermind is played as follows: One player (the code maker) chooses a secret arrange-

ment of colored pegs and the other player (the code breaker) tries to guess it. For each guess, the code

breaker puts forth an arrangement of colored pegs, and the code maker reports two numbers:

1. The number of pegs that are the correct color and in the correct position.

2. The number of pegs that are the correct color regardless of whether they are in the

correct position.

Create a Mastermind application that plays the game of Mastermind with the computer as the code

maker and the user as the code breaker. The application should use a mastermindGame class, which has

a constructor with parameters for the number of pegs in the code (1 to 10) and the number of colors for

the pegs (1 to 9). The secret code generated by a mastermindGame object can contain duplicate colors.

For example, a 5-peg code could be 1 2 2 5 6. A guess with duplicates will require extra attention when

counting the number of pegs of the correct color. For example, if the code is 1 2 3 4 5 6 and the guess

is 2 1 1 2 2 2, then the mastermindGame object should only report two correct colors (a single 1 and a

single 2). Application output should look similar to:

Chapter 10 Arrays 269

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Exercise 8 ———————————————————— Palindrome

Create a Palindrome application that prompts the user for a string and then displays a message

indicating whether or not the string is a palindrome. A palindrome is a word or phrase that is

spelled the same backwards and forwards. For example, “mom” is a palindrome, as well as “kayak”

and “Never odd or even”.

Exercise 9 ————————————————— CountConsonants

Create a CountConsonants application that prompts the user for a string and then displays the

number of consonants in the string. Application output should look similar to:

Exercise 10 ——————————————————————— Coder

Create a Coder application that prompts the user for a string and then displays an encoded string.

The encoding should add 2 to the Unicode value of each letter to create a new letter. The application

should keep all spaces between the words in their original places and the letters x and y should

be converted to a and b, respectively. Coder application output should look similar to:

270 Chapter 10 Arrays

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Exercise 11 ———————————————————— SortedArray

An array is said to be sorted if its elements are in either increasing or decreasing order. One way the

selection sort algorithm works is by repeatedly taking the lowest element from an array and adding it

to a new array, so that all the elements in the new array are sorted from lowest to highest.

Create a SelectionSort class with a constructor that has an int array parameter, member variables

originalArray and sortedArray, public method display() that displays the contents of the sorted array,

private methods sort() that populates a new array with the elements of the original array in order from

lowest to highest, and findLowest() that returns the index of the element containing the lowest value.

Hint: Since elements of an array cannot actually be “removed” an element can be set to a very high

value after determining its value is the lowest.

Create client code SortedArray, which tests the SelectionSort class. Use the pseudocode below when

implementing the SortedArray client code:

int[] myNums;

SelectionSort sortedArray;

prompt user for the number of values to populate array with

myNums = new int[values];

populate array with random integers between 0 and 100

display contents of original array

sortedArray = new SelectionSort(myNums);

sortedArray.display();

Exercise 12 ——————————————————— CourseGrades

Create a CourseGrades application that simulates a grade book for a class with 12 students that each have

5 test scores. The CourseGrades application should use a GradeBook class that has member variables

grades, which is a two-dimensional array or integers, and methods getGrades() for prompting the user

for the test grades for each student, showGrades() that displays the grades for the class, studentAvg()

that has a student number parameter and then returns the average grade for that student, and testAvg()

that has a test number parameter and then returns the average grade for that test.

Exercise 13 —————————————————————PennyPitch

The Penny Pitch game is popular in amusement parks. Pennies are tossed onto a board that has certain

areas marked with different prizes. For example:

The prizes available on this board are puzzle, game, ball, poster, and doll. At the end of the game, if all

of the squares that say BALL are covered by a penny, the player gets the ball. This is also true for the

other prizes. The board is made up of 25 squares (5 x 5). Each prize appears on three randomly chosen

squares so that 15 squares contain prizes.

Chapter 10 Arrays 271

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Create a PennyPitch application that displays a Penny Pitch board (use [ and ] to indicate squares) with

prizes randomly placed and then simulates ten pennies being randomly pitched onto the board. After

the pennies have been pitched, the application should display a message indicating which prizes have

been won, it any.

Exercise 14 ———————————————————————— Life

The Game of Life was devised by mathematician John Conway in 1970. It models a very simple world.

The Life world is a two-dimensional plane of cells. Each cell may be empty or contain a single creature.

Each day, creatures are born or die in each cell according to the number of neighboring creatures on

the previous day. A neighbor is a cell that adjoins the cell either horizontally, vertically, or diagonally.

The rules in pseudocode style are:

if (the cell is alive on the previous day) {

if (the number of neighbors was 2 or 3) {

the cell remains alive

} else {

the cell dies

}

} else if (the cell is not alive on the previous day) {

if (the number of neighbors was exactly 3) {

the cell becomes alive

} else {

the cell remains dead

}

For example, the world displayed as:

0000000000

000XXX0000

0000000000

where X’s indicate living cells, becomes:

0000000000

0000X00000

0000000000

Create a Life application that has a 20 x 20 grid. To initialize the grid, the application should prompt the

user for the coordinates of live cells on the first day. The application should then generate each day’s

world as long as the user wishes to continue or until there are no more live cells.

272 Chapter 10 Arrays

sample

Exercise 15 ————————————————————— Manacala

The game of Mankala is played on a board like that illustrated below:

Players sit on opposite sides with the large bin to a player’s right designated her home bin. On a turn,

a player selects one of the six pits to remove the stones from and then “sows” the stones counterclock-

wise around the board, placing one stone in each pit including the player’s home bin (but excluding

the opponent’s home bin). If the last stone lands in the player’s home bin, the player gets another turn.

If the last stone lands in an empty pit on the player’s side of the board, the player takes all stones in

the corresponding pit on the opponent’s side and places them in the player’s home bin. When a player

cannot play, the game is over and all stones remaining in the opponent’s pits go to the opponent’s home

bin. The winner is the player with the most stones in the player’s home bin at the end of the game.

For example, if the bottom player plays first and chooses the fourth pit to play from, the board

looks like:

Since the last stone landed in the player’s home bin, the player takes nother turn. The player may

choose the first pit this time in order to capture the opponent’s stones:

The player’s turn is now over, and the opponent now has a turn.

Create a Mankala application. The application should use simple characters to illustrate the board,

and letters to identify the pits, similar to that shown below:

3 3 3 3 3 3

0 0

3 3 3 3 3 3

A B C D E F

Chapter 10 Arrays 273

sample

Exercise 16 ————————————————————— Inventory

Create an Inventory application that keeps track of the inventory for a sports store. Each item has a

stock number, with the first item having a stock number of 1000. The second item has a stock number

1001, the third has stock number 1002, and so on. Along with a stock number, each item has an item

name and an amount in stock. New items can be added to the inventory at any time. When added, the

item stock number is generated and displayed to the user. Discontinued items should not be deleted

from the inventory, but rather their item name should be changed to “discontinued” and the amount

in stock should be decreased to 0. The Inventory application should use an ArrayList for maintaining

the invemtory and application output should display a menu of choices, which allow for adding an

item, discontinuing an item, and displaying the amount in stock for an item.

274 Chapter 10 Arrays

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Chapter 11 GUIs and Event-Driven Programming 275

sample

wing is a Java package that provides a set of classes for creating

graphical user interfaces (GUIs). This chapter explains how to use the

basic Swing components to create applications with a GUI. Components

covered in this chapter include frames, panels, labels, buttons, combo

boxes, and text fields.

What is a GUI?

A GUI is a graphical user interface (sometimes pronounced “gooey”). An

application written for the Microsoft Windows or Mac OSX Tiger operating

system typically has a GUI. The GUI below includes a frame, also called

a window, and a label:

Not only does a GUI use components such as frames, buttons, and

text fields to communicate with the user, but GUIs are event-driven. An

event-driven application executes code in response to events. An event is an

interaction from the user, such as a button click. A GUI responds to an

event by executing a method called an event handler. For example, when

the user clicks a button, the application must be able to determine which

button was clicked and then execute the code that relates to that button.

The Swing Package

The Swing API is part of the Java Foundation Classes (JFC) and contains

numerous components for creating GUIs. This chapter focuses on the

javax.swing package. Two classes in this package are JFrame and JLabel.

The JFrame class is used to instantiate a frame. A frame is a window with

a border, title, and buttons for minimizing, maximizing, and closing the

frame. A frame is a top-level container for a GUI, which holds and displays

all the other components of an interface in a content frame. One of the most

common components in a content frame is a label. Labels, created with the

JLabel class, are used to display text that cannot be changed by the user.

Chapter 11

GUIs and Event-Driven

Programming

TIP The applications created

prior to this chapter had a text-

based, or console, interface.

event-driven application

event handler

javax.swing

frame

container, content frame

labels

276 Chapter 11 GUIs and Event-Driven Programming

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The swing package includes the JFrame class with the following

methods:

Class JFrame (javax.swing.JFrame)

Method

setDefaultLookAndFeelDecorated(boolean)

sets the frames created after this class method

is called to have Java Window decorations, such

as borders and a title, when the boolean argu-

ment is true.

setDefaultCloseOperation(class _ constant)

sets the operation that occurs when the user

clicks the Close button. The class _ constant

argument is usually JFrame.EXIT _ ON _ CLOSE.

getContentPane()

returns a Container object corresponding to the

content pane.

setContentPane(Container contentPane)

sets the content pane to contentPa ne. The

Container class is the superclass for the JPanel

class, a class for creating content panes.

pack() sizes the frame so that all of its contents are at

or above their preferred sizes.

setVisible(boolean)

displays the frame when the boolean argument

is true.

A JFrame object uses a content pane to hold GUI components. A JPanel

object is one choice for a simple content pane. The JPanel class includes

the following methods for adding and removing components:

Class JPanel (javax.swing.JPanel)

Method

add(Component GUIcomponent)

adds a GUIcomponent to the content pane. When

added, components are given an index value,

with the first component at index 0.

remove(int index)

removes the component with index value

index.

After adding components to the JPanel object, the content frame is added

to the JFrame object using the JFrame setContentPane() method described

above.

The swing package includes the JLabel class for creating labels that

can be added to a content pane. JLabels have several constructors, two of

which are described, in addition to the setText() method:

JPanel content pane

Chapter 11 GUIs and Event-Driven Programming 277

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Class JLabel (javax.swing.JLabel)

Constructor/Method

JLabel(String str)

creates a JLabel object with text str.

JLabel(String str, align _ constant)

creates a JLabel object with text str and align-

ment align _ constant that can be set to JLabel

class constants LEADING or TRAILING, which are

left and right alignment, respectively.

setText(String str)

sets the text of the JLabel object to str.

The HelloWorldWithGUI1 application creates a frame and a content

pane, adds the content pane to the frame, and then displays the frame:

import javax.swing.*;

public class HelloWorldWithGUI1 {

final static String LABEL _ TEXT = "Hello, world!";

JFrame frame;

JPanel contentPane;

JLabel label;

public HelloWorldWithGUI1(){

/* Create and set up the frame */

frame = new JFrame("HelloWorldWithGUI");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane */

contentPane = new JPanel();

/* Create and add label */

label = new JLabel(LABEL _ TEXT);

contentPane.add(label);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

/**

* Create and show the GUI.

private static void runGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

HelloWorldWithGUI1 greeting = new HelloWorldWithGUI1();

}

public static void main(String[] args) {

/* Methods that create and show a GUI should be

run from an event-dispatching thread */

javax.swing.SwingUtilities.invokeLater(new Runnable() {

public void run() {

runGUI();

}

});

}

TIP The HelloWorldWithGUI1

application output is shown on

the first page of this chapter.

278 Chapter 11 GUIs and Event-Driven Programming

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The implementation of a Swing application is different from previous

applications presented in this text. The controlling class contains a con-

structor and members in addition to the main() method. Therefore, the

controlling class is actually used to instantiate an object, which imple-

ments the GUI.

The statement in the main() method runs the GUI from an event-

dispatching thread. A thread is simply a process that runs sequentially

from start to finish. GUIs should be invoked from an event-dispatching

thread to ensure that each event-handler finishes executing before the

next one executes. Thorough coverage of this topic is beyond the scope

of this text. However, the code shown is needed in every application that

implements a Swing GUI.

Review: Name – part 1 of 2

Create a Name application that displays your name in a label inside a JFrame.

The JButton Class

A button is a commonly used GUI component. A button can be clicked

by the user to communicate with the application. For example, the

HelloWorldWithGUI2 application includes a button that when clicked

either hides or displays text in the label:

The swing package includes the JButton class for creating buttons:

Class JButton (javax.swing.JButton)

Method

JButton(String str)

creates a JButton object displaying the text

str.

setActionCommand(String cmd)

sets the name of the action performed when the

button is clicked to cmd .

getActionCommand()

returns the name of the action that has been

performed by the button.

addActionListener(Object)

adds an object that listens for the user to click

this component.

Unlike a JLabel, a JButton can respond to interaction from the user.

thread

Chapter 11 GUIs and Event-Driven Programming 279

sample

Handling Events

Swing components use listeners to determine if an event has occurred. A

listener is an object that listens for action events. When an event is heard, the

listener responds by executing an event handler named actionPerformed().

The actionPerformed() method has an ActionEvent parameter passed by

the GUI when an event occurs. The ActionEvent object includes an action

command. An action command is a string describing an event, or action.

The HelloWorldWithGUI2 application output is shown in the previous

section. When the Hide button is clicked, the application GUI changes to

display:

The HelloWorldWithGUI2 application code is below. For this GUI, a

JButton is created, the JButton action command is set, and the current

object is the listener for JButton action events. Note the use of the keyword

this for the listener object to indicate the HelloWorldWithGUI2 object

itself:

import javax.swing.*;

import java.awt.event.*

public class HelloWorldWithGUI2 implements ActionListener {

final static String LABEL _ TEXT = "Hello, world!";

JFrame frame;

JPanel contentPane;

JLabel label;

JButton button;

public HelloWorldWithGUI2(){

/* Create and set up the frame */

frame = new JFrame("HelloWorldWithGUI");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane */

contentPane = new JPanel();

/* Create and add label */

label = new JLabel(LABEL _ TEXT);

contentPane.add(label);

/* Create and add button */

button = new JButton("Hide");

button.setActionCommand("Hide");

button.addActionListener(this);

contentPane.add(button);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

listener

action command

this

280 Chapter 11 GUIs and Event-Driven Programming

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/**

* Handle button click action event

* pre: Action event is Hide or Show

* post: Clicked button has different text, and label

* displays message depending on when the button was clicked.

public void actionPerformed(ActionEvent event) {

String eventName = event.getActionCommand();

if (eventName.equals("Hide")) {

label.setText(" ");

button.setText("Show");

button.setActionCommand("Show");

} else {

label.setText(LABEL _ TEXT);

button.setText("Hide");

button.setActionCommand("Hide");

}

/**

* Create and show the GUI.

private static void runGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

HelloWorldWithGUI2 greeting = new HelloWorldWithGUI2();

}

public static void main(String[] args) {

/* Methods that create and show a GUI should be

run from an event-dispatching thread */

javax.swing.SwingUtilities.invokeLater(new Runnable() {

public void run() {

runGUI();

}

});

}

A class that uses a listener must implement an ActionListener. This is

done by adding implements ActionListener to the class declaration and then

defining an actionPerformed() method, which is the only method in the

ActionListener interface. An import java.awt.event statement is required

to import the package containing the ActionListener interface.

The GUI is implemented in the constructor. The segment of code that

creates and adds the button does four things. First, a button that displays

Hide is created. Second, because the user will see a Hide button the action

command associated with this button should be “Hide”. Third, a listener

is needed to determine when the user clicks the button. The listener is set

to the HelloWorldWithGUI2 object itself (this). Fourth, the button is added

to the content pane.

The actionPerformed() method is passed an ActionEvent argument

by the GUI when the button is clicked. ActionEvent objects have a

getActionCommand() method. This method returns the string assigned

as the object’s action command. For the Show/Hide button, the action

command, as well as the button text, is changed each time the button is

clicked.

TIP awt stands for Abstract

Windows Toolkit.

Chapter 11 GUIs and Event-Driven Programming 281

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Review: Name – part 2 of 2

Modify the Name application to display or hide your name depending on the button clicked by the user,

similar to the HelloWorldWithGUI2 application.

Review: NumClicks

Create a NumClicks application that contains a button displaying how many times the user has clicked that

button. The application interface should look similar to the following after the user has clicked the button

12 times:

For this application it is not necessary to set the action command. A call to the getActionCommand() method

in the actionPerformed() method is also not needed.

Controlling Layout

Layout refers to the arrangement of components. In a Swing GUI, the

layout of a content pane can be controlled by adding borders, using a layout

manager, and setting alignments.

A border can be added to most components, including the content pane.

An invisible, or empty, border can be used to add “padding” around a

component to give it distance from other components. Adding an empty

border to the content pane adds space between the components and the

edges of the frame. For example, the content pane in the GUI on the left

has no border, but the content pane on the right has an empty border of

20 pixels on the top, left, bottom, and right:

An empty border in the content pane on the right provides

padding between the components and the frame

A layout manager determines the order of components on a content pane.

There are many layout managers to choose from, including FlowLayout,

BoxLayout, and GridLayout. The FlowLayout manager places components

one next to the other in a row. When a row becomes too long, a new

row is started. The FlowLayout manager is the default manager. The

HelloWorldWithGUI applications use this manager.

layout manager

layout

TIP Pixel stands for picture

element and the number of

pixels in a surface depends on

the screen resolution.

borders

FlowLayout manager

282 Chapter 11 GUIs and Event-Driven Programming

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The BoxLayout manager places components one after the other in a col-

umn, with one component per line. For example, the GUI below uses the

BoxLayout manager:

The BoxLayout manager places components one after the

other in a column

The GridLayout manager places components into a grid of rows and col-

umns. The intersection of a row and column is called a cell. There is one

component per cell in a GridLayout. The GUI below uses a GridLayout.

An additional button was added to illustrate the grid:

The GridLayout manager places components

into a grid of cells

Another factor that affects layout is alignment. Alignment refers to the

placement of a component within a layout. For example, both GUIs below

use a BoxLayout, have an empty border of 20, 20, 20, and 20 in the content

pane, and a 20, 50, 20, 50 empty border around the label. The GUI on the

left specifies no aligment for the components, and the GUI on the right

center aligns the label and the button:

Alignment affects the placement of components

within a layout

The HelloWorldWithGUI2 application modified to use a layout manager,

borders, and alignment:

GridLayout manager

BoxLayout manager

alignment

TIP The BoxLayout manager

also includes methods for add-

ing “glue” and “rigid areas” to

a layout to control placement

of components.

Chapter 11 GUIs and Event-Driven Programming 283

sample

import javax.swing.*;

import java.awt.event.*;

public class HelloWorldWithGUI2 implements ActionListener {

final static String LABEL _ TEXT = "Hello, world!";

JFrame frame;

JPanel contentPane;

JLabel label;

JButton button;

public HelloWorldWithGUI2(){

/* Create and set up the frame */

frame = new JFrame("HelloWorldWithGUI");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a BoxLayout and

empty borders */

contentPane = new JPanel();

contentPane.setLayout(new BoxLayout(contentPane,

BoxLayout.PAGE _ AXIS));

contentPane.setBorder(BorderFactory.createEmptyBorder(20,20,20,20));

/* Create and add label that is centered and

has empty borders */

label = new JLabel(LABEL _ TEXT);

label.setAlignmentX(JLabel.CENTER _ ALIGNMENT);

label.setBorder(BorderFactory.createEmptyBorder(20, 50, 20, 50));

contentPane.add(label);

/* Create and add button that is centered */

button = new JButton("Hide");

button.setAlignmentX(JButton.CENTER _ ALIGNMENT);

button.setActionCommand("Hide");

button.addActionListener(this);

contentPane.add(button);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

…rest of HelloWorldWithGUI2 code

The JPanel setLayout() method is used to specify a layout for the content

pane. A BoxLayout object requires arguments for the content pane and the

arrangement. To arrange components in a vertical line, the class constant

PAGE _ AXIS is specified.

The JPanel setBorder() method is used to specify borders for the con-

tent pane. The BorderFactory class has many different kinds of borders

to choose from. For invisible, or empty borders, the createEmptyBorder()

method is used. The arguments specify the width of the top, left, bottom,

and right of the border.

The JLabel and JButton setAlignmentX() methods are used to specify

the vertical alignment of the components within the layout. Both classes

include several alignment constants, including CENTER _ ALIGNMENT.

TIP Experiment with the

numerous types of borders.

setLayout() method

setBorder() method

setAlignment() method

284 Chapter 11 GUIs and Event-Driven Programming

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The modified HelloWorldWithGUI2 application produces a GUI that

looks similar to:

For GUIs with components that should be side by side in rows, the

GridLayout manager may be a better choice. The GridLayout manager is

specified in a statement similar to:

contentPane.setLayout(new GridLayout(0, 2, 10, 5))

The GridLayout object requires arguments for specifying the number

of rows and columns and the space between columns and rows. If 0 is

specified for either the rows or columns, the class creates an object with

as many rows or columns as needed. However, only one argument can be

0. In the statement above, the GridLayout object will have as many rows

as needed and 2 columns. There will be 10 pixels between columns and 5

pixels between rows. The GridLayout class is part of the java.awt package.

Code using this manager requires an import java.awt.* statement.

Review: Sunflower

Create a Sunflower application that displays the Latin name for the sunflower when Latin is clicked and the

English name when English is clicked. The application GUI should use a BoxLayout manager and look similar

to the following after Latin has been clicked:

Review: Riddle

Create a Riddle application that displays a riddle and then solves it when Answer is clicked. The application

GUI should use a GridLayout manager and look similar to the following after Answer has been clicked:

GridLayout manager

java.awt

TIP The GridLayout manager

places components in rows

from left to right in the order

that they are added to the con-

tent pane.

Chapter 11 GUIs and Event-Driven Programming 285

sample

Getting Input from the User

A text field allows a user to enter information at run time. Text fields

are usually placed next to a label to prompt the user for the type of data

expected in the text field. For example, the SemesterAvg application

prompts the user to enter three test grades and then displays the average

of the grades when Average is clicked:

The swing package includes the JTextField class with the following

constructors and methods:

Class JTextField (javax.swing.JTextField)

Constructor/Methods

JTextField(int col)

creates a JTextField object with width col.

