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He is the author of numerous bestsellers, including Java 2: The Complete Reference, Java 2: A Beginner's Guide, Java 2 Programmers Reference, C++: The Complete Reference, C: The Complete

The Complete Reference,

Fifth Edition

programming author He is an authority on the

C, C++, Java, and C# languages, and is a masterWindows programmer His programming bookshave sold more that 3 million copies worldwideand have been translated into all major foreignlanguages He is the author of numerous

bestsellers, including Java 2: The Complete Reference, Java 2: A Beginner's Guide, Java 2 Programmers Reference, C++: The Complete Reference, C: The Complete Reference, and C#: The Complete Reference Schildt holds a master's

degree in computer science from the University

of Illinois He can be reached at his consultingoffice at (217) 586-4683

Java 2: The Complete Reference,

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Contents at a Glance

Part I The Java Language

1 The Genesis of Java 3

2 An Overview of Java 17

3 Data Types, Variables, and Arrays 41

4 Operators 73

5 Control Statements 99

6 Introducing Classes 129

7 A Closer Look at Methods and Classes 155

8 Inheritance 189

9 Packages and Interfaces 223

10 Exception Handling 249

11 Multithreaded Programming 273

12 I/O, Applets, and Other Topics 313

v

Part II The Java Library

13 String Handling 347

14 Exploring java.lang 379

15 java.util Part 1: The Collections Framework 439

16 java.util Part 2: More Utility Classes 505

17 Input/Output: Exploring java.io 537

18 Networking 587

19 The Applet Class 627

20 Event Handling 653

21 Introducing the AWT: Working with Windows, Graphics, and Text 687

22 Using AWT Controls, Layout Managers, and Menus 735

23 Images 799

24 New I/O, Regular Expressions, and Other Packages 843

Part III Software Development Using Java 25 Java Beans 885

26 A Tour of Swing 921

27 Servlets 949

28 Migrating from C++ to Java 981

Part IV Applying Java 29 The DynamicBillboard Applet 1011

30 ImageMenu: An Image-Based Web Menu 1047

31 The Lavatron Applet: A Sports Arena Display 1057

32 Scrabblet: A Multiplayer Word Game 1069

A Using Java’s Documentation Comments 1133

Index 1141

Preface xxv

Part I The Java Language 1 The Genesis of Java 3

Java’s Lineage 4

The Birth of Modern Programming: C 4

The Need for C++ 6

The Stage Is Set for Java 7

The Creation of Java 7

The C# Connection 9

Why Java Is Important to the Internet 9

Java Applets and Applications 10

Security 10

Portability 11

Java’s Magic: The Bytecode 11

The Java Buzzwords 12

Simple 13

Object-Oriented 13

vii

Robust 13

Multithreaded 14

Architecture-Neutral 14

Interpreted and High Performance 14

Distributed 15

Dynamic 15

The Continuing Revolution 15

2 An Overview of Java 17

Object-Oriented Programming 18

Two Paradigms 18

Abstraction 18

The Three OOP Principles 19

A First Simple Program 25

Entering the Program 25

Compiling the Program 26

A Closer Look at the First Sample Program 27

A Second Short Program 29

Two Control Statements 31

The if Statement 31

The for Loop 33

Using Blocks of Code 35

Lexical Issues 37

Whitespace 37

Identifiers 37

Literals 37

Comments 38

Separators 38

The Java Keywords 38

The Java Class Libraries 39

3 Data Types, Variables, and Arrays 41

Java Is a Strongly Typed Language 42

The Simple Types 42

Integers 43

byte 44

short 44

int 44

long 45

Floating-Point Types 45

float 46

double 46

Characters 47

Booleans 48

A Closer Look at Literals 50

Integer Literals 50

Floating-Point Literals 50

Boolean Literals 51

Character Literals 51

String Literals 52

Variables 52

Declaring a Variable 52

Dynamic Initialization 53

The Scope and Lifetime of Variables 54

Type Conversion and Casting 57

Java’s Automatic Conversions 57

Casting Incompatible Types 57

Automatic Type Promotion in Expressions 59

The Type Promotion Rules 60

Arrays 61

One-Dimensional Arrays 61

Multidimensional Arrays 64

Alternative Array Declaration Syntax 70

A Few Words About Strings 70

A Note to C/C++ Programmers About Pointers 71

4 Operators 73

Arithmetic Operators 74

The Basic Arithmetic Operators 74

The Modulus Operator 76

Arithmetic Assignment Operators 76

Increment and Decrement 78

The Bitwise Operators 80

The Bitwise Logical Operators 82

The Left Shift 84

The Right Shift 86

The Unsigned Right Shift 87

Bitwise Operator Assignments 89

Relational Operators 90

Boolean Logical Operators 92

Short-Circuit Logical Operators 93

The Assignment Operator 94

The ? Operator 95

Operator Precedence 96

Using Parentheses 96

5 Control Statements 99

Java’s Selection Statements 100

if 100

switch 104

Iteration Statements 109

while 109

do-while 111

for 114

Some for Loop Variations 117

Nested Loops 119

Jump Statements 119

Using break 120

Using continue 124

return 126

6 Introducing Classes 129

Class Fundamentals 130

The General Form of a Class 130

