Weak References in Listener Lists

Question

I've found a common source of memory leaks is when objects that add themselves to listener lists forget to remove themselves when they are done.
It would be nice to generalize and say that listener lists should contain weak references, but there are probably valid cases where a listener's only valid reference is through the listener list.
It would be nice to extend the listener pattern so that the listener could specify if they should be referenced weakly, for examplemodel.addChangeListener(this, true)where true indicates the reference to the listener should be weak.
In some cases like the Model View Controller pattern, it probably makes sense that whenever a view listens to a model it should be weakly referenced. For example, when you construct a JTable and pass the model as a parameter to the constructor, the JTable should always specify a weak reference when it listens to the model.
I think supporting a feature like this in the listener APIs could help reduce the potential for memory leaks and make code a little more maintainable.

Answer 1

There was another time that I dabbled in this idea.
But it always comes back to objects cleaning up
after themselves. Now if its not your code and you
cant ensure good behavior, then perhaps there is
cause. But I'd keep an assert and report the issue
if I saw it trigger.What would fire the assert? The Listener will never be garbage collected while it is listening to something. I assume that you are talking about when the listener is a Swing Object like a JFrame. I don't really like to use gui components as listeners.
If you have to write a clean up method, it kind of defeats the value of having automatic garbage collection to a degree. I like to be able to let my Objects just fall out of scope or just become unreachable when they are no longer needed without having to actively manage their deallocation.