java按键事件求指教。。。。

Question

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class Demo extends JFrame {
public Demo() {
JLabel l = new JLabel("没有点击键盘Q键");// 创建标签
add(l);// 添加标签
l.addKeyListener(new KeyListener() {// 为标签添加键盘事件监听
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub

    }

    @Override
    public void keyReleased(KeyEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_Q) {// 如果按下的是Q键
            l.setText("点击了Q键");// 更改标签的值
        }

    }
});
setSize(200, 200);// 设置大小
setDefaultCloseOperation(EXIT_ON_CLOSE);// 关闭窗口退出程序
setVisible(true);// 窗体可以显示

}

public static void main(String[] args) {
new Demo();
}
}
这里按Q了，它不显示，怎么办？？？？

Answer 1

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

public class KeyEventDemo extends JFrame{
        private KeyboardPanel keyboardPanel = new KeyboardPanel();

        public KeyEventDemo(){
              add( keyboardPanel);

               keyboardPanel.setFocusable(true);

       }

        public static void main(String[] args){
              KeyEventDemo frame = new KeyEventDemo();
              frame.setTitle( "KeyEventDemo");
              frame.setSize(300,300);
              frame.setLocationRelativeTo( null);
              frame.setDefaultCloseOperation(JFrame. EXIT_ON_CLOSE);
              frame.setVisible( true);

       }

        static class KeyboardPanel extends JPanel{
               private int x = 100;
               private int y = 100;
               private char KeyChar = 'A' ;

               public KeyboardPanel(){
                     addKeyListener( new KeyAdapter(){
                            public void keyPressed(KeyEvent e){
                                   switch(e.getKeyCode()){
                                   case KeyEvent.VK_DOWN: y += 10;break;
                                   case KeyEvent.VK_UP: y -= 10; break;
                                   case keyEvent.VK_LEFT: x -= 10; break;
                                   case KeyEvent.VK_RIGHT: x += 10; break;
                                   default: keyChar = e.getKeyChar();
                                  }

                                  repaint();
                           }
                     });
              }

               protected void paintComponent(Graphics g){
                      super.paintComponent(g);

                     g.setFont( new Font("TimesRoman" ,Font.PLAIN,24));
                     g.drawString(String. valueOf(KeyChar), x, y);
              }
       }
}