java編寫一個可以上下移動的小球：運行後，可以通過上下左右鍵進行移動

/*
* 功能:加深對事件處理機制的理解
* 1.通過控制上下左右鍵，來控制一個小球的位置
*/
package com.test1;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Demo9_4 extends JFrame{
Mypanel mp = null;
public static void main(String[] args){
Demo9_4 demo_4 = new Demo9_4();
}
//構造函數
public Demo9_4(){
mp = new Mypanel();

this.add(mp);

this.addKeyListener(mp);
this.setSize(300,400);
this.setVisible(true);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
}
}

//定義自己的面板
class Mypanel extends JPanel implements KeyListener{
int x=10;
int y=10;
public void paint(Graphics g){
super.paint(g);
g.setColor(Color.red);
g.fillOval(x,y, 30, 30);
}

//鍵被按下
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
//System.out.println("鍵被按下"+(char)e.getKeyCode());

}

//鍵被按下
public void keyPressed(KeyEvent e) {
// TODO Auto-generated method stub
if(e.getKeyCode() == KeyEvent.VK_DOWN){
y+=5;

}else if(e.getKeyCode() == KeyEvent.VK_LEFT){
x-=5;
}else if(e.getKeyCode() == KeyEvent.VK_UP){
y-=5;
}else if(e.getKeyCode() == KeyEvent.VK_RIGHT){
x+=5;
}

this.repaint();
}

//鍵一個值被輸出
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub

}
}