teach_your_self_java_in_21_days

v Sa m s. ne t Le a rn in g Ce nt er abcd P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 M T W R F S S 201 West 103rd Street Indianapolis, Indiana 46290 Laura Lemay Charles L. Perkins Teach Yourself JAVA in 21 Days 030-4 FM 1/29/96, 8:10 PM5 Note: Click anywhere on this page to jump to the Table of Contents. i Sa m s. ne t Le a rn in g Ce nt er abcd P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 W R F S M T W R About This Book This book teaches you all about the Java language and how to use it to create applets and applications. By the time you get through with this book, you’ll know enough about Java to do just about anything, inside an applet or out. Who Should Read This Book This book is intended for people with at least some basic programming back- ground, which includes people with years of programming experience or people with only a small amount of experience. If you understand what variables, loops, and functions are, you’ll be just fine for this book. The sorts of people who might want to read this book include you, if nn You’re a real whiz at HTML, understand CGI programming (in perl, AppleScript, Visual Basic, or some other popular CGI language) pretty well, and want to move on to the next level in Web page design. nn You had some Basic or Pascal in school and you have a basic grasp of what programming is, but you’ve heard Java is easy to learn, really powerful, and very cool. nn You’ve programmed C and C++ for many years, you’ve heard this Java thing is becoming really popular and you’re wondering what all the fuss is all about. nn You’ve heard that Java is really good for Web-based applets, and you’re curious about how good it is for creating more general applications. What if you know programming, but you don’t know object-oriented program- ming? Fear not. This book assumes no background in object-oriented design. If you know object-oriented programming, in fact, the first couple of days will be easy for you. How This Book Is Structured This book is intended to be read and absorbed over the course of three weeks. During each week, you’ll read seven chapters that present concepts related to the Java language and the creation of applets and applications. 030-4 FM 1/29/96, 8:10 PM1 Teach Yourself JAVA in 21 Days M T W T F S S 21 ii P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 Conventions Note: A Note box presents interesting pieces of information related to the surround- ing discussion. Technical Note: A Technical Note presents specific technical information related to the surrounding discussion. Tip: A Tip box offers advice or teaches an easier way to do something. Caution: A Caution box alerts you to a possible problem and gives you advice to avoid it. Warning: A Warning box advises you about potential problems and helps you steer clear of disaster. New terms are introduced in New Term boxes, with the term in italics. A type icon identifies some new HTML code that you can type in yourself. An Output icon highlights what the same HTML code looks like when viewed by either Netscape or Mosaic. An analysis icon alerts you to the author’s line-by-line analysis. !! Analysis Output Type NEW TERM * 030-4 FM 1/29/96, 8:10 PM2 Teach Yourself JAVA in 21 Days M T W T F S S 21 vi P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 To Eric, for all the usual reasons (moral support, stupid questions, comfort in dark times). LL For RKJP, ARL, and NMH the three most important people in my life. CLP Copyright ©1996 by Sams.net Publishing and its licensors FIRST EDITION All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. No patent liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein. For information, address Sams.net Publishing, 201 W. 103rd St., Indianapolis, IN 46290. International Standard Book Number: 1-57521-030-4 Library of Congress Catalog Card Number: 95-78866 99 98 97 96 4 3 2 1 Interpretation of the printing code: the rightmost double-digit number is the year of the book’s printing; the rightmost single-digit, the number of the book’s printing. For example, a printing code of 96-1 shows that the first printing of the book occurred in 1996. Composed in AGaramond and MCPdigital by Macmillan Computer Publishing Printed in the United States of America All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Sams.net Publishing cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. President, Sams Publishing: Richard K. Swadley Publisher, Sams.net Publishing: George Bond Publishing Manager: Mark Taber Managing Editor: Cindy Morrow Marketing Manager: John Pierce Acquisitions Editor Mark Taber Development Editor Fran Hatton Software Development Specialist Merle Newlon Production Editor Nancy Albright Technical Reviewer Patrick Chan Editorial Coordinator Bill Whitmer Technical Edit Coordinator Lynette Quinn Formatter Frank Sinclair Editorial Assistant Carol Ackerman Cover Designer Tim Amrhein Book Designer Alyssa Yesh Production Team Supervisor Brad Chinn Production Michael Brumitt Jason Hand Cheryl Moore Ayanna Lacey Nancy Price Bobbi Satterfield Tim Taylor Susan Van Ness Mark Walchle Todd Wente Indexer Tim Griffin 030-4 FM 1/29/96, 8:10 PM6 vii Sa m s. ne t Le a rn in g Ce nt er abcd P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 M T W R F S S Overview Introduction xxi Week 1 at a Glance Day 1 An Introduction to Java Programming 3 2 Object-Oriented Programming and Java 19 3 Java Basics 41 4 Working with Objects 61 5 Arrays, Conditionals, and Loops 79 6 Creating Classes and Applications in Java 95 7 More About Methods 111 Week 2 at a Glance Day 8 Java Applet Basics 129 9 Graphics, Fonts, and Color 149 10 Simple Animation and Threads 173 11 More Animation, Images, and Sound 195 12 Managing Simple Events and Interactivity 217 13 User Interfaces with the Java Abstract Windowing Toolkit 237 14 Windows, Networking, and Other Tidbits 279 Week 3 at a Glance Day 15 Modifiers 305 16 Packages and Interfaces 323 17 Exceptions 341 18 Multithreading 353 19 Streams 375 20 Native Methods and Libraries 403 21 Under the Hood 421 Appendixes A Language Summary 473 B The Java Class Library 483 C How Java Differs from C and C++ 497 D How Java Differs from C and C++ 507 Index 511 030-4 FM 1/29/96, 8:11 PM7 ix Sa m s. ne t Le a rn in g Ce nt er abcd P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 M T W R F S S Contents Introduction xxi Week 1 at a Glance 1 Day 1 An Introduction to Java Programming 3 What Is Java? .............................................................................................. 