A Simple Class 131

Declaring Objects 134

A Closer Look at new 136

Assigning Object Reference Variables 137

Introducing Methods 138

Adding a Method to the Box Class 138

Returning a Value 140

Adding a Method That Takes Parameters 142

Constructors 145

Parameterized Constructors 147

The this Keyword 149

Instance Variable Hiding 149

Garbage Collection 150

The finalize( ) Method 150

A Stack Class 151

7 A Closer Look at Methods and Classes 155

Overloading Methods 156

Overloading Constructors 159

Using Objects as Parameters 162

A Closer Look at Argument Passing 165

Returning Objects 168

Recursion 169

Introducing Access Control 172

Understanding static 176

Introducing final 178

Arrays Revisited 179

Introducing Nested and Inner Classes 181

Exploring the String Class 185

Using Command-Line Arguments 188

8 Inheritance 189

Inheritance Basics 190

Member Access and Inheritance 192

A More Practical Example 193

A Superclass Variable Can Reference a Subclass Object 196

Using super 197

Using super to Call Superclass Constructors 197

A Second Use for super 202

Creating a Multilevel Hierarchy 203

When Constructors Are Called 207

Method Overriding 208

Dynamic Method Dispatch 211

Why Overridden Methods? 213

Applying Method Overriding 214

Using Abstract Classes 216

Using final with Inheritance 219

Using final to Prevent Overriding 219

Using final to Prevent Inheritance 220

The Object Class 220

9 Packages and Interfaces 223

Packages 224

Defining a Package 225

Finding Packages and CLASSPATH 226

A Short Package Example 226

Access Protection 227

An Access Example 229

Importing Packages 232

Interfaces 235

Defining an Interface 235

Implementing Interfaces 236

Applying Interfaces 239

Variables in Interfaces 243

Interfaces Can Be Extended 246

10 Exception Handling 249

Exception-Handling Fundamentals 250

Exception Types 251

Uncaught Exceptions 251

Using try and catch 253

Displaying a Description of an Exception 254

Multiple catch Clauses 255

Nested try Statements 257

throw 260

throws 261

finally 263

Java’s Built-in Exceptions 265

Creating Your Own Exception Subclasses 267

Chained Exceptions 269

Using Exceptions 271

11 Multithreaded Programming 273

The Java Thread Model 275

Thread Priorities 275

Synchronization 276

Messaging 276

The Thread Class and the Runnable Interface 277

The Main Thread 277

Creating a Thread 280

Implementing Runnable 280

Extending Thread 282

Choosing an Approach 284

Creating Multiple Threads 284

Using isAlive( ) and join( ) 286

Thread Priorities 289

Synchronization 292

Using Synchronized Methods 292

The synchronized Statement 295

Interthread Communication 297

Deadlock 302

Suspending, Resuming, and Stopping Threads 305

Suspending, Resuming, and Stopping Threads Using Java 1.1 and Earlier 305

Suspending, Resuming, and Stopping Threads Using Java 2 308

Using Multithreading 311

12 I/O, Applets, and Other Topics 313

I/O Basics 314

Streams 314

Byte Streams and Character Streams 315

The Predefined Streams 318

Reading Console Input 318

Reading Characters 319

Reading Strings 320

Writing Console Output 322

The PrintWriter Class 323

Reading and Writing Files 324

Applet Fundamentals 328

The transient and volatile Modifiers 331

Using instanceof 332

strictfp 335

Native Methods 335

Problems with Native Methods 340

Using assert 340

Assertion Enabling and Disabling Options 343

Part II The Java Library 13 String Handling 347

The String Constructors 348

String Length 351

Special String Operations 351

String Literals 351

String Concatenation 352

String Concatenation with Other Data Types 352

String Conversion and toString( ) 353

Character Extraction 355

charAt( ) 355

getChars( ) 355

getBytes( ) 356

toCharArray( ) 356

String Comparison 356

equals( ) and equalsIgnoreCase( ) 357

regionMatches( ) 358

startsWith( ) and endsWith( ) 358

equals( ) Versus == 359

compareTo( ) 359

Searching Strings 361

Modifying a String 363

substring( ) 363

concat( ) 364

replace( ) 364

trim( ) 365

Data Conversion Using valueOf( ) 366

Changing the Case of Characters Within a String 367

String Methods Added by Java 2, Version 1.4 368

StringBuffer 369

StringBuffer Constructors 369

length( ) and capacity( ) 369

ensureCapacity( ) 370

setLength( ) 370

charAt( ) and setCharAt( ) 371

getChars( ) 371

append( ) 372

insert( ) 373

reverse( ) 373

delete( ) and deleteCharAt( ) 374

replace( ) 375

substring( ) 375

StringBuffer Methods Added by Java 2, Version 1.4 376

14 Exploring java.lang 379

Simple Type Wrappers 380

Number 381

Double and Float 381

Byte, Short, Integer, and Long 387

Character 397

Boolean 401

Void 402

Process 402

Runtime 403

Memory Management 405

Executing Other Programs 406

System 407

Using currentTimeMillis( ) to Time Program Execution 410

Using arraycopy( ) 411

Environment Properties 412

Object 412

Using clone( ) and the Cloneable Interface 412

Class 416

