Java event事件监听属性值变化 demo

Posted 2022-08-01 teamlet

1、定义一个 ValueChangedEvent 

ValueChangedEvent用于在设置属性值的时候，触发事件。

 
package org.teamlet;

import java.util.EventObject;

public class ValueChangeEvent extends EventObject 

	/**
	 * 
	 */
	private static final long serialVersionUID = 767352958358520268L;
	private int value;

	public ValueChangeEvent(Object source) 
		this(source, 0);
	

	public ValueChangeEvent(Object source, int newValue) 
		super(source);
		value = newValue;
	

	public int getValue() 
		return value;
	


 

2、定义监听接口 ValueChangeListener

ValueChangeListener 提供属性值变化的接口。

 
package org.teamlet;

public interface ValueChangeListener extends java.util.EventListener 

	public abstract void performed(ValueChangeEvent e);

 

3、事件的产生者

EventProducer提供了监听容器listenerRegister，负责消费者的注册。

 
package org.teamlet;

public class EventProducer 
	ListenerRegister register = new ListenerRegister();
	private int value;

	public int getValue() 
		return value;
	

	public void setValue(int newValue) 
		if (value != newValue) 
			value = newValue;
			ValueChangeEvent event = new ValueChangeEvent(this, value);
			fireAEvent(event);
		
	

	public void addListener(ValueChangeListener a) 
		register.addListener(a);
	

	public void removeListener(ValueChangeListener a) 
		register.removeListener(a);
	

	public void fireAEvent(ValueChangeEvent event) 
		register.fireAEvent(event);
	


  

4、注册器

ListenerRegister负责注册和分发事件。

 
package org.teamlet;

import java.util.Vector;

public class ListenerRegister 

	private Vector<ValueChangeListener> listeners = new Vector<ValueChangeListener>();

	public synchronized void addListener(ValueChangeListener a) 
		listeners.addElement(a);
	

	public synchronized void removeListener(ValueChangeListener a) 
		listeners.removeElement(a);
	

	@SuppressWarnings("unchecked")
	public void fireAEvent(ValueChangeEvent evt) 
		Vector<ValueChangeListener> currentListeners = null;
		synchronized (this) 
			currentListeners = (Vector<ValueChangeListener>) listeners.clone();
		
		for (int i = 0; i < currentListeners.size(); i++) 
			ValueChangeListener listener = (ValueChangeListener) currentListeners
					.elementAt(i);
			listener.performed(evt);
		
	

   

5、事件的消费者

EventConsumer实现ValueChangedListener，当EventProducer 发送事件时，接收事件。

 
package org.teamlet;

public class EventConsumer implements ValueChangeListener 

	@Override
	public void performed(ValueChangeEvent e) 
		System.out.println("value changed, new value = " + e.getValue());
	


 

6、使用

 
package org.teamlet;

public class Main 

	public static void main(String[] args) 
		EventProducer producer = new EventProducer();
		producer.addListener(new EventConsumer());
		producer.setValue(2);