4 Java’s Past, Present, and Future ................................................................... 6 Why Learn Java? ......................................................................................... 7 Java Is Platform-Independent................................................................. 7 Java Is Object-Oriented ......................................................................... 9 Java Is Easy to Learn .............................................................................. 9 Getting Started with Programming in Java .............................................................................. 10 Getting the Software ............................................................................ 10 Applets and Applications ..................................................................... 11 Creating a Java Application .................................................................. 11 Creating a Java Applet ......................................................................... 13 Summary .................................................................................................. 16 Q&A ........................................................................................................ 16 Day 2 Object-Oriented Programming and Java 19 Thinking in Objects: An Analogy ............................................................. 20 Objects and Classes .................................................................................. 21 Behavior and Attributes ............................................................................ 23 Attributes ............................................................................................. 23 Behavior .............................................................................................. 24 Creating a Class ................................................................................... 24 Inheritance, Interfaces, and Packages ........................................................ 28 Inheritance........................................................................................... 29 Creating a Class Hierarchy................................................................... 30 How Inheritance Works ...................................................................... 32 Single and Multiple Inheritance ........................................................... 34 Interfaces and Packages ........................................................................ 34 Creating a Subclass ................................................................................... 35 Summary .................................................................................................. 38 Q&A ........................................................................................................ 39 Day 3 Java Basics 41 Statements and Expressions ...................................................................... 42 Variables and Data Types ......................................................................... 43 Declaring Variables .............................................................................. 43 Notes on Variable Names .................................................................... 44 030-4 FM 1/29/96, 8:11 PM9 Teach Yourself JAVA in 21 Days M T W T F S S 21 x P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 Variable Types ..................................................................................... 45 Assigning Values to Variables ............................................................... 46 Comments ................................................................................................ 47 Literals ...................................................................................................... 47 Number Literals ................................................................................... 47 Boolean Literals ................................................................................... 48 Character Literals ................................................................................. 48 String Literals ...................................................................................... 49 Expressions and Operators ........................................................................ 50 Arithmetic ........................................................................................... 50 More About Assignment ...................................................................... 52 Incrementing and Decrementing ......................................................... 52 Comparisons ........................................................................................ 54 Logical Operators ................................................................................ 55 Bitwise Operators ................................................................................ 55 Operator Precedence ............................................................................ 56 String Arithmetic ...................................................................................... 57 Summary .................................................................................................. 58 Q&A ........................................................................................................ 60 Day 4 Working with Objects 61 Creating New Objects .............................................................................. 62 Using new ............................................................................................ 63 What new Does ................................................................................... 64 A Note on Memory Management ........................................................ 64 Accessing and Setting Class and Instance Variables ................................... 65 Getting Values ..................................................................................... 