ClassLoader 419

Math 420

Transcendental Functions 420

Exponential Functions 420

Rounding Functions 421

Miscellaneous Math Methods 422

StrictMath 422

Compiler 423

Thread, ThreadGroup, and Runnable 423

The Runnable Interface 423

Thread 423

ThreadGroup 426

ThreadLocal and InheritableThreadLocal 432

Package 432

RuntimePermission 434

Throwable 434

SecurityManager 434

StackTraceElement 435

The CharSequence Interface 436

The Comparable Interface 436

The java.lang.ref and java.lang.reflect Packages 437

java.lang.ref 437

java.lang.reflect 437

15 java.util Part 1: The Collections Framework 439

Collections Overview 441

The Collection Interfaces 442

The Collection Interface 443

The List Interface 445

The Set Interface 447

The SortedSet Interface 447

The Collection Classes 448

The ArrayList Class 449

The LinkedList Class 452

The HashSet Class 454

The LinkedHashSet Class 456

The TreeSet Class 456

Accessing a Collection via an Iterator 457

Using an Iterator 457

Storing User-Defined Classes in Collections 460

The RandomAccess Interface 462

Working with Maps 462

The Map Interfaces 462

The Map Classes 466

Comparators 471

Using a Comparator 472

The Collection Algorithms 475

Arrays 480

The Legacy Classes and Interfaces 484

The Enumeration Interface 484

Vector 485

Stack 490

Dictionary 492

Hashtable 494

Properties 498

Using store( ) and load( ) 502

Collections Summary 504

16 java.util Part 2: More Utility Classes 505

StringTokenizer 506

BitSet 508

Date 512

Date Comparison 514

Calendar 514

GregorianCalendar 519

TimeZone 521

SimpleTimeZone 522

Locale 523

Random 524

Observable 527

The Observer Interface 528

An Observer Example 528

Timer and TimerTask 531

Currency 534

The java.util.zip Package 536

The java.util.jar Package 536

17 Input/Output: Exploring java.io 537

The Java I/O Classes and Interfaces 538

File 539

Directories 542

Using FilenameFilter 543

The listFiles( ) Alternative 544

Creating Directories 545

The Stream Classes 545

The Byte Streams 546

InputStream 546

OutputStream 547

FileInputStream 548

FileOutputStream 550

ByteArrayInputStream 552

ByteArrayOutputStream 553

Filtered Byte Streams 555

Buffered Byte Streams 555

SequenceInputStream 559

PrintStream 561

RandomAccessFile 561

The Character Streams 562

Reader 562

Writer 562

FileReader 562

FileWriter 565

CharArrayReader 566

CharArrayWriter 567

BufferedReader 569

BufferedWriter 570

PushbackReader 571

PrintWriter 572

Using Stream I/O 572

Improving wc( ) Using a StreamTokenizer 574

Serialization 577

Serializable 577

Externalizable 578

ObjectOutput 578

ObjectOutputStream 579

ObjectInput 580

ObjectInputStream 581

A Serialization Example 583

Stream Benefits 585

18 Networking 587

Networking Basics 588

Socket Overview 588

Client/Server 589

Reserved Sockets 589

Proxy Servers 590

Internet Addressing 590

Java and the Net 591

The Networking Classes and Interfaces 592

InetAddress 592

Factory Methods 593

Instance Methods 594

TCP/IP Client Sockets 594

Whois 596

URL 597

Format 597

URLConnection 599

TCP/IP Server Sockets 601

A Caching Proxy HTTP Server 602

Source Code 602

Datagrams 623

DatagramPacket 624

Datagram Server and Client 624

Inet4Address and Inet6Address 626

The URI Class 626

19 The Applet Class 627

Applet Basics 628

The Applet Class 629

Applet Architecture 632

An Applet Skeleton 632

Applet Initialization and Termination 634

Overriding update( ) 635

Simple Applet Display Methods 636

Requesting Repainting 638

A Simple Banner Applet 639

Using the Status Window 642

The HTML APPLET Tag 643

Passing Parameters to Applets 644

Improving the Banner Applet 647

getDocumentBase( ) and getCodeBase( ) 648

AppletContext and showDocument( ) 649

The AudioClip Interface 651

The AppletStub Interface 652

Outputting to the Console 652

20 Event Handling 653

Two Event Handling Mechanisms 654

The Delegation Event Model 654

Events 655

Event Sources 655

Event Listeners 656

Event Classes 656

The ActionEvent Class 658

The AdjustmentEvent Class 659

The ComponentEvent Class 660

The ContainerEvent Class 660

The FocusEvent Class 661

The InputEvent Class 661

The ItemEvent Class 662

The KeyEvent Class 663

The MouseEvent Class 664

The MouseWheelEvent Class 665

The TextEvent Class 666

The WindowEvent Class 667

Sources of Events 668

Event Listener Interfaces 669

The ActionListener Interface 670

The AdjustmentListener Interface 670

The ComponentListener Interface 670

The ContainerListener Interface 670

The FocusListener Interface 670

The ItemListener Interface 671

The KeyListener Interface 671

The MouseListener Interface 671

The MouseMotionListener Interface 671

The MouseWheelListener Interface 672

The TextListener Interface 672

The WindowFocusListener Interface 672

The WindowListener Interface 672

Using the Delegation Event Model 673

Handling Mouse Events 673

Handling Keyboard Events 676

Adapter Classes 680

