What is the opposite of the observer pattern?

Question

As I understand it, the observer pattern allows for multiple observers to monitor a single subject. Is there a pattern for the opposite scenario? Is there a pattern for a single observer that monitors several subjects and responds when any one of them raises, say, a Notify event?

Answer 1

The Observer pattern can still be used: just have the same object register as an observer to many monitored objects. You'll probably want the "Notify" event to receive some kind of observed-object identifier (the "this" pointer, a unique id number etc) so that the observer object can choose an action appropriate to the object reporting the event.