Mastering PowerBuilder

Nested General Purpose Classes

Classes of this type define the generic functionality in the super ancestor. The ancestor class is sub-classed, and the functionality is added until all required combinations of functionality are defined. For example, in the following diagram, u_dw_for_data_entry has methods for adding a new record, and for find & replace. u_dw_for_reports has method for sorting the DataWindow.

Later, if you need a DataWindow with adding new record, find & replace as well as sorting features, all you need to do is create one more class by inheriting from one of those two sub-classes u_dw_for_data_entry, u_dw_for_reports and duplicate the code from the other class. This is because, multiple inheritance is not possible in PowerBuilder. What does it mean to us?

• Potentially a deep class hierarchy to provide every combination of functionality.
• Objects & code duplication instead of re-using them.
• More maintenance because of multiple copies of code & objects.

The developer (user of your class library) turns on the functionality by using the appropriate class from the hierarchy.

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