Inner Classes 682

Anonymous Inner Classes 684

21 Introducing the AWT: Working with Windows, Graphics, and Text 687

AWT Classes 688

Window Fundamentals 691

Component 691

Container 692

Panel 692

Window 693

Frame 693

Canvas 693

Working with Frame Windows 693

Setting the Window’s Dimensions 694

Hiding and Showing a Window 694

Setting a Window’s Title 694

Closing a Frame Window 694

Creating a Frame Window in an Applet 695

Handling Events in a Frame Window 697

Creating a Windowed Program 702

Displaying Information Within a Window 704

Working with Graphics 705

Drawing Lines 705

Drawing Rectangles 706

Drawing Ellipses and Circles 708

Drawing Arcs 709

Drawing Polygons 710

Sizing Graphics 711

Working with Color 712

Color Methods 713

Setting the Current Graphics Color 714

A Color Demonstration Applet 714

Setting the Paint Mode 715

Working with Fonts 717

Determining the Available Fonts 719

Creating and Selecting a Font 720

Obtaining Font Information 722

Managing Text Output Using FontMetrics 723

Displaying Multiple Lines of Text 725

Centering Text 727

Multiline Text Alignment 728

Exploring Text and Graphics 733

22 Using AWT Controls, Layout Managers, and Menus 735

Control Fundamentals 736

Adding and Removing Controls 736

Responding to Controls 737

Labels 737

Using Buttons 739

Handling Buttons 739

Applying Check Boxes 743

Handling Check Boxes 743

CheckboxGroup 745

Choice Controls 748

Handling Choice Lists 748

Using Lists 751

Handling Lists 752

Managing Scroll Bars 754

Handling Scroll Bars 756

Using a TextField 758

Handling a TextField 759

Using a TextArea 761

Understanding Layout Managers 763

FlowLayout 764

BorderLayout 766

Using Insets 768

GridLayout 770

CardLayout 772

Menu Bars and Menus 775

Dialog Boxes 782

FileDialog 788

Handling Events by Extending AWT Components 790

Extending Button 792

Extending Checkbox 793

Extending a Check Box Group 794Extending Choice 795Extending List 795Extending Scrollbar 797Exploring the Controls, Menus, and Layout Managers 798

23 Images 799File Formats 800Image Fundamentals: Creating, Loading, and Displaying 801Creating an Image Object 801Loading an Image 801Displaying an Image 802ImageObserver 803ImageObserver Example 805Double Buffering 807MediaTracker 811ImageProducer 815MemoryImageSource 815ImageConsumer 817PixelGrabber 818ImageFilter 821CropImageFilter 821RGBImageFilter 823Cell Animation 837Additional Imaging Classes 840

24 New I/O, Regular Expressions, and Other Packages 843The Core Java API Packages 844The New I/O Packages 847NIO Fundamentals 847Charsets and Selectors 851Using the New I/O System 851

Is NIO the Future of I/O Handling? 859Regular Expression Processing 859Pattern 859Matcher 860Regular Expression Syntax 861Demonstrating Pattern Matching 861Two Pattern-Matching Options 868Exploring Regular Expressions 869Reflection 869Remote Method Invocation (RMI) 874

A Simple Client/Server Application Using RMI 874Text Formatting 878DateFormat Class 878SimpleDateFormat Class 880

Part III

Software Development Using Java

25 Java Beans 885What Is a Java Bean? 886Advantages of Java Beans 887Application Builder Tools 887Using the Bean Developer Kit (BDK) 888Installing the BDK 888Starting the BDK 889Using the BDK 889JAR Files 891Manifest Files 892The JAR Utility 892Introspection 894Design Patterns for Properties 894Design Patterns for Events 896Methods 897Developing a Simple Bean Using the BDK 897Create a New Bean 898Using Bound Properties 902Steps 902Using the BeanInfo Interface 903Constrained Properties 905Persistence 905Customizers 906The Java Beans API 906Using Bean Builder 911Building a Simple Bean Builder Application 913

26 A Tour of Swing 921JApplet 923Icons and Labels 923Text Fields 925Buttons 927The JButton Class 927Check Boxes 930Radio Buttons 932Combo Boxes 934Tabbed Panes 936Scroll Panes 939Trees 941Tables 946Exploring Swing 948

27 Servlets 949Background 950

The Life Cycle of a Servlet 951Using Tomcat For Servlet Development 951

A Simple Servlet 953Create and Compile the Servlet Source Code 953Start Tomcat 954Start a Web Browser and Request the Servlet 954The Servlet API 954The javax.servlet Package 955The Servlet Interface 955The ServletConfig Interface 956The ServletContext Interface 957The ServletRequest Interface 957The ServletResponse Interface 957The SingleThreadModel Interface 957The GenericServlet Class 960The ServletInputStream Class 960The ServletOutputStream Class 960The Servlet Exception Classes 960Reading Servlet Parameters 960The javax.servlet.http Package 962The HttpServletRequest Interface 963The HttpServletResponse Interface 965The HttpSession Interface 966The HttpSessionBindingListener Interface 967The Cookie Class 967The HttpServlet Class 969The HttpSessionEvent Class 970The HttpSessionBindingEvent Class 971Handling HTTP Requests and Responses 971Handling HTTP GET Requests 971Handling HTTP POST Requests 973Using Cookies 975Session Tracking 977Security Issues 979

