A system publishing ActionEvent instances (such as an event bus), may
implement this interface. An observable (event listener), in case of being of
type Observer, may be notified using the
The listener implementing this interface is notified of an event via this
method. The publisher pushes the event to the subscriber. When this
method exits, then all listeners have been notified with the given event.
I.e. even if each event is dispatched in an own thread, then the longest
running thread determines when this method finishes.
aEvent - aEvent The event to be pushed from the publisher to the