Implementation.

Implementing the factoring application was straightforward and easy after the basic components were already implemented. As shown in Fig.5, it involved defining application-specific extensions of the work, work GUI, result, resultGUI, and problem objects. In general, generic parts of the system can be reused as-is, and only application-specific parts need to be modified. Modifying the application-specific parts can often be done by subclassing the available basic components, so that programmers usually need only to implement application-specific methods, and not entire classes. The main task in implementing FactorWork, for example, is to override the process() method of the basic Work object already provided.

  

Figure 5: Implementing the factoring application. Double-bordered items indicate application-specific objects implemented by extending basic components. Shaded items indicate unchanged generic objects from the basic component library.

Figure6 shows a screen shot of the factoring application.

  

Figure 6: A screen shot of the factoring application with one worker applet and one watcher applet. The applets are started by simply browsing a web page with a Java-capable browser.