Avoiding 'instanceof' in Java

Question

I have the following (maybe common) problem and it absolutely puzzles me at the moment:

There are a couple of generated event objects which extends the abstract clas

Answer 1

You could register each of your handler classes against each event type, and perform dispatch when event happens like this.

class EventRegister {

   private Map> listerMap;


   public void addListener(Event event, EventListener listener) {
           // ... add it to the map (that is, for that event, get the list and add this listener to it
   }

   public void dispatch(Event event) {
           List listeners = map.get(event);
           if (listeners == null || listeners.size() == 0) return;

           for (EventListener l : listeners) {
                    l.onEvent(event);  // better to put in a try-catch
           }
   }
}

interface EventListener {
    void onEvent(Event e);
}

And then get your specific handlers to implement the interface, and register those handlers with the EventRegister.