java中的事件处理_让小球上下左右移动

package com.event1;
//通过上下左右键，来控制一个小球的位置

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class CircleRun extends JFrame{

  MyPanel mp=null;
  
  public static void main(String[] args) {
    CircleRun cr=new CircleRun();   
  }
  public CircleRun(){
    mp=new MyPanel();
    this.add(mp);
    
    this.addKeyListener(mp);
    
    this.setSize(400,300);
    this.setVisible(true);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    
  } 
}

//定义自己的面板
class MyPanel extends JPanel implements KeyListener{
  int x=10;
  int y=10;
  
  public void paint(Graphics g){
    super.paint(g);
    g.fillOval(x, y, 10, 10);
  }

  
  //键的一个值被输出  
  @Override
  public void keyTyped(KeyEvent e) {  
    
  }

  //键被按下
  @Override
  public void keyPressed(KeyEvent e) {
    //System.out.println("键被按下"+e.getKeyCode());
    if(e.getKeyCode()==KeyEvent.VK_DOWN){
      //System.out.println("12");
      y++;
    }else if(e.getKeyCode()==KeyEvent.VK_UP){
      y--;
    }else if(e.getKeyCode()==KeyEvent.VK_LEFT){
      x--;
    }else if(e.getKeyCode()==KeyEvent.VK_RIGHT){
      x++;
    }   
    //调用repaint()函数，来重绘界面
    this.repaint();
  } 
  //键被释放
  @Override
  public void keyReleased(KeyEvent e) {   
  } 
}