| 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 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?
 |
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)
turn the functionality on by using appropriate
class from the hierarchy.
|
