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Developing Professional Java Applets


                           Java™ Applets

by  K.C. Hopson
     Stephen E. Ingram

C  O  N  T  E  N  T  S


Chapter 1  The Java Development Environment

Chapter 2  Object-Oriented Development in Java

Chapter 3  Building a Spreadsheet Applet

Chapter 4  Enhancing the Spreadsheet Applet

Chapter 5  Adding Graphs and Scrollbars to the Spreadsheet

Chapter 6  Building a Catalog Applet

Chapter 7  Java and Images

Chapter 8  Adding Threads to Applets

Chapter 9  Java Socket Programming

Chapter 10  Native Methods and Java

Chapter 11  Building a Live Data Applet

Chapter 12  Handling Dynamic Content

Chapter 13  Animation and Image Filters

Chapter 14  Advanced Image Processing

Appendix A  Inside the Java Virtual Machine

Appendix B  Language Grammar


To my wife, Ann, whose love, patience, assistance, and encouragement made it possible for me to write this book.-K.C. Hopson
To my wife, Anne, and my son, Mitchell; their love and encouragement gave me the strength to write this book.-Stephen Ingram

Copyright © 1996 by Publishing


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 author 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 Publishing, 201 W. 103rd St., Indianapolis, IN 46290.

International Standard Book Number: 1-57521-083-5

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All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. 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.

Java is a trademark of Sun Microsystems, Inc.

President, Sams Publishing Richard K. Swadley
Publishing Manager Mark Taber
Managing Editor Cindy Morrow
Marketing Manager John Pierce
Assistant Marketing Manager Kristina Perry

Acquisitions Editor Mark Taber Development Editor Kelly Murdock
Software Development Specialist Cari Skaggs Production Editor Lisa M. Lord
Copy Editors Howard Jones, Anne Owen Technical Reviewer Greg Guntle
Editorial Coordinator Bill Whitmer Technical Edit Coordinator Lynette Quinn
FormatterFrank Sinclair Editorial Assistant Sharon Cox
Cover Designer Tim AmrheinBook Designer Alyssa Yesh
Production Team Supervisor Brad Chinn
ProductionMary Ann Abramson, Stephen Adams, Carol G. Bowers, Georgiana Briggs, Jeanne Clark, Jason Hand, Daniel Harris, Mike Henry, Clint Lahnen, Paula Lowell, Steph Mineart, Ryan Oldfather, Casey Price, Laura Robbins, Bobbi Satterfield, Ian Smith, SA Springer, Chris Wilcox


We would like to thank our acquisitions editor, Mark Taber, our development editor, Kelly Murdock, and our production editor, Lisa Lord, for patiently guiding some lost sheep through their first book.

About the Authors

K.C. Hopson is president of Geist Software and Services, Inc., an independent consultant firm in the Baltimore/Washington D.C. metro area. However, K.C. thrives in cyberspace and enjoys using it anywhere in the world. He specializes in distributed computing solutions and has deep experience in GUI programming (especially Windows), relational databases, and client/server programming. K.C. was a lead architect of the software used in Bell Atlantic's Stargazer interactive television system and writes regularly about Java. K.C. has a B.S. in applied mathematics from the University of California-Irvine and a master's in computer science from the University of Maryland, Baltimore County. In his spare time, K.C. enjoys his family, worships music of all kinds, studies history, and loves literature.

K.C. can be reached at, or visit his home page at

Stephen E. Ingram is an computer consultant in the Washington D.C. metro area, specializing in embedded data communications and object-oriented design. He holds an electrical engineering degree from Virginia Tech and has been programming for 15 years. He was the architect behind the language of Bell Atlantic's Stargazer interactive television project; it was here that he first encountered Java. When he's not working, Steve likes to sail the Chesapeake Bay with his wife and son. Steve can be reached at


Java is frequently described as a programming language for the Internet. This reference mainly alludes to Java's ability to be executed as an applet, which is a program that runs inside a Java-enabled World Wide Web browser, such as Netscape Navigator 2.0 or HotJava. Applets naturally function as small programs that can enhance your Web page. This stems from Java's structure as a distributed language and its corresponding ability to load small pieces of code as needed. In the short run, programmers will use Java to add small snippets of code, such as animations, to enhance a Web page experience.

