The TooManyListenersException Exception is used as part of the Java Event model to annotate and implement a unicast special case of a multicast Event Source.

The presence of a "throws TooManyListenersException" clause on any given concrete implementation of the normally multicast "void addXyzEventListener" event listener registration pattern is used to annotate that interface as implementing a unicast Listener special case, that is, that one and only one Listener may be registered on the particular event listener source concurrently.