JTextField(String text, int col)

creates a JTextField object displaying default

text text in a field with width col.

getText() returns a String containing the text in the

JTextField.

addActionListener(Object)

adds an object that listens for the user to press

the Enter key in this component.

The information typed into a text field is a string, even when numeric

data is entered. Conversly, the setText() method of a JLabel expects a string

even when the data is numeric. Class methods in the Double and Integer

classes can be used to convert data between numeric and String types:

Class Double (java.lang.Double)

Method

parseDouble(String text)

returns the double value in the String text.

toString(double num)

returns the String representation of num.

Class Integer (java.lang.Integer)

Method

parseInteger(String text)

returns the int value in the String text.

toString(int num)

returns the String representation of num.

converting between text and

numeric data

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The parseDouble() and parseInteger() methods are used to convert

String data to numeric. The SemesterAvg application, the GIUI shown on

the previous page, uses parseDouble():

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class SemesterAvg implements ActionListener {

JFrame frame;

JPanel contentPane;

JLabel prompt1, prompt2, prompt3, average;

JTextField grade1, grade2, grade3;

JButton avgButton;

public SemesterAvg(){

/* Create and set up the frame */

frame = new JFrame("Semester Average");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a GridLayout */

contentPane = new JPanel();

contentPane.setLayout(new GridLayout(0, 2, 10, 5));

contentPane.setBorder(BorderFactory.createEmptyBorder

(10, 10, 10, 10));

/* Create and add a prompt and then a text field */

prompt1 = new JLabel("Enter the first grade: ");

contentPane.add(prompt1);

grade1 = new JTextField(10);

contentPane.add(grade1);

/* Create and add a second prompt and

then a text field */

prompt2 = new JLabel("Enter the second grade: ");

contentPane.add(prompt2);

grade2 = new JTextField(10);

contentPane.add(grade2);

/* Create and add a third prompt and then a text field */

prompt3 = new JLabel("Enter the third grade: ");

contentPane.add(prompt3);

grade3 = new JTextField(10);

contentPane.add(grade3);

/* Create and add button that will display the

average of the grades */

avgButton = new JButton("Average");

avgButton.setActionCommand("Average");

avgButton.addActionListener(this);

contentPane.add(avgButton);

/* Create and add a label that will display the

average */

average = new JLabel(" ");

contentPane.add(average);

/* Add content pane to frame */

frame.setContentPane(contentPane);

Chapter 11 GUIs and Event-Driven Programming 287

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/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

/**

* Handle button click action event

* pre: none

* post: The average of the grades entered has been

* calculated and displayed.

public void actionPerformed(ActionEvent event) {

String eventName = event.getActionCommand();

if (eventName.equals("Average")) {

double avgGrade;

String g1 = grade1.getText();

String g2 = grade2.getText();

String g3 = grade3.getText();

avgGrade = (Double.parseDouble(g1) + Double.parseDouble(g2)

+ Double.parseDouble(g3))/3;

average.setText(Double.toString(avgGrade));

}

/**

* Create and show the GUI.

private static void runGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

SemesterAvg myGrades = new SemesterAvg();

}

…main() method of SemesterAvg code

In the actionPerformed() method, the strings are read from the text

fields. To calculate the average grade, each string is parsed for a double

value (with parseDouble()). The avgGrade value was then converted to a

String with the Double class method toString().

Review: DivisibleBy3

Create a DivisibleBy3 application that prompts the user for an integer and then displays a message when

Check is clicked indicating whether the number is divisible by 3. The application interface should look similar

to the following after the user has typed a number and clicked Check:

288 Chapter 11 GUIs and Event-Driven Programming

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JComboBox event

Combo Boxes

A combo box offers a user a way to select from a limited set of choices.

Combo boxes can offer choices without taking up much room on the inter-

face. The user simply clicks the combo box arrow to display additional

choices. The LatinPlantNames application allows the user to select a plant

name from a combo box:

The swing package includes the JComboBox class for creating combo

boxes:

Class JComboBox (javax.swing.JComboBox)

Methods

JComboBox(Object[] items)

creates a JComboBox object that contains the

items from the items array, which must be an

array of objects.

setSelectedIndex(int index)

makes the item at index index the selected

item.

getSelectedItem()

returns the String corresponding to the selected

JComboBox item.

setEditable(boolean)

allows text to be typed in the combo box when

true is the boolean argument.

addActionListener(Object)

adds an object that listens for the user to select

an item from this component’s list.

Handling an event from a JComboBox requires two lines of code that

are similar to:

JComboBox comboBox = (JComboBox)event.getSource();

String itemName = (String)comboBox.getSelectedItem();

The first statement determines the source of the action event and then the

second statement determines which item has been selected.

Chapter 11 GUIs and Event-Driven Programming 289

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The LatinPlantNames application code includes a JComboBox object:

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class LatinPlantNames implements ActionListener {

JFrame frame;

JPanel contentPane;

JComboBox plantNames;

JLabel plantListPrompt, latinName;

public LatinPlantNames(){

/* Create and set up the frame */

frame = new JFrame("LatinPlantNames");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a BoxLayout and

empty borders */

contentPane = new JPanel();

contentPane.setLayout(new BoxLayout(contentPane,

BoxLayout.PAGE _ AXIS));

contentPane.setBorder(BorderFactory.createEmptyBorder

(10, 10, 10, 10));

/* Create a combo box and a descriptive label */

plantListPrompt = new JLabel("Select a plant name: ");

plantListPrompt.setAlignmentX(JLabel.LEFT _ ALIGNMENT);

contentPane.add(plantListPrompt);

String[] names = {"basil", "lavender", "parsley",

"peppermint", "saffron", "sage"};

plantNames = new JComboBox(names);

plantNames.setAlignmentX(JComboBox.LEFT _ ALIGNMENT);

plantNames.setSelectedIndex(0);

plantNames.addActionListener(this);

contentPane.add(plantNames);

/* Create and add a label that will display the

Latin names */

latinName = new JLabel("Ocimum");

latinName.setBorder(BorderFactory.createEmptyBorder

(20, 0, 0, 0));

contentPane.add(latinName);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

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/**

* Handle a selection from the combo box

* pre: none

* post: The Latin name for the selected plant

* has been displayed.

public void actionPerformed(ActionEvent event) {

JComboBox comboBox = (JComboBox)event.getSource();

String plantName = (String)comboBox.getSelectedItem();

if (plantName == "basil") {

latinName.setText("Ocimum");

} else if (plantName == "lavender") {

latinName.setText("Lavandula spica");

} else if (plantName == "parsley") {

latinName.setText("Apium");

} else if (plantName == "perppermint") {

latinName.setText("Mentha piperita");

} else if (plantName == "saffron") {

latinName.setText("Crocus");

} else if (plantName == "sage") {

latinName.setText("Salvia");

}

…runGUI() and main() method of LatinPlantNames code

The LatinPlantNames application displays the following output after

sage has been selected:

Review: MetricConversion

Create a MetricConversion application that allows the user to select a type of conversion from a combo box

and then the corresponding formula is displayed in a label. To convert from the length measurement inches

to centimeters, the formula is 1 inch = 2.54 centimeters. The formula 1 foot = 0.3048 meters converts the dis-

tance measurement feet to meters. The volume measurement gallon is converted to liters with the fomula

1 gallon = 4.5461 liters. The formula 1 pound = 0.4536 kilograms converts the mass measurement pound to

kilograms. The application interface should look similar to the following after the user has selected feet to

meters:

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Changing Colors

Swing components have methods for changing their colors. For example,

the content pane can be green, buttons can be magenta, combo boxes can

display text in pink. When making color choices, keep the end user in

mind because colors can give an application a fun and exciting look or

completely turn users away.

The java.awt package includes the Color class with numerous color

constant members. The following methods, in the Swing component

classes, can be used to change the background and foreground colors of

the components:

setBackground(Color.constant)

sets the background color of a component to

constant from the Color class.

setForeground(Color.constant)

sets the foreground color of a component to

constant from the Color class.

How the color change affects the component varies. For a JLabel, the

foreground color refers to the color of the text. For a JComboBox, the fore-

ground color refers to the color of the text in the list.

The ColorDemo application demonstrates the color possibilities for

components. The application GUI and the code, except for the runGUI()

and main() methods, follow:

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class ColorDemo implements ActionListener {

JFrame frame;

JPanel contentPane;

JTextField name;

JButton displayMessage;

JLabel textFieldPrompt, hello;

public ColorDemo(){

/* Create and set up the frame */

frame = new JFrame("ColorDemo");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a BoxLayout

and empty borders */

contentPane = new JPanel();

contentPane.setBorder(BorderFactory.createEmptyBorder

(10, 10, 10, 10));

contentPane.setBackground(Color.white);

contentPane.setLayout(new GridLayout(0, 2, 5, 10));

Color class

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/* Create a text field and a descriptive label */

textFieldPrompt = new JLabel("Type your name: ");

textFieldPrompt.setForeground(Color.red);

contentPane.add(textFieldPrompt);

name = new JTextField(10);

name.setBackground(Color.pink);

name.setForeground(Color.darkGray);

contentPane.add(name);

/* Create a Display Message button */

displayMessage = new JButton("Display Message");

displayMessage.setBackground(Color.yellow);

displayMessage.setForeground(Color.blue);

displayMessage.addActionListener(this);

contentPane.add(displayMessage);

/* Create a label that will display a message */

hello = new JLabel(" ");

hello.setForeground(Color.green);

contentPane.add(hello);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

/**

* Handle a the button click

* pre: none

* post: A message has been displayed.

public void actionPerformed(ActionEvent event) {

String text = name.getText();

hello.setText("Hello " + text);

}

…runGUI() and main() method of ColorDemo code

Adding Images

Images can make an application more informative, easier to to use, and

fun. Labels and buttons are often used to display an image, but many

Swing components support images. Images that are GIF and JPG format

work best. Unless a different path is specified in the application code, the

image files must be in the same location as the compiled code.

The JLabel class includes a constructor and a method for displaying

images in a label:

Class JLabel (javax.swing.JLabel)

Constructor/Method

JLabel(ImageIcon pic)

creates a JLabel object containing pic.

setIcon(ImageIcon pic)

sets the JLabel to contain pic.

GIF, JPG

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The JButton class includes a constructor and a method for displaying

images in a button:

Class JButton (javax.swing.JButton)

Constructor/Method

JButton(String str, ImageIcon pic)

creates a JButton object containing the text str

and the image pic.

JButton(ImageIcon pic)

creates a JButton object containing the image

pic.

setIcon(ImageIcon pic)

sets the JButton to contain pic.

The Roll application displays a die face. The user can click Roll Die to

“roll the die” and display the outcome of the roll. The application GUI and

the code, except for the runGUI() and main() methods, follow:

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

import java.util.Random;

public class Roll implements ActionListener {

JFrame frame;

JPanel contentPane;

JButton rollDie;

JLabel dieFace;

public Roll(){

/* Create and set up the frame */

frame = new JFrame("Roll");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a BoxLayout and

empty borders */

contentPane = new JPanel();

contentPane.setBorder(BorderFactory.createEmptyBorder

(10, 10, 10, 10));

contentPane.setBackground(Color.white);

contentPane.setLayout(new BoxLayout(contentPane,

BoxLayout.PAGE _ AXIS));

/* Create a label that shows a die face */

dieFace = new JLabel(new ImageIcon("die3.gif"));

dieFace.setAlignmentX(JLabel.CENTER _ ALIGNMENT);

dieFace.setBorder(BorderFactory.createEmptyBorder

(0, 0, 10, 0));

contentPane.add(dieFace);

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/* Create a Roll Die button */

rollDie = new JButton("Roll Die");

rollDie.setAlignmentX(JButton.CENTER _ ALIGNMENT);

rollDie.addActionListener(this);

contentPane.add(rollDie);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

/**

* Handle a button click

* pre: none

* post: A die has been rolled. Matching image shown.

public void actionPerformed(ActionEvent event) {

Random rand = new Random();

int newRoll;

newRoll = rand.nextInt(6) + 1;

if (newRoll == 1) {

dieFace.setIcon(new ImageIcon("die1.gif"));

} else if (newRoll == 2) {

dieFace.setIcon(new ImageIcon("die2.gif"));

} else if (newRoll == 3) {

dieFace.setIcon(new ImageIcon("die3.gif"));

} else if (newRoll == 4) {

dieFace.setIcon(new ImageIcon("die4.gif"));

} else if (newRoll == 5) {

dieFace.setIcon(new ImageIcon("die5.gif"));

} else if (newRoll== 6) {

dieFace.setIcon(new ImageIcon("die6.gif"));

}

An image must be an object of the ImageIcon class for use in a Swing

GUI. The ImageIcon class, from the java.swing package, has a constructor

that accepts a file name as an argument and then converts that file to an

ImageIcon object.

Review: Roll

Modify the Roll application to roll two dice. Include an image for each die. Change the colors of the com-

ponents to be more exciting, while still allowing the user to easily read the text on the button and to see the

die images. The die images are name die1.tif, die2.tif, die3.tif, die5.tif, and die6.tif and are supplied as data

files for this text.

Chapter 11 GUIs and Event-Driven Programming 295

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Using Nested Classes to Handle Events

A GUI can quickly become complex, as a combination of buttons, text

fields, and other components that must handle events are added. When a

variety of components are on a single interface, separate actionPerformed()

methods should handle their events.

Up to this point, an instance of the controlling class (this) implemented

an actionPerformed() method. This single method was used to handle

events for every component on the GUI. This was sufficient for a simple

GUI. However, a GUI with more than one type of component responding

to an event should have multiple listeners. One way to implement multiple

listeners in a single application is to create each listener from a nested

class.

A nested class is a class within a class. A nested class is a member of the

class it is within. As a class member, it has access to all the other members

of the class, including private member variables and methods. A class

that contains a class member is called an outer class. The Semester Stats

application uses two nested classes to respond to events:

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class SemesterStats {

JFrame frame;

JPanel contentPane;

JLabel prompt1, prompt2, prompt3, stat;

JTextField grade1, grade2, grade3;

JButton avgButton, minButton, maxButton;

public SemesterStats(){

/* Create and set up the frame */

frame = new JFrame("Semester Stats");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create content pane with a GridLayout and empty borders */

contentPane = new JPanel();

contentPane.setLayout(new GridLayout(0, 2, 10, 5));

contentPane.setBorder(BorderFactory.createEmptyBorder

(10, 10, 10, 10));

/* Create and add a prompt and then a text field */

prompt1 = new JLabel("Enter the first grade: ");

contentPane.add(prompt1);

grade1 = new JTextField(10);

contentPane.add(grade1);

/* Create and add a second prompt and then a text field */

prompt2 = new JLabel("Enter the second grade: ");

contentPane.add(prompt2);

grade2 = new JTextField(10);

contentPane.add(grade2);

/* Create and add a third prompt and then a text field */

prompt3 = new JLabel("Enter the third grade: ");

contentPane.add(prompt3);

grade3 = new JTextField(10);

contentPane.add(grade3);

TIP A nested class is also

called an inner class.

outer class

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/* Create and add button that will display the average grade */

avgButton = new JButton("Average");

avgButton.addActionListener(new AvgListener());

contentPane.add(avgButton);

/* Create and add button that will display the min grade */

minButton = new JButton("Min");

minButton.setActionCommand("Min");

minButton.addActionListener(new MinMaxListener());

contentPane.add(minButton);

/* Create and add button that will display the max grade */

maxButton = new JButton("Max");

maxButton.setActionCommand("Max");

maxButton.addActionListener(new MinMaxListener());

contentPane.add(maxButton);

/* Create and add a label that will display stats */

stat = new JLabel(" ");

stat.setBorder(BorderFactory.createEmptyBorder(10, 0, 10, 0));

contentPane.add(stat);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

class AvgListener implements ActionListener {

/**

* Handle Average button click event

* pre: none

* post: The grade average has been calculated and displayed.

public void actionPerformed(ActionEvent event) {

double avgGrade;

String g1 = grade1.getText();

String g2 = grade2.getText();

String g3 = grade3.getText();

avgGrade = (Double.parseDouble(g1) + Double.parseDouble(g2) +

Double.parseDouble(g3))/3;

stat.setText(Double.toString(avgGrade));

}

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class MinMaxListener implements ActionListener {

/**

* Handles the Min and Max button click events

* pre: none

* post: The minimum or maximum grade has been

* determined and displayed.

public void actionPerformed(ActionEvent event) {

String eventName = event.getActionCommand();

double minGrade = 999;

double maxGrade = 0;

double[] grades = new double[3];

grades[0] = Double.parseDouble(grade1.getText());

grades[1] = Double.parseDouble(grade2.getText());

grades[2] = Double.parseDouble(grade3.getText());

if (eventName.equals("Min")) {

for (int i = 0; i < 3; i++) {

if (minGrade > grades[i]) {

minGrade = grades[i];

}

stat.setText(Double.toString(minGrade));

} else if (eventName.equals("Max")) {

for (int i = 0; i < 3; i++) {

if (maxGrade < grades[i]) {

maxGrade = grades[i];

}

stat.setText(Double.toString(maxGrade));

}

/**

* Create and show the GUI.

private static void runGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

SemesterStats myGrades = new SemesterStats();

}

public static void main(String[] args) {

/* Methods that create and show a GUI should be

run from an event-dispatching thread */

javax.swing.SwingUtilities.invokeLater(new Runnable() {

public void run() {

runGUI();

}

});

}

One class (AvgListener) was used to implement a listener for the Average

button and a second class (MinMaxListener) implements a listener for

the Min and Max buttons. These buttons were combined into one listener

because their algorithms closely match.

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The SemesterStats application displays output similar to:

Chapter 11 Case Study

In this case study, a Swing GUI will be created for an application that

plays a carnival game called Break-A-Plate. The Break-A-Plate game allows

a player to try to break all three plates. If all three plates are broken, a first

prize is awarded, otherwise, a consolation prize is awarded.

BreakAPlate Specification

The BreakAPlate application displays three unbroken plates at the start.

Clicking Play plays the game, displays broken plates, and displays the prize

won. If all three plates are broken, a tiger plush first prize is awarded. If

less than three plates are broken, a sticker consolation prize is awarded.

At the end of a game the Play button changes to Play Again. Clicking Play

Again displays a set of unbroken plates and the button changes back to Play

allowing the user to play repeatedly. The application ends when the user

closes the window.

The BreakAPlate game uses random numbers to determine if a player

has broken all three plates. When three 1s are generated by the random

number generator then the application displays three broken plates. If zero,

one, or two ones are generated, then the application displays two broken

plates indicating a loss.

The BreakAPlate interface should be a GUI that includes a label for dis-

playing the image of the plates, a button for allowing the user to play or

play again, and a label for displaying the the prize won. The BreakAPlate

GUI should look similar to the following before a game is played, after

a losing game has been played, and after a winning game has been

played:

Chapter 11 GUIs and Event-Driven Programming 299

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















The BreakAPlate algorithm:

1. When a game is played, generate three random numbers between

0 and 1.

2. If three ones are generated, display three broken plates and the

names of the first prize. Otherwise, display two broken plates and

the name of the consolation prize.

BreakAPlate Code Design

The BreakAPlate application simulates a game booth at a carnival. The

game can therefore be modeled with a GameBooth object. The GameBooth

class was created in Chapter 8 and contains the following methods:

Class GameBooth (Lawrenceville Press)

Constructor/Methods

GameBooth(int cost, String p1, String p2)

creates a GameBooth object that charges cost

amount to play, awards a first prize p1, and a

consolation prize p2. If there is no charge for

the game, or the charge is not a consideration,

then 0 should be the argument for cost.

start() simulates a a game that allows the player three

plays. If the player succeeds all three times,

then the name of the first prize is retuned.

Otherwise, the name of the consolation prize

is returned.

getCost() returns the cost of the game.

TIP Refer to Chapter 8 for the

GameBooth code.

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The cost of the game is not a factor in this application, so 0 will be the

argument for the cost parameter in the constructor, and the getCost()

method will not be needed.

Based on the algorithm and the GameBooth class, the BreakAPlate

actionPerformed() method pseudocode looks similar to:

String eventName = event.getActionCommand();

String prize;

if (Play) {

prize = breakAPlate.start();

if (prize is tiger plush) {

display all broken plates;

} else if (prize is sticker)) {

display two broken plates

}

display prize won

change button to Play Again

} else if (Play Again) {

display unbroken plates

clear prize won text

change button to Play

BreakAPlate Implementation

The BreakAPlate implementation involves creating the BreakAPlate java

file and adding the GameBooth java file to the project.

The BreakAPlate application is implemented below:

/**

* BreakAPlate.

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class BreakAPlate implements ActionListener {

static final String FIRST _ PRIZE = "tiger plush";

static final String CONSOLATION _ PRIZE = "sticker";

JFrame frame;

JPanel contentPane;

JButton play;

JLabel plates, prizeWon;

GameBooth breakAPlate;

public BreakAPlate(){

/* initialize game booth and player */

breakAPlate = new GameBooth(0, FIRST _ PRIZE, CONSOLATION _ PRIZE);

/* Create and set up the frame */

frame = new JFrame("BreakAPlate");

frame.setDefaultCloseOperation(JFrame.EXIT _ ON _ CLOSE);

/* Create a content pane with a BoxLayout and empty borders */

contentPane = new JPanel();

contentPane.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

contentPane.setBackground(Color.white);

contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.PAGE _ AXIS));

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/* Create a label that shows the start of the game */

plates = new JLabel(new ImageIcon("plates.gif"));

plates.setAlignmentX(JLabel.CENTER _ ALIGNMENT);

plates.setBorder(BorderFactory.createEmptyBorder(10, 10, 20, 10));

contentPane.add(plates);

/* Create a Play button */

play = new JButton("Play");

play.setActionCommand("Play");

play.setAlignmentX(JButton.CENTER _ ALIGNMENT);

play.addActionListener(this);

contentPane.add(play);

/* Create a label that will show prizes won */

prizeWon = new JLabel(" ");

prizeWon.setAlignmentX(JLabel.CENTER _ ALIGNMENT);

prizeWon.setBorder(BorderFactory.createEmptyBorder(20, 0, 0, 0));

contentPane.add(prizeWon);

/* Add content pane to frame */

frame.setContentPane(contentPane);

/* Size and then display the frame. */

frame.pack();

frame.setVisible(true);

}

/**

* Handle the button click

* pre: none

* post: The appropriate image and message are displayed.

public void actionPerformed(ActionEvent event) {

String eventName = event.getActionCommand();

String prize;

if (eventName == "Play") {

prize = breakAPlate.start();

if (prize.equals(FIRST _ PRIZE)) {

plates.setIcon(new ImageIcon("plates _ all _ broken.gif"));

} else if (prize.equals(CONSOLATION _ PRIZE)) {

plates.setIcon(new ImageIcon("plates _ two _ broken.gif"));

}

prizeWon.setText("You win: " + prize);

play.setText("Play Again");

play.setActionCommand("Play Again");

} else if (eventName == "Play Again") {

plates.setIcon(new ImageIcon("plates.gif"));

prizeWon.setText(" ");

play.setText("Play");

play.setActionCommand("Play");

}

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/**

* Create and show the GUI.

private static void runGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

BreakAPlate carnivalGame = new BreakAPlate();

}

public static void main(String[] args) {

/* Methods that create and show a GUI should be

run from an event-dispatching thread */

javax.swing.SwingUtilities.invokeLater(new Runnable() {

public void run() {

runGUI();

}

});

}

Running the BreakAPlate application displays a GUI similar to:

When Play is clicked, the user either wins or loses. The output below

shows a losing game:

Chapter 11 GUIs and Event-Driven Programming 303

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The application GUI below shows a winning game:

BreakAPlate Testing and Debugging

The application should be tested by playing several games, making sure

that the correct prize is named and that the buttons and images change

appropriately.

