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 is defined. For example, in the following diagram, u_dw_for_data_entry has methods for adding a new record, find & replace. u_dw_for_reports has method for sorting the DataWindow.
DataWindow
User Objects with deep hirerchy
Later if you need a DataWindow with adding new record, find & replace as well as sorting the DataWindow, you need to 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 other class. This is because, multiple inheritance is not possible in PowerBuilder. What it means to us?
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Potentially a deep class hierarchy to provide every combination of functionality |
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Objects & code duplication instead of re-using them |
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More maintenance because of multiple copies of code & objects |
The developer (user of your class library) turn the functionality on by using appropriate class from the hierarchy.