We started out in Part I by creating a simple framework for the purpose of obtaining an ArrayList of Struts LabelValueBeans to support an html:options tag. In Part II, we added an additional implementing class to our portfolio, then went back and enhanced our base framework. This time, we'll reverse the order of things and first enhance our base framework, then add yet another implementing class.

Incremental Improvement #1: adding support for filtered lists
Currently, our little framework supports two kinds of lists: those with just the valid options and those with the valid options plus an additional option for leaving the field empty. In either case, the list of valid options is always the same. There are situations, however, where the available options will change based on some other event or data element.

For example, based on your security level, you may only be able to choose from four items off of a list while someone with a different security level may be authorized to select from six. In this case, the different lists of possible choices are filtered based on who you are.

To support filtered option lists, we can add two new methods to our interface that take as an argument an Object for the filter. We will need two of them to parallel the two existing methods that do not take a filter as an argument, one that includes the "required" flag and one that does not. We could have used a String for the filter, but by using an Object, we maximize the flexibility of the interface. That way certain implementations that require more than one filter String or use as a filter something other than a String can still implement the same methods. Listing 1 contains our revised interface.