A helper base class for notify listeners. It holds reference to its WeakListener wrapper.

Without this class, an observer which uses weak listeners would need to hold two references. The first to the original ChangeListener to prevent it from being garbage collected. The second to the WeakListener wrapper so it can unregister once registered listener. The second reference is eliminated by using this class.

Example:

public class Observer {
    private AbstractNotifyListener listener = new AbstractNotifyListener() {
        public void handle(Bean bean, PropertyReference property) {
            // do something
        }
    };

    public void start() {
        subject.addChangeListener(property, listener.getWeakListener());
    }

    public void stop() {
        subject.removeChangeListener(property, listener.getWeakListener());
    }
}