Charles L. Perkins
201 West 103rd Street
Indianapolis, Indiana 46290
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.
This book is intended for people with at least some basic programming background, 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
What if you know programming, but you don't know object-oriented programming? 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.
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.
To Eric, for all the usual reasons
(moral support, stupid questions, comfort in dark times).
For RKJP, ARL, and NMH
the three most important people in my life.
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 in
formation 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
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.
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 ma
President, Sams Publishing:
Richard K. Swadley
Publisher, Sams.net Publishing:
Software Development Specialist
Technical Edit Coordinator
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Week 1 at a Glance
Day 1 An Introduction to Java Programming
2 Object-Oriented Programming and Java
3 Java Basics
4 Working with Objects
5 Arrays, Conditionals, and Loops
6 Creating Classes and Applications in Java
7 More About Methods111
Week 2 at a Glance
Day 8 Java Applet Basics
9 Graphics, Fonts, and Color
10 Simple Animation and Threads
11 More Animation, Images, and Sound
12 Managing Simple Events and Interactivity
13 User Interfaces with the Java Abstract Windowing Toolkit
14 Windows, Networking, and Other Tidbits
Week 3 at a Glance
Day 15 Modifiers
16 Packages and Interfaces
20 Native Methods and Libraries
21 Under the Hood
A Language Summary
B Class Hierarchy Diagrams
C The Java Class Library
D How Java Differs from C and C++
From Laura Lemay:
To Sun's Java team, for all their hard work on Java the language and on the browser, and particularly to Jim Graham, who demonstrated Java and HotJava to me on very short notice in May and planted the idea for this book.
To everyone who bought my previous books, and liked them. Buy this one too.
From Charles L. Perkins:
To Patrick Naughton, who first showed me the power and the promise of OAK (Java) in early 1993.
To Mark Taber, who shepherded this lost sheep through his first book.
Laura Lemay is a technical writer and a nerd. After spending six years writing software documentation for various computer companies in Silicon Valley, she decided writing books would be much more fun (but has still not yet made up her mind). In her spare time she collects computers, e-ma
il addresses, interesting hair colors, and nonrunning motorcycles. She is also the perpetrator of Teach Yourself Web Publishing with HTML in 14 Days.
You can reach her by e-mail at firstname.lastname@example.org, or visit her home page at http://www.lne.com/lemay/.
Charles L. Perkins is the founder of Virtual Rendezvous, a company building a Java-based service that will foster socially focused, computer-mediated, real-time filtered interactions between people's personas in the virtual environments of the near future. In previous lives, he has evange
lized NeXTSTEP, Smalltalk, and UNIX, and has degrees in both physics and computer science. Before attempting this book, he was an amateur columnist and author. He's done research in speech recognition, neural nets, gestural user interfaces, computer graphics, and language theory, but had the most f
un working at Thinking Machines and Xerox PARC's Smalltalk group. In his spare time, he reads textbooks for fun.
You can reach him via e-mail at email@example.com, or visit his Java page at http://rendezvous.com/java.
The World Wide Web, for much of its existence, has been a method for distributing passive information to a widely distributed number of people. The Web has, indeed, been exceptionally good for that purpose. With the addition of forms and image maps, Web pages began to become interactivebut
the interaction was often simply a new way to get at the same information. The limitations of Web distribution were all too apparent once designers began to try to stretch the boundaries of what the Web can do. Even other innovations, such as Netscape's server push to create dynamic animations, we
re merely clever tricks layered on top of a framework that wasn't built to support much other than static documents with images and text.
Enter Java, and the capability for Web pages to contain Java applets. Applets are small programs that create animations, multimedia presentations, real-time (video) games, multi-user networked games, and real interactivityin fact, most anything a small program can do, Java applets can. Dow
nloaded over the net and executed inside a Web page by a browser that supports Java, applets are an enormous step beyond standard Web design.
The disadvantage of Java is that to create Java applets right now, you need to write them in the Java language. Java is a programming language, and as such, creating Java applets is more difficult than creating a Web page or a form using HTML. Soon there will be tools and programs that will make
creating Java applets easierthey may be available by the time you read this. For now, however, the only way to delve into Java is to learn the language and start playing with the raw Java code. Even when the tools come out, you may want to do more with Java than the tools can provide, and yo
u're back to learning the language.
That's where Teach Yourself Java in 21 Days comes in. This book teaches you all about the Java language and how to use it to create not only applets, but also applications, which are more general Java programs that don't need to run inside a Web browser. By the time you get through with t
his book, you'll know enough about Java to do just about anything, inside an applet or out.
Teach Yourself Java in 21 Days is intended for people with at least some basic programming backgroundwhich includes people with years of programming experience and people with only a small amount of experience. If you understand what variables, loops, and functions are, you'll be ju
st fine for this book. The sorts of people who might want to read this book include you, if one or more of the following is true:
What if you know programming, but you don't know object-oriented programming? Fear not. Teach Yourself Java in 21 Days assumes no background in object-oriented design. If you know object-oriented programming, the first couple of days will be easy for you.
What if you're a rank beginner? This book might move a little fast for you. Java is a good language to start with, though, and if you take it slow and work through all the examples, you may still be able to pick up Java and start creating your own applets.
Teach Yourself Java in 21 Days describes Java primarily in its current statewhat's known as the 1.0 API (Application Programming Interface). This is the version of Java that Netscape and other browsers, such as Spyglass's Mosaic, support. A previous version of Java, the alpha API, w
as significantly different from the version described in this book, and the two versions are not compatible with each other. There are other books that describe only the alpha API, and there may still be programs and browsers out there that can only run using alpha Java programs.
The 1.0 API is, as of this writing, the most current version, the one supported by Java-enabled browsers like Netscape Navigator 2.0, and the one most likely to be supported in the future. The alpha API is obsolete and will eventually die out. If you learn Java using the current API, you'll be m
uch better prepared for Java's future than if you have to worry about both APIs at once.
Java is still in development. "Beta" means that Java is not complete and that things may change between the time this book is being written and the time you read this. Keep this in mind as you work with Java and with the software you'll use to create and compile programs. If things are
n't behaving the way you expect, check the Web sites mentioned at the end of this introduction for more information.
Teach Yourself Java in 21 Days covers the Java language and its class libraries in 21 days, organized as three separate weeks. Each week covers a different broad area of developing Java applets and applications.
In the first week, you'll learn about the Java language itself:
Week 2 is dedicated to applets and the Java class libraries:
Week 3 finishes up with advanced topics, for when you start doing larger and more complex Java programs, or when you want to learn more:
Text that you type and text that should appear on your screen is presented in monospace type:
It will look like this.
to mimic the way text looks on your screen. Variables and placeholders will appear in monospace italic.
The end of each chapter offers common questions asked about that day's subject matter with answers from the authors.
Before, while, and after you read this book, there are two Web sites that may be of interest to you as a Java developer.
The official Java web site is at http://java.sun.com/. At this site, you'll find the Java development software, the HotJava web browser, and online documentation for all aspects of the Java language. It has several mirror sites that it lists online, and yo
u should probably use the site "closest" to you on the Internet for your downloading and Java Web browsing. There is also a site for developer resources, called Gamelan, at http://www.gamelan.com/.
This book also has a companion Web site at http://www.lne.com/Web/Java/. Information at that site includes examples, more information and background for this book, corrections to this book, and other tidbits that were not included here.