The ListenersCollection class

/** 
 *  Copyright 2005-2006 Aviad Ben Dov 
 * 
 *  Licensed under the Apache License, Version 2.0 (the "License"); 
 *  you may not use this file except in compliance with the License. 
 *  You may obtain a copy of the License at 
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0 
 * 
 *  Unless required by applicable law or agreed to in writing, software 
 *  distributed under the License is distributed on an "AS IS" BASIS, 
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 *  See the License for the specific language governing permissions and 
 *  limitations under the License. 
 */

package com.crazyredpanda.util.collections; 

import java.util.Collection; 
import java.util.TreeSet; 
import java.util.Map; 
import java.util.TreeMap; 

public final class ListenersCollection<Listener, EventArgs> { 
  public interface ListenerInvoker<Listener, EventArgs> { 
    void invoke(Listener l, EventArgs args); 
  } 

  private final ListenerInvoker<Listener, EventArgs> invoker; 
  private final Collection<Listener> listeners = new TreeSet<Listener>(); 
  private final Map<Listener, Boolean> delayedListeners = new TreeMap<Listener, Boolean>(); 
  private boolean isDelayed = false; 

  public ListenersCollection(ListenerInvoker<Listener, EventArgs> invoker) { 
    this.invoker = invoker; 
  } 

  public synchronized void addListener(Listener l) { 
    if (isDelayed) { 
      delayedListeners.put(l, true); 
    } else { 
      listeners.add(l); 
    } 
  } 

  public synchronized void removeListener(Listener l) { 
    if (isDelayed) { 
      delayedListeners.put(l, false); 
    } else { 
      listeners.remove(l); 
    } 
  } 

  public synchronized void fireEvent(EventArgs args) { 
    isDelayed = true; 

    for (Listener l : listeners) { 
      invoker.invoke(l, args); 
    } 

    isDelayed = false; 

    // handing delayed un/registartions
    for (Map.Entry<Listener, Boolean> entry : delayedListeners.entrySet()) { 
      if (entry.getValue()) { 
        listeners.add(entry.getKey()); 
      } else { 
        listeners.remove(entry.getKey()); 
      } 
    } 
    delayedListeners.clear();
  } 
}