Review: BreakAPlate

Modify the BreakAPlate application to display a picture of the prize won rather than text naming the prize.

The tiger_plush.gif, sticker.gif, and placeholder.gif are supplied as data files for this text. The placeholder.gif

file is a white square that is the same size as the tiger_plush and sticker images. The placeholder.gif file

should be displayed in the label at the start of each game. The modified BreakAPlate interface should look

similar to the following after the user has played a winning game:

304 Chapter 11 GUIs and Event-Driven Programming

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Chapter Summary

This chapter introduced graphical user interfaces that use the Swing

API. The Java swing package contains many component classes, including

JFrames, JPanels, JLabels, JButtons, JComboBoxes, and JTextFields.

Applications with a GUI are event-driven. The GUI must be run from

an event-dispatching thread. A GUI application responds to interactions

from the user called events. An event executes a method called an event

handler. A Swing event handler is also called an action event handler.

A frame is a container for content panels. A commonly used content

panel is the JPanel component. A JPanel can contain other components

such as labels and buttons. A label is a component that does not receive

events. A button is a commonly used component for accepting input from

the user.

Only components with a listener object can execute an event handler.

A listener executes the actionPerformed() event handler, passing it the

an ActionEvent object that contains the action command describing the

event.

The layout of components in a JPanel can be controlled with layout man-

ager and the use of borders and alignment. The FlowLayout, BoxLayout,

and GridLayout are the three managers covered in this chapter. The place-

ment of components within a layout can be controlled further with empty

borders for padding and using alignment.

The text field component allows a user to type information into the

interface. The information typed into a text field is a string. The Integer

and Double classes include class methods for converting information to

numeric data. The label component requires a string when setting the

text. The Integer and Double classes also provide the toString() method

for converting numeric data to a String.

Combo boxes allow the user to select from a limited set of choices. A

combo box does not take up much space and displays a list of choices when

its arrow button is clicked.

Most of the components include methods for setting the background

and foreground colors. Color can make an application easier to use and

more interesting, but should be selected with the user in mind.

GIF and JPG images can be included in an application GUI. A label or

a button is commonly used to display an image.

Nested classes are used to implement multiple event handlers. Nested

classes, like any other member of a class, have access to other members of

the class, including private variables and method members. A class that

contain a class member is called an outer class.

Chapter 11 GUIs and Event-Driven Programming 305

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Vocabulary

Action command A string describing an event.

Alignment The placement of components within

a layout.

BoxLayout manager A layout manager that places

components one after the other in a column.

Button A GUI component that the user can click.

Combo box A GUI component that offers a user a

way to select from a limited set of choices.

Container A component that holds and displays

all the other components of a GUI.

Content frame A top-level container.

Event A user interaction with an application’s

GUI.

Event-driven application An application that

responds to events.

Event handler A method that executes in response

to an event.

FlowLayout manager A layout manager that places

components one next to the other in a row.

Frame A GUI window that contains a border, title,

and maximize, minimize, and close buttons.

GridLayout manager A layout manager that places

components in a grid of rows and columns.

Label A GUI component that displays text or an

image and does not interact with the user.

Layout The arrangement of components.

Layout manager Used to specify the order of com-

ponents on a content pane.

Listener An object that listens for action events.

Nested class A class that is a member of another

class. A class within a class.

Outer class A class that contains a class member.

Text field A GUI component that allows a user to

enter information at run time.

Thread A process that runs sequentially from start

to finish.

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Java

ActionListener The java.awt.event interface that

contains the actionListener() method.

actionPerformed() A method that is implemented

to respond to events. This method is the only method

in the ActionListener interface.

BorderFactory The java.lang class with class meth-

ods for creating a border object.

BoxLayout A javax.swing class for setting the layout

of a content pane.

Color The java.awt class that contains constants

for changing component colors.

Double A java.lang class for converting numbers

between numeric and text data.

GridLayout A java.awt class for setting the layout

of a content pane.

ImageIcon A java.swing class for converting

an image, such as a GIF or JPG, to an ImageIcon

object.

Integer A java.lang class for converting numbers

between numeric and text data.

java.awt The package containing the GridLayout

class and Color class constants.

java.awt.event The package containing the

ActionListener interface.

java.swing The package containing the Swing

API classes.

JButton A java.swing class for creating a button in

a GUI. The class includes methods for adding text

or images to the label.

JComboBox A java.swing class for creating a combo

box in a GUI.

JFrame A java.swing class for creating a window,

also called a frame, in a GUI.

JLabel The java.swing class for creating a label in

a GUI. The class includes methods for adding text

or images to the label.

JPanel The java.swing class for creating a content

panel for a frame. The class includes methods for

adding and removing components.

JTextField The java.swing class for creating a text

field.

FlowLayout A javax.swing class for setting the

layout of a content pane.

Swing API A part of the Java Foundation Classes

that contains numerous components for creating

GUIs.

this The keyword for indicating an object itself.

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Critical Thinking

1. Explain the difference between an event-driven

application and a console-based application.

2. Explain how code is executed in an event-driven

application.

3. Can components be added directly to a frame?

Explain.

4. Can a label respond to events? Explain.

5. Why do you think a GUI needs to be run from

an event-dispatching thread?

6. What is the difference between a label and a

button?

7. a) What does this indicate when used as the

argument for the the addActionListener()

method?

b) What must the object listening for an event

contain?

8. List three ways to control the layout of a content

pane.

9. What type of borders are used to add padding

around components?

10. List three layout managers and explain how

each arranges the components on a content

pane.

11. Which class is used to return an object for the

setBorder() method?

12. Are borders for padding necessary when the

GridLayout manager is used? Explain.

13. What must first be done with numeric data

typed in a text field before it can be used in a

calculation?

14. What is the value of num1 in the last statement

below?

double num1;

Double num2 = new Double(3);

String num3 = "5";

num1 = num2.doubleValue() +

Double.valueOf(num3).doubleValue();

15. An application prompts a user to select a name

from a list of six names. Which is a better

component choice: a text field or a combo box?

Explain.

16. Would white text on a pink background be a

good color combination for a GUI? Why or why

not?

17. What image types are supported in a Swing

GUI?

18. Which components are often used to display an

image?

19. What must an image be converted to in order

to be displayed by a Swing component?

True/False

20. Determine if each of the following are true or

false. If false, explain why.

a) JFrame is a class in the javax.swing

package.

b) A button click is an event handler.

c) Labels can be changed by the user.

d) A JFrame object uses a content pane to hold

GUI components.

e) The index value for the first component on

a content pane is 1.

f) The JLabel class constant LEADING indicates

right alignment.

g) A thread is a sequential process that runs

from start to finish.

h) Swing components use listeners to determine

if an event has occurred.

i) A class that uses a listener must implement

an ActionListener class.

j) An empty border indicates that there is no

space around a component.

k) The FlowLayout manager places components

one after the other in a column, with one

column per line.

l) All components on a GUI must have the

same alignment.

m) The class content PAGE_AXIS specifies that

components should be arranged in a vertical

line.

n) The JLabel setAlignmentX() method is used

to specify the horizontal alignment of the

components within the layout.

308 Chapter 11 GUIs and Event-Driven Programming

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o) Code using the BoxLayout manager requires

an import java.awt.* statement.

p) Information is entered into a text field at run

time.

q) A text field can only accept numeric data.

r) The JLabel foreground color refers to the text

color.

s) A Swing GUI can have only one listener.

t) A nested class has access to the private vari-

able members of the outer class.

Chapter 11 GUIs and Event-Driven Programming 309

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Exercises

Exercise 1 ——————————————————— LocalBankGUI

Create LocalBankGUI application that implements a GUI for the Local Bank case study in Chapter 9.

Exercise 2 ——————————————————— TicTacToeGUI

Create a TicTacToeGUI application that allows two players to play a computerized tic-tac-toe game.

Refer to the TicTacToe application presented in Chapter 9. The TTT class code will need to be modified

for the GUI version of the application. Use a button for each “box” in the tic-tac-toe board.

Exercise 3 ———————————————————— PhotoAlbum

Create a PhotoAlbum application that displays a new picture each time Next is clicked. Use the

grayangel.jpg, scorpionfish.jpg, sponges.jpg, and starfish.jpg files supplied as data files for this text.

The application should allow the user to continously cycle through the images.

Exercise 4 —————————————————————— Clacker

In the game Clacker, the numbers 1 through 12 are initially displayed. The player throws two dice and

may cover the number representing the total or the two numbers on the dice. For example, for a throw

of 3 and 5, the player may cover the 3 and the 5 or just the 8. Play continues until all the numbers are

covered. The goal is to cover all the numbers in the fewest rolls.

Create a Clacker application that displays 12 buttons numbered 1 through 12. Each of these buttons

can be clicked to ”cover” it. A covered button displays nothing. Another button labeled Roll can be

clicked to roll the dice. Include labels to display the appropriate die images for each roll. Another label

displays the number of rolls taken. A New Game button can be clicked to clear the labels and uncover

the buttons for a new game.

Exercise 5 ö ————————————————————— LifeGUI

Create a LifeGUI application that is based on the Life application created in Chapter 10, Exercise 14.

The 20 x 20 grid should be buttons that initially display all 0s. To select the live cells for the first day,

the user clicks the buttons in the positions of live cells. When clicked, a button changes from display-

ing a 0 to displaying a X. A Next button below the grid can be clicked repeatedly to display the next

generations until the user quits or there are no more live cells.

310 Chapter 11 GUIs and Event-Driven Programming

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Chapter 12 Files and Exception Handling 311

sample

iles are used by many applications for storing and retrieving data. In

this chapter, sequential file access, including object serialization will be

discussed. Exception handling will also be explained.

What is a File?

Up to this point, the applications created in this text have stored data

in the computer’s memory. However, storage in memory is available only

when the computer is on and an application is running. A file is a collec-

tion of related data stored on a persistent medium such as a hard disk or

a CD. Persistent simply means lasting.

Files often store data used by an application. Files are also used to store

the data generated by an application. In either case, a file is separate from

the application accessing it and can be read from and written to by more

than one application. Most applications require access to one or more files

on disk.

The File Classes

The File class, part of the java.io package, is used for creating an object

that represents a file. A File object can be used to create a new file, test

for the existence of a file, and delete a file. Some of the File class methods

include:

Class File (java.io)

Constructor/Methods

File(String f) creates a File object that refers to the file f.

createNewFile()

creates a new file using the file name specified

in the constructor if the file does not already

exist. Returns true if the file is created, false

otherwise. This method throws an IOException

exception if the file cannot be created.

delete() permanently deletes the file represented by the

File object. Returns true if the file is deleted,

false otherwise.

exists() Returns true if the file represented by the File

object exists, false otherwise.

Chapter 12

Files and Exception Handling

persistent

java.io

312 Chapter 12 Files and Exception Handling

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The application below checks for the existence of a file:

import java.io.*;

public class TestFiles {

public static void main(String[] args) {

File textFile = new File("c:\\temp\\supplies.txt");

if (textFile.exists()) {

System.out.println("File already exists.");

} else {

System.out.println("File does not exist.");

}

The name of a file is specified as a String. If a path is included in the

file name, escape sequences (\\) must be used to separate the drive, folder,

and file names.

Review: MyFile – part 1 of 2

Create a MyFile application that prompts the user for the name of a file and then displays a message that

indicates whether the files exists or not. Note that if the user types in a full path, any single backslashes (\)

will need to be replaced with an escape sequence(\\) in order to create a new File object.

Handling Exceptions

An exception is an error affecting program execution. If an exception is

not taken care of, or handled, the application abruptly terminates. Although

many types of exceptions may still require program termination, an excep-

tion handler can allow an application to terminate gracefully by providing

the user with an informative error message.

An exception handler is a block of code that performs an action when an

exception occurs. The try-catch-finally statement can be used to write

an exception handler. It takes the form:

try {

} catch (exception err _ code) {

} …additional catch clauses

} finally (exception err _ code) {

The try statements are the statements that could possibly generate an

exception. The catch clause waits for the exception matching the exception

parameter and then executes its code. If more than one type of exception is

possible from the statements in the try clause, then a separate catch should

be written for each type of exception. The finally clause is optional and

executes its statements regardless of what happens in the try-catch por-

tion of the error handler.

exception

exception handler

try-catch-finally

Chapter 12 Files and Exception Handling 313

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An exception handler is required when calling certain methods.

For example, the createNewFile() method in the File class generates an

IOException exception when the specified file name cannot be used to cre-

ate a file. The createNewFile() method includes code to throw, or generate,

an exception object if it cannot complete its task.

The modified TestFiles application checks for the existence of a file

before creating a new one:

import java.io.*;

public class TestFiles {

public static void main(String[] args) {

File textFile = new File("c:\\supplies.txt");

if (textFile.exists()) {

System.out.println("File already exists.");

} else {

try {

textFile.createNewFile();

System.out.println("New file created.");

} catch (IOException e) {

System.out.println("File could not be created.");

System.err.println("IOException: " + e.getMessage());

}

An exception, such as IOException, is an object of the Throwable class.

Throwable objects have a getMessage() member that returns a String

containing information about the exception. The err stream is used for

displaying error messages on the screen.

Review: MyFile – part 2 of 2

Create a MyFile application that creates a file named zzz.txt and then displays a message indicating that the

file has been created. The application should prompt the user to either keep or delete the file. If the file is

deleted, a message should notify the user when the file has been successfully deleted.

The File Streams

A file must be associated with a stream in order to perform operations

such as reading the contents, writing over existing contents, and adding to

the existing contents. A stream processes characters, and in Java, streams

are implemented with classes.

The file stream keeps track of the file position, which is the point where

reading or writing last occurred. File streams are used to perform sequential

file access, with all the reading and writing performed one character after

another or one line after another.

The Exception Stack

When an exception is thrown,

the current block of code is

first checked for an exception

handler. Next, the calling

method is checked for a

handler, and so on until the

Java interpreter is reached.

sequential file access

file position

throw

err stream

TIP The Scanner class requires

an input stream.

IOException

314 Chapter 12 Files and Exception Handling

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A stream can be thought of as a sequence of characters. For example,

a file containing a list of names and scores may look like the following

when viewed in a word processor:

Drew 84

Tia 92

However, when thinking about file operations, the file should be visual-

ized as a stream of data:

              

The carriage return character (Cr) followed by a line feed character (Lf) is

called a line terminator. A –1 is the end of file.

The FileReader and BufferedReader

Classes

The FileReader and BufferedReader classes, both from the java.io pack-

age, are used together to read the contents of an existing file. The FileReader

class is used to create an input file stream. Next, the BufferedReader class

is used to read text from the stream. The following is a summary of the

FileReader and BufferedReader classes:

Class FileReader (java.io)

Constructor/Method

FileReader(File fileName)

creates an input file stream for the File object. This

constructor throws a FileNotFoundException

exception if the file does not exist.

close() closes the input file stream. This method throws

an IOException exception if the file cannot be

closed.

Class BufferedReader (java.io)

Constructor/Methods

BufferedReader(Reader stream)

creates a buffered-input stream from stream.

Reader is the FileReader superclass.

read() reads a single character from the input stream.

This method throws an IOException exception

if the stream cannot be read.

readLine() reads a line of text from the input stream. This

method throws an IOException exception if the

stream cannot be read.

close() closes the input file stream. This method throws

an IOException exception if the stream cannot

be closed.

The application on the next page reads an existing file line-by-line to

show the contents of the file:

Reading Characters

The read() method returns an

int, which corresponds to a

Unicode value. In Unicode, a

space corresponds to 32, a tab

to 9, carriage return to 13, and

line feed to 10.

Data Streams

A stream applies to data input/

output in general. For example,

memory, information sent to

a printer, and data sent and

received from an Internet site

can all be streamed.

input file stream

line terminator, end of file

TIP A buffer stores a large

number of characters from

the stream so that more than

one character at a time can be

read, such as in a readLine().

FileNotFoundException

Chapter 12 Files and Exception Handling 315

sample

import java.util.Scanner;

import java.io.*;

public class ReadFile {

public static void main(String[] args) {

File textFile = new File("wonder.txt");

FileReader in;

BufferedReader readFile;

String lineOfText;

try {

in = new FileReader(textFile);

readFile = new BufferedReader(in);

while ((lineOfText = readFile.readLine()) != null ) {

System.out.println(lineOfText);

}

readFile.close();

in.close();

} catch (FileNotFoundException e) {

System.out.println("File does not exist or could

not be found.");

System.err.println("FileNotFoundException: "

+ e.getMessage());

} catch (IOException e) {

System.out.println("Problem reading file.");

System.err.println("IOException: " + e.getMessage());

}

The ReadFile application reads and displays the file contents within

a try-catch statement because both the FileReader and BufferedReader

constructors and methods throw exceptions if there is a problem reading

the file. A try can have multiple catch statements. The catch statements are

in the order that they may occur. For example, the FileNotFoundException

is handled first because the FileReader object is created first in the try

statement.

The close() methods are used to close the FileReader and BufferedReader

streams. It is important that the streams be closed in the reverse order that

they were opened.

The ReadFile application displays the following output when run:

Review: Assignment

Create a Assignment application that reads and then displays the contents of a file containing instructions for

this assignment. Use Notepad or some other word processor to create the file. Be sure that the file is saved as

a Text file (TXT). The Assignment application will need to include the correct path to the location of the file.

If a path is not specified, the file must be placed in the same folder as the Assignment executable file.

316 Chapter 12 Files and Exception Handling

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Processing Numeric Data

A file on disk is a set of characters, even when the file contains numeric

data, such as test scores. An application written to process numeric data

from a file must convert the data after it is read. The Double and Integer

classes include class methods for converting a string to a primitive data

type:

Class Double (java.lang.Double)

Method

parseDouble(String text)

returns the double value in the String text.

Class Integer (java.lang.Integer)

Method

parseInteger(String text)

returns the int value in the String text.

The AvgScore application reads tests scores that are stored one score

per line in a text file and then reports the average:

import java.io.*;

public class AvgScore {

public static void main(String[] args) {

File dataFile = new File("scores.dat");

FileReader in;

BufferedReader readFile;

String score;

double avgScore;

double totalScores = 0;

int numScores = 0;

try {

in = new FileReader(dataFile);

readFile = new BufferedReader(in);

while ((score = readFile.readLine()) != null ) {

numScores += 1;

System.out.println(score);

totalScores += Double.parseDouble(score);

}

avgScore = totalScores / numScores;

System.out.println("Average = " + avgScore);

readFile.close();

in.close();

} catch (FileNotFoundException e) {

System.out.println("File does not exist or could

not be found.");

System.err.println("FileNotFoundException: "

+ e.getMessage());

} catch (IOException e) {

System.out.println("Problem reading file.");

System.err.println("IOException: " + e.getMessage());

}

DAT Files

Text files that contain numeric

data often have the file name

extension .dat, also referred

to as a DAT file.

Chapter 12 Files and Exception Handling 317

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The application produces the output:

Review: Stats – part 1 of 2

Create a Stats application that reads names and scores from a data file named test1.dat, supplied with this

text. The file contains a student name on one line followed by the student’s test score on the next line. The

Stats application should read and display each name and score. After all the scores have been displayed, the

lowest score, highest score, and average score should be displayed.

The FileWriter and BufferedWriter

Classes

The FileWriter and BufferedWriter classes, both from the java.io pack-

age, are used together to write data to a file. The FileWriter class is used

to create an output file stream. A BufferedWriter class object is then used to

send text to the stream. Some of the FileWriter and BufferedWriter classes

methods include:

Class FileWriter (java.io)

Constructor/Method

FileWriter(File fileName, boolean append)

creates an input file stream for the File object. If

append is true, then data written to the file will

be added after existing data, otherwise the file

will be overwritten. This constructor throws

an IOException exception if the file cannot be

created or opened.

close() closes the output file stream. This method

throws an IOException exception if the file

cannot be closed.

When a FileWriter object is created, the file referenced by the File object

is automatically overwritten unless the FileWriter object is set to append. In

either case, if the file does not yet exist, a new one will be created. Caution

must be used so that a file is not inadvertently overwritten.

output file stream

318 Chapter 12 Files and Exception Handling

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Class BufferedWriter (java.io)

Constructor/Methods

BufferedWriter(Writer stream)

creates a buffered-writer stream from stream.

Writer is the FileWriter superclass.

newLine() writes a newline character to the output stream.

This method throws an IOException exception

if the stream cannot be written to.

write(String str)

writes the string str to the output stream. This

method throws an IOException exception if the

stream cannot be written to.

write(char c) writes the character c to the output stream. This

method throws an IOException exception if the

stream cannot be written to.

close() closes the output file stream. This method

throws an IOException exception if the stream

cannot be closed.