28 Migrating from C++ to Java 981The Differences Between C++ and Java 982What Java Has Removed from C++ 982New Features Added by Java 984Features That Differ 985Eliminating Pointers 985Converting Pointer Parameters 986Converting Pointers that Operate on Arrays 988C++ Reference Parameters Versus Java Reference Parameters 991Converting C++ Abstract Classes into Java Interfaces 995Converting Default Arguments 999Converting C++ Multiple-Inheritance Hierarchies 1001Destructors Versus Finalization 1003

Part IV

Applying Java

29 The DynamicBillboard Applet 1011

The APPLET Tag 1012

Source Code Overview 1014

30 ImageMenu: An Image-Based Web Menu 1047

The Source Image 1049

The APPLET Tag 1050

31 The Lavatron Applet: A Sports Arena Display 1057

How Lavatron Works 1059

The Source Code 1060

The APPLET Tag 1060

Lavatron.java 1060

IntHash( ) 1065

Hot Lava 1067

32 Scrabblet: A Multiplayer Word Game 1069

Network Security Concerns 1070

The Game 1071

Scoring 1074

The Source Code 1076

The APPLET Tag 1076

Scrabblet.java 1077

IntroCanvas.java 1090

Board.java 1091Bag.java 1109Letter.java 1111ServerConnection.java 1117The Server Code 1123Server.java 1123ClientConnection.java 1127Enhancing Scrabblet 1131

A Using Java’s Documentation Comments 1133The javadoc Tags 1134

@author 1135

@deprecated 1135{@docRoot} 1135

@exception 1135{@inheritDoc} 1136{@link} 1136{@linkplain} 1136

@version 1138The General Form of a Documentation Comment 1138What javadoc Outputs 1138

An Example that Uses Documentation Comments 1139Index 1141

The past few years document the following fact: The Web has irrevocably recast

the face of computing and programmers unwilling to master its environment will

be left behind

The preceding is a strong statement It is also true More and more, applicationsmust interface to the Web It no longer matters much what the application is, nearuniversal Web access is dragging, pushing, and coaxing programmers to program forthe online world, and Java is the language that many will use to do it Frankly, fluency

in Java is no longer an option for the professional programmer, it is a requirement Thisbook will help you acquire it

Aside from being the preeminent language of the Internet, Java is important foranother reason: it has altered the course of computer language development Many ofthe features first mainstreamed by Java are now finding their way into other languages.For example, the new C# language is strongly influenced by Java Knowledge of Javaopens the door to the latest innovations in programming Put directly, Java is one of theworld’s most important computer languages

xxv

A Book for All Programmers

To use this book does not require any previous programming experience However,

if you come from a C/C++ background, then you will be able to advance a bit morerapidly As most readers will know, Java is similar, in form and spirit, to C/C++ Thus,knowledge of those langauges helps, but is not necessary Even if you have neverprogrammed before, you can learn to program in Java using this book

What’s Inside

This book covers all aspects of the Java programming language Part 1 presents anin-depth tutorial of the Java language It begins with the basics, including such things

as data types, control statements, and classes Part 1 also discusses Java’s

exception-handling mechanism, multithreading subsystem, packages, and interfaces.Part 2 examines the standard Java library As you will learn, much of Java’s power

is found in its library Topics include strings, I/O, networking, the standard utilities,the Collections Framework, applets, GUI-based controls, and imaging

Part 3 looks at some issues relating to the Java development environment, including

an overview of Java Beans, Servlets, and Swing

Part 4 presents a number of high-powered Java applets that serve as extendedexamples of the way Java can be applied The final applet, called Scrabblet, is a complete,multiuser networked game It shows how to handle some of the toughest issues involved

in Web-based programming

What’s New in the Fifth Edition

The differences between this and the previous editions of this book mostly involve thosefeatures added by Java 2, version 1.4 Of the many new features found in version 1.4,

perhaps the most important are the assert keyword, the channel-based I/O subsystem,

chained exceptions, and networking enhancements This fifth edition has been fullyupdated to reflect those and other additions New features are clearly noted in the text,

as are features added by previous releases

This fifth edition also updates and restores the Sevlets chapter Previouslythis chapter relied upon the now out-dated JSDK (Java Servlets Developers Kit)

to develop and test servlets It now uses Apache Tomcat, which is the currentlyrecommended tool

Don’t Forget: Code on the Web

Remember, the source code for all of the examples and projects in this book is available

free-of-charge on the Web at www.osborne.com.

Special Thanks

Special thanks to Patrick Naughton Patrick was one of the creators of the Java

language He also helped write the first edition of this book For example, much of

the material in chapters 17, 18, 23, 29, 30, 31, and 32 was initially provided by Patrick

His insights, expertise, and energy contributed greatly to the success of this book

Thanks also go to Joe O'Neil for providing the initial drafts for chapters 24, 25, 26,

and 27 Joe has helped on several of my books and, as always, his efforts are appreciated

HERBERT SCHILDT

May 25, 2002

Mahomet, Illinois

For Further Study

Java 2: The Complete Reference is your gateway to the Herb Schildt series of programming

books Here are some others that you will find of interest:

To learn more about Java programming, we recommend the following:

Java 2: A Beginner's Guide

Java 2 Programmer's Reference

To learn about C++, you will find these books especially helpful:

C++: The Complete Reference

C++: A Beginner's Guide

Teach Yourself C++

C++ From the Ground Up

STL Programming From the Ground Up

To learn about C#, we suggest the following Schildt books:

C#: A Beginner's Guide

C#: The Complete Reference

If you want to learn more about the C language, the foundation of all modernprogramming, then the following titles will be of interest:

C: The Complete Reference

Teach Yourself C

When you need solid answers, fast, turn to Herbert Schildt,

the recognized authority on programming.

