16.10

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

public class Test_16_10 extends JFrame{
    public Test_16_10(){
        JP jp1 = new JP();
        add(jp1);
        jp1.setFocusable(true);
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Test_16_10 t1 = new Test_16_10();
        t1.setSize(300,400);
        t1.setTitle("Test_16_10");
        t1.setLocationRelativeTo(null);
        t1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t1.setVisible(true);
    }
    
    static class JP extends JPanel{
        private StringBuffer str = new StringBuffer();
        private String str1 = "A";
        private int x,y;
        
        public JP(){
            addKeyListener(new KeyAdapter(){
                public void keyTyped(KeyEvent e){
                    str.append(e.getKeyChar());                    
                }
                public void keyPressed(KeyEvent e){
                    if(e.getKeyCode() == KeyEvent.VK_ENTER)
                        str1 = str.toString().trim();
                    str.setLength(0);//将stringbuffer重置为空
                    repaint();
                }
            });
        }
        protected void paintComponent(Graphics g){
            x = getWidth()/2;
            y = getHeight()/2;
            super.paintComponent(g);
            g.drawString(str1, x, y);
        }
    }
}

效果图：