The CreateDataFile application prompts the user for names and scores

and then writes them to a new file:

import java.io.*;

import java.util.Scanner;

public class CreateDataFile {

public static void main(String[] args) {

File dataFile = new File("StuScores.dat");

FileWriter out;

BufferedWriter writeFile;

Scanner input = new Scanner(System.in);

double score;

String name;

try {

out = new FileWriter(dataFile);

writeFile = new BufferedWriter(out);

for (int i = 0; i < 5; i++) {

System.out.print(:Enter student name: ");

name = input.next();

System.out.print("Enter test score: ");

score = input.nextDouble();

writeFile.write(name);

writeFile.newLine();

writeFile.write(String.valueOf(score));

writeFile.newLine();

}

writeFile.close();

out.close();

System.out.println("Data written to file.");

} catch (IOException e) {

System.out.println("Problem writing to file.");

System.err.println("IOException: " + e.getMessage());

}

Note that the application will overwrite the StuScores.dat file each time

that it is run. The CreateDataFile application displays output similar to

that shown on the next page:

Chapter 12 Files and Exception Handling 319

sample

Review: Stats – part 2 of 2

Modify the Stats application to allow the user to enter the names and grades of the students. The user should

be prompted for the name of the file to create and for the number of student grades that will be entered.

After the data has been entered and the written to a file, the file should be read and the lowest, highest, and

average score displayed.

Object Serialization

A file can also be used to store object data. Writing objects to a file is

called object serialization. In this process, class information about an object

is written out to a stream. If a class uses another class, this information is

also written out, and so on. When information about an object is retrieved

from a file, it is called object deserialization.

Object serialization and deserialization is performed with object out-

put and input streams. The FileOutputStream and ObjectOutputStream

classes, both from the java.io package, are used together to write objects

to a file. The FileInputStream and ObjectInputStream classes, also from

the java.io package, are used together to read objects from a file. Some of

the methods from the classes for writing and reading objects include:

Class FileOutputStream (java.io)

Constructor/Method

FileOutputStream(File fileName, boolean append)

creates an output file stream for the File object.

If append is true, then data written to the file

will be added after existing data, otherwise

the file will be overwritten or created if the

file does not exist. This method throws a

FileNotFoundException exception if the file

cannot be opened or created.

close() closes the output file stream. This method

throws an IOException exception if the file

cannot be closed.

320 Chapter 12 Files and Exception Handling

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In addition to methods for writing objects to the output stream, the

ObjectOutputStream class also contains method for writing primitive

data types.

Class ObjectOutputStream (java.io)

Constructor/Method

ObjectOutputStream(FileOutputStream stream)

creates an object stream from stream.

writeObject(Object obj)

writes object information to the output stream.

This method throws an IOException exception

if there are problems with the class or if the

stream cannot be written to.

writeInt(int num)

writes an int to the output stream. This method

throws an IOException exception if the stream

cannot be written to.

writeDouble(double num)

writes a dou ble to the output stream. This

method throws an IOException exception if

the stream cannot be written to.

close() closes the output stream. This method throws

an IOException exception if the stream cannot

be closed.

Objects are read from a FileInputStream stream object:

Class FileInputStream (java.io)

Constructor/Method

FileInputStream(File fileName)

creates an input file stream for the File object.

This method throws a FileNotFoundException

exception if the file cannot be read.

close() closes the input file stream. This method throws

an IOException exception if the file cannot be

closed.

The ObjectInputStream class contains method for reading both objects

and primitive data types.

Class ObjectInputStream (java.io)

Constructor/Method

ObjectInputStream(FileInputStream stream)

creates an object stream from stream. This con-

structor throws an IOException exception if the

stream cannot be read.

readObject() reads an object from the input stream. This

method throws exceptions IOException and

ClassNotFoundException if the the stream can-

not be read or a class cannot be deserialized.

readInt() reads an int from the input stream. This method

throws an IOException exception if the file can-

not be read.

Chapter 12 Files and Exception Handling 321

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readDouble() reads a double from the input stream. This

method throws an IOException exception if the

file cannot be read.

close() closes the input stream. This method throws

an IOException exception if the file cannot be

closed.

The ObjectWriteRead application demonstrates writing and reading

objects from a file:

import java.io.*;

public class ObjectWriteRead {

public static void main(String[] args) {

File stuFile = new File("students.dat");

try {

/* write objects */

FileOutputStream out = new FileOutputStream(stuFile);

ObjectOutputStream writeStu = new ObjectOutputStream(out);

writeStu.writeObject(new Student("Drew", 87));

writeStu.writeObject(new Student("Tia", 92));

writeStu.close();

System.out.println("Data written to file.");

/* read objects */

FileInputStream in = new FileInputStream(stuFile);

ObjectInputStream readStu = new ObjectInputStream(in);

Student stu1 = (Student)readStu.readObject();

Student stu2 = (Student)readStu.readObject();

readStu.close();

System.out.println(stu1);

System.out.println (stu2);

} catch (FileNotFoundException e) {

System.out.println("File could not be found.");

System.err.println("FileNotFoundException: "

+ e.getMessage());

} catch (IOException e) {

System.out.println("Problem with input/output.");

System.err.println("IOException: " + e.getMessage());

} catch (ClassNotFoundException e) {

System.out.println("Class could not be used to

cast object.");

System.err.println("ClassNotFoundException: "

+ e.getMessage());

}

The ObjectWriteRead application writes two Student objects to the

students.dat file. The Student class is shown on the next page:

322 Chapter 12 Files and Exception Handling

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import java.io.*;

public class Student implements Serializable {

private String stuName;

private double stuGrade;

/**

* constructor

* pre: none

* post: A Student object has been created.

* Student data has been initialized with parameters.

public Student(String name, double grade) {

stuName = name;

stuGrade = grade;

}

/**

* Creates a string representing the student object

* pre: none

* post: A string representing the student object

* has been returned.

public String toString() {

String stuString;

stuString = stuName + " grade: " + stuGrade;

return(stuString);

}

If the objects of a class are to be written to a file, the class must imple-

ment the Serializable interface. This interface is part of the java.io package

and contains no methods to implement. It simply allows information about

an instance of the class to be written out.

Note that reading an object from a file requires casting. The readObject()

method reads Object data from the file. It is up to the programmer to cast

the object to the appropriate type.

The ObjectWriteRead application catches several exceptions. First, a

FileNotFoundException occurs when there is a problem creating a File

object. IOException is a more general exception and occurs for various

input/output problems. If IOException were first in the catch clauses,

the other more specific exceptions would not be caught and the user

would not be able to read their descriptive error messages. Finally, the

ClassNotFoundException occurs if the class for an object written to the

file cannot be found.

Review: Roster

Create a Roster application that prompts the user for the name of the file to store student names and then

prompts the user for the number of students in a class. The application should then prompt the user for

the first and last name of each student and write this data to a file. After all the data is written to a file, the

application display the class roster with one name after the other in a list. Create a StuName class that has

member variables firstName and lastName and a toString() member method.

Serializable interface

Chapter 12 Files and Exception Handling 323

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Chapter 12 Case Study

In this case study, a LocalBank2 application will be created. LocalBank2

is the Chapter 10 case study modified to read and write account informa-

tion from a file.

LocalBank2 Specification

The LocalBank2 application has the same specification as LocalBank.

It allows accounts to be opened, modified, and closed. Each account

has a unique account number, which is required for all transactions.

Transactions include deposits and withdrawals. An account balance can

also be checked.

The LocalBank2 interface will not change from LocalBank. It will pro-

vide a menu of options:

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

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The LocalBank2 algorithm will not change from the LocalBank applica-

tion algorithm.

324 Chapter 12 Files and Exception Handling

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LocalBank2 Code Design

The LocalBank2 application will be modeled with a Bank object, Account

objects, and Customer objects, just as LocalBank. However, the Bank object

will store and retrieve accounts from a file. To do this, the Bank construc-

tor should create a file stream for the File object specified when the Bank

object is instantiated. The constructor should also load accounts from the

file stream into an ArrayList. An updateAccounts() method will need to

be added to the Bank class so that any account changes can be written

back to the file.

Because account objects will be read from and written to a file, the

Account class and any classes it uses must implement the Serializable

interface. This includes the Customer class.

The LocalBank2 client code must be modified to create a File object that

stores the account information. Before ending the LocalBank application,

the updateAccounts() method is called to write account information back

to the file. The pseudocode for the LocalBank2 client code follows:

File accountsFile = new File("LBAccounts.dat");

Bank easySave = new Bank(accountsFile);

do {

prompt user for transaction type

if (add account) {

easySave.addAccount();

} else if (not Quit) {

prompt user for account ID;

if (deposit) {

prompt user for deposit amount

easySave.transaction(make deposit, acctID, amt);

} else if (withdrawal) {

prompt user for withdrawal amount

easySave.transaction(make withdrawal, acctID, amt);

} else if (check balance) {

easySave.checkBalance(acctID);

} else if (remove account) {

easySave.deleteAccount(acctID);

}

} while (not quit);

easySave.updateAccounts(accountsFile);

LocalBank Implementation

The LocaBank2 application is shown below:

/**

* LocalBank2 client code.

import java.io.*;

import java.util.Scanner;

public class LocalBank {

public static void main(String[] args) {

File accountsFile = new File("LBAccounts.dat");

Bank easySave = new Bank(accountsFile);

Chapter 12 Files and Exception Handling 325

sample

Scanner input = new Scanner(System.in);

String action, acctID;

Double amt;

/* display menu of choices */

do {

System.out.println("\nDeposit\\Withdrawal\\Check balance");

System.out.println("Add an account\\Remove an account");

System.out.println("Quit\n");

System.out.print("Enter choice: ");

action = input.next();

if (action.equalsIgnoreCase("A")) {

easySave.addAccount();

} else if (!action.equalsIgnoreCase("Q")) {

System.out.print("Enter account ID: ");

acctID = input.next();

if (action.equalsIgnoreCase("D")) {

System.out.print("Enter deposit amount: ");

amt = input.nextDouble();

easySave.transaction(1, acctID, amt);

} else if (action.equalsIgnoreCase("W")) {

System.out.print("Enter withdrawal amount: ");

amt = input.nextDouble();

easySave.transaction(2, acctID, amt);

} else if (action.equalsIgnoreCase("C")) {

easySave.checkBalance(acctID);

} else if (action.equalsIgnoreCase("R")) {

easySave.deleteAccount(acctID);

}

} while (!action.equalsIgnoreCase("Q"));

easySave.updateAccounts(accountsFile); //write accounts to file

}

The Bank class is shown below. The accounts are expected to be loaded

from a file. Additionally, the number of accounts is also kept in the file.

This number is the first data item in the file. It is read first and then used

to determine how many accounts to read from the file. Throughout the

class, the number of accounts is updated when a new account is added and

when an account is deleted. When updateAccounts() is called, the number

of accounts is written to the file first, followed by the accounts:

/**

* Bank class.

import java.util.ArrayList;

import java.io.*;

import java.util.Scanner;

public class Bank {

private ArrayList accounts;

private int numAccts;

326 Chapter 12 Files and Exception Handling

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/**

* constructor

* pre: none

* post: accounts have been loaded from acctFile.

public Bank(File acctsFile) {

accounts = new ArrayList();

Account acct;

/* Create a new file for accounts if one does not exist */

if (!acctsFile.exists()) {

try {

acctsFile.createNewFile();

System.out.println("There are no existing accounts.");

} catch (IOException e) {

System.out.println("File could not be created.");

System.err.println("IOException: " + e.getMessage());

}

numAccts = 0;

} else { /* load existing accounts */

try {

FileInputStream in = new FileInputStream(acctsFile);

ObjectInputStream readAccts = new ObjectInputStream(in);

numAccts = (int)readAccts.readInt();

if (numAccts == 0) {

System.out.println("There are no existing accounts.");

} else {

for (int i = 0; i < numAccts; i++) {

acct = (Account)readAccts.readObject();

accounts.add(acct);

}

readAccts.close();

} catch (FileNotFoundException e) {

System.out.println("File could not be found.");

System.err.println("FileNotFoundException: " + e.getMessage());

} catch (IOException e) {

System.out.println("Problem with input/output.");

System.err.println("IOException: " + e.getMessage());

} catch (ClassNotFoundException e) {

System.out.println("Class could not be used to cast object.");

System.err.println("ClassNotFoundException: " + e.getMessage());

}

/**

* Adds a new account to the bank accounts.

* pre: none

* post: An account has been added to the bank's accounts.

public void addAccount() {

Account newAcct;

double bal;

String fName, lName;

Scanner input = new Scanner(System.in);

System.out.print("First name: ");

fName = input.nextLine();

System.out.print("Last name: ");

lName = input.nextLine();

System.out.print("Beginning balance: ");

bal = input.nextDouble();

Chapter 12 Files and Exception Handling 327

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newAcct = new Account(bal, fName, lName); //create account object

accounts.add(newAcct); //add account to bank accounts

numAccts += 1; //increment number of accounts

System.out.println("Account created. Account ID is: " + newAcct.getID());

}

/**

* Deletes an existing account.

* pre: none

* post: An existing account has been deleted.

public void deleteAccount(String acctID) {

int acctIndex;

Account acctToMatch;

acctToMatch = new Account(acctID);

acctIndex = accounts.indexOf(acctToMatch); //retrieve location of account

if (acctIndex > -1) {

accounts.remove(acctIndex); //remove account

System.out.println("Account removed.");

numAccts -= 1; //decrement number of accounts

} else {

System.out.println("Account does not exist.");

}

The Account class need only be modified to implement the Serializable

class:

/**

* Account class.

import java.io.*;

import java.text.NumberFormat;

public class Account implements Serializable {

…rest of Account class (refer to Chapter 10 case study)

The Customer class need only be modified to implement the Serializable

class:

/**

* Customer class.

import java.io.*;

public class Customer implements Serializable {

…rest of Customer class (refer to Chapter 10 case study)

328 Chapter 12 Files and Exception Handling

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Running the LocalBank2 application displays the same output as the

LocalBank application:

LocalBank2 Testing and Debugging

The LocalBank2 application should be tested to be sure that it works

appropriately when no file exists, when a file with no accounts exists, and

when a file with accounts exists.

Review: LocalBank2

Modify the Bank class to keep track of accounts with low balances. A low balance is an account with less

than $20.00. The number of low balance accounts should be stored after the number of accounts, but before

the account objects in the account file. Have the number of low balance accounts displayed when a Bank

object is created and again when the updateAccounts() method is called.

Chapter 12 Files and Exception Handling 329

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Chapter Summary

This chapter discussed files and exception handling. A file is a data

stored on a persistent medium such as a hard disk or CD. In Java, a File

object is associated with a file name. A File object can be used to create or

delete a file.

An exception is an error affecting program execution. An exception

handler is a block of code that performs an action when an exception

occurs. This chapter introduced the try-catch-finally statement for writ-

ing exception handlers.

A file must be associated with a stream in order to read and write to the

file. A file stream processes characters and is used to perform sequential

file access. The FileReader, BufferedReader, FileWriter, and BufferWriter

classes are used to read and write to a file.

An application written to process numeric data from a file must convert

the file data from a strings to numerics. The Double and Integer classes

contain methods for converting numeric characters in a string to an int

or a double.

Objects can be written to a file in a process called object serialization.

Reading objects from a file is called object deserialization. Serialization and

deserialization are performed with an object stream. The FileOutputStream,

ObjectOutputStream, FileInputStream, and ObjectInputStream classes are

used to write and read objects to a file. The ObjectOutputStream and

ObjectInputStream classes can also be used to write and read primitve

data to a file.

330 Chapter 12 Files and Exception Handling

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Vocabulary

ClassNotFoundException An exception thrown

if a stream cannot be read or a class cannot be

deserialized.

End of file A –1 in the file stream.

err stream The stream used for displaying error

messages to the user.

Exception An error affecting program execution.

Exception handler A block of code that performs

an action when an exception occurs.

File A collection of related data stored on a per-

sistent medium.

FileNotFoundException An exception thrown

when a file does not exist.

File position The point at which reading or writing

in the stream last occurred.

Handle Take care of.

Input file stream A file stream for reading a file.

IOException An exception thrown when a file

cannot be created, or when there is a general input/

output problem.

Line terminator A carriage return followed by a

line feed in the file stream.

Object deserialization The process used to read

objects from a file.

Object serialization The process used to write

objects to a file.

Output file stream A file stream for writing to a

file.

Persistent Lasting.

Sequential file access Reading and writing one

character after another.

Stream The construct used for processing

characters.

Throw Generate.

Java

BufferedReader A java.io class used for creating

a buffered file stream for reading a file.

BufferedWriter A java.io class used for creating a

buffered file stream for writing to a file.

Double A java.lang class for converting numeric

text in a string to a double.

File The java.io class used for creating an object

that refers to a file.

FileInputStream A java.io class used for creating

an object input stream.

FileOutputStream A java.io class used for creating

an object output stream.

FileReader The java.io class used for creating a file

stream for reading a file.

FileWriter The java.io class used for creating a file

stream for writing to a file.

Integer A java.lang class for converting numeric

text in a string to an int.

try-catch-finally Statement used to write an excep-

tion handler.

ObjectInputStream A java.io class used for creating

an object for reading objects from a file.

ObjectOutputStream A java.io class used for creat-

ing an object for writing objects to a file.

Chapter 12 Files and Exception Handling 331

sample

Critical Thinking

1. Can data in memory be called a file? Explain.

2. Write the import statement required to access

the File Class in an application.

3. Identify the error in the following statement:

File textFile = new File("c:\inventory.txt");

4. a) Which statement is used to write an excep-

tion handler?

b) Write an exception handler to handle an

IOException if a specified file name cannot

be used to create a file. The exception han-

dler should display appropriate messages to

the user.

5. a) What is the name of the stream for display-

ing error messages.

b) Where are these messages displayed?

6. a) What does the file stream keep track of?

b) What characters together make up a line

terminator?

7. What two classes are used together to write data

to a file?

8. Write a statement to convert account balances

that have been read from a text file to a double

value and add them to totalBalance.

9. Explain the difference between object serializa-

tion and object deserialization.

10. What interface must be implemented if objects

of a class are to be written to a file?

11. Describe two situations where an IOException

exception could be thrown, and write an exam-

ple exception handler for each situation to out-

put an appropriate message if the exception

occurs.

True/False

12. Determine if each of the following are true or

false. If false, explain why.

a) An exception always results in program

termination.

b) Sequential file access reads and writes data

one character after another or one line after

another.

c) Z-1 is the end of file.

d) A file on disk is a set of numbers ranging

from 0 to 9.

e) Numeric data in a file must be converted to

a primitive data type before it can be pro-

cessed numerically.

f) A FileNotFoundException exception is

thrown if a file cannot be closed.

g) The output file stream is a file stream for

writing to the screen.

h) Reading an object from a file requires

casting.

332 Chapter 12 Files and Exception Handling

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Exercises

Exercise 1 ———————————————————— WordCount

Create a WordCount application that displays the number of words and the average word length in a

text file named source.txt. Consider a word to be any sequence of letters terminated by nonletters. For

example, forty-nine is two words.

Exercise 2 ————————————————————— WordStats

a) Create a WordStats application that lists all the unique words in a file and how many

times they occurred. WordStats should ignore capitalization. The application should

provide a listing similar to:

WORD OCCURENCES

the 57

and 12

zoo 3

b) Modify the WordStats application to list the words in alphabetical order. This can be

done by either using the sorting algorithm presented in Chapter 10, Exercise 11 or by

keeping the words in order as they are read.

Exercise 3 ——————————————————— TestProcessor

Test results for a multiple choice test can be stored in a text file as follows:

Line 1: The correct answers, one character per answer

Line 2: Name of the first student (length <= 30 chars)

Line 3: Answers for the student in line 2

The remaining lines: student names and answers on separate lines

For example:

BADED

Smithgall

BADDD

DeSalvo

CAEED

Darji

BADED

Create a TestProcessor application that processes the test results file for any number of students. The

application should provide statistics similar to:

Smithgall 80%

DeSalvo 60%

Darji 100%

Chapter 12 Files and Exception Handling 333

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Exercise 4 —————————————————————— MadLib

A Mad-Lib story is a story where nouns and verbs in a paragraph are randomly replaced with other

nouns and verbs, usually with humorous results. Create a MadLib application that displays a Mad-Lib

story. The application will require three files:

• story.txt which contains a story with # signs as noun placeholders, and % signs as

verb placeholders. For example:

Bugsy Kludge is a # with our company.

His job is to % all of the #s.

• verbs.txt which contains verbs, one per line. For example:

run

display

eat

• nouns.txt which contains nouns, one per line. For example:

banana

soprano

elephant

vegetable

Application output should display the story with apporpriate replacements made. A possible output

would produce a MadLib similar to:

Bugsy Kludge is a vegetable with our company.

His job is to display all of the elephants.

Exercise 5 ———————————————————— MergeFiles

The idea of merging two or more files is an important one in programming. One approach is to merge

the ordered data of two files into a third file, keeping the data in order.

Create a MergeFiles application that merges the integers ordered from low to high in two files into a

third file, keeping the order from low to high. For example, two files of integers could contain:

File 1: 12 23 34 45 56 67 69 123 133

File 2: 4 5 10 20 35 44 100 130 150 160 180

The application should not use an array to temporarily store the numbers, but should merge the two

files by taking one element at a time from each. After MergeFiles has been run, the third file should

contain:

4 5 10 12 20 23 34 35 44 45 56 67 69 100 123 130 133 150 160 180

Exercise 6 ö ——————————————————— MergeLarge

The algorithm used implemented in Exercise 5 is sometimes used as part of a sorting algorithm with

data that is too large to be stored in memory at once. For example, to sort a large file large.dat that is

twice as large as will fit in memory, half can be read into an array, the array sorted, and then written

to a file numbers1.dat. Next, the second half of large.dat can be read into the array, sorted, and then

written to numbers2.dat. Finally, the two files can be merged in order back into large.dat. Create a

MergeLarge application that implements this algorithm. Test the application with a file that contains

30 integers sorted from low to high.