Part I

The Java Language

Chapter 1

The Genesis of Java

3

When the chronicle of computer languages is written, the following will be said:

B led to C, C evolved into C++, and C++ set the stage for Java To understandJava is to understand the reasons that drove its creation, the forces thatshaped it, and the legacy that it inherits Like the successful computer languages thatcame before, Java is a blend of the best elements of its rich heritage combined with theinnovative concepts required by its unique environment While the remaining chapters

of this book describe the practical aspects of Java—including its syntax, libraries, andapplications—in this chapter, you will learn how and why Java came about, and whatmakes it so important

Although Java has become inseparably linked with the online environment of theInternet, it is important to remember that Java is first and foremost a programminglanguage Computer language innovation and development occurs for two fundamentalreasons:

■ To adapt to changing environments and uses

■ To implement refinements and improvements in the art of programming

As you will see, the creation of Java was driven by both elements in nearly

equal measure

Java’s Lineage

Java is related to C++, which is a direct descendent of C Much of the character of Java

is inherited from these two languages From C, Java derives its syntax Many of Java’sobject-oriented features were influenced by C++ In fact, several of Java’s definingcharacteristics come from—or are responses to—its predecessors Moreover, the creation

of Java was deeply rooted in the process of refinement and adaptation that has beenoccurring in computer programming languages for the past three decades For thesereasons, this section reviews the sequence of events and forces that led up to Java Asyou will see, each innovation in language design was driven by the need to solve afundamental problem that the preceding languages could not solve Java is no exception

The Birth of Modern Programming: C

The C language shook the computer world Its impact should not be underestimated,because it fundamentally changed the way programming was approached and thoughtabout The creation of C was a direct result of the need for a structured, efficient, high-level language that could replace assembly code when creating systems programs Asyou probably know, when a computer language is designed, trade-offs are often made,such as the following:

■ Ease-of-use versus power

■ Safety versus efficiency

■ Rigidity versus extensibility

Prior to C, programmers usually had to choose between languages that optimized

one set of traits or the other For example, although FORTRAN could be used to write

fairly efficient programs for scientific applications, it was not very good for systems

code And while BASIC was easy to learn, it wasn’t very powerful, and its lack of

structure made its usefulness questionable for large programs Assembly language

can be used to produce highly efficient programs, but it is not easy to learn or use

effectively Further, debugging assembly code can be quite difficult

Another compounding problem was that early computer languages such as BASIC,

COBOL, and FORTRAN were not designed around structured principles Instead, they

relied upon the GOTO as a primary means of program control As a result, programs

written using these languages tended to produce “spaghetti code”—a mass of tangled

jumps and conditional branches that make a program virtually impossible to

understand While languages like Pascal are structured, they were not designed for

efficiency, and failed to include certain features necessary to make them applicable to

a wide range of programs (Specifically, given the standard dialects of Pascal available

at the time, it was not practical to consider using Pascal for systems-level code.)

So, just prior to the invention of C, no one language had reconciled the conflicting

attributes that had dogged earlier efforts Yet the need for such a language was

pressing By the early 1970s, the computer revolution was beginning to take hold, and

the demand for software was rapidly outpacing programmers’ ability to produce it

A great deal of effort was being expended in academic circles in an attempt to create a

better computer language But, and perhaps most importantly, a secondary force was

beginning to be felt Computer hardware was finally becoming common enough that a

critical mass was being reached No longer were computers kept behind locked doors

For the first time, programmers were gaining virtually unlimited access to their

machines This allowed the freedom to experiment It also allowed programmers to

begin to create their own tools On the eve of C’s creation, the stage was set for a

quantum leap forward in computer languages

Invented and first implemented by Dennis Ritchie on a DEC PDP-11 running the

UNIX operating system, C was the result of a development process that started with

an older language called BCPL, developed by Martin Richards BCPL influenced a

language called B, invented by Ken Thompson, which led to the development of C

in the 1970s For many years, the de facto standard for C was the one supplied with

the UNIX operating system and described in The C Programming Language by Brian

Kernighan and Dennis Ritchie (Prentice-Hall, 1978) C was formally standardized in

December 1989, when the American National Standards Institute (ANSI) standard for

C was adopted

The creation of C is considered by many to have marked the beginning of the

modern age of computer languages It successfully synthesized the conflicting

attributes that had so troubled earlier languages The result was a powerful, efficient,

structured language that was relatively easy to learn It also included one other, nearly

intangible aspect: it was a programmer’s language Prior to the invention of C, computer

languages were generally designed either as academic exercises or by bureaucratic

committees C is different It was designed, implemented, and developed by real,

working programmers, reflecting the way that they approached the job of programming.Its features were honed, tested, thought about, and rethought by the people whoactually used the language The result was a language that programmers liked to use.Indeed, C quickly attracted many followers who had a near-religious zeal for it Assuch, it found wide and rapid acceptance in the programmer community In short,

C is a language designed by and for programmers As you will see, Java has inheritedthis legacy

The Need for C++

During the late 1970s and early 1980s, C became the dominant computer programminglanguage, and it is still widely used today Since C is a successful and useful language,

you might ask why a need for something else existed The answer is complexity.

