Re: Generics
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kofa schreef:
I've tried filling in the gaps, and ended up with:
===
public class EventDispatcherImpl implements EventDispatcher {
[...]
public <T> void dispatchEvent(T event) {
for (EventListener<? super T> listener :
myListeners.get(event.getClass())) {
listener.eventRaised(event);
}
}
/**
* Utility class to map events to listeners
*/
private static class EventMap {
/**
* Stores the event type -> listners mapping.
*/
private final Map<Class<?>, Set<EventListener<?>>> myListenersByType
= new HashMap<Class<?>, Set<EventListener<?>>>();
/**
* Gets all listeners that can handle the specified event class.
* @param <T> the event type
* @param eventClass the event class
* @return the listeners that can handles the event class
*/
<T> Set<EventListener<? super T>> get(Class<? extends T> eventClass)
{
Set<EventListener<? super T>> listeners = new
HashSet<EventListener<? super T>>();
synchronized (myListenersByType) {
for (Map.Entry<Class<?>, Set<EventListener<?>>> entry :
myListenersByType.entrySet()) {
if (entry.getKey().isAssignableFrom(eventClass)) {
for (EventListener<?> listener : entry.getValue()) {
/* warning here:
Type safety: The cast from EventListener<capture-of ?> to
EventListener<? super T> is actually checking against the erased type
EventListener
*/
listeners.add((EventListener<? super T>) listener);
}
}
}
}
return listeners;
}
[...]
===
Now at least there's no need for an Event superclass/interface: I can
dispatch any object (that is, I can maintain multiple, unrelated event
hierarchies, and use a single dispatcher).
Is there a way (aside from @SuppressWarning) to eliminate the warning?
By making your map store EventListener<? super T> instead of <?>. I am
unsure whether that won???t cause other warnings/errors though.
H.
- --
Hendrik Maryns
http://tcl.sfs.uni-tuebingen.de/~hendrik/
==================
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