modelupdatenotifier.java

来自「一个优秀的供应商管理系统」· Java 代码 · 共 55 行

package apusic.myshop.control.web;



import java.util.HashMap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

import apusic.myshop.util.Debug;

/**
 * This class is responsible for providing methods to add objects as listeners
 * for a particular model update event and for notifying the listeners when the
 * event actually occurs.
 */
 
//观察者模式中的抽象主题
public class ModelUpdateNotifier {

    private HashMap listenerMap;
    
    //构造函数初始哈西表
    public ModelUpdateNotifier() {
	    listenerMap = new HashMap();
    }
    
    //通知观察者

    public void notifyListeners(Collection updatedModelList) {

      for (Iterator it1 = updatedModelList.iterator() ; it1.hasNext() ;) {
	      String modelType = (String) it1.next();
	      Collection listeners = (Collection)listenerMap.get(modelType);
        if (listeners != null) {
          for (Iterator it2 = listeners.iterator(); it2.hasNext(); ) {
		        ((ModelUpdateListener) it2.next()).performUpdate();
	        }
        }
      }
    }

    //增加观察者
    public void addListener(String modelType, Object listener) {

	    Debug.println("adding " + listener.toString() + "To" + modelType);
	    if (listenerMap.get(modelType) == null) {
	      ArrayList listeners = new ArrayList();
	      listeners.add(listener);
	      listenerMap.put(modelType,listeners);
	    } else {
	      ((ArrayList) listenerMap.get(modelType)).add(listener);
	    }
    }
}