Throughout the history of programming, the increasing complexity of programs hasdriven the need for better ways to manage that complexity C++ is a response to thatneed To better understand why managing program complexity is fundamental to thecreation of C++, consider the following

Approaches to programming have changed dramatically since the invention of thecomputer For example, when computers were first invented, programming was done

by manually toggling in the binary machine instructions by use of the front panel Aslong as programs were just a few hundred instructions long, this approach worked

As programs grew, assembly language was invented so that a programmer could dealwith larger, increasingly complex programs by using symbolic representations of themachine instructions As programs continued to grow, high-level languages wereintroduced that gave the programmer more tools with which to handle complexity.The first widespread language was, of course, FORTRAN While FORTRAN was

an impressive first step, it is hardly a language that encourages clear and

easy-to-understand programs The 1960s gave birth to structured programming This is the

method of programming championed by languages such as C The use of structuredlanguages enabled programmers to write, for the first time, moderately complexprograms fairly easily However, even with structured programming methods, once aproject reaches a certain size, its complexity exceeds what a programmer can manage

By the early 1980s, many projects were pushing the structured approach past its limits

To solve this problem, a new way to program was invented, called object-oriented programming (OOP) Object-oriented programming is discussed in detail later in this

book, but here is a brief definition: OOP is a programming methodology that helpsorganize complex programs through the use of inheritance, encapsulation, andpolymorphism

In the final analysis, although C is one of the world’s great programming languages,there is a limit to its ability to handle complexity Once a program exceeds somewherebetween 25,000 and 100,000 lines of code, it becomes so complex that it is difficult tograsp as a totality C++ allows this barrier to be broken, and helps the programmercomprehend and manage larger programs

C++ was invented by Bjarne Stroustrup in 1979, while he was working at Bell

Laboratories in Murray Hill, New Jersey Stroustrup initially called the new language

“C with Classes.” However, in 1983, the name was changed to C++ C++ extends C

by adding object-oriented features Because C++ is built upon the foundation of C,

it includes all of C’s features, attributes, and benefits This is a crucial reason for the

success of C++ as a language The invention of C++ was not an attempt to create a

completely new programming language Instead, it was an enhancement to an already

highly successful one

The Stage Is Set for Java

By the end of the 1980s and the early 1990s, object-oriented programming using C++

took hold Indeed, for a brief moment it seemed as if programmers had finally found

the perfect language Because C++ blended the high efficiency and stylistic elements of

C with the object-oriented paradigm, it was a language that could be used to create a

wide range of programs However, just as in the past, forces were brewing that would,

once again, drive computer language evolution forward Within a few years, the World

Wide Web and the Internet would reach critical mass This event would precipitate

another revolution in programming

The Creation of Java

Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and

Mike Sheridan at Sun Microsystems, Inc in 1991 It took 18 months to develop the first

working version This language was initially called “Oak” but was renamed “Java”

in 1995 Between the initial implementation of Oak in the fall of 1992 and the public

announcement of Java in the spring of 1995, many more people contributed to the design

and evolution of the language Bill Joy, Arthur van Hoff, Jonathan Payne, Frank Yellin,

and Tim Lindholm were key contributors to the maturing of the original prototype

Somewhat surprisingly, the original impetus for Java was not the Internet! Instead,

the primary motivation was the need for a platform-independent (that is,

architecture-neutral) language that could be used to create software to be embedded in various

consumer electronic devices, such as microwave ovens and remote controls As you

can probably guess, many different types of CPUs are used as controllers The trouble

with C and C++ (and most other languages) is that they are designed to be compiled

for a specific target Although it is possible to compile a C++ program for just about

any type of CPU, to do so requires a full C++ compiler targeted for that CPU The

problem is that compilers are expensive and time-consuming to create An easier—

and more cost-efficient—solution was needed In an attempt to find such a solution,

Gosling and others began work on a portable, platform-independent language that

could be used to produce code that would run on a variety of CPUs under differing

environments This effort ultimately led to the creation of Java

About the time that the details of Java were being worked out, a second, andultimately more important, factor was emerging that would play a crucial role

in the future of Java This second force was, of course, the World Wide Web Hadthe Web not taken shape at about the same time that Java was being implemented,Java might have remained a useful but obscure language for programming consumerelectronics However, with the emergence of the World Wide Web, Java was propelled

to the forefront of computer language design, because the Web, too, demandedportable programs

Most programmers learn early in their careers that portable programs are aselusive as they are desirable While the quest for a way to create efficient, portable(platform-independent) programs is nearly as old as the discipline of programmingitself, it had taken a back seat to other, more pressing problems Further, because much

of the computer world had divided itself into the three competing camps of Intel,Macintosh, and UNIX, most programmers stayed within their fortified boundaries,and the urgent need for portable code was reduced However, with the advent of theInternet and the Web, the old problem of portability returned with a vengeance Afterall, the Internet consists of a diverse, distributed universe populated with many types

of computers, operating systems, and CPUs Even though many types of platformsare attached to the Internet, users would like them all to be able to run the sameprogram What was once an irritating but low-priority problem had become a

high-profile necessity

By 1993, it became obvious to members of the Java design team that the problems

of portability frequently encountered when creating code for embedded controllersare also found when attempting to create code for the Internet In fact, the same problemthat Java was initially designed to solve on a small scale could also be applied to theInternet on a large scale This realization caused the focus of Java to switch fromconsumer electronics to Internet programming So, while the desire for an architecture-neutral programming language provided the initial spark, the Internet ultimately led toJava’s large-scale success

