16.10

 1 import java.awt.*;
 2 import java.awt.event.*;
 3 import javax.swing.*;
 4
 5 public class Test_16_10 extends JFrame{
 6     public Test_16_10(){
 7         JP jp1 = new JP();
 8         add(jp1);
 9         jp1.setFocusable(true);
10     }
11
12     public static void main(String[] args) {
13         // TODO Auto-generated method stub
14         Test_16_10 t1 = new Test_16_10();
15         t1.setSize(300,400);
16         t1.setTitle("Test_16_10");
17         t1.setLocationRelativeTo(null);
18         t1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
19         t1.setVisible(true);
20     }
21
22     static class JP extends JPanel{
23         private StringBuffer str = new StringBuffer();
24         private String str1 = "A";
25         private int x,y;
26
27         public JP(){
28             addKeyListener(new KeyAdapter(){
29                 public void keyTyped(KeyEvent e){
30                     str.append(e.getKeyChar());
31                 }
32                 public void keyPressed(KeyEvent e){
33                     if(e.getKeyCode() == KeyEvent.VK_ENTER)
34                         str1 = str.toString().trim();
35                     str.setLength(0);//将stringbuffer重置为空
36                     repaint();
37                 }
38             });
39         }
40         protected void paintComponent(Graphics g){
41             x = getWidth()/2;
42             y = getHeight()/2;
43             super.paintComponent(g);
44             g.drawString(str1, x, y);
45         }
46     }
47 }

Test_16_10.java

效果图：