使用泛型处理事件

Question

I have several events (and listeners for each). I'd like to, instead of this:

private void alertListeners(EventType1 ev){
    for(EventType1Listener el : et1Listeners){
        el.handle(ev);
    }
}
private void alertListeners(EventType2 ev){
    for(EventType2Listener el : et2Listeners){
        el.handle(ev);
    }
}
private void alertListeners(EventType3 ev){
    for(EventType3Listener el : et3Listeners){
        el.handle(ev);
    }
}

have something more like:

private <T extends MyEventTypeSuperclass> void alertListeners(T ev)

Except I can't figure out how to actually code the for loop... Is it possible to do what I want, or will I have to write a bunch of nearly identical methods?

Answer 1

Well, why not encapsulate the listener stuff into a dedicate class?

public class Observable<E> {
    private List<Listener<E>> listeners = new ArrayList<L>();

    public void subscribe(Listener<E> listener) {
        listeners.add(listener);
    }

    public void alert(E e) {
        for (Listener<E> l : listeners) {
            l.handle(e);
        }
    }
}

and in the type that offers the event:

public final Observable<String> messageChannel = new Observable<String>();

public final Observable<Integer> resultChannel = new Observable<Integer>();

Answer 2

private <L extends MyEventTypeListenerSuperclass, E extends MyEventTypeSuperclass> void alertListeners(E ev, List<L> listeners){
    for(L el : listeners){
        el.handle(ev);
    }
}

or something like that