Java applets, however, are much more than small programs that supplement Web pages. Java is a sophisticated and extendable environment, providing the foundation for building industrial-strength applications. This power stems from Java's many facets-from its object-oriented nature to its simplicity to its ability to function in distributed environments. Consequently, to view Java as a "neat" tool for sprucing up your Web pages is a serious understatement of its capabilities. Java applets will appear in more guises than just the Internet, and Java's role inside internal networks-the so-called "Intranet"-is already being given serious consideration.

Developing Professional Java Applets aims to help bring Java applets out of the world of lightweight programs-like simple animations-into the world of practical programming. This book attempts to fill a gap that has been seriously lacking in currently existing Java literature: a book full of serious, practical, and professional Java projects and examples. The projects in this book illustrate how to create Java applets that solve real-life problems, and they do so in such a way that you will learn all the general features, as well as subtleties, of Java while you're working through practical applications of serious projects. In doing so, you will not only become a more capable Java programmer, but you might also develop insights on how to use Java to create a great new application.

Who Should Read This Book

Developing Professional Java Applets is intended for people who do not want to spend 200 pages learning basic Java (such as for loops), but want to quickly step into serious Java programming. To do this, however, requires you to have some background. In general, a basic background in programming and a rudimentary understanding of the principles of object-oriented programming should be enough. If you have any of the following credentials, then you are set:

If you are lacking these credentials, don't worry. Just take more time going through the first part of the book (an introduction to Java). If you have the background just described, however, this book will lead you deep into Java programming before you know it!

How This Book Is Organized

This book is based on the Java Development Kit (JDK), version 1.0. Most of the chapters of Developing Professional Java Applets have a tutorial section that covers some JDK topics, followed by a serious chapter project. The chapter project is accompanied by a discussion of the project's general architecture, as well as any Java subtleties it might uncover. By the time you are done with any given chapter, you will have been exposed to at least one serious Java programming concept.

Part I of the book is a quick overview of the fundamentals of Java programming. If you have no experience with Java, this part should be enough to get you ready for the heart of the book. It includes plenty of examples to illustrate key ideas. However, the book's focus is on practical Java programming, so some of the discussions of Java basics are terse. However, almost all the topics broached in Part I will reappear frequently throughout the rest of the book.

Parts II through IV are the heart of the book. Each of these parts walks through a serious project over the course of three chapters. By the end of each part, you will not only have seen the development of a major project, but will have attained some deep understanding of one or more crucial topics in Java programming.

In Part II, you'll see the development of a spreadsheet applet. This applet will guide you through the basics of Java's graphical toolkit, AWT. You will not only learn the general workings of AWT, but will also be exposed to some of its hidden gems, such as its Toolkit class. Since (at least for a while) most Java applets will use AWT as the basis for their user interfaces, a solid understanding of the package is indispensable. Part II also includes in-depth discussions of I/O streams in Java, as well as an exploration of Java's powerful approach to exception handling.

Part III uses a catalog-style applet to introduce you to the more advanced concepts of URL streams, threads, and image processing. This catalog applet shows how to tie information on one catalog page to that on another. The applet features a media loader that uses threads and advanced imaging concepts to bring in images that may be needed in the future; this is a "pre-loader" that can be used to reduce the latencies often associated with images. By the end of this part, you will have been through some of Java's most complex features.

Part IV takes you into the world of Java client/server programming. It introduces you to Java network programming through the creation of an HTTP server. This server will actually download Java applets to a client! You will also be shown how to use Java native methods-code written in C-by tying in databases (through the ODBC mechanism) to your server. Finally, you will see an applet that gets data from the server as it changes in real-time-what the book calls "live data." After this part of the book, you will have seen serious treatments of most of the major concepts in Java programming.

Part V lets you have a little break-but just a little one. Rather than one large project, each chapter has a smaller project. The focus is on more advanced uses of images and threads, but there is also a discussion of HotJava and its content-handling features. The goal of Part V is to further refine the knowledge you have gained in the first four parts of the book. By the time the book ends, you should feel that you have a solid understanding of everything needed to build high-quality, professional Java applets.

Thoughts Before Starting

There are a variety of Web sites cropping up that help you with various aspects of Java. The main launching pad for Java is, which is where you can download the latest Java release and all kinds of first-rate documentation. The newsgroup has excellent discussions of all aspects of Java programming, from novice to advanced. A couple of other Web sites, such as and, offer good starting places for exploring Java in cyberspace.

Finally, it should be pointed out that the JDK 1.0 is not without bugs. An unfortunate side-effect of this is that some features that work on one platform might not work on another. If you are having isolated, inexplicable problems running any of the applets in this book, consider downloading the latest version of the JDK for your platform.