AWT ItemListener类

1 什么是Java AWT ItemListener

处理 ItemEvent 的类应该实现这个接口。该类的对象必须注册到一个组件中。可以使用 addItemListener() 方法注册该对象。当动作事件发生时，该对象的 itemStateChanged 方法被调用。

2 Java AWT ItemListener的语法

public interface ItemListener
   extends EventListener

3 Java AWT ItemListener的方法

4 Java AWT ItemListener的例子

让我们看一个简单的Java AWT ItemListener类示例。

package com.yiidian;

import java.awt.*;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class AwtListenerDemo {
   private Frame mainFrame;
   private Label headerLabel;
   private Label statusLabel;
   private Panel controlPanel;

   public AwtListenerDemo(){
      prepareGUI();
   }

   public static void main(String[] args){
      AwtListenerDemo  awtListenerDemo = new AwtListenerDemo();  
      awtListenerDemo.showItemListenerDemo();
   }

   private void prepareGUI(){
      mainFrame = new Frame("一点教程网：Java AWT Examples");
      mainFrame.setSize(400,400);
      mainFrame.setLayout(new GridLayout(3, 1));
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
            System.exit(0);
         }        
      });    
   
      headerLabel = new Label();
      headerLabel.setAlignment(Label.CENTER);
      statusLabel = new Label();        
      statusLabel.setAlignment(Label.CENTER);
      statusLabel.setSize(350,100);

      controlPanel = new Panel();
      controlPanel.setLayout(new FlowLayout());

      mainFrame.add(headerLabel);
      mainFrame.add(controlPanel);
      mainFrame.add(statusLabel);
      mainFrame.setVisible(true);  
   }

   private void showItemListenerDemo(){
      headerLabel.setText("Listener in action: ItemListener");      
      Checkbox chkApple = new Checkbox("Apple");
      Checkbox chkMango = new Checkbox("Mango");
      Checkbox chkPeer = new Checkbox("Peer");
      
      chkApple.addItemListener(new CustomItemListener());
      chkMango.addItemListener(new CustomItemListener());
      chkPeer.addItemListener(new CustomItemListener());

      controlPanel.add(chkApple);
      controlPanel.add(chkMango);
      controlPanel.add(chkPeer);               
      mainFrame.setVisible(true); 
   }

   class CustomItemListener implements ItemListener {
      public void itemStateChanged(ItemEvent e) {
         statusLabel.setText(e.getItem()
         +" Checkbox: " 
         + (e.getStateChange()==1?"checked":"unchecked"));
      }    
   }
}

输出结果为：