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Java :

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Herbert Schildt



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About the Author

Herbert Schildt is the world's leading programming author.
He is an authority on the C, C++, Java, and C# languages,
and he is a master Windows programmer. His programming
books have sold more than 3 million copies worldwide and
have been translated into all major languages. He is the author
of numerous bestsellers, including Java: The Complete
Reference, C++: The Complete Reference, C: The Complete
Reference, and C#: The Complete Reference, and he is the
co-author of The Art of Java. Schildt holds both graduate and
undergraduate degrees from the University of Illinois. He can
be reached at his consulting office at (217) 586-4683. His Web
site is www.HerbSchildt.com.



Copyright © 2005 The McGraw-Hill Companies. Click here for terms of use.



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Contents at a Glance

1 Java Fundamentals 1

2 Introducing Data Types and Operators 35

3 Program Control Statements 71

4 Introducing Classes, Objects, and Methods 115

5 More Data Types and Operators 151

6 A Closer Look at Methods and Classes 201

7 Inheritance 251

8 Packages and Interfaces 301

9 Exception Handling 333

10 Using I/O 365

1 1 Multithreaded Programming 407

1 2 Enumerations, Autoboxing, and Static Import 447

13 Generics 481

14 Applets, Events, and Miscellaneous Topics 525



VII



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viii Java: A Beginner's Guide



A Answers to Mastery Checks 557

B Using Java's Documentation Comments 603

Index 613



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For more information about this title, click here



Contents

PREFACE xix

1 Java Fundamentals 1

The Origins of Java 2

How Java Relates to C and C++ 3

How Java Relates to C# 4

Java's Contribution to the Internet 5

Java Applets 5

Security 5

Portability 6

Java's Magic: The Bytecode 6

The Java Buzzwords 7

Object-Oriented Programming 8

Encapsulation 9

Polymorphism 10

Inheritance 10

Obtaining the Java Development Kit 12

A First Simple Program 12

Entering the Program 13

Compiling the Program 13

The First Sample Program Line by Line 14

ix

term Line



X Java: A Beginner's Guide



Handling Syntax Errors 17

A Second Simple Program 17

Another Data Type 20

Project 1-1 Converting Gallons to Liters 22

Two Control Statements 23

The if Statement 23

The for Loop 25

Create Blocks of Code 27

Semicolons and Positioning 29

Indentation Practices 29

Project 1-2 Improving the Gallons-to-Liters Converter 30

The Java Keywords 32

Identifiers in Java 32

The Java Class Libraries 33

Module 1 Mastery Check 34

2 Introducing Data Types and Operators 35

Why Data Types Are Important 36

Java's Primitive Types 36

Integers 37

Floating-Point Types 38

Characters 40

The Boolean Type 41

Project 2-1 How Far Away Is the Lightning? 43

Literals 44

Hexadecimal and Octal Constants 44

Character Escape Sequences 45

String Literals 45

A Closer Look at Variables 47

Initializing a Variable 47

Dynamic Initialization 48

The Scope and Lifetime of Variables 49

Operators 52

Arithmetic Operators 52

Increment and Decrement 54

Relational and Logical Operators 55

Short-Circuit Logical Operators 57

The Assignment Operator 58

Shorthand Assignments 60

Type Conversion in Assignments 61

Casting Incompatible Types 62

Operator Precedence 64

Project 2-2 Display a Truth Table for the Logical Operators 65



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Contents



Expressions 66

Type Conversion in Expressions 66

Spacing and Parentheses 68

Module 2 Mastery Check 69

3 Program Control Statements 71

Input Characters from the Keyboard 72

The if Statement 74

Nested ifs 75

The if-else-if Ladder 76

The switch Statement 78

Nested switch Statements 82

Project 3-1 Start Building a Java Help System 83

The for Loop 86

Some Variations on the for Loop 87

Missing Pieces 88

Loops with No Body 90

Declaring Loop Control Variables Inside the for Loop 91

The Enhanced for Loop 92

The while Loop 92

The do-while Loop 94

Project 3-2 Improve the Java Help System 97

Use break to Exit a Loop 100

Use break as a Form of goto 102

Use continue 106

Project 3-3 Finish the Java Help System 109

Nested Loops 112

Module 3 Mastery Check 113

4 Introducing Classes, Objects, and Methods 115

Class Fundamentals 116

The General Form of a Class 116

Defining a Class 117

How Objects Are Created 121

Reference Variables and Assignment 121

Methods 122

Adding a Method to the Vehicle Class 123

Returning from a Method 125

Returning a Value 126

Using Parameters 129

Adding a Parameterized Method to Vehicle 130

Project 4-1 Creating a Help Class 133

Constructors 139

Parameterized Constructors 140

Adding a Constructor to the Vehicle Class 141



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xii Java: A Beginner's Guide



