Java AWT Reference

Peter Kitson

ISBN : 1-56592-240-9

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Sample Chapter From Java AWT Reference
     Copyright © John Zukowski



1. Abstract Window Toolkit Overview

For years, programmers have had to go through the hassles of porting software from BSD-based UNIX to System V Release 4-based UNIX, from OpenWindows to Motif, from PC to UNIX to Macintosh (or some combination thereof), and between various other alternatives, too numerous to mention. Getting an application to work was only part of the problem; you also had to port it to all the platforms you supported, which often took more time than the development effort itself. In the UNIX world, standards like POSIX and X made it easier to move applications between different UNIX platforms. But they only solved part of the problem and didn't provide any help with the PC world. Portability became even more important as the Internet grew. The goal was clear: wouldn't it be great if you could just move applications between different operating environments without worrying about the software breaking because of a different operating system, windowing environment, or internal data representation?

In the spring of 1995, Sun Microsystems announced Java, which claimed to solve this dilemma. What started out as a dancing penguin (or Star Trek communicator) named Duke on remote controls for interactive television has become a new paradigm for programming on the Internet. With Java, you can create a program on one platform and deliver the compilation output (byte-codes/class files) to every other supported environment without recompiling or worrying about the local windowing environment, word size, or byte order. The first generation of Java programs consisted mostly of fancy animation applets that ran in a web browser like Netscape Navigator, Internet Explorer, or HotJava. We're beginning to see the next generation now: powerful distributed applications in areas ranging from commerce to medical imaging to network management. All of these applications require extreme portability: Joe's Online Bait Shop doesn't have the time or energy to port its "Online Bait Buyer" program to every platform on the Internet but doesn't want to limit its market to a specific platform. Java neatly solves their problem.

Windowing systems present the biggest challenges for portability. When you move an application from Windows to the Macintosh, you may be able to salvage most of the computational guts, but you'll have to rewrite the window interface code completely. In Java, this part of the portability challenge is addressed by a package called AWT, which stands for Abstract Window Toolkit (although people have come up with many other expansions). AWT provides the magic of maintaining the local look and feel of the user's environment. Because of AWT, the same application program can look appropriate in any environment. For example, if your program uses a pull-down list, that list will look like a Windows list when you run the program under Windows; a Macintosh list when you run the program on a Mac; and a Motif list when you run the program on a UNIX system under Motif. The same code works on all platforms. In addition to providing a common set of user interface components, AWT provides facilities for manipulating images and generating graphics.

This book is a complete programmer's guide and reference to the java.awt package (including java.awt.image, java.awt.event, java.awt.datatransfer, and java.awt.peer). It assumes that you're already familiar with the Java language and class libraries. If you aren't, Exploring Java, by Pat Niemeyer and Josh Peck, provides a general introduction, and other books in the O'Reilly Java series provide detailed references and tutorials on specific topics. This chapter provides a quick overview of AWT: it introduces you to the various GUI elements contained within the java.awt package and gives you pointers to the chapters that provide more specific information about each component. If you're interested in some of the more advanced image manipulation capabilities, head right to Chapter 12, Image Processing. The book ends with a reference section that summarizes what you need to know about every class in AWT.

In using this book, you should be aware that it covers two versions of AWT: 1.0.2 and 1.1. The Java 1.1 JDK (  Java Developer's Kit) occurred in December 1996. This release includes many improvements and additions to AWT and is a major step forward in Java's overall functionality. It would be nice if I could say, "Forget about 1.0.2, it's obsolete--use this book to learn 1.1." However, I can't; at this point, since browsers (Netscape Navigator in particular) still incorporate 1.0.2, and we have no idea when they will incorporate the new release. As of publication, Navigator 4.0 is in beta test and incorporates 1.0.2. Therefore, Java release 1.0.2 will continue to be important, at least for the foreseeable future.

In this summary, we'll point out new features of Java 1.1 as they come up. However, one feature deserves mention and doesn't fit naturally into an overview. Many of the methods of Java 1.0.2 have been renamed in Java 1.1. The old names still work but are "deprecated." The new names adhere strictly to the design patterns discussed in the JavaBeans documentation:[1] all methods that retrieve the value of an object's property begin with "get," all methods that set the value of a property begin with "set," and all methods that test the value of some property begin with "is." For example, the size() method is now called getSize(). The Java 1.1 compiler issues warnings whenever you used a deprecated method name.