334 Chapter 12 Files and Exception Handling

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Exercise 7 ————————————————————HTMLViewer

The early success of the Web is largely due to the simplicity of HTML (HyperText Markup Language),

for designing a Web page. HTML documents are text documents containing content and tags that

describe the format of the content. An HTML document could look similar to:

JUNE BUGS<p>June bugs RAM in megabytes of fleshy fruit,<br>downsize fine fat

figs<br>chip away at melon bits.<br>They monitor windows for open screens,<br>seeking

felicity in electricity.<br>Built-in memory warns of websites<br>hiding spiders

with sly designs.<br>Scrolling the scene of leaves and trees,<br>they network the

neighborhood in flashy green jackets,<br>each bug a browser, scanner, looter-

<br>not even knowing the word "computer."<p>by Avis Harley<p><hr>

Tags are enclosed in angle brackets, < >. The tag <br> means to start a new line. The tag <p> means to

start a new paragraph (a blank line). The tag <hr> means to draw a horizontal rule. When these tags

are interpreted, the HTML document above is displayed as:

JUNE BUGS

June bugs RAM in megabytes of fleshy fruit,

downsize fine fat figs

chip away at melon bits.

They monitor windows for open screens,

seeking felicity in electricity.

Built-in memory warns of websites

hiding spiders with sly designs.

Scrolling the scene of leaves and trees,

they network the neighborhood in flashy green jackets,

each bug a browser, scanner, looter-

not even knowing the word "computer."

by Avis Harley

------------------------------------------------

a) HTML documents are interpreted by browser software. Create an HTMLViewer appli-

cation that interprets an HTML file to display the Web content as intended, similar to

the way a browser decides how to display an HTML document.

b) Modify the HTMLViewer application to allow the user to specify the display line width.

For example, a width of 35 should display the HTML document as:

JUNE BUGS

June bugs RAM in megabytes of

fleshy fruit,

downsize fine fat figs

chip away at melon bits.

They monitor windows for open

screens,

seeking felicity in electricity.

Built-in memory warns of websites

hiding spiders with sly designs.

Scrolling the scene of leaves and

trees,

they network the neighborhood in

flashy green jackets,

each bug a browser, scanner,

looter-

not even knowing the word

"computer."

by Avis Harley

-----------------------------------

...

Chapter 12 Files and Exception Handling 335

sample

Exercise 8 ö ———————————————————— CarRecall

Modify the CarRecall application created in Chapter 6, Exercise 4 to load the defective car model

numbers from a file.

Exercise 9 ö ——————————————————— WordGuess

Modify the WordGuess case study from Chapter 6 to use a word from a file as the secret word. The file

should contain a list of words, with one word per line. The WordGuess application should determine

which word to use, by generating a random number that corresponds to one of the words in the file.

Exercise 10 —————————————————— FindAndReplace

Create a FindAndReplace application that prompts the user for a file name, a search word or phrase,

and a replacement word or phrase. After entering the replacement word or phrase, FindAndReplace

finds all occurrences of the search word or phrase in a file and replaces them with the specified replace-

ment word or phrase.

Exercise 11 —————————————————— ApplicationDoc

Create an ApplicationDoc application that prompts the user for the file name of a Java source code file

(the file name extension should be java) and then copies all the documentation comments (/** */) to

a separate file.

Exercise 12 ö ———————————————————— MySavings

Modify the MySavings application from Chapter 8, Exercise 1 to store and load the PiggyBank object

from a file.

Exercise 13 ö —————————————————————— Adder

Modify the Adder application from Chapter 8, Exercise 8 to keep track of player scores in a file. The

application should prompt the player for his or her name and then create a file based on the player

name. For example, if the player’s name is Jo, then a file named JoScores.txt should be created. The

application should write the player’s score to their file at the end of the game and then display the

player’s previous scores.

Exercise 14 ö ———————————————————CountVowels

Modify the CountVowels application created in Chapter 6, Exercise 20 to count the number of vowels

in a text file. The application should prompt the user for the file name.

336 Chapter 12 Files and Exception Handling

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Exercise 15 ö —————————————————————— Coder

Modify the Coder application created in Chapter 10, Exercise 10 to encode the text in one file and write

it to a new file.

Exercise 16 ö —————————————————— CourseGrades

Modify the CourseGrades application created in Chapter 10, Exercise 12 to write the GradeBook object

to a file.

Exercise 17 ö ——————————————————————— Life

Modify the Life application created in Chapter 10, Exercise 14 to retrieve the initial life grid from a

file.

Exercise 18 ö ———————————————————— Inventory

Modify the Inventory application created in Chapter 10, Exercise 16 to write the inventory items to a

file.

Chapter 13 Recursion and Advanced Algorithms 337

sample

Algorithms for searching and sorting data will be covered in this

chapter. Recursion will be used in the implementation of some of these

algorithms.

Selection Sort

Sorting is the process of putting items in a designated order, either from

low to high or high to low. The selection sort algorithm starts by finding

the lowest item in a list and swapping it with the first. Next, the lowest

item among items 2 through the last is found and swapped with item 2,

and then the lowest item among items 3 through the last is swapped with

item 3. This process is continued until the last item is reached, at which

point all the items are sorted.

The selection sort algorithm compares an element to the items in the

array after the element. This algorithm can be implemented with nested

for loops. The outer loop controls which element to compare and the inner

for loop iterates through the array after the element (the subarray). The

selection sort pseudocode for sorting an array of items from low to high

appears like:

for (arrayIndex = 0 to numItems-1)

for (subarrayIndex = arrayIndex to numItems-1)

if (items[subarrayIndex] < items[arrayIndex]) {

swap items[arrayIndex] and items[arrayIndex]

}

The Sorts class on the next page implements a selectionSort() method:

Chapter 13

Recursion and Advanced Algorithms

338 Chapter 13 Recursion and Advanced Algorithms

sample

public class Sorts {

/**

* Sorts an array of data from low to high

* pre: none

* post: items has been sorted from low to high

public static void selectionSort(int[] items) {

for (int index=0; index<items.length; index++) {

for (int subIndex=index; subIndex<items.length; subIndex++) {

if (items[subIndex] < items[index]) {

int temp = items[index];

items[index] = items[subIndex];

items[subIndex] = temp;

}

The TestSorts application generates an array of integers and then calls

selectionSort() to sort the array elements:

import java.util.Scanner;

import java.util.Random;

public class TestSorts {

public static void displayArray(int[] array) {

for (int i = 0; i < array.length; i++) {

System.out.print(array[i] + " ");

}

System.out.println("\n");

}

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

int numItems;

int[] test;

Random rand = new Random();

System.out.print("Enter number of elements: ");

numItems = input.nextInt();

/* populate array with random integers */

test = new int[numItems];

for (int i = 0; i < test.length; i++) {

test[i] = rand.nextInt(100);

}

System.out.println("Unsorted:");

displayArray(test);

Sorts.selectionSort(test);

System.out.println("Sorted:");

displayArray(test);

}

Chapter 13 Recursion and Advanced Algorithms 339

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The TestSorts application produces output similar to:

Sorting Objects

Relational operators, such as > and <, cannot be used to compare objects.

Objects use methods of their class to determine if one object is greater

than, less than, or equal to another. The equals() method in a class is used

to determine equality. For determining order, the compareTo() method is

used.

Objects that are to be sorted must have a class that implements the

Comparable interface. The String, Double, and Integer clases implement

the Comparable interface. The Circle class in Chapter 9 also implements

the Comparable interface.

An interface cannot be used to instantiate a class. However, an interface

can be used as a data type. An interface data type can reference any class

that implements it. This polymorphic behavior makes it possible to imple-

ment a generic sort that works with any list of objects that implement the

Comparable interface.

The Sorts class has been modified to include an overloaded SelectionSort()

method, which has a Comparable array parameter:

/**

* Sorts an array of objects from low to high

* pre: none

* post: Objects have been sorted from low to high

public static void selectionSort(Comparable[] items) {

for (int index = 0; index < items.length; index++) {

for (int subIndex=index; subIndex<items.length; subIndex++) {

if (items[subIndex].compareTo(items[index]) < 0) {

Comparable temp = items[index];

items[index] = items[subIndex];

items[subIndex] = temp;

}

The TestSorts application, on the next page, has been modified to sort

an array of Circle objects:

polymorphism

Comparable interface

equals(), compareTo()

340 Chapter 13 Recursion and Advanced Algorithms

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import java.util.Scanner;

import java.util.Random;

public class TestSorts {

public static void displayArray(Circle[] array) {

for (int i = 0; i < array.length; i++) {

System.out.println(array[i] + " ");

}

System.out.println("\n");

}

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

int numObjects;

Circle[] test;

Random rand = new Random();

System.out.print("Enter number of objects: ");

numObjects = input.nextInt();

input.close();

/* populate array with Circle objects of varying radii */

test = new Circle[numObjects];

for (int i = 0; i < test.length; i++) {

test[i] = new Circle(rand.nextInt(10));

}

System.out.println("Unsorted:");

displayArray(test);

Sorts.selectionSort(test);

System.out.println("Sorted:");

displayArray(test);

}

The TestSorts application produces output similar to:

Chapter 13 Recursion and Advanced Algorithms 341

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Review: ArrayListSort

Create an ArrayListSort application that implements a selection sort on an ArrayList object. Test the sort with

an ArrayList containing Double objects.

Insertion Sort

More efficient than the selection sort algorithm is the insertion sort

algorithm. An insertion sort starts by sorting the first two items in a list.

This sort is performed by shifting the first item into the second spot if

the second item belongs in the first spot. Next, the third item is properly

inserted within the first three items by again shifting items into their

appropriate position to make room for the moved item. This process is

repeated for the remaining elements.

The insertion sort is illustrated below with an array containing four

elements. Step 1 shows the original list, which contains items 40, 10, 30,

and 20. Step 2 shows that 40 is shifted to make room for the second item,

10. Next, 30 compared to the value in the previous position (40), 40 is

shifted into position 3, 30 is then compared to the value in the previous

position (10), and then 30 is placed at position 2. This process repeats for

the remaining items.

Based on the algorithm, the insertion sort pseudocode for an array of

integers is:

for (index = 1 To array.length - 1) {

temp = array[index]

previousIndex = index - 1

while (array[previousIndex] > temp && previousIndex > 0) {

shift array[previousIndex] up one element

previousIndex = previousIndex - 1

}

if (array[previousIndex] > temp) {

swap the two elements

} else {

insert element at appropriate location

}

342 Chapter 13 Recursion and Advanced Algorithms

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The Sorts class has been modified to include an insertionSort()

method:

/**

* Sorts an array of integer from low to high

* pre: none

* post: Integers have been sorted from low to high

public static void insertionSort(int[] items) {

int temp, previousIndex;

for (int index = 1; index < items.length; index++) {

temp = items[index];

previousIndex = index - 1;

while ((items[previousIndex] > temp) && (previousIndex > 0)) {

items[previousIndex + 1] = items[previousIndex];

previousIndex -= 1; //decrease index to compare current

} //item with next previous item

if (items[previousIndex] > temp) {

/* shift item in first element up into next element */

items[previousIndex + 1] = items[previousIndex];

/* place current item at index 0 (first element) */

items[previousIndex] = temp;

} else {

/* place current item at index ahead of previous item */

items[previousIndex + 1] = temp;

}

The TestSorts application has been modified to use the insertionSort()

method to sort an array of integers:

import java.util.Scanner;

import java.util.Random;

public class TestSorts {

public static void displayArray(int[] array) {

for (int i = 0; i < array.length; i++) {

System.out.print(array[i] + " ");

}

System.out.println("\n");

}

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

int numItems;

int[] test;

Random rand = new Random();

System.out.print("Enter number of elements: ");

numItems = input.nextInt();

/* populate array with random integers */

test = new int[numItems];

for (int i = 0; i < test.length; i++) {

test[i] = rand.nextInt(100);

}

System.out.println("Unsorted:");

displayArray(test);

Sorts.insertionSort(test);

Chapter 13 Recursion and Advanced Algorithms 343

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System.out.println("Sorted:");

displayArray(test);

}

The TestSorts application produces output similar to:

Review: ObjectsInsertionSort

Create an ObjectsInsertionSort application that implements an insertion sort on an array of objects. Test the

sort on an array of String objects.

Recursion

A method can call itself. This process is called recursion and the calls

are referred to as recursive calls. The RecursiveDemo application contains

a method that calls itself:

public class RecursiveDemo {

public static void showRecursion(int num) {

System.out.println("Entering method. num = " + num);

if (num > 1) {

showRecursion(num - 1);

}

System.out.println("Leaving method. num = " + num);

}

public static void main(String[] args) {

showRecursion(2);

}

The call showRecursion(2) from the main() method is the initial call. In

the showRecursion() method, a call is made to itself passing num - 1. When

showRecursion is called with num equal to 1, the if is skipped and the

remaining statement in the method is executed. At this point the stack of

calls made before num was 1 are executed in the reverse order they were

made, with each call executing the statement in the method after the

recursive call (after the if).

The RecursiveDemo produces the output shown on the next page:

recursive call

344 Chapter 13 Recursion and Advanced Algorithms

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Recursion is a programming technique that can be used whenever a

problem can be solved by solving one or more smaller versions of the same

problem and combining the results. The recursive calls solve the smaller

problems.

One problem that has a recursive solution is raising a number to a power.

For example, 2

can be thought of as:

= 2 * 2

which can be thought of as

= 2 * 2

which can be thought of as

= 2 * 2

which can be thought of as

= 2 * 2

which can be thought of as

In each case, the power problem is reduced to a smaller power problem.

A more general solution is:

= x * x

n–1

However, carefully analyzing this solution shows that there is no stopping

point. For example, 2

would be 2 * 2

, which would return 2 * 2

, which

returns 2 * 2

, which returns 2 * 2

–1

, and so on. This solution would cause

infinite recursion. To prevent this, a recursive solution must have a base

case that requires no recursion. For this solution, when the power is 0, 1

should be returned.

The intPower() method in the Power application implements a recursive

solution for calculating an int raised to an int power to return an int (as

opposed to Math.pow(), which returns a double):

public class Power {

/**

* Returns num to the power power.

* pre: num and power are not 0.

* post: num to the power power has been returned.

public static int intPower(int num, int power) {

int result;

if (power == 0) {

result = 1;

} else {

result = num * intPower(num, power-1);

}

return(result);

}

public static void main(String[] args) {

int x = intPower(2, 5);

System.out.println(x);

}

The Power application produces the output:

infinite recursion

base case

Chapter 13 Recursion and Advanced Algorithms 345

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Review: RecursiveFactorial

Create a RecursiveFactorial application that returns the factorial of an integer. The factorial of a number is

the product of all positive integers from 1 to the number. For example, 5! = 5*4*3*2*1. Computing 5! could be

thought of as 5*4! or more generally, n*(n–1)!. By definition, 0! is equal to 1. Compare your recursive solution

to the nonrecursive solution created in the Factorial Review completed in Chapter 6.

Mergesort

The selection sort is simple, but inefficient, especially for large arrays.

Imagine using the selection sort process by hand for a pile of 1000 index

cards. Searching through the cards for the lowest item would take a long

time, but more importantly, after each search the remaining cards must

be searched again! Each card ends up being examined about 500 times.

The mergesort algorithm takes a “divide-and-conquer” approach to sort-

ing. Imagine the 1000 cards being divided into two piles of 500. Each pile

could then be sorted (a simpler problem) and the two sorted piles could

be combined (merged) into a single ordered pile. To further simplify the

sorting, each subpile could be divided and sorted, and so on. This algo-

rithm is best implemented recursively.

The mergesort pseudocode is:

if there are items remaining {

mergesort the left half of the items

mergesort the right half of the items

merge the two halves into a completely sorted list

}

The mergesort subtasks are recursive calls to mergeSort() and a call to

merge(). The mergesort() method will need arguments indicating which

portion of the array is to be sorted. Similarly, merge() implements the

merging of two halves and needs arguments indicating which portion of

the array is to be merged.

The mergesort() method is defined as:

/**

* Sorts items[start..end]

* pre: start > 0, end > 0

* post: items[start..end] is sorted low to high

public static void mergesort(int[] items, int start, int end) {

if (start < end) {

int mid = (start + end) / 2;

mergesort(items, start, mid);

mergesort(items, mid + 1, end);

merge(items, start, mid, end);

}

The stopping condition for the recursive function is determined by

comparing start and end. The middle of the array is calculated using

integer division, which automatically truncates the decimal portion of the

quotient.

TIP Measuring an algorithm’s

efficiency is discussed later in

this chapter.

346 Chapter 13 Recursion and Advanced Algorithms

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The merge() method uses a temporary array to store items moved from

two sorted portions of the items array. The elements are moved so that the

temporary array is sorted. To illustrate the merge() algorithm, suppose at

entry to merge() the array looks like:

The array is sorted from start to mid and from mid+1 to end. The merge()

method starts by examining the first element of each sorted portion, start

and mid+1, as indicated by pos1 and pos2:

Since items[pos1] < items[pos2], the element items[pos1] is moved to the

new array, and pos1 is incremented:







In this case, items[pos1] > items[pos2], so the the element items[pos2] is

moved to the new array and pos2 incremented:

This process is repeated until all items have been moved. Since it is likely

that one array portion will be exhausted before the other, merge() tests for

this case and just moves items from the remaining list. Finally, merge()

copies the merged items in the temporary array to the original array.

The Sorts class has been modified to include a mergesort() method.

Note that the merge() method is private because it is a helper method:

Chapter 13 Recursion and Advanced Algorithms 347

sample

/**

* Merges two sorted portion of items array

* pre: items[start..mid] is sorted. items[mid+1..end] sorted.

* start <= mid <= end

* post: items[start..end] is sorted.

private static void merge(int[] items, int start,

int mid, int end) {

int[] temp = new int[items.length];

int pos1 = start;

int pos2 = mid + 1;

int spot = start;

while (!(pos1 > mid && pos2 > end)) {

if ((pos1 > mid) ||

((pos2 <= end) && (items[pos2] < items[pos1]))) {

temp[spot] = items[pos2];

pos2 += 1;

} else {

temp[spot] = items[pos1];

pos1 += 1;

}

spot += 1;

}

/* copy values from temp back to items */

for (int i = start; i <= end; i++) {

items[i] = temp[i];

}

/**

* Sorts items[start..end]

* pre: start > 0, end > 0

* post: items[start..end] is sorted low to high

public static void mergesort(int[] items, int start, int end) {

if (start < end) {

int mid = (start + end) / 2;

mergesort(items, start, mid);

mergesort(items, mid + 1, end);

merge(items, start, mid, end);

}

The if in the merge() method says that if the pos1 (left) subarray is

exhausted, or if the pos2 (right) subarray is not exhausted and the pos2

element is less than the pos1 element, then move an item from the pos2

subarray to the temp array, otherwise move an item from the pos1 subar-

ray. This process continues until both subarrays are exhausted.

348 Chapter 13 Recursion and Advanced Algorithms

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The TestSorts application has been modified to use the mergesort()

method to sort an array of integers:

import java.util.Scanner;

import java.util.Random;

public class TestSorts {

public static void displayArray(int[] array) {

for (int i = 0; i < array.length; i++) {

System.out.print(array[i] + " ");

}

System.out.println("\n");

}

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

int numItems;

int[] test;

Random rand = new Random();

System.out.print("Enter number of elements: ");

numItems = input.nextInt();

/* populate array with random integers */

test = new int[numItems];

for (int i = 0; i < test.length; i++) {

test[i] = rand.nextInt(100);

}

System.out.println("Unsorted:");

displayArray(test);

Sorts.mergesort(test, 0, test.length - 1);

System.out.println("Sorted:");

displayArray(test);

}

The TestSorts application produces output similar to:

Review: ObjectsMergesort

Create an ObjectsMergesort application that implements a mergesort on an array of objects. Test the sort on

an array of String objects.

Chapter 13 Recursion and Advanced Algorithms 349

sample

Binary Search

Arrays are sorted in order to perform a more efficient search. A binary

search is used with a sorted list of items to quickly find the location of

a value. Like the mergesort algorithm, the binary search algorithm also

takes a divide-and-conquer approach. It works by examining the middle

item of an array sorted from low to high, and determining if this is the

item sought, or if the item sought is above or below this middle item. If

the item sought is below the middle item, then a binary search is applied

to the lower half of the array; if above the middle item, a binary search is

applied to the upper half of the array, and so on.

For example, a binary search for the value 5 in a list of items 1, 2, 3, 4, 5,

6, and 7 could be visualized as:

The binary search algorithm is very efficient. For example, an array of

100 elements checks no more than 8 elements in a search, and in an array

of one million items no more than 20 items are checked. If a list of the

entire world’s population were to be searched using this algorithm, less

than 40 checks are made to find any one person.

The binary search algorithm can be implemented recursively. The

pseudocode for a recursive solution appears like:

if (goal == items[mid]) {

return(mid)

} else if (goal < items[mid]) {

return(binarySearch(lowerhalf)

} else {

return(binarySearch(upperhalf)

}

The Searches class on the next page implements a binary search:

TIP The linear search algorithm

was introduced in Chapter 10.

A linear search, also called a

sequential search, is much less

efficient than a binary search.

However, a linear search does

not require a sorted list.

350 Chapter 13 Recursion and Advanced Algorithms

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public class Searches{

/**

* Searches items array for goal

* pre: items is sorted from low to high

* post: Position of goal has been returned,

* or -1 has been returned if goal not found.

public static int binarySearch(int[] items, int start,

int end, int goal) {

if (start > end) {

return(-1);

} else {

int mid = (start + end) / 2;

if (goal == items[mid]) {

return(mid);

} else if (goal < items[mid]) {

return(binarySearch(items, start, mid-1, goal));

} else {

return(binarySearch(items, mid+1, end, goal));

}

The TestSorts application has been modified to sort an array of integers

and then prompt the user for a number to search for:

import java.util.Scanner;

import java.util.Random;

public class TestSorts {

public static void displayArray(int[] array) {

for (int i = 0; i < array.length; i++) {

System.out.print(array[i] + " ");

}

System.out.println("\n");

}

public static void sortIntArray() {

Scanner input = new Scanner(System.in);

int numItems, searchNum, location;

int[] test;

Random rand = new Random();

System.out.print("Enter number of elements: ");

numItems = input.nextInt();

/* populate and sort array */

test = new int[numItems];

for (int i = 0; i < test.length; i++) {

test[i] = rand.nextInt(100);

}

Sorts.mergesort(test, 0, test.length - 1);

System.out.println("Sorted:");

displayArray(test);

Chapter 13 Recursion and Advanced Algorithms 351

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/* search for number in sorted array */

System.out.print("Enter a number to search for: ");

searchNum = input.nextInt();

while (searchNum != -1){

location = Searches.binarySearch(test, 0,

test.length-1, searchNum);

System.out.println("Number at position: " + location);

System.out.print("Enter a number to search for: ");

searchNum = input.nextInt();

}

public static void main(String[] args) {

sortIntArray();

}

The modified TestSorts application displays output similar to:

Review: SearchLocations

Create a SearchLocations application that displays the positions examined during a binary search. The

application output should look similar to:

352 Chapter 13 Recursion and Advanced Algorithms

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Review: ObjectsBinarySearch

Create an ObjectsBinarySearch application that implements a binary search on an array of objects. Test the

search on an array of String objects.