The new Operator Revisited 142

Garbage Collection and Finalizers 143

The fmalize( ) Method 144

Project 4-2 Demonstrate Finalization 145

The this Keyword 147

Module 4 Mastery Check 149

5 More Data Types and Operators 151

Arrays 152

One-Dimensional Arrays 152

Project 5-1 Sorting an Array 156

Multidimensional Arrays 158

Two-Dimensional Arrays 158

Irregular Arrays 1 60

Arrays of Three or More Dimensions 161

Initializing Multidimensional Arrays 161

Alternative Array Declaration Syntax 163

Assigning Array References 164

Using the length Member 165

Project 5-2 A Queue Class 168

The For-Each Style for Loop 172

Iterating Over Multidimensional Arrays 175

Applying the Enhanced for 177

Strings 178

Constructing Strings 178

Operating on Strings 179

Arrays of Strings 181

Strings Are Immutable 182

Using Command-Line Arguments 183

The Bitwise Operators 185

The Bitwise AND, OR, XOR, and NOT Operators 186

The Shift Operators 191

Bitwise Shorthand Assignments 193

Project 5-3 A ShowBits Class 193

The? Operator 196

Module 5 Mastery Check 198

6 A Closer Look at Methods and Classes 201

Controlling Access to Class Members 202

Java's Access Specifiers 202

Project 6-1 Improving the Queue Class 208

Pass Objects to Methods 209

How Arguments Are Passed 211

Returning Objects 214



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Contents xiii



Method Overloading 216

Overloading Constructors 222

Project 6-2 Overloading the Queue Constructor 225

Recursion 228

Understanding static 230

Static Blocks 233

Project 6-3 The Quicksort 235

Introducing Nested and Inner Classes 238

Varargs: Variable-Length Arguments 242

Varargs Basics 242

Overloading Varargs Methods 246

Varargs and Ambiguity 247

Module 6 Mastery Check 249

7 Inheritance 251

Inheritance Basics 252

Member Access and Inheritance 255

Constructors and Inheritance 258

Using super to Call Superclass Constructors 260

Using super to Access Superclass Members 266

Project 7-1 Extending the Vehicle Class 267

Creating a Multilevel Hierarchy 270

When Are Constructors Called? 273

Superclass References and Subclass Objects 274

Method Overriding 280

Overridden Methods Support Polymorphism 283

Why Overridden Methods? 285

Applying Method Overriding to TwoDShape 285

Using Abstract Classes 290

Using final 295

final Prevents Overriding 295

final Prevents Inheritance 295

Using final with Data Members 296

The Object Class 298

Module 7 Mastery Check 299

8 Packages and Interfaces 301

Packages 302

Defining a Package 302

Finding Packages and CLASSPATH 304

A Short Package Example 304

Packages and Member Access 306

A Package Access Example 307

Understanding Protected Members 309

Importing Packages 311



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xiv Java: A Beginner's Guide