As mentioned earlier, Java derives much of its character from C and C++ This is

by intent The Java designers knew that using the familiar syntax of C and echoingthe object-oriented features of C++ would make their language appealing to thelegions of experienced C/C++ programmers In addition to the surface similarities,Java shares some of the other attributes that helped make C and C++ successful First,Java was designed, tested, and refined by real, working programmers It is a languagegrounded in the needs and experiences of the people who devised it Thus, Java is also

a programmer’s language Second, Java is cohesive and logically consistent Third,except for those constraints imposed by the Internet environment, Java gives you, theprogrammer, full control If you program well, your programs reflect it If you programpoorly, your programs reflect that, too Put differently, Java is not a language withtraining wheels It is a language for professional programmers

Because of the similarities between Java and C++, it is tempting to think of Java as

simply the “Internet version of C++.” However, to do so would be a large mistake Java

has significant practical and philosophical differences While it is true that Java was

influenced by C++, it is not an enhanced version of C++ For example, Java is neither

upwardly nor downwardly compatible with C++ Of course, the similarities with C++

are significant, and if you are a C++ programmer, then you will feel right at home with

Java One other point: Java was not designed to replace C++ Java was designed to

solve a certain set of problems C++ was designed to solve a different set of problems

Both will coexist for many years to come

As mentioned at the start of this chapter, computer languages evolve for two

reasons: to adapt to changes in environment and to implement advances in the art

of programming The environmental change that prompted Java was the need for

platform-independent programs destined for distribution on the Internet However,

Java also embodies changes in the way that people approach the writing of programs

Specifically, Java enhances and refines the object-oriented paradigm used by C++

Thus, Java is not a language that exists in isolation Rather, it is part of an ongoing

process begun many years ago This fact alone is enough to ensure Java a place in

computer language history Java is to Internet programming what C was to systems

programming: a revolutionary force that changed the world

The C# Connection

The reach and power of Java continues to be felt in the world of computer language

development Many of its innovative features, constructs, and concepts have become

part of the baseline for any new language The success of Java is simply too important

to ignore

Perhaps the most important example of Java’s influence is C# Recently created by

Microsoft to support the NET Framework, C# is closely related to Java For example,

both share the same general C++-style syntax, support distributed programming, and

utilize the same object model There are, of course, differences between Java and C#,

but the overall “look and feel” of these languages is very similar This “cross-pollination”

from Java to C# is the strongest testimonial to date that Java redefined the way we

think about and use a computer language

Why Java Is Important to the Internet

The Internet helped catapult Java to the forefront of programming, and Java, in turn,

has had a profound effect on the Internet The reason for this is quite simple: Java

expands the universe of objects that can move about freely in cyberspace In a network,

two very broad categories of objects are transmitted between the server and your

personal computer: passive information and dynamic, active programs For example,

when you read your e-mail, you are viewing passive data Even when you download aprogram, the program’s code is still only passive data until you execute it However, asecond type of object can be transmitted to your computer: a dynamic, self-executingprogram Such a program is an active agent on the client computer, yet is initiated bythe server For example, a program might be provided by the server to display properlythe data that the server is sending.

As desirable as dynamic, networked programs are, they also present seriousproblems in the areas of security and portability Prior to Java, cyberspace was

effectively closed to half the entities that now live there As you will see, Java addressesthose concerns and, by doing so, has opened the door to an exciting new form ofprogram: the applet

Java Applets and Applications

Java can be used to create two types of programs: applications and applets An

application is a program that runs on your computer, under the operating system of that

computer That is, an application created by Java is more or less like one created using C

or C++ When used to create applications, Java is not much different from any othercomputer language Rather, it is Java’s ability to create applets that makes it important

An applet is an application designed to be transmitted over the Internet and executed by

a Java-compatible Web browser An applet is actually a tiny Java program, dynamicallydownloaded across the network, just like an image, sound file, or video clip The

important difference is that an applet is an intelligent program, not just an animation or

media file In other words, an applet is a program that can react to user input anddynamically change—not just run the same animation or sound over and over

As exciting as applets are, they would be nothing more than wishful thinking ifJava were not able to address the two fundamental problems associated with them:security and portability Before continuing, let’s define what these two terms meanrelative to the Internet

Security

As you are likely aware, every time that you download a “normal” program, youare risking a viral infection Prior to Java, most users did not download executableprograms frequently, and those who did scanned them for viruses prior to execution.Even so, most users still worried about the possibility of infecting their systems with

a virus In addition to viruses, another type of malicious program exists that must beguarded against This type of program can gather private information, such as creditcard numbers, bank account balances, and passwords, by searching the contents ofyour computer’s local file system Java answers both of these concerns by providing

a “firewall” between a networked application and your computer

When you use a Java-compatible Web browser, you can safely download Javaapplets without fear of viral infection or malicious intent Java achieves this protection

by confining a Java program to the Java execution environment and not allowing it