Software Reusability

Java programmers concentrate on crafting new classes and reusing existing classes. Many class libraries exist, and others are being developed worldwide. Software is then constructed from existing, well-defined, carefully tested, well-documented, portable, widely available components. This kind of software reusability speeds the development of powerful, high-quality software. Rapid application development (RAD) is of great interest today.

Java programmers now have thousands of classes in the Java API from which to choose to help them implement Java programs. Indeed, Java is not just a programming language. It is a framework in which Java developers can work to achieve true reusability and rapid application development. Java programmers can focus on the task at hand when developing their programs and leave the lower-level details to the classes of the Java API. For example, to write a program that draws graphics, a Java programmer does not require knowledge of graphics on every computer platform where the program will execute. Instead, the programmer can concentrate on learning Java's graphics capabilities (which are quite substantial and growing) and write a Java program that draws the graphics, using Java's API classes, such as Graphics. When the program executes on a given computer, it is the job of the JVM to translate Java commands into commands that the local computer can understand.

The Java API classes enable Java programmers to bring new applications to market faster by using preexisting, tested components. Not only does this reduce development time, it also improves the programmer's ability to debug and maintain applications. To take advantage of Java's many capabilities, it is essential that programmers familiarize themselves with the variety of packages and classes in the Java API. There are many Web-based resources at java.sun.com to help you with this task. The primary resource for learning about the Java API is the Java API documentation, which can be found at

java.sun.com/j2se/5.0/docs/api/index.html

We overview how to use the documentation in Appendix G, Using the Java API Documentation. You can download the API documentation from

java.sun.com/j2se/5.0/download.html

In addition, java.sun.com provides many other resources, including tutorials, articles and sites specific to individual Java topics.

Good Programming Practice 8.2

Avoid reinventing the wheel. Study the capabilities of the Java API. If the API contains a class that meets your program's requirements, use that class rather than create your own.

To realize the full potential of software reusability, we need to improve cataloging schemes, licensing schemes, protection mechanisms which ensure that master copies of classes are not corrupted, description schemes that system designers use to determine whether existing objects meet their needs, browsing mechanisms that determine what classes are available and how closely they meet software developer requirements, and the like. Many interesting research and development problems have been solved and many more need to be solved. These problems will likely be solved because the potential value of increased software reuse is enormous.