Java's Class Library Is Contained in Packages 314

Interfaces 315

Implementing Interfaces 316

Using Interface References 320

Project 8-1 Creating a Queue Interface 322

Variables in Interfaces 328

Interfaces Can Be Extended 329

Module 8 Mastery Check 330

9 Exception Handling 333

The Exception Hierarchy 334

Exception Handling Fundamentals 334

Using try and catch 335

A Simple Exception Example 336

The Consequences of an Uncaught Exception 339

Exceptions Enable You to Handle Errors Gracefully 340

Using Multiple catch Statements 342

Catching Subclass Exceptions 343

Try Blocks Can Be Nested 344

Throwing an Exception 346

Rethrowing an Exception 346

A Closer Look at Throwable 348

Using finally 350

Using throws 352

Java's Built-in Exceptions 354

Creating Exception Subclasses 356

Project 9-1 Adding Exceptions to the Queue Class 359

Module 9 Mastery Check 362

10 Using I/O 365

Java's I/O Is Built upon Streams 366

Byte Streams and Character Streams 366

The Byte Stream Classes 367

The Character Stream Classes 367

The Predefined Streams 367

Using the Byte Streams 370

Reading Console Input 370

Writing Console Output 372

Reading and Writing Files Using Byte Streams 373

Inputting from a File 374

Writing to a File 376

Reading and Writing Binary Data 378

Project 10-1 A File Comparison Utility 382

Random Access Files 384



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Contents XV



Using Java's Character-Based Streams 387

Console Input Using Character Streams 388

Console Output Using Character Streams 391

File I/O Using Character Streams 393

Using a File Writer 393

Using a FileReader 394

Using Java's Type Wrappers to Convert Numeric Strings 396

Project 10-2 Creating a Disk-Based Help System 399

Module 10 Mastery Check 406

1 1 Multithreaded Programming 407

Multithreading Fundamentals 408

The Thread Class and Runnable Interface 409

Creating a Thread 410

Some Simple Improvements 413

Project 11-1 Extending Thread 415

Creating Multiple Threads 418

Determining When a Thread Ends 421

Thread Priorities 424

Synchronization 428

Using Synchronized Methods 428

The synchronized Statement 43 1

Thread Communication Using notify( ), wait( ), and notify All( ) 434

An Example That Uses wait( ) and notify( ) 435

Suspending, Resuming, and Stopping Threads 440

Project 11-2 Using the Main Thread 444

Module 1 1 Mastery Check 446

1 2 Enumerations, Autoboxing, and Static Import 447

Enumerations 448

Enumeration Fundamentals 449

Java Enumerations Are Class Types 452

The values( ) and valueOf( ) Methods 452

Constructors, Methods, Instance Variables, and Enumerations 454

Two Important Restrictions 456

Enumerations Inherit Enum 456

Project 12-1 A Computer-Controlled Traffic Light 458

Autoboxing 464

Type Wrappers 465

Autoboxing Fundamentals 467

Autoboxing and Methods 468

Autoboxing/Unboxing Occurs in Expressions 470

A Word of Warning 471

Static Import 472



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xvi Java: A Beginner's Guide



Metadata 476

Module 12 Mastery Check 479

13 Generics 481

Generics Fundamentals 482

A Simple Generics Example 483

Generics Work Only with Objects 487

Generic Types Differ Based on Their Type Arguments 487

A Generic Class with Two Type Parameters 488

The General Form of a Generic Class 490

Bounded Types 490

Using Wildcard Arguments 494

Bounded Wildcards 498

Generic Methods 501

Generic Constructors 504

Generic Interfaces 505

Project 13-1 Create a Generic Queue 508

Raw Types and Legacy Code 513

Erasure 516

Ambiguity Errors 517

Some Generic Restrictions 519

Type Parameters Can't Be Instantiated 519

Restrictions on Static Members 520

Generic Array Restrictions 520

Generic Exception Restriction 522

Continuing Your Study of Generics 522

Module 13 Mastery Check 522

14 Applets, Events, and Miscellaneous Topics 525

Applet Basics 526

Applet Organization and Essential Elements 530

The Applet Architecture 530

A Complete Applet Skeleton 531

Applet Initialization and Termination 532

Requesting Repainting 533

The update( ) Method 534

Project 14-1 A Simple Banner Applet 535

Using the Status Window 539

Passing Parameters to Applets 540

The Applet Class 542

Event Handling 544

The Delegation Event Model 544

Events 544

Event Sources 545



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Contents xvii



Event Listeners 545

Event Classes 545

Event Listener Interfaces 546

Using the Delegation Event Model 548

Handling Mouse Events 548

A Simple Mouse Event Applet 549

More Java Keywords 552

The transient and volatile Modifiers 552

instanceof 553

strictfp 553

assert 553

Native Methods 554

What Next? 555

Module 14 Mastery Check 556

A Answers to Mastery Checks 557

B Using Java's Documentation Comments 603

The javadoc Tags 604

@author 605

{@code} 605

©deprecated 605

{@docRoot} 606

©exception 606

{@inheritDoc} 606

{@link} 606

{@linkplain} 606

{©literal} 606

@param 607

@return 607

@see 607

@serial 607

@serialData 608

@serialField 608

@since 608

©throws 608

{@value} 608

@version 609

The General Form of a Documentation Comment 609

What javadoc Outputs 609

An Example that Uses Documentation Comments 610

Index 613



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Preface



Java is the preeminent language of the Internet. Moreover, it is the universal language of
Web programmers around the world. To be a professional Web developer today implies
proficiency in Java. Therefore, if Internet-based programming is in your future, you have
chosen the right language to learn — and, this book will help you learn it.

