1. Usage Kind of “2D Abstraction” (or by Rumbaugh “nested generalizations”) both on Interface(Window in example below) and on Implementation(WindowImp). So both Abstraction and Implementation should be extensible by sub-classing.Another name for this pattern is Handle-Body.This Pattern often used in Window Libraries e.g. AWT. Qt library uses this pattern for switching Style at run-time. Reasons […]