in API we could find class Component implements interface MenuContainer My puzzles are 1. why class Frame still declared implements MenuContainer explicitly? isn't it true that a subclass automatically implements all the interfaces that implemented by its superclass? 2. why class Component implements MenuContainer? since only a few special subclass can actually hold a menu component? to be the worst, i find there's only one method "remove" in the MenuContainer is related to the Menu component, and Component provides no real implementation! Any comments are greatly welcomed James