The purpose of this book is to teach you the fundamentals of Java programming. It uses a
step-by-step approach complete with numerous examples, self-tests, and projects. It assumes
no previous programming experience. The book starts with the basics, such as how to compile
and run a Java program. It then discusses every keyword in the Java language. It concludes
with some of Java's most advanced features, such as multithreaded programming, generics,
and applets. By the time you finish, you will have a firm grasp of the essentials of Java
programming.

It is important to state at the outset that this book is just a starting point. Java is more than
just the elements that define the language. Java also includes extensive libraries and tools that
aid in the development of programs. Furthermore, Java provides a sophisticated set of libraries
that handle the browser user interface. To be a top-notch Java programmer implies mastery of
these areas, too. After completing this book, you will have the knowledge to pursue any and
all other aspects of Java.



xix

Copyright © 2005 The McGraw-Hill Companies. Click here for terms of use.



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XX Java: A Beginner's Guide



The Evolution of Java

Only a few languages have fundamentally reshaped the very essence of programming. In this
elite group, one stands out because its impact was both rapid and widespread. This language
is, of course, Java. It is not an overstatement to say that the original release of Java 1.0 in
1995 by Sun Microsystems caused a revolution in programming. This revolution radically
transformed the Web into a highly interactive environment. In the process, Java set a new
standard in computer language design.

Over the years, Java continued to grow, evolve, and otherwise redefine itself. Unlike many
other languages, which are slow to incorporate new features, Java has continually been at the
forefront of computer language design. One reason for this is the culture of innovation and
change that came to surround Java. As a result, Java has gone through several upgrades — some
relatively small, others more significant.

The first major update to Java was version 1.1. The features added by Java 1 . 1 were more
substantial than the small increase in the version number would have you think. For example,
Java 1 . 1 added many new library elements, redefined the way events are handled, and
reconfigured many features of the original 1.0 library.

The next major release of Java was Java 2, where the 2 indicates "second generation." The
creation of Java 2 was a watershed event, marking the beginning of Java's "modern age."
The first release of Java 2 carried the version number 1.2. It may seem odd that the first release
of Java 2 used the 1.2 version number. The number originally referred to the internal version
number of the Java libraries, but then was generalized to refer to the entire release, itself. With
Java 2, Sun repackaged the Java product as J2SE (Java 2 Platform Standard Edition), and the
version numbers began to be applied to that product.

The next upgrade of Java was J2SE 1.3. This version of Java was the first major upgrade
to the original Java 2 release. For the most part it added to existing functionality and
"tightened up" the development environment. The release of J2SE 1.4 further enhanced Java.
This release contained several important new features, including chained exceptions, channel-
based I/O, and the assert keyword.

The latest release of Java is J2SE 5. As important as each of the preceding upgrades to
Java have been, none compares in scale, size, and scope to that of J2SE 5. It has fundamentally
reshaped the Java world!



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Preface xxi



J2SE 5: The Second Java Revolution

Java 2 Platform Standard Edition, version 5 (J2SE 5) marks the beginning of the second Java
revolution. J2SE 5 adds many new features to Java that fundamentally change the character of
the language, increasing both its power and its range. So profound are these additions that they
will forever alter the way that Java code is written. J2SE 5 is a revolutionary force that cannot
be ignored.

To give you an idea of the scope of the changes caused by J2SE 5, here is a list of its major
new features covered in this book:



•


Generics


•


Autoboxing/unboxing


•


Enumerations


•


The enhanced, "for-each" style for loop


•


Variable-length arguments (varargs)


•


Static import


•


Metadata (annotations)



This is not a list of minor tweaks or incremental upgrades. Each item in the list represents
a significant addition to the Java language. Some, such as generics, the enhanced for, and
varargs, introduce new syntax elements. Others, such as autoboxing and auto-unboxing, alter
the semantics of the language. Metadata adds an entirely new dimension to programming.
In all cases, substantial functionality has been added.

