The reason this class does not extend JComboBox directly
is because of a namespace conflict between JComboBox and
my Editor interface (editable property)
The goal is to [again] study my single/working implementation
of ComplexTypePersister and put the junk in this class
so that i don't have to start from scratch each time.
have two constructors in order to be able to constrain the
association type to a specific/concrete type when the association
is to an abstract type / interface.