public List<Listener> listeners(String event) {
        ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
        return callbacks != null ?
                new ArrayList<Listener>(callbacks) : new ArrayList<Listener>();
    }
public List<Listener> listeners(String event) {
        ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
        return callbacks != null ?
                new ArrayList<Listener>(callbacks) : new ArrayList<Listener>();
    }
public List < Listener > listeners ( String event ) { ConcurrentLinkedQueue < Listener > callbacks = this . callbacks . get ( event ) ; return callbacks != null ? new ArrayList < Listener > ( callbacks ) : new ArrayList < Listener > ( ) ; }
Returns a list of listeners for the specified event.

@param event an event name.
@return a reference to this object.
Returns a list of listeners for the specified event .