The importance of these new features is reflected in the use of the version number 5. The
next version number for Java would normally have been 1.5. However, the changes and new
features are so significant that a shift from 1.4 to 1.5 just didn't seem to express the magnitude
of the change. Instead, Sun elected to increase the version number to 5 as a way of emphasizing
that a major event was taking place. Thus, the current product is called J2SE 5, and the
developer's kit is called JDK 5. However, in order to maintain consistency, Sun decided to
use 1.5 as its internal version number. Thus, 5 is the external version number and 1.5 is the
internal version number.



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xxii Java: A Beginner's Guide



Because of Sun's use of 1.5 as the internal version number, when you ask the compiler its
version, it will respond with 1.5 rather than 5. Also, the online documentation supplied by
Sun uses 1.5 to refer to features added by the J2SE 5. In general, whenever you see 1.5, it
simply means 5.

This book has been fully updated to include the new features added by J2SE 5. To handle
all of the new material, two entirely new modules where added to this edition. Module 12
discusses enumerations, autoboxing, static import, and metadata. Module 13 examines generics.
Descriptions of the "for-each" style for loop and variable-length arguments were integrated
into existing modules.



This book presents an evenly paced tutorial in which each section builds upon the previous
one. It contains 14 modules, each discussing an aspect of Java. This book is unique because it
includes several special elements that reinforce what you are learning.



Each module begins with a set of critical skills that you will learn. The location of each skill
within the module is indicated.



Each module concludes with a Mastery Check, a self-test that lets you test your knowledge.
The answers are in Appendix A.



At the end of each major section, Progress Checks are presented which test your understanding
of the key points of the preceding section. The answers to these questions are at the bottom of
the page.



Sprinkled throughout the book are special "Ask the Expert" boxes. These contain additional
information or interesting commentary about a topic. They use a question-and-answer format.



How This Book Is Organized



Critical Skills



Mastery Check



Progress Checks




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Preface xxiii



Projects



Each module contains one or more projects that show you how to apply what you are learning.
These are real-world examples that you can use as starting points for your own programs.



This book assumes no previous programming experience. Thus, if you have never programmed
before, you can use this book. If you do have some previous programming experience, you
will be able to advance a bit more quickly. Keep in mind, however, that Java differs in several
key ways from other popular computer languages. It is important not to jump to conclusions.
Thus, even for the experienced programmer, a careful reading is advised.



To compile and run the programs in this book, you will need the latest Java Development
Kit (JDK) from Sun, which at the time of this writing is Java 2 Platform Standard Edition,
version 5 (J2SE 5). Instructions for obtaining the Java JDK are given in Module 1.

If you are using an earlier version of Java, such as J2SE 1.4, then you will still be able to
use this book, but you won't be able to compile and run the programs that use the new features
addedbyJ2SE5.



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.



No Previous Programming
Experience Required




Don't Forget: Code on the Web



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xxiv Java: A Beginner's Guide



For Further Study

Java: A Beginner's Guide 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: The Complete Reference, J2SE 5 Edition

• The Art of Java

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

C++: The Complete Reference

Teach Yourself C+ +

C++ from the Ground Up

STL Programming from the Ground Up

The Art of C++

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, 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.



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Module 1



Java Fundamentals



CRITICAL SKILLS



1.1 Know the history and philosophy of Java

1.2 Understand Java's contribution to the Internet

1.3 Understand the importance of bytecode

1 .4 Know the Java buzzwords

1.5 Understand the foundational principles of object-oriented programming

1.6 Create, compile, and run a simple Java program

1.7 Use variables

1.8 Use the if and for control statements

1.9 Create blocks of code

1.10 Understand how statements are positioned, indented, and terminated

1.11 Know the Java keywords

1.12 Understand the rules for Java identifiers



Copyright © 2005 The McGraw-Hill Companies. Click here for terms of use.



1

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2 Module 1 : Java Fundamentals

The rise of the Internet and the World Wide Web fundamentally reshaped computing. In
the past, the cyber landscape was dominated by stand-alone PCs. Today, nearly all PCs
are connected to the Internet. The Internet, itself, was transformed — originally offering a
convenient way to share files and information, today it is a vast, distributed computing universe.
With these changes came a new way to program: Java.