Review: BinarySearch2

Create a BinarySearch2 application that implements a nonrecursive binary search. The binary search algo-

rithm can be implemented without recursion by doing the following:

• Enclose the method body with a do-while loop

• Replace the recursive calls with appropriate assignments to the values of start or

end.

Depth-First Searching

Many programs generate and search through a series of possibilities,

such as:

• different paths through a maze

• different possible ways of making change

• different possible plays in a game

• different schedules for a student in a school

• different pixels reachable from an initial pixel

All these tasks can be solved through the recursive technique called depth-

first searching. The depth-first searching algorithm works by searching from

a given starting position, processing that position, and then (recursively)

searching from all adjacent positions.

Depth-first searching can be illustrated in a DetectColonies application

that allows a researcher to determine the number and size of distinct

colonies of bacteria on a microscope slide. The slide has been converted to

digital format, where a * represents a cell that is part of a colony, and a -

represents the background color of the slide. A slide file has the format:

First line: length of slide

Second line: width of slide

Remaining lines: slide data.

For example, a slide file could look similar to:

---------

---*--*--

--***-**-

***---*--

**-**----

---****--

---*--*--

Chapter 13 Recursion and Advanced Algorithms 353

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Cells are considered to be part of the same colony if they touch hori-

zontally or vertically. The example slide contains three colonies. Counting

rows and columns starting from zero, one colony has a cell at (1, 3) and

contains 9 elements. Another colony has four elements with a cell at (1,

6), and the third has eight elements with a cell at (4, 3). Note that the first

and third colonies are considered separate because they touch across a

diagonal but not horizontally or vertically.

The DetectColonies application analyzes the slide and displays the fol-

lowing output:

A depth-first search is appropriate here because once a colony cell is

detected, all the possible directions for connected cells must be searched.

If a connected cell is a colony cell, then all the possible directions for that

cell must be searched, and so on. The basic idea is that, given a starting

cell at (row, col) in a colony, the total number of connected cells in that

colony can be found as:

1 for the starting cell

+ count of connected cells starting with (row+1, col)

+ count of connected cells starting with (row–1, col)

+ count of connected cells starting with (row, col+1)

+ count of connected cells starting with (row, col–1)

The latter four lines are recursive calls. To find the starting cells, each cell

in the slide is tested with a nested for loop.

When implementing a depth-first search algorithm, code must be

included to avoid infinite recursion. For example, a starting cell of (1, 3)

generates a recursive call with cell (2, 3), which generates a call with (1, 3)

again, which generates a call with (2, 3), and so on. For this application, a

cell will be changed to the background color once it has been examined.

This makes counting colonies a destructive algorithm.

The DetectColonies application can be modeled with a Slide class. The

constructor will load the slide data into variable member slideData, which

is a two-dimensional array appropriate for modeling the slide. Method

members displaySlide() and displayColonies() will display the slide and

determine the colonies. Member constants COLONY and NON _ COLONY will

represent * and -.

The displayColonies() method checks each cell of the entire slide, and

whenever a colony cell is encountered, displayColonies() determines the

colony size and displays data about the colony. To determine the size,

displayColonies() calls a private member method collectCells(), which

changes a cell to the background once it is counted.

The Slide class is implemented on the next page:

354 Chapter 13 Recursion and Advanced Algorithms

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import java.io.*;

public class Slide {

private char COLONY = '*', NON _ COLONY = '-';

private char[][] slideData;

/**

* constructor

* pre: Slide file contains valid slide data in the format:

* first line: lenght of slide

* second line: width of slide

* remaining lines: slide data

* post: Slide data has been loaded from slide file.

public Slide(String s) {

try {

File slideFile = new File(s);

FileReader in = new FileReader(slideFile);

BufferedReader readSlide = new BufferedReader(in);

int length = Integer.parseInt(readSlide.readLine());

int width = Integer.parseInt(readSlide.readLine());

slideData = new char[length][width];

for (int row = 0; row < length; row++) {

for (int col = 0; col < width; col++) {

slideData[row][col] = (char)readSlide.read();

}

readSlide.readLine(); //read past end-of-line

}

readSlide.close();

in.close();

} catch (FileNotFoundException e) {

System.out.println("File does not exist or could not

be found.");

System.err.println("FileNotFoundException: "

+ e.getMessage());

} catch (IOException e) {

System.out.println("Problem reading file.");

System.err.println("IOException: " + e.getMessage());

}

/**

* Determines a colony size

* pre: none

* post: All colony cells adjoining and including

* cell (Row, Col) have been changed to NON _ COLONY,

* and count of these cells is returned.

private int collectCells(int row, int col) {

if ((row < 0) || (row >= slideData.length) ||

(col < 0) || (col >= slideData[0].length)

|| (slideData[row][col] != COLONY)) {

return(0);

} else {

slideData[row][col] = NON _ COLONY;

return(1+

collectCells(row+1, col)+

collectCells(row-1, col)+

collectCells(row, col+1)+

collectCells(row, col-1));

}

Chapter 13 Recursion and Advanced Algorithms 355

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/**

* Analyzes a slide for colonies and displays colony data

* pre: none

* post: Colony data has been displayed.

public void displayColonies() {

char[][] temp;

int count;

for (int row = 0; row < slideData.length - 1; row++) {

for (int col = 0; col < slideData[0].length; col++) {

if (slideData[row][col] == COLONY) {

count = collectCells(row, col);

System.out.println("Colony at (" + row + "," + col

+ ") with size " + count);

}

/**

* Displays a slide.

* pre: none

* post: Slide data has been displayed.

public void displaySlide() {

for (int row = 0; row < slideData.length; row++) {

for (int col = 0; col < slideData[0].length; col++) {

System.out.print(slideData[row][col]);

}

System.out.println();

}

The depth-first search algorithm is implemented in the helper method

collectCells(). The first if statement checks to see that the current posi-

tion is on the slide and contains a colony cell. This eliminates the need to

check before each recursive call. As good programming style, it is better

to check data at the start of the recursive function rather than before each

call.

The DetectColonies application is relatively simple:

public class DetectColonies {

public static void main(String[] args) {

Slide culture = new Slide("slide.dat");

culture.displaySlide();

culture.displayColonies();

}

356 Chapter 13 Recursion and Advanced Algorithms

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The DetectColonies application displays output similar to:

Review: DetectColonies – part 1 of 3

How must the DetectColonies application be modified if the definition of a colony allowed the colony to be

connected across diagonals? What colonies would be reported by DetectColonies for the sample slide?

Review: DetectColonies – part 2 of 3

Modify the DetectColonies application to display the slide colonies from largest to smallest.

Review: DetectColonies – part 3 of 3

What slide will be output by the second culture.displaySlide() statement if DetectColonies contained the

statements below? Explain.

public static void main(String[] args) {

Slide culture = new Slide("slide.dat");

culture.displaySlide();

culture.displayColonies();

culture.displaySlide();

}

Algorithm Analysis

Algorithm analysis includes measuring how efficiently an algorithm

performs its task. A more efficient algorithm has a shorter running time.

Running time is related to the number of statements executed to implement

an algorithm. It can be estimated by calculating statement executions.

Running time estimations are usually based on a worst-case set of data.

For example, an array that is already sorted or nearly sorted may require

fewer statement executions than an array of data that is in reverse sorted

order. Since the original state of the data is usually unknown, the worst

case should be assumed.

As a first analysis, consider the selection sort algorithm, which uses

nested for loops to sort items. If the sort is thought of in simplified terms,

with each for statement containing a single statement, for an array of n

items, n * n statements are executed. The selection sort is therefore said

to have a running time of n

TIP Theoretical running times

can be written in Big Oh

notation, which is a theoretical

measure of an algorithm’s

efficiency.

Chapter 13 Recursion and Advanced Algorithms 357

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The insertion sort algorithm seems more efficient because a while loop

is used within a for loop. This could allow for a faster sort in some cases,

but in the worst case, the insertion sort algorithm executes n statements *

n–1 statements for a running time of about n

The mergesort is a more complicated algorithm, but a divide and conquer

approach can be much more efficient than a linear approach. Because this

algorithm divides the array and each subarray in half until the base case

of one element is reached, there are Log

n calls to mergesort() and then n

calls to merge. The mergesort algorithm is said to have running time of

n Log

The binary search also implements a divide and conquer approach.

However, the elements are already ordered. The algorithm is simply

performing a search. Because this algorithm divides the array and each

subarray in half until the base case of one element is reached, there are

Log

n calls to binarySearch(). Therefore, the algorithm is said to have a

running time of Log

Chapter Summary

Sorting is the process of putting items in a designated order, either from

low to high or high to low. The selection sort, insertion sort, and mergesort

algorithms were presented in this chapter. The merge sort algorithm takes

a divide-and-conquer approach to sorting. It is implemented recursively

and is much faster than the selection and insertion sorts.

Objects cannot be compared with relational operators. Therefore, lists of

objects are sorted by implementing an algorithm that uses the Comparable

interface. Interfaces can be used as data types, which allows a generic

implementation of an algorithm that sorts objects. Objects that are to be

sorted must have a class that implements the Comparable interface.

A method can call itself in a process called recursion. Recursion is a

programming technique that can be used whenever a problem can be

solved by solving one or more smaller versions of the same problem and

combining the results. To prevent infinite recursion, a base case that

requires no recursion must be part of the recursive solution.

A binary search algorithm can be used to find an element in a sorted

array. Binary search is implemented recursively and is very efficient. The

depth-first searching algorithm can be used to search through a series

of possibilities. When implementing depth-first searching, code must be

included to avoid infinite recursion.

Algorithm analysis includes how efficiently an algorithm performs its

task. A more efficient algorithm has a shorter running time.

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Vocabulary

Binary search A searching algorithm that recursively

checks the middle of a sorted list for the item being

searched for.

Base case The part of a recursive solution that

requires no recursion.

Depth-first search A searching algorithm that

recursively checks a starting position, processes that

position, and then searches adjacent positions.

Infinite recursion A recursive solution which has

no base case.

Mergesort A sorting algorithm that recursively

divides a list into halves, sorting those halves,

and then merging the lists so that the items are in

order.

Insertion sort A sorting algorithm that repeat-

edly inserts an item into the appropriate position

of a subarray until the subarray has no items left

to insert.

Recursion The process in which a method calls

itself. A programming technique that can be used

whenever a problem can be solved by solving one

or more smaller versions of the same problem and

combining the results.

Recursive call A call to a method from within the

same method.

Selection sort A sorting algorithm that repeatedly

selects the lowest item in a subarray of an array and

moves it to the position just before the subarray until

the subarray has no items left to search.

Java

Comparable A java.lang interface that is required

to be implemented by a class if their objects are to

be sorted. Comparable can also be used as a data

type.

Chapter 13 Recursion and Advanced Algorithms 359

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Critical Thinking

1. For the list 4, 6, 2, 10, 9, show how the numbers

are ordered after each loop iteration of the

algorithms:

a) selection sort

b) insertion sort

2. What must be done to a list of items in order to

use a binary search to find a specific item?

3. Use the recursive method below to answer the

questions:

public void ct(int n) {

System.out.println("Starting " + n);

if (n > 0) {

ct(n/3);

System.out.println("Middle " + n);

}

a) What output is generated when ct(13) is

called?

b) What output is generated when ct(3) is

called?

c) What output is generated when ct(0) is

called?

4. Use the recursive method below to answer the

questions:

public void ct(int n) {

System.out.println(n);

if (n > 0) {

if (n % 2 == 1) {

ct(n/3);

} else {

ct(n/2);

}

a) What output is generated when ct (13) is

called?

b) What output is generated when ct(14) is

called?

c) What output is generated when ct(15) is

called?

5. Use the recursive method below to answer the

questions:

public void ct(int n) {

if (n > 0) {

ct(n/10);

System.out.println(n % 10);

}

a) What output is generated when ct (13) is

called?

b) What output is generated when ct(124) is

called?

c) What output is generated when ct(21785) is

called?

d) What in general does this method do?

6. Use the recursive method below to answer the

questions:

public void whatzItDo() {

Scanner input = new Scanner(System.in);

String letter = input.next();

if (!letter.equals(".")) {

whatzItDo();

System.out.print(letter);

}

a) What output is generated when the user

enters T, E, S, T, . ?

b) What in general does this method do?

7. A sorting algorithm is said to be “stable” if two

items in the original array that have the same

“key value” (the value to be sorted on) maintain

their relative position in the sorted version. For

example, assume an array with the following

data:

Ann Jon Mel Tom Kim

20 19 18 19 22

When the array is sorted by age, a stable sort

would guarantee that Jon would stay ahead of

Tom in the sorted array, as in:

Kim Ann Jon Tom Mel

22 20 19 19 18

and not:

Kim Ann Tom Jon Mel

22 20 19 19 18

Which of the sorts presented in this chapter

(selection, mergesort) is stable? For each which

is not stable, give an example of data to illustrate

this.

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True/False

8. Determine if each of the following are true or

false. If false, explain why.

a) Sorting always puts items in order from low

to high.

b) One measure of the efficiency of a sorting

algorithm is the speed at which it can com-

plete a sort.

c) The selection sort algorithm is more efficient

than the insertion sort.

d) A method can call itself.

e) The merge sort algorithm is more efficient

than the selection sort algorithm for large

arrays.

f) A binary search is used to sort a list of

items.

g) A binary search starts by examining the last

item in an array.

h) The more statements required to complete a

task, the more efficient the algorithm.

i) An interface can be used as a data type.

j) A recursive solution that has no base case

results in infinite recursion.

k) An insertion sort recursively divides a list

into halves, sorting those halves, and then

merging the lists in order.

Chapter 13 Recursion and Advanced Algorithms 361

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Exercises

Exercise 1 —————————————————————— Friends

Create a Friends database application that maintains a file of Friend objects that contain names, tele-

phone numbers, and email addresses. The Friends application should load Friend records from a file

and then allow the user to add new friends, delete friends, display a list of all friends by either first

name or last name, and search for a friend. The application should display a menu similar to:

Exercise 2 ——————————————————— TernarySearch

Modify the Searches class to include a ternarySearch() method. A ternary search, similar to a binary

search, divides an array into three pieces rather than two. A ternary search finds the points that divide

the array into three roughly equal pieces, and then uses these points to determine where the goal

should be searched for.

Exercise 3 ———————————————— InterpolationSearch

Modify the Searches class to include an interpolationSearch() method. An interpolation search is a

variation of the binary search. The idea is to look in a likely spot, not necessarily the middle of the

array. For example, if the value sought is 967 in an array that holds items ranging from 3 to 1022, it

would be intelligent to look nearly at the end of the array. Mathematically, because 967 is about 95% of

the way from 3 to 1022, the position to start searching at is a position 95% of the way down the array.

For example, if the array holds 500 elements, the first position to examined is 475 (95% of the way from

1 to 500). The search then proceeds to a portion of the array (either 1..474 or 476..500) depending upon

whether 967 is greater or less than the 475th element.

Exercise 4 ————————————————————— NumDigits

Create a NumDigits application that includes a recursive method numDigits() that returns the number

of digits in its integer parameter. Numbers –9 through 9 have one digit; numbers –99 to –10 and 10 to

99 have two digits, and so on. (Hint: the number of digits of a number n is one more than the number

of digits in n/10.)

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Exercise 5 —————————————————— DetectColonies2

Create a DetectColonies2 application that is based on DetectColonies presented in this chapter. This

application gives improved colony results because slides are now digitized to report color. For example,

a slide file could look similar to:

00550000

00050000

00005500

01200000

01111000

00000030

The digits 1 through 9 represent various colors. The digit 0 represents black (background color).

The DetectColonies2 application should display a listing of the size, location, and color value of each

colony on the slide. A colony is defined as a connected (horizontally or vertically) sequence of cells

holding the same color value. For the above slide, the application should report:

Color Size Location

5 3 1, 3

5 2 3, 5

1 5 4, 2

2 1 4, 3

3 1 6, 7

Exercise 6 ————————————————————— Knapsack

A well-known problem in computer science is called the knapsack problem. A variation is as follows:

Given a collection of weights of (possibly) different integral values, is it possible to

place some of the weights in a knapsack so as to fill it to some exact total weight?

For example, if the weights are 3, 5, 6, and 9, then it is possible for such totals as 3, 8,

11, 14, 17, etc. to be made exactly, but 2, 4, 22, etc. are not possible.

Create a Knapsack application that solves this problem. The fillKnapsack() method handles the first

weight, and then recursively handles the remaining weights with an isPossible() helper method.

fillKnapsack() and isPossible() have the following declarations:

/* Returns true if there exists a subset of the items in

* weights[start..weights.length] that sum to goal.

* pre: items in weights[start..weights.length] > 0

* post: true has been returned if there exists a subset

* of items in weights[start..weights.length] that sum to goal.

fillKnapsack(int[] weights, int goal, int start)

Chapter 13 Recursion and Advanced Algorithms 363

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/* Returns true if there exists a subset of the items in

* weights that sum to goal.

* pre: items in weights > 0

* post: true has been returned if there exists a subset

* of items in weight that sum to goal.

isPossible(int[] weights, int goal)

The fillKnapsack algorithm determines if the goal can be found in all of the items not including the

first, or if it can be found by including the first in the subset. The pseudocode is:

if (simple case) {

handle simple cases

} else {

if (fillKnapsack(weights, goal, start+1)) {

return(true);

} else if (fillKnapsack(weights, goal-weights[start], start+1)) {

return(true);

} else {

return(false);

}

Note that the simple cases will need to be determined and handled properly.

Exercise 7 ——————————————————————— Maze

A maze can be defined in a file using X characters to represent walls, space characters to represent paths,

and a $ character to represent the goal. For example, a file containing a maze could look similar to:

XXXXXXXXXX

X X

XX XXX XXX

XX X X

XXXX X X X

X X XXX

X XXXX $X

XXXXXXXXXX

The starting point is assumed to be location (1, 1) and the maze is assumed to have a border. Create a

Maze application that displays the sequence of positions in a path from the start to the goal, or indicate

if no path is available. For example, for the maze above, the application should report:

Path: (1,1) (1,2) (1,3) (1,4) (1,5) (1,6)

(2,6) (3,6) (4,6) (5,6) (6,6) (6,7) (6,8)

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Exercise 8 ————————————————————— MyBoggle

The game of Boggle is played on a square board with random letters. The object is to find words

formed on the board by contiguous sequences of letters. Letters are considered to be touching if they

are horizontally, vertically, or diagonally adjacent. For example, the board:

Q W E R T

A S D F G

Z X C V B

Y U A O P

G H J K L

contains the words WAS, WAXY, JOB, and others, but not the word BOX. Words can contain duplicate

letters, but a single letter on the board may not appear twice in a single word, for example POP is not

contained on this board.

Create a MyBoggle application that displays a board of random letters, and allows the user to enter

words found on the board. The application should report if the word entered by the user is indeed on

the board.

Hint: Search the board for the first letter of the word entered, and then recursively search around the

found letter for the remaining letters of the word.

Chapter 14 Data Structures 365

sample

ata structures are discussed in this chapter. Stacks, queues, and

linked lists are covered.

The Stack Data Structure

A data structure organizes data. The stack data structure can contain

many data items just as an array can. Additionally, it has a set of operations

that can be performed on the data.

A stack structure has a top. For example, the stack shown below holds

three integers. The value 11 is the top item in the stack:

There are two standard operations that can be performed on the items

in a stack, and only the top item of a stack can be processed. The pop

operation removes the top item. For example, when a pop is executed on

the stack above, the top value, 11, is removed:

The next item, 34, is now at the top of the stack, and is the only item that

can be accessed.

Another operation is the push operation, which adds an item to the top

of the stack. For example, if the value 27 is pushed onto the stack, the stack

becomes:

Chapter 14

Data Structures

top

pop

push

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Other stack operations include the isEmpty query, which returns true

when there are no items in the stack, and false otherwise. The size opera-

tion determines the number of items in a stack. A stack can be emptied

with the makeEmpty operation.

Since the stack is designed so that the last item pushed on is the first

item to be popped, it is sometimes referred to as a last-in-first-out (LIFO)

data structure. There are a number of applications of stacks, particularly in

writing compiler software. For example, each of the following is generally

performed using a stack:

• Matching of braces, { and }. In Java, a close brace, }, always goes

with the last open brace, {.

• Matching else with if: An else always goes with the last if.

• Matching of parentheses in an expression: A closing parenthesis

always goes with the last open parenthesis.

• Recursion: After completion of a recursive call, control returns

to the last call that was executed. In fact, recursion is sometimes

replaced with a stack.

The Stack Class

A data structure has a specific set of operations that can be performed

on the data it stores. Therefore, a class is often used to implement the data

structure.

The StackDemo application uses a stack:

public class StackDemo {

public static void main(String[] args) {

Stack s = new Stack(10);

System.out.println("Adding 10 and 13 to stack.");

s.push(10);

s.push(13);

System.out.println("Top of stack: " + s.top());

System.out.println("Items in stack: " + s.size());

System.out.println("Removing top item.");

s.pop();

System.out.println("Top of stack: " + s.top());

System.out.println("Items in stack: " + s.size());

System.out.println("Adding a new item.");

s.push(40);

System.out.println("Top of stack: " + s.top());

System.out.println("Items in stack: " + s.size());

}

LIFO

isEmpty

size

makeEmpty

Chapter 14 Data Structures 367

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The StackDemo produces the output:

The Stack class below is a very simple stack implementation that stores

data in an array:

public class Stack {

private int[] data;

private int top;

/**

* constructor

* pre: none

* post: An empty stack that can hold up to maxItems

* has been created.

public Stack(int maxItems) {

data = new int[maxItems];

top = -1; //no items in the array

}

/**

* Returns the top item without removing it from the stack.

* pre: Stack contains at least one item.

