One of the challenges programmers face every day is creating reusable components with a minimum of overhead.

We will consider an example of a service component and a service container, as well as their design and code evolution from a specific to a very flexible solution.

This chapter starts with a single Java class, which then evolves into a visual component. Then, a service container takes the central place on the stage. The chapter teaches how to build a container that is reusable in a Java applet or an application (desktop) program. It provides a solution to one of the most difficult problems: how to make the service container extensible and ready for more services, including those unknown at this time.

This very first example demonstrates one of Java code's benefits. Imagine a small device, such as a wristwatch, with a built-in Java chip. A single text line in the middle of this small screen usually displays the current time. With wireless Internet connection we will enable this device to display weather, stock, traffic, news from friends and family, community or business information (delivered via Short Message Service), and turn it into a “news watch.” Figure 3.1 illustrates this device that can be viewed as an extended wireless pager or scaled down wireless messenger described in the Chapter 11 (J2ME).