Java is the preeminent language of the Internet, but it is more than that. Java
revolutionized programming, changing the way that we think about both the form and the
function of a program. To be a professional programmer today implies the ability to program
in Java — it is that important. In the course of this book, you will learn the skills needed to
master it.

The purpose of this module is to introduce you to Java, including its history, its design
philosophy, and several of its most important features. By far, the hardest thing about learning a
programming language is the fact that no element exists in isolation. Instead, the components of
the language work in conjunction with each other. This interrelatedness is especially pronounced
in Java. In fact, it is difficult to discuss one aspect of Java without involving others. To help
overcome this problem, this module provides a brief overview of several Java features,
including the general form of a Java program, some basic control structures, and operators.
It does not go into too many details but, rather, concentrates on the general concepts common
to any Java program.



Computer language innovation is driven forward by two factors: improvements in the art of
programming and changes in the computing environment. Java is no exception. Building upon
the rich legacy inherited from C and C++, Java adds refinements and features that reflect the
current state of the art in programming. Responding to the rise of the online environment, Java
offers features that streamline programming for a highly distributed architecture.

Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and
Mike Sheridan at Sun Microsystems in 1991. This language was initially called "Oak" but
was renamed "Java" in 1995. Somewhat surprisingly, the original impetus for Java was not
the Internet! Instead, the primary motivation was the need for a platform-independent language
that could be used to create software to be embedded in various consumer electronic devices,
such as toasters, microwave ovens, and remote controls. As you can probably guess, many
different types of CPUs are used as controllers. The trouble was that most computer languages
are designed to be compiled for a specific target. For example, consider C++.

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, however, is that compilers
are expensive and time-consuming to create. In an attempt to find a better solution, Gosling



CRITICAL SKILL




TERM LlflG



Java: A Beginner's Guide



and others worked on a portable, cross-platform language that could 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, and ultimately
more important, factor emerged that would play a crucial role in the future of Java. This
second force was, of course, the World Wide Web. Had the 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 consumer electronics. However, with the emergence of the Web,
Java was propelled to the forefront of computer language design, because the Web, too,
demanded portable programs.

Most programmers learn early in their careers that portable programs are as elusive 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 programming itself, it had taken a back seat to
other, more pressing problems. However, with the advent of the Internet and the Web, the old
problem of portability returned with a vengeance. After all, the Internet consists of a diverse,
distributed universe populated with many types of computers, operating systems, and CPUs.
What was once an irritating but a 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 controllers are also found
when attempting to create code for the Internet. This realization caused the focus of Java to
switch from consumer electronics to Internet programming. So, while it was the desire for an
architecture-neutral programming language that provided the initial spark, it was the Internet
that ultimately led to Java's large-scale success.

How Java Relates to C and C++

Java is directly related to both C and C++. Java inherits its syntax from C. Its object model is
adapted from C++. Java's relationship with C and C++ is important for several reasons. First,
many programmers are familiar with the C/C++ syntax. This makes it easy for a C/C++
programmer to learn Java and, conversely, for a Java programmer to learn C/C++.

Second, Java's designers did not "reinvent the wheel." Instead, they further refined an
already highly successful programming paradigm. The modern age of programming began
with C. It moved to C++, and now to Java. By inheriting and building upon that rich heritage,
Java provides a powerful, logically consistent programming environment that takes the best of
the past and adds new features required by the online environment. Perhaps most important,
because of their similarities, C, C++, and Java define a common, conceptual framework for
the professional programmer. Programmers do not face major rifts when switching from one
language to another.

One of the central design philosophies of both C and C++ is that the programmer is in
charge! Java also inherits this philosophy. Except for those constraints imposed by the Internet
environment, Java gives you, the programmer, full control. If you program well, your programs



4 Module 1 : Java Fundamentals



reflect it. If you program poorly, your programs reflect that, too. Put differently, Java is not a
language with training wheels. It is a language for professional programmers.

Java has one other attribute in common with C and C++: it was designed, tested, and refined
by real, working programmers. It is a language grounded in the needs and experiences of the
people who devised it. There is no better way to produce a top-flight professional programming
language.