* post: The top item has been returned while leaving it

* on the stack.

public int top() {

return(data[top]);

}

/**

* Removes the top item from the stack and returns it.

* pre: Stack contains at least one item.

* post: The top item of the stack has been removed

* and returned.

public int pop() {

top -= 1;

return(data[top + 1]);

}

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/**

* Adds an item to the top of the stack if there is room.

* pre: none

* post: A new item has been added to the top of the stack.

public void push(int num) {

if (top < data.length - 1) {

top += 1;

data[top] = num;

}

/**

* Determines if there are items on the stack.

* pre: none

* post: true returned if there are items on the stack,

* false returned otherwise.

public boolean isEmpty() {

if (top == -1) {

return(true);

} else {

return(false);

}

/**

* Returns the number of items in the stack.

* pre: none

* post: The number of items in the stack is returned.

public int size() {

if (isEmpty()) {

return(0);

} else {

return(top + 1);

}

/**

* Empties the stack.

* pre: none

* post: There are no items in the stack.

public void makeEmpty() {

top = -1;

}

The Stack class implements a stack for int values. A generic implemen-

tation would use objects. This implementation is completed in the Stack2

review.

Review: Stack2

Create a Stack2 class that implements a stack data structure for data type Object. Since Object is the super-

class of other objects, a Stack2 object can store objects from any class. Write appropriate client code to test

the Stack2 class.

Chapter 14 Data Structures 369

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Review: Stack3

The Stack class is limited because the stack size cannot change from its initial size. Create a Stack3 class

that implements a stack data structure using an ArrayList. Write appropriate client code to test the Stack3

class.

The Queue Data Structure

A queue is a data structure similar to a stack in that it holds a number

of data items. However, one end of the queue is referred to as the rear and

the other end the front. For example, the queue shown below holds three

items:

All insertions are made at the rear and all removals are made at the

front.

There are two standard operations that can be performed on a queue.

The dequeue operation removes an item from the front. For example, when

a dequeue is executed on the queue above, the value at the front, 12, is

removed from the queue:

The enqueue operation adds an item to the rear of the queue. For example,

if the value 27 is enqueued, the queue becomes:

Other queue operations include the front operation, which returns the

front item without removing it from the queue. The isEmpty query returns

true when there are no items in the queue, and false otherwise. The size

operation determines the number of items in a queue. A queue can be

emptied with the makeEmpty operation.

A queue is analogous to a line at a ticket counter where “first come,

first served,” and is sometimes referred to as a first in first out (FIFO) data

structure. There are a number of real-world situations that can be repre-

sented as a queue structure. For example:

rear, front

dequeue

enqueue

FIFO

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• Lines at a toll booth or bank teller

• Waiting lists for tickets on planes

• Pages of data queued up for a printer

• Performing breadth-first-searching where all items near the start-

ing position are examined before looking at those farther away.

The Queue Class

The QueueDemo application uses a queue:

public class QueueDemo {

public static void main(String[] args) {

Queue q = new Queue(10);

System.out.println("Adding 10 and 13 to queue.");

q.enqueue(10);

q.enqueue(13);

System.out.println("Front of queue: " + q.front());

System.out.println("Items in queue: " + q.size());

System.out.println("Dequeueing front item.");

q.dequeue();

System.out.println("Front of queue: " + q.front());

System.out.println("Items in queue: " + q.size());

System.out.println("Queueing a new item.");

q.enqueue(40);

System.out.println("Front of queue: " + q.front());

System.out.println("Items in queue: " + q.size());

}

The QueueDemo produces the output:

The Queue class below is a very simple queue implementation that

stores data in an array:

public class Queue {

private int[] data;

private int front, rear, maxSize;

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/**

* constructor

* pre: none

* post: An empty queue that can hold up to maxItems

* has been created.

public Queue(int maxItems) {

data = new int[maxItems];

front = -1; //no items in the array

rear = -1;

maxSize = maxItems;

}

/**

* Returns the front item without removing it from

* the queue.

* pre: Queue contains at least one item.

* post: The front item has been returned while leaving

* it in the queue.

public int front() {

return(data[front]);

}

/**

* Removes the front item from the queue and returns it.

* pre: Queue contains at least one item.

* post: The front item of the queue has been removed

* and returned.

public int dequeue() {

front = (front + 1) % maxSize;

return(data[front - 1]);

}

/**

* Adds an item to the queue if there is room.

* pre: none

* post: A new item has been added to the queue.

public void enqueue(int num) {

if (isEmpty()) { //first item queued

rear = 0;

front = 0;

data[rear] = num;

} else {

rear = (rear + 1) % maxSize;

data[rear] = num;

}

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/**

* Determines if there are items on the queue.

* pre: none

* post: true returned if there are items on the queue,

* false returned otherwise.

public boolean isEmpty() {

if (front == -1 && rear == -1) {

return(true);

} else {

return(false);

}

/**

* Returns the number of items in the queue.

* pre: none

* post: The number of items in the queue is returned.

public int size() {

if (isEmpty()) {

return(0);

} else {

return(rear - front + 1);

}

/**

* Empties the queue.

* pre: none

* post: There are no items in the queue.

public void makeEmpty() {

front = -1;

rear = -1;

}

Because the queue is limited to the number of items it can store, the

front and rear pointers must cycle through the spots available in the

array. Therefore, the front and rear values are calculated using modular

arithmetic (%).

The Queue class implements a queue for int values. A generic imple-

mentation would use objects. This implementation is left as a review.

Review: Queue2

Create a Queue2 class that implements a queue data structure for data type Object. Since Object is the super-

class of other objects, a Queue2 object can store objects from any class. Write appropriate client code to test

the Object2 class.

Review: Queue3

The Queue class is limited because the queue size cannot change from its initial size. Create a Queue3 class

that implements a queue data structure using an ArrayList. Write appropriate client code to test the class.

Chapter 14 Data Structures 373

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The Linked List Data Structure

Another way of storing lists of data in memory requires each item to

store information that indicates where the next item is stored. The addi-

tional information is a reference, or pointer, to a data location. This kind

of list data structure is called a linked list, and can be illustrated like:

The first item in a linked list is called the head. The last item points to

null and is called the tail. Each element of a linked list is called a node.

There are three nodes in the list above.

Because each item in a linked list must contain data and a pointer, an

item is best modeled with a class. Therefore, a linked list is a list of objects.

The objects in a linked list are organized because they point to each other.

There is no need to place them in a structure, such as an array, for orga-

nization. This mean that linked links are not restricted by the size of an

array.

There are two standard operations that can be performed on a linked

list. The addAtFront operation adds a new node to the front of the list. When

a new node is added to the front of a linked list, it is simply designated

the head and its pointer is set to the current head. For example, if Raj was

the head, adding a new item means that the new object is now the head

and its pointer points to the Raj object:

The remove operation removes an item from the linked list. Removing

an item from a linked list means that the pointer of the previous item is

changed to point to the item after the one to be removed. For example,

removing Raj from the list below means that the object is no longer refer-

enced by another object in the list:

Linked lists are useful for maintaining dynamic lists because the num-

ber of items in a linked list can shrink and grow as needed.

TIP Objects stored in memory

are stored in dynamic memory.

Dynamic memory is allocated

from an area called the heap,

which is used during program

execution.

head, tail

node

addAtFront

remove

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The LinkedList Class

The LinkedListDemo application uses a linked link:

public class LinkedListDemo {

public static void main(String[] args) {

LinkedList list = new LinkedList();

list.addAtFront("Sachar");

list.addAtFront("Osborne");

list.addAtFront("Suess");

System.out.println(list);

list.remove("Suess");

list.remove("Sachar");

list.remove("Osborne");

System.out.println(list);

}

The LinkedListDemo produces the output:

The LinkedList class below contains a nested class. A nested class is a

class within a class. A nested class is a member of the class it is within. As

a class member, it has access to all the other members of the class, includ-

ing private member variables and methods. A class that contains a class

member is called an outer class. The Node class is a nested class because

its members should only be accessed by a LinkedList object:

public class LinkedList {

private Node head;

/**

* constructor

* pre: none

* post: A linked list with a null item has been created.

public LinkedList() {

head = null;

}

/**

* Adds a node to the linked list.

* pre: none

* post: The linked list has a new node at the head.

public void addAtFront(String str) {

Node newNode = new Node(str);

newNode.setNext(head);

head = newNode;

}

outer class

nested class

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/**

* Deletes a node in the linked list.

* pre: none

* post: The first node containing str has been deleted.

public void remove(String str) {

Node current = head;

Node previous = head;

if (current.getData().equals(str)) {

head = current.getNext();

} else {

while (current.getNext() != null) {

previous = current;

current = current.getNext();

if (current.getData().equals(str)) {

previous.setNext(current.getNext());

}

/**

* Creates a string that lists the nodes of the

* linked list.

* pre: none

* post: The linked list has been written to a string.

public String toString() {

Node current = head;

String listString;

if (current != null) {

listString = current.getData() + "\n";

while (current.getNext() != null) {

current = current.getNext();

listString += current.getData() + "\n";

}

return(listString);

} else {

return("There are no items in list.");

}

private class Node {

private String data;

private Node next;

/**

* constructor

* pre: none

* post: A node has been created.

public Node(String newData) {

data = newData;

next = null;

}

TIP Nested classes were also

introduced in Chapter 11.

376 Chapter 14 Data Structures

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/**

* The node pointed to by next is returned

* pre: none

* post: A node has been returned.

public Node getNext() {

return(next);

}

/**

* The node pointed to by next is changed to newNode

* pre: none

* post: next points to newNode.

public void setNext(Node newNode) {

next = newNode;

}

/**

* The node pointed to by next is returned

* pre: none

* post: A node has been returned.

public String getData() {

return(data);

}

Review: LinkedList – part 1 of 3

Modify the LinkedList class to include a member function size() that returns the number of items in the

list.

Review: LinkedList – part 2 of 3

Modify the LinkedList class to include a member function addAtEnd() that adds a new item to the end of

the linked list.

Review: LinkedList – part 3 of 3

Modify the LinkedList class to include a member function makeEmpty() that removes all the items in the

list

Chapter 14 Data Structures 377

sample

Chapter Summary

The stack, queue, and linked list data structures were introduced in this

chapter. Each data structure organizes data and can be used to perform a

set of operations on that data.

The stack data structure is also called a LIFO structure because the

last item in the first item out. A stack has a top. Operations that can be

performed on a stack include pop, push, isEmpty, size, and makeEmpty.

The queue data structure is also called a FIFO structure because the

first item in is the first item out. A queue has a front and rear. Operations

that can be performed on a queue include enqueue, dequeue, isEmpty,

size, and makeEmpty.

The linked list data structure is a list of objects that point to each other.

The linked list does not have the size limitations of a data structure imple-

mented using an array. A linked list has a head and a tail. Each item in a

linked list is called a node. Operations that can be performed on a linked

list include addAtFront and remove.

Vocabulary

addAtFront A linked list operation where an item

is added to the front of the list.

Dequeue A queue operation that removes the item

at the front of the queue.

Enqueue A queue operation that adds an item to

the rear of the queue.

FIFO First In First Out. A queue data structure.

Front The start of a queue.

Head The first node in a linked list.

isEmpty A stack or queue operation that returns

true when there are no items in the data structure

and false otherwise.

LIFO Last In First Out. A stack data structure.

Linked list A data structure that has a head and

tail and contains nodes that point to each other.

Nested class A class that is a member of another

class. A class within a class.

Node A linked list element. A node contains the

item and a pointer to the next node.

Outer class A class that contains a class member.

Pop A stack operation where the top item is

removed.

Push A stack operation where a new item is

added.

Queue A data structure that has a front and rear

and organizes data so that the first item in is the

first item out.

Rear The end of a queue.

Remove A linked list operation where an item is

removed from the list.

Size A stack or queue operation that returns the

number of items in the data structure.

Stack A data structure that has a top and organizes

data so that the last item in is the first item out.

Tail The last node in a linked list. The tail points

to null.

Top The last item pushed onto a stack.

378 Chapter 14 Data Structures

sample

Critical Thinking

1. Explain the similarities between an array and

a stack.

2. Describe how a programmer might use a stack

when writing compiler software.

3. What output is generated by the following state-

ments if s is a Stack object?

Stack s = new Stack(10);

s.push(5);

s.push(8);

int x = s.pop();

s.push(x);

s.push(12);

s.push(13);

int y = s.pop();

System.out.println(x + " " + y);

y = s.pop();

x = s.top();

System.out.println(x + " " + y);

4. Consider the “hot plate” problem: In a busy res-

taurant, fresh salad plates are brought out and

added to the existing pile of plates. This means

that, even though there may be plates that were

washed long ago, the customer is frequently

stuck with a warm plate for salad. Explain how

this is analogous to a stack.

5. What output is generated by the following state-

ments if q is a Queue object?

Queue q = new Queue(10);

q.enqueue(5);

q.enqueue(8);

int x = q.dequeue();

q.enqueue(x);

q.enqueue(12);

q.enqueue(13);

int y = q.dequeue();

System.out.println(x + " " + y);

y = q.dequeue();

x = q.front();

System.out.println(x + " " + y);

6. Explain the difference between a FIFO and a

LIFO data structure.

7. List two real-world situations that could be rep-

resented as a queue structure other than those

listed in the chapter.

True/False

8. Determine if each of the following are true or

false. If false, explain why.

a) A stack data structure has a front and a

rear.

b) A stack can be emptied.

c) In a stack, top refers to the first item pushed

onto a stack.

d) The isEmpty operation returns an i nt

value.

e) A queue can hold more than one data item.

f) In a queue, all removals are made at the

rear.

g) The enqueue operation adds an item to the

front of the queue.

h) The first item in a linked list is called the

head.

i) A node refers to an item in a stack.

j) The number of items in a stack or queue can

be determined with the length operation.

k) In a linked list, the tail points to null.

Chapter 14 Data Structures 379

sample

Exercises

Exercise 1 ——————————————————————StackList

The Stack class implemented a stack using an array. A stack can also be implemented using a linked

list. Create a StackList class that implements a stack using a linked list that can store Object data. The

StackList class should implement the standard stack operations. Note that the standard linked list opera-

tions will not be implemented when the linked list is implementing a stack. What are the advantages

or disadvantages of using a linked list rather than an array?

Exercise 2 ———————————————————— ReverseList

Create a ReverseList application that uses a stack to reverse a set of integers entered by the user. The

user should be prompted to enter up to 10 numbers or to terminate the list of numbers by entering 999.

Application output should look similar to:

Exercise 3 ——————————————————— ParenChecker

To analyze an expression with parentheses, the computer must be able to determine which left paren-

thesis any given right parenthesis matches.

a) Create a ParenChecker application that prompts the user to enter an expression with

parentheses, and then displays a list of the positions of pairs of parentheses. The

application should store the positions of the left parentheses on a stack when they are

found. Application output should look similar to:

b) Modify the ParenChecker application to detect the two errors below and display

appropriate error messages:

1. Attempt to pop an empty stack.

2. Stack not empty at the end of the program.

380 Chapter 14 Data Structures

sample

Exercise 4 ————————————————————— QueueList

The Queue class implemented a queue using an array. A queue can also be implemented using a linked

list. Create a QueueList class that implements a queue using a linked list that can store Object data.

The QueueList class should implement the standard queue operations. Note that the standard linked

list operations will not be implemented when the linked list is implementing a queue. What are the

advantages or disadvantages of using a linked list rather than an array?

Exercise 5 ———————————————————————— Stats

a) Create a Stats interface that declares methods sum(), min(), and max(). The member

methods should return an int value that represents the sum of the items in a list, the

minimum value in a list, and the maximum value in a list.

b) Create a LinkedList class that implements the Stats interface and stores int values.

Write client code that tests the modified class.

Exercise 6 ————————————————— DoublyLinkedList

The nodes in a doubly-linked list point to the next and previous nodes, and can be thought of as:

The node of the doubly-linked list may be represented as:

private class Node {

private String data;

private Node next;

private Node prev;

…rest of class

The previous field of the head is set to null.

a) What advantages does this structure offer? What disadvantages?

b) Compare the doubly-linked list with the singly linked list implemented in this chapter.

When would you choose to use one rather than the other?

c) Create a DoublyLinkedList class. Include member methods addAtFront(), addAtEnd(),

remove(), and displayList() and displayReverseList().

Appendix A Unicode 381

sample

Appendix A

Unicode

Every letter of an alphabet (Latin, Japanese, Cherokee, and so on) and

symbols of every culture (=, @, ½, and so on) have been given a repre-

sentation in a digital code called Unicode. Unicode uses a set of sixteen

1s and 0s to form a 16-bit binary code for each symbol. For example, the

uppercase letter V is Unicode 00000000 01010110, which can be thought

of as the base 10 number 86 (8610). Lowercase v has a separate code of

00000000 01110110, or 11810. Below is a table of some Unicode symbols and

their corresponding decimal and binary equivalents.

