Java中的事件处理—通过点击不同的按钮，让面板的背景色发生变化

package com.event;import java.awt.*;import javax.swing.*;import java.awt.event.*;//Java事件处理public class EventDemo extends JFrame implements ActionListener {// 定义一个panelPanel mp = null;JButton jb1 = null;JButton jb2 = null;public static void main(String[] args) {EventDemo ed = new EventDemo();}public EventDemo() {mp = new Panel();jb1 = new JButton("黑色");jb2 = new JButton("红色");this.add(jb1, BorderLayout.NORTH);mp.setBackground(Color.black);this.add(mp);this.add(jb2, BorderLayout.SOUTH);Cat myCat=new Cat();jb1.addActionListener(myCat);jb2.addActionListener(myCat);// 注册监听jb1.addActionListener(this);//指定action命令jb1.setActionCommand("aa");jb2.addActionListener(this);jb2.setActionCommand("bb");this.setSize(200, 150);this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);this.setVisible(true);}// 对事件处理的方法@Overridepublic void actionPerformed(ActionEvent e) {//判断是哪个按钮被点击if(e.getActionCommand().equals("aa")){//System.out.println("黑色");mp.setBackground(Color.BLACK);}else if(e.getActionCommand().equals("bb")){//System.out.println("红色");mp.setBackground(Color.RED);}}}//一个普通的类也可以监听class Cat implements ActionListener{@Overridepublic void actionPerformed(ActionEvent e) {if(e.getActionCommand().equals("aa")){System.out.println("猫也知道你按下了黑色按钮");}else if(e.getActionCommand().equals("bb")){System.out.println("猫也知道你按下了红色按钮");}}}