65 Changing Values .................................................................................. 65 Class Variables ..................................................................................... 66 Calling Methods ....................................................................................... 67 Class Methods ..................................................................................... 69 References to Objects ............................................................................... 70 Casting and Converting Objects and Primitive Types .............................. 71 Casting Primitive Types ...................................................................... 71 Casting Objects .................................................................................. 72 Converting Primitive Types to Objects and Vice Versa ................................................................. 73 Odds and Ends ......................................................................................... 73 Comparing Objects ............................................................................. 74 Copying Objects .................................................................................. 75 Determining the Class of an Object ..................................................... 76 The Java Class Libraries ............................................................................ 76 Summary .................................................................................................. 77 Q&A ........................................................................................................ 78 030-4 FM 1/29/96, 8:11 PM10 xi Sa m s. ne t Le a rn in g Ce nt er abcd P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 Day 5 Arrays, Conditionals, and Loops 79 Arrays ....................................................................................................... 80 Declaring Array Variables .................................................................... 80 Creating Array Objects ........................................................................ 81 Accessing Array Elements ..................................................................... 81 Changing Array Elements .................................................................... 82 Multidimensional Arrays...................................................................... 83 Block Statements ...................................................................................... 83 if Conditionals .......................................................................................... 83 The Conditional Operator ................................................................... 84 switch Conditionals ................................................................................... 85 for Loops .................................................................................................. 86 while and do Loops ................................................................................... 88 while Loops .......................................................................................... 88 do...while Loops ................................................................................... 89 Breaking Out of Loops ............................................................................. 89 Labeled Loops ...................................................................................... 90 Summary .................................................................................................. 91 Q&A ........................................................................................................ 92 Day 6 Creating Classes and Applications in Java 95 Defining Classes ....................................................................................... 96 Creating Instance and Class Variables ....................................................... 96 Defining Instance Variables ................................................................. 97 Constants ............................................................................................. 97 Class Variables ..................................................................................... 98 Creating Methods ..................................................................................... 99 Defining Methods ............................................................................... 99 The this Keyword ............................................................................... 101 Variable Scope and Method Definitions ............................................ 101 Passing Arguments to Methods .......................................................... 102 Class Methods ................................................................................... 104 Creating Java Applications ...................................................................... 105 Java Applications and Command-Line Arguments ................................. 106 Passing Arguments to Java Programs .................................................. 106 Handling Arguments in Your Java Program ....................................... 106 Summary ................................................................................................ 108 Q&A ...................................................................................................... 109 Day 7 More About Methods 111 Creating Methods with the Same Name, Different Arguments ............... 112 Constructor Methods ............................................................................. 115 Basic Constructors ............................................................................. 116 Calling Another Constructor ............................................................. 117 Overloading Constructors .................................................................. 117 030-4 FM 1/29/96, 8:11 PM11 Teach Yourself JAVA in 21 Days M T W T F S S 21 xii P2/V4SQC6 TY Java in 21 Days 030-4 louisa 12.31.95 FM LP#4 Overriding Methods ............................................................................... 119 Creating Methods that Override Existing Methods ............................ 119 Calling the Original Method .................................