JAVA中ActionEvent不使用内部类

This program shows mainly how to add the events to the buttons. Normally we use the internal class, but this example does not use it. Instead, it uses a bloc "actionPerformed" that enables a couple of buttons to call it. To determine on which
button the action event occurred, we use e.getSource().

package com.han;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JFrame;
/**
* This program shows mainly how to add the events to the buttons.
* Normally we use the internal class, but this example does not use it.
* Instead, it uses a bloc "actionPerformed" that enables a couple of buttons to call it.
* To determine on which button the action event occurred, we use e.getSource().
* @author han
*
*/
@SuppressWarnings("serial")
public class SwingButtonEvents extends JFrame implements ActionListener{
/*declare some variables*/
Button btn1;
Button btn2;
Button btn3;
Container c=getContentPane();
/*the construct function*/
public SwingButtonEvents(){
setTitle("Action Event");
setSize(200,150);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
c.setLayout(new FlowLayout(FlowLayout.CENTER)); //use FlowLayout
btn1=new Button("Yellow");
btn2=new Button("Green");
btn3=new Button("Exit");
c.add(btn1);
c.add(btn2);
c.add(btn3);
btn1.addActionListener(this); // 把事件聆听者向btn1注册
btn2.addActionListener(this); // 把事件聆听者向btn2注册
btn3.addActionListener(this); // 把事件聆听者向btn3注册
}
public static void main(String args[]){
new SwingButtonEvents();
}
@Override
public void actionPerformed(ActionEvent e){ //方法重写
Button btn=(Button) e.getSource(); // 取得事件源对象
if(btn.equals(btn1)){ // 如果是按下btn1按钮
c.setBackground(Color.yellow); //背景颜色是在Container中改的！而不是在JFrame中改！
}else if(btn==btn2){ // 如果是按下btn2按钮
c.setBackground(Color.green);
}else{ // 如果是按下btn3按钮
System.exit(0);
}
}
}