16.18

 1 import java.awt.Graphics;
 2 import java.awt.event.*;
 3 import javax.swing.*;
 4
 5 public class Test_16_18 extends JFrame{
 6     private JP jp = new JP();
 7     public Test_16_18()
 8     {
 9         add(jp);
10         jp.setFocusable(true); //必须在JPanel这里设置focusable
11     }
12     public static void main(String[] args) {
13         // TODO Auto-generated method stub
14         Test_16_18 frame = new Test_16_18();
15         frame.setSize(300,300);
16         frame.setTitle("Test_16_18");
17         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
18         frame.setLocationRelativeTo(null); // Center the frame
19         frame.setVisible(true);
20     }
21
22     static class JP extends JPanel{
23         private int x = 140, y = 140;
24         public JP(){
25             addKeyListener(new KeyAdapter(){
26                 public void keyPressed(KeyEvent e){
27                     switch(e.getKeyCode()){
28                     case KeyEvent.VK_UP: y -= 10; break;
29                     case KeyEvent.VK_DOWN: y += 10; break;
30                     case KeyEvent.VK_LEFT: x -= 10; break;
31                     case KeyEvent.VK_RIGHT: x += 10; break;
32                     }repaint();
33                 }
34             });
35         }
36         protected void paintComponent(Graphics g){
37             super.paintComponent(g);
38             g.drawOval(x, y, 30, 30);
39         }
40     }
41 }

Test_16_18.java

需要注意的是，必须给JPanel设置焦点，否则键盘无用。