Hi
Actually the on getting some cue from the GUI (View) the controller updates the Model. The controller acts as a a mediator between view and the model, thus mediator pattern.
The moment the model changes its state the view comes to know about it, as it has subscribed itself as an observer. thus, Observer pattern.
you ofcourse need not implement these patterns urself as they are inbuilt into the swing components
Regards
Arup