Because of the similarities between Java and C++, especially their support for object-
oriented programming, it is tempting to think of Java as simply the "Internet version of C++."
However, to do so would be a mistake. Java has significant practical and philosophical differences.
Although Java was influenced by C++, it is not an enhanced version of C++. For example, it
is neither upwardly nor downwardly compatible with C++. Of course, the similarities with
C++ are significant, and if you are a C++ programmer, you will feel right at home with Java.
Another 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.



Recently a new language called C# has come on the scene. Created by Microsoft to support
its .NET Framework, C# is closely reated to Java. In fact, many of C#'s features were directly
adapted from Java. Both Java and C# 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
means that if you already know C#, then learning Java will be especially easy. Conversely, if
C# is in your future, then your knowledge of Java will come in handy.

Given the similarity between Java and C#, one might naturally ask, "Will C# replace
Java?" The answer is No. Java and C# are optimized for two different types of computing
environments. Just as C++ and Java will co-exist for a long time to come, so will C# and Java.



How Java Relates to C#




1 . Java is useful for the Internet because it can produce



programs.



2. Java is the direct descendent of what languages?



1 . portable

2. C and C++.



TERM LlflG



Java: A Beginner's Guide



CRITICAL SKILL




Java's Contribution 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, there are two very broad
categories of objects that 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 a program, the program's code is still
only passive data until you execute it. However, a second type of object can be transmitted to
your computer: a dynamic, self-executing program. Such a program is an active agent on the
client computer, yet it is initiated by the server. For example, a program might be provided by
the server to properly display the data that it is sending.

As desirable as dynamic, networked programs are, they also present serious problems in
the areas of security and portability. Prior to Java, cyberspace was effectively closed to half
of the entities that now live there. As you will see, Java addresses those concerns and, in doing
so, has defined a new form of program: the applet.



An applet is a special kind of Java program that is designed to be transmitted over the Internet
and automatically executed by a Java-compatible Web browser. Furthermore, an applet is
downloaded on demand, 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 and dynamically 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 if Java
were not able to address the two fundamental problems associated with them: security and
portability. Before continuing, let's define what these two terms mean relative to the Internet.



As you are almost certainly aware, every time you download a "normal" program, you are
risking a viral infection. Prior to Java, most users did not download executable programs
frequently, and those that did, scanned them for viruses prior to execution. Even so, most users
still worried about the possibility of infecting their systems with a virus or allowing a malicious
program to run wild in their systems. (A malicious program might gather private information,
such as credit card numbers, bank account balances, and passwords by searching the contents
of your computer's local file system.) Java answers these concerns by providing a firewall
between a networked application and your computer.





6 Module 1 : Java Fundamentals



When using a Java-compatible web browser, it is possible to safely download Java applets
without fear of viral infection. The way that Java achieves this is by confining a Java program
to the Java execution environment and not allowing it access to other parts of the computer.
(You will see how this is accomplished, shortly.) Frankly, the ability to download applets with
confidence that no harm will be done to the client computer is the single most important aspect
of Java.



As discussed earlier, many types of computers and operating systems are connected to the
Internet. For programs to be dynamically downloaded to all of the various types of platforms,
some means of generating portable executable code is needed. As you will soon see, the same
mechanism that helps ensure security also helps create portability. Indeed, Java's solution to
these two problems is both elegant and efficient.



The key that allows Java to solve both the security and the portability problems just described
is that the output of a Java compiler is not executable code. Rather, it is bytecode. Bytecode
is a highly optimized set of instructions designed to be executed by the Java run-time system,
which is called the Java Virtual Machine (JVM). That is, the Java Virtual Machine is an
interpreter for bytecode. This may come as a bit of a surprise. As you know, most modern
languages, such as C++, are designed to be compiled, not interpreted — mostly because of
performance concerns. However, the fact that a Java program is executed by the JVM helps
solve the major problems associated with downloading programs over the Internet. Here is why.

Translating a Java program into bytecode makes it much easier to run a program in a wide
variety of environments. The reason is straightforward: only the Java Virtual Machine needs to
be implemented for each platform. Once the run-time package exists for a given system, any
Java program can run on it. Remember that although the details of the JVM will differ from
platform to platform, all understand the same Java bytecode. If a Java program were compiled
to native code, then different versions of the same program would have to exist for each type
of CPU connected to the Internet. This is, of course, not a feasible solution. Thus, the
interpretation of bytecode is the easiest way to create truly portable programs.

The fact that a Java program is interpreted also helps m
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