So what have we done?
We created a Java Interface, an abstract class, and a final class. But what have we really accomplished? We have created the foundation for producing any number of implementing classes to obtain option list data from any number of potential sources. And we have done it in a way that insulates the using applications from the actual source of the information. From the perspective of the using class, the method to obtain the possible values for any input field that can be supported by an HTML select statement will always be the same:

For our specific implementation, we can instantiate our option source by passing our list as an argument to the constructor. For example, if we have a simple three-tier priority structure, the following line of code will create an OptionListSource to support it:

Now what?
From this simple starting point, not only can we create additional implementing classes to obtain data from other sources, we can also begin to enhance our framework to add additional features and functions. For example, our simple framework assumes that input is required, or in other words, that you must select one of the options from the list. It also assumes that the data is static, or can be loaded once and reused without ever having to be refreshed from the persistent source. Next time, we'll take a look at growing our simple framework to add features and functions without disrupting any existing users that are already happy with the current version as it stands.

Jeff Chilton is Vice President of Fulfillment at Echo Technology Group, Inc., an IT consulting firm that specializes in enterprise-focused best practices. He can be reached at jchilton@teametg.com.