382 Appendix A Unicode

sample

Index 383

Index

Symbols

! 112

!= 105

“ 63

% 83

%= 86

&& 112

* 78, 81, 83

*= 86

+ 83, 138

toString() 187

++ 135

+= 86

-- 135

. 80, 81

.class extension 62

.java extension 62

/ 83

/** */ 62, 164

/* */ 62

// 62

/= 86

< 105

46

<= 105

<a> 48

<applet> 44

<body> 37

<br> 46, 334

<h1> 46

<h2> 46

<h3> 46

<h4> 46

<h5> 46

<h6> 46

<head> 37

<hr> 46, 334

<html> 37

<img> 48

<li> 46

<object> 44

<ol> 47

<p> 46, 334

<script> 38

<table> 48

<title> 37

<ul> 46

= 78, 86

== 105

comparing objects 186

> 105

>= 105

[] 239, 248

\ 63

\” 63

\\ 63, 312

\n 63

\t 63

{ } 61

|| 112

– 83

–= 86

3GL 5

4GL 5

802.11 network 8

abs(), Math class 113

abstract class 222

abstract data type 80

abstract keyword 222

abstract method 222

Abstract Windows Toolkit 280

accessibility 44

accessor method 182

access level, method 159

access modifier 159

acos(), Math class 130

ActionListener interface 280

action command 279

ActiveX 44

add(), ArrayList class 252

add(), JPanel class 276

addActionListener(), JButton 278

addActionListener(), JComboBox

288

addActionListener(), JTextField 285

addAtFront, linked list 373

addition 83

address 10

address bus 2

algorithm 66

design 66

stable 359

algorithm analysis 356

algortihm analysis 246

alignment, Swing API 282

ALU 2

Amaya 35

AMD 2

anchor tag 48

And 112

evaluation 113

antivirus software 21

appending data to a file 317

applets 41, 43

adding color 43

drawing shapes 43

parameters 44

placing in an HTML document

appletviewer 42

application, terminating gracefully

312

applications software 2

argument 63, 160

object 161

passed by value 161

primitive data type 161

ArithmeticException 89

Arithmetic Logic Unit 2

array 239

algorithm 242

characters 244

data structure 239

dynamic 252

element 239

initializing 240

length 240

offset indexes 243

parameter 241, 248

reference data type 242

traversing 240

two-dimensional 247

ArrayIndexOutOfBoundsException

240, 241

384 Index

ArrayList, data structure analysis

252

ArrayList class 252

array element 239

accessing 240

assigning a new value 240

artificial intelligence 5

ASCII 10

asin(), Math class 130

assembly language 5

assignment 78, 86

array element 240

constant 87

variable 78

atan(), Math class 130

attributes 46

auxiliary storage 12

awt 280

backslash character in a string 63

backslash for escape sequence 63

backup copy 21

backup tools 4

bahavior of an object 179

bandwidth 7

base 10 logarithm 128

base class 214

Basic 5

Big Oh notation 246, 252, 356

binary files 11

binary number system 9

binary search 152, 349

binary search algorithm analysis

357

BIOS 2

bit 9

blog 15

Bluetooth 4

boolean 79, 106

Boolean class 253

Boolean expression 105, 131

evaluation 113

Boolean logic 17

border, Swing API 281

boundary value 168

BoxLayout manager, Swing API 282

breadth-first-searching 370

breakpoint 136

break statement 109

broadcast radio 7

buffer 314

BufferedReader(), BufferedReader

class 314

BufferedReader class 314

BufferedWriter(), BufferedWriter

class 318

BufferedWriter class 317, 318

bug 136

built-in data types 79

bus 2, 7

bus topology 7

button, Swing API 278

for displaying an image 292

byte 9, 79

bytecode 62

converting to machine code 62

Byte class 253

C 5

C++ 6, 62

cable modem 14

cache 2

calling a method 159

carpal tunnel syndrome 19

carriage return character 314

case clause 109

case sensitivity, identifiers 88

casting, see type casting 85

CD-R 12

CD-RW/DVD drive 1

cellular radio 7

Central Processing Unit 2

chaos theory 154

char 79, 244

array 244

Character class 253

charAt(), String class 244

char array, initializing 245

Children’s Online Privacy

Protection Act of 1998 18

circuit boards 1

citations 18

class 59

abstract 222

base 214

body 180

constructor 182

declaration 180

derived 214

designing 180

extending 213

inner 188, 295

naming 181

nested 188, 295, 374

outer 295, 374

variables 180, 184

wrapper 253

writing 180

class, objects to be written to a file

322

ClassCastException 186

classes using classes 187

ClassNotFoundException 322

class method 159, 184

client/server network 7

client code 180

close() 81

close(), BufferedReader class 314

close(), BufferedWriter class 318

close(), FileInputStream class 320

close(), FileOutputStream class 319

close(), FileReader class 314

close(), FileWriter class 317

close(), ObjectInputStream class

321

close(), ObjectOutputStream class

320

coaxial cable 7

COBOL 5

code convention

variable identiﬁer 77

code conventions 65

collection 252

collections framework 252

colors, Swing API 291

combo box, Swing API 288

comments 46, 61, 62

block 62

documentation 62, 164

for debugging 137

inline 108

method 164

multiline 62

postcondition documentation

164

precondition documentation

164

single line 62

Communications Privacy Act of

1986 22

communications satellites 7

Comparable interface 225, 339

compareTo(), Comparable interface

225

compareTo(), Double class 254

compareTo(), Integer class 253

compareTo(), String class 140

compareTo(), when sorting 339

compareToIgnoreCase(), String

class 140

compiler 5, 62

just-in-time 62

method overloading 162

compiling source code 62

compound interest 103

compression program 11

computers

desktop 1

handhelds 5

notebook 4

wearable 5

wrist-top 5

computer vision syndrome 19

concatenation 138

toString() 187

conditional control structure 105,

109

constant 87

constructor 180, 183

subclass 215

writing 183

Index 385

container, Swing 275

content frame, Swing 275

controlling class 61

Swing application 278

control bus 2

conventional modem 14

conversion, numeric 84

cookie 18

cos(), Math class 130

counter 133

counting values 133

CPU 2

crackers 21

createNewFile(), File class 311

cross-platform connectivity 5

data

boundary values 168

passing to a method 160

processing 81

processing from a ﬁle 316

reading from a ﬁle 314

reading objects from a ﬁle 319

testing a method 168

writing objects to a ﬁle 319

writing to a ﬁle 317

data structure

array 239

ArrayList 252

data structures 365

linked list 373

queue 369

stack 365

data structure analysis

ArrayList 252

data type 77

abstract 80

interface 339

primitive 79

debugger 136

debugging 111, 136

commenting out statements 137

debugger 136

variable trace 136

with println() 137

Debug Window 136

decision structure 105, 109

declaration

array 239

class 180, 214

method 159

two-dimensional array 248

variable 77

decrement operator 135

Default package name 61

delete(), File class 311

depth-first searching 352

dequeue, queue 369

derived class 214

desktop computer 1

device driver 4

digital camera 1

digital signature 15

Digital Subscriber Line 14

disk defragmentation 4

disk drive 1

divide-and-conquer 152, 345, 349

division 83

integer 83

modulus 83

real 83

type casting 85

do-while 131

documentation

comments 62

external 62

package 80

postcondition comments 164

precondition comments 164

documentation comments 164

Double 254

double 79

doubleValue(), Double class 254

Double class 285

downloading 17

DSL 14

DVD drive 13

dynamic array 252

dynamic lists 373

dynamic memory 373

e, natural logarithm 128

E-FOIA 18

e-mail 15

address 15

attachments 21

composition 16

etiquette 16

protocol 16

EBCDIC 10

ECPA 18

Electronic Communications Privacy

Act of 1986 18, 21

Electronic Freedom of Information

Act of 1996 18

electronic mail 15

element

array 239

ArrayList 252

ArrayList, adding 252

ArrayList, ﬁnding 252

ArrayList, removing 252

employee monitoring 19

encapsulation 59, 179, 182

encryption 19

endsWith(), String class 140

end of file 314

enqueue, queue 369

environment 3

distributed 3

multiprocessing 3

multitasking 3

multiuser 3

environmental concerns 19

equals() 186

equals(), String class 140

equals(), use by ArrayList 252

equals() versus == 186

equalsIgnoreCase(), String class

140

equal sign 78

ergonomics 19

error 62, 89

exception handling 312

logic 89

roundoff 106

run time 89, 240

semantic 89

syntax 62, 88, 132

err stream 313

escape sequence 63, 312

Ethernet 7

ethical implications of computer

use 19

ethical responsibilities, IT

professional 22

ethical responsibilities of an IT

professional 22

Euclid’s Algorithm 153

Eudora 15

event 275

event-driven application 275

event handler 275

exabyte 13

exception 81, 89, 312

array 240

handling 89

exception handler 312

execution

program 62

exists(), File class 311

exp(), Math class 128

expansion boards 1

expectations vii

exponent 10

exponentiation 113

extends keyword 214

extension 11

extranet 13

factorial 136

Fair Credit Reporting Act of 1970

false 79

fiber optic cable 7

386 Index

file 11, 311

creating 317

HTML 37, 334

processing numeric data 316

reading 314

stream 313

writing to 317

File(), File class 311

FileInputStream(), FileInputStream

class 320

FileInputStream class 319, 320

FileNotFoundException 315, 322

FileOutputStream(),

FileOutputStream class 319

FileReader(), FileReader class 314

FileReader class 314

files

organizing 181

FileWriter(), FileWriter class 317

FileWriter class 317

File class 311

file organization 61

file position 313

file size 11

final 87

Financial Privacy Act of 1978 20

Firefox 35

firewall 13

FireWire port 12

flag 134

float 79

floating point 79

floating point numbers 10

comparing 106

Float class 253

flowchart 66

flowchart symbols 67

FlowLayout manager, Swing API

281

folders 11

format() method 64

formatting output 64

Fortran 5

for statement 240

array iteration, traversing 241

nested 248

frame, Swing 275

front, queue 369

functional decomposition 180

Fundamental Theorem of

Arithmetic 150

game

Adder 212, 335

BirthdayGame 90

Bowling 211

Break-A-Plate 298

Carnival 191

DiceRolls 242

Dice Roll 210

Game of 21 211

GuessingGame 126, 151, 178

Life 271, 336

Mad-Lib story 333

Mankala 272

Mastermind 268

Maze 363

MyBoggle 364

Nim 210

Penny Pitch 270

Rock Paper Scissors 114, 196

TicTacToe 248

WordGuess 141, 335

generic collection classes 254

get(), ArrayList 252

getActionCommand(), JButton 278

getContentPane(), JFrame 276

getMessage(), Throwable class 313

getSelectedItem(), JComboBox 288

getText(), JTextField 285

GIF 48, 292

gigabytes 10

gigahertz 2

graphical user interface 3, 275

greatest common divisor 153

GridLayout manager, Swing API

282, 284

GUI 3, 275

Gutenburg, Johann 59

Gutenburg Press 59

hackers 21

hailstone numbers 154

HAN 6

handheld computers 5

handwriting recognition software

hard-coded data 243

hardware 1

has-a relationship 187

head, linked list 373

heading tags 46

heap 373

helper method 182

hexadecimal 9, 50

histogram 268

Home Area Network 6

horizontal rule tag 46

Hotmail 15

HTML 35, 334

alignment 51

attributes 46

background color 50

comments 46

documents 36, 37

document tags 37

elements 36

hyperlinks 47

images 47

lists 46

style sheets 49

tables 47

tags 36, 45

text color 50

validating 37

HTML 4 45

HTTP 16

hub 8

hyperlink 48

hypertext 35

HyperText Markup Language 35

identifier 77

choosing 88

identity theft 20

if-else if statement 108

if-else statement 106

nested 107

if statement 105

IllegalArgumentException 161

IMAP 16

immutable 139

import, package 60

import statement 81

increment operator 135

index 138

index, array element 239

indexOf(), ArrayList 252

indexOf(), String class 140

infinite loop 132

infinite recursion 344

information age 19

information hiding 179, 182

infrared signals 7

inherit 186

inheritance 59, 213

initializing an array 240

initializing an object 80

ink jet printer 1

inline comments 108

inner class 188, 295

input, getting from user 81

input, getting from user in a GUI

285

InputMismatchException 81, 89, 95

input devices 1

input file stream 314

input stream 81

input validation loop 149

insertion sort 341

insertion sort algorithm analysis

357

instance 179

instance methods 184

instance variables 184

instantiation 80

instant messaging 15

int 79

Integer 253

Index 387

Integer class 285

integrated circuits 2

Integrated Services Digital Network

Intel 2

interface 225

as data type 339

Comparable 339

console 275

graphical 275

implementing 225

implementing multiple 227

text-based 275

interface, as variable type 339

interface, object 181

Internet 13

history of 13

Internet Acceptable Use Policy 19

Internet Explorer 15, 35

Internet filtering software 19

Internet privacy issues 18

Internet services 15

Internet Service Provider 14

interpolation search 361

interpreter 6

Java VM 62

interpreting bytecode 62

intranet 13

intValue(), Integer class 253

IOException 322

IP address 18

is-a relationship 213

ISDN 14

isEmpty, queue 369

isEmpty, stack 366

IT 22

Itanium 2

iteration 131

IT Careers 22

Java 6

enabling 41

java.awt 284, 291

java.awt.event 280

java.io 311, 314, 317, 319

java.lang 63, 79, 80, 113, 225, 254

java.lang.Double 254, 285, 316

java.lang.Integer 253, 285, 316

java.lang.Math 113, 128

java.lang.Object 186

java.text 86

java.util 80

java.util.ArrayList 252

java.util.Random 110, 138

java.util.Scanner 81, 110, 138, 140,

244

JavaScript 38, 40

javax.swing 275

javax.swing.Frame 276, 277, 278, 292

javax.swing.JPanel 276

javax.swing.JTextField 285

Java applets 41

adding color 43

drawing shapes 43

parameters 44

placing in an HTML document

Java application 61

Java Foundation Classes 275

Java Runtime Environment 80

Java Virtual Machine 41, 62

Jaz drives 12

JButton(), JButton class 278, 293

JButton class 293

JComboBox(), JComboBox 288

JComboBox class 288

JCreator 41

JFrame class 276

JIT 62

JLabel(), JLabel class 277

JLabel class 276

JPanel class 276

JPG 48, 292

JRE 80, 191

JTextField 285

JTextField(), JTextField class 285

just-in-time compiler 62

K 11

Kbps 14

keyboard 1, 81

keyword 88

kilobytes 11

knapsack problem 362

label, Swing API 276

for displaying an image 292

LAN 6

laser printer 1

lastIndexOf(), String class 140

layout, Swing API 281

layout manager, Swing API 281

leased/dedicated lines 14

length(), String class 138

length, array 240

library 60

Life 271

with GUI 309

Linear Congruential Method 110

linear search 246, 349

linear search, algorithm analysis

246

line feed character 314

line terminator 314

link 48

linked list 373

Linux 2

list, linked 373

listener, Swing API 279

Listserv 16

Local-Area Network 6

local scope 160

log(), Math class 128

log10(), Math class 128

logical topology 8

logic error 89, 132

logistic equation 154

long 79

Long class 253

loop, controlling iterations 134

loop control variable 135

loop structure 131

lowercase, converting strings 138

machine code 62

machine language 5

MACS 1

Mac OSX Tiger 275

Mac OS X Tiger 2

magnetic technology 13

mailing list server 16

main() method 61, 62, 157

mainframe 3

main memory 2

Majordomo 16

makeEmpty, queue 369

malicious code 21

MAN 6

mantissa 10

Mastermind 268

Math class 113, 128, 130

maze 363

Mbps 14

median, determining 268

megabytes 10

megahertz 2

member, accessing 80

members, class 180

memory, dynamic 373

memory-resident 4

memory keys 1

mergesort 345

mergesort algorithm analysis 357

message, passing 193

method 157

abstract 222

accessor 182

array parameter 241

body 159

calling 159

class 159, 184

declaration 159, 162

documentation 164

helper 182

instance 184

modiﬁer 182

naming 160

overloading 162

overriding 186

parameters 160

388 Index

returning a value 163

testing 167

test data 168

writing 159

methods

behavior of object 179

Metropolitan Area Network 6

microphone 1

Microsoft Internet Explorer 15

Microsoft Windows 275

microwaves 7

MLA 17

MLA Handbook for Writers of

Research Papers, Fourth

Edition 17

mobile computing devices 4

modem 14

modifier method 182

modular 193

modulus division 83

monitor 1

motherboard 1

mouse 1

MP3 players 5

multimedia 36

multiplication 83

multiprocessing 3

multitasking 3

multithreading 3

multiuser OS 3

Mylar 12

native format 11

natural logarithm 128

necklace problem 153

nested class 188, 295, 374

nested statements 107

netiquette 9

Netscape 35

networked environment 7

networks 6

beneﬁts 6

size classiﬁcations 6

network architecture 7

network interface card 6

network operating system 7

NET Act 18

new 80, 239, 248

newLine(), BufferedWriter class 318

newline character 63

next(), Scanner class 81

nextBoolean(), Scanner class 81

nextDouble(), Random class 110

nextDouble(), Scanner class 81

nextInt(), Random class 110

nextInt(), Scanner class 81

node 7

node, linked list 373

Not 112

notebook computer 4

No Electronic Theft Act of 1997 20

null 139, 240

NullPointerException 139

number

converting type 84

whole 77

number systems 9

numeric expression 83

object 59, 80, 179

argument 161

object, to be written to a file 322

object-oriented development 191

object-oriented programming 6, 59

ObjectInputStream 319

ObjectInputStream(),

ObjectInputStream class 320

ObjectOutputStream 319

ObjectOutputStream(),

ObjectOutputStream class 320

objects, sorting 339

Object class 185, 213

object deserialization 319

Object parameter 186

object serialization 319

offset array index 243

online profiling 18

OOP 6, 59

Opera 35

operand 83

operating systems 2

operations, order of 84

operator 83

relational 105

operators, built-in 83

operator precedence 84

Opteron™ 2

optical technology 12

Or 112

evaluation 113

order of operations 113

out 63

outer class 295, 374

Outlook 15

Outlook Express 15

output, formatting 64

output devices 1

output file stream 317

output stream 63

overflow 132

overflow error 10

overloading, methods 162

overriding

methods 214

overriding a method 186

overwriting a file 317

pack(), JFrame 276

package 60

documentation 80

naming 61, 81

package statement 61

paradigm

object-oriented 213

parallel processing 3

parameter

array, two-dimensional 248

Object 186

parameters 44

array 241

constructor 183

method 160

pass by value 161

parentheses 84

parseDouble(), Double class 285,

316

parseInteger(), Integer class 285,

316

Pascal 5

passing an array 242

passing data to a method 160

pass by value 161

PC 1

PDAs 5

peer-to-peer network 7

Pentium 2

peripheral devices 1

persistent data 311

persistent media 11

petabyte 13

phishing 22

PI, Math class 113

piracy 21

pixel 281

pixels 42

pixel tags 18

platform 3

platform-dependent languages 62

platform independence 59, 62

PNG 48

polymorphism 59, 217

polymorphism, interfaces 339

pop, stack 365

POP3 16

ports 1

Bluetooth 1

FireWire 1

parallel 1

serial 1

USB 1

post 164

postcondition, method

documentation 164

postfix 135

pow(), Math class 113

pre 164

Index 389

precondition, method

documentation 164

prefix 135

primary memory 2

prime factors 150

prime number 150

primitive data type 79

argument 161

primitve data type

array element 242

print() method 63

printer 1

println()

debugging 137

toString() 187

println() method 63

privacy 20

Privacy Act of 1974 20

private keyword 182, 215

procedural abstraction 157

programming language

ﬁrst generation 5

second generation 5

program specification 59

modeling 213

program specification, modeling

191

prompt 82

prompt, in a GUI 285

pseudocode 66

pseudorandom 110

public 159

public keyword 159

public static void main(String[]

args) 61

push, stack 365

queue 369

quotation mark 63

in a string 63

quotient 83

RAM 2

Random Access Memory 2

Random class 110

random numbers 110

random walk 155

range, determining 268

read(), BufferedReader class 314

readDouble(), ObjectInputStream

class 321

reading numeric and string data 82

reading objects 319

readInt(), ObjectInputStream class

320

readLine(), BufferedReader class

314

readObject(), ObjectInputStream

class 320

Read Only Memory 2

real-time clock 2

real-time OS 3

real numbers 10

rear, queue 369

recursion 343

recursive algorithm, binary search

349

recursive algorithm, depth-first

search 352

recursive algorithm, mergesort 345

recycling 19

reference data type

array 242

interface 339

object 80

object parameters 161

polymorphism 217

String 139

relational operator 105

remove(), ArrayList 252

remove(), JPanel 276

remove, linked list 373

replaceAll(), String class 138

replaceFirst(), String class 138

reserved words 88

return statement 163

reusability 60

code 191

ring topology 8

ROM 2

rounding 84

rounding double to int 85

roundoff error 11, 106

router 8, 14

run-time error 89

array 240

running a program 62

running time 356

Safari 35

Safety and Freedom through

Encryption Act of 1999 19

scanner 1

Scanner object, closing 82

scope 135

scope, local in a method 160

scripts 38, 40

SDK 42

search, binary 349

search, depth-first 352

search, interpolation 361

search, linear 349

search, sequential 349

search, ternary 361

searching an array 246

Search class 246

search engines 16

secondary memory 2

seed, for random numbers 111

selection sort 270, 337

selection sort algorithm analysis

356

semantic error 89

semicolon 62

sentinel 134

sequential file access 313

sequential search 349

Serializable interface 322

server 7

setActionCommand(), JButton 278

setBackground(), Swing API 291

setContentPane(), JFrame 276

setDefaultCloseOperation(), JFrame

276

setDefaultLookAndFeelDecorated()

, JFrame 276

setEditable(), JComboBox 288

setForeground(), Swing API 291

setIcon(), JButton class 293

setSelectedIndex(), JComboBox 288

setText(), JLabel 277

setVisible(), JFrame 276

short 79

short-circuit evaluation 113

Short class 253

simple interest 103

sin(), Math class 130

size(), ArrayList 252

size, queue 369

size, stack 366

smartphones 5

social implications of computer

use 19

software development 157, 191

solid state technology 13

sorting, numbers 337

sorting objects 339

sorts 337

sound cards 1

source code 62

spam 16

spec 59

spyware 18

SQL 5

sqrt(), Math class 113

square root 113

SRAM 2

stack 365

startsWith(), String class 140

star topology 8

statement 61

state of an object 179

static 159

static method 184

Static Random Access Memory 2

static variables 184

step-wise refinement 157

Step command 136

storage, file 311

storage devices 12

390 Index

storage media

care of 13

stream 313

input 81

string 63

formatting 64

strings 79

comparing 140

creating 138

joining 138

String class 79, 138

student expectations vii

style sheets 49

class 50

embedded 49

linked 50

rules 50

stylus 4

subclass 214, 217

subclasses 185

subject tree 17

substring(), String class 138

subtraction 83

summing values 133

Sun’s Java Software Development

Kit 42

superclass 185, 217

Object class 213

supercomputer 3

super keyword 215

Swing API 275

switch statement 109

syntax error 62, 88, 132

System.in 81

System class 63

system reliability 22

system restore 4

tablet PC 4

tab character 63

tail, linked list 373

tan(), Math class 130

TCP/IP 14

telecommunications 14

terabyte 13

ternary search 361

text field, GUI 285

this keyword 189, 279

thread 278

Throwable class 313

Tim Berners-Lee 36

toCharArray(), String class 244

toDegrees(), Math class 130

toLowerCase(), String class 138

top, stack 365

top-down design 157

top-down development 157

topology 7

toRadians(), Math class 130

toString() 186

toString(), Double 285

toString(), Integer 285

toUpperCase(), String class 138

transmission media 7

traversing

array 240

ArrayList 254

trim(), String class 138

Trojan horse 21

true 79

truncate

modulus division 83

toward 0 84

truth table 112

try-catch-finally statement 312

twisted-pair wiring 7

two-dimensional array 247

accessing elements 248

type casting 84, 245

generic collection classes 254

object 186

objects 254

ultra-portable devices 12

underscore (_) 87

Unicode 10, 79, 244, 314, 381

Unicode Standard 140

Unix 2

uppercase, converting strings 138

USB 12

utility program 4

variable 77

class 180, 184

initializing in a class 183

instance 184

in println() 78

member 181

state of object 179

variable trace 136

video adapters 1

virtual 62

Virtual Machine 62

virus 21

visibility 159, 182

subclasses 215

Visual Basic .NET 6, 62

visual organizer 66

VM 62

void 159

W3C 36

WAI 44

WAN 6

Watch window 136

wearable computers 5

Web 15

website 35

website citations 17

Web Accessibility Initiative 44

web beacons 18

web browser 15

web browsers 35

web bugs 18

web directory 17

while 131

whole number 77

Wi-Fi 8

Wide-Area Network 6

Windows 2

Windows media player 44

Windows XP environment 3

WinZip 11

wireless access point 8

Wireless Fidelity 8

wireless networks 8, 14

wireless transmission media 7

words 10

World Wide Web 15, 35

World Wide Web Consortium 36

worm 21

wrapper classes 253

wrist-top computers 5

write(), BufferedWriter class 318

writeDouble(), ObjectOutputStream

class 320

writeInt(), ObjectOutputStream

class 320

writeObject(), ObjectOutputStream

class 320

writing data to a file 319

WWW 35

www.sun.com 80

Yahoo! 15

Zip drives 12

A Guide to Programming in Java emphasizes the development of good problem-solving and programming

skills in a clear, easy-to-understand format, continuing the tradition of the Lawrenceville Press series of

programming texts. To date, more than two million students have learned computing using a Lawrenceville

Press text. A Guide to Programming in Java has been developed for the AP Computer Science curriculum

and is an excellent text for an introductory programming course.

Features of A Guide to Programming in Java:

 AP COMPUTER SCIENCE CURRICULUM Content matches the College Board’s AP Computer

Science topic outline and Java subset.

 JAVA 2 PLATFORM STANDARD EDITION 5 Supports the Java 2 Platform Standard Edition 5

and is backwards-compatible with previous editions.

 OBJECT-ORIENTED DEVELOPMENT APPROACH Object-oriented programming is introduced

from the very start of the text.

 PROGRAMMING CONCEPTS An emphasis is placed on fundamental concepts including

variables, conditional control structures, loops, strings, methods, classes, arrays, and ﬁles.

 PROGRAMMING TECHNIQUES Solutions are designed using algorithms and Java code

conventions are modelled throughout the text.

 DEMONSTRATION APPLICATIONS Each chapter includes many demonstration applications

that illustrate both the source code and generated output.

 REVIEWS AND EXERCISES After a new concept is discussed, review problems provide an

opportunity for students to apply the concepts to creating an application. At the end of each

chapter are numerous hands-on exercises of varying difﬁculty, appropriate for students with a

wide range of abilities.

 CASE STUDIES A case study is presented at the end of most chapters. The case study illustrates

a complex application using good programming methodology of speciﬁcation, design, coding,

testing, and debugging.

 TEACHING APPROACH The text is written for a variety of Java compilers. It is also written

for different student learning styles and effectively uses screen shots of source code, generated

output, and ﬁnished projects to strengthen understanding.

 CRITICAL THINKING A variety of written-response questions that provoke critical thinking

are provided at the end of each chapter.

 GUI AND EVENT-DRIVEN PROGRAMMING The Swing Java package is introduced for creating

GUI event-driven applications.

 APPLETS AND WEB PROGRAMMING Applets and web programming are introduced.

This text is available in hardcover and softcover editions.

ISBN 1-58003-072-6

~<(sl&s!=adahce< Hardcover