本來(lái)想寫一個(gè)，根據(jù)輸入上下左右來(lái)反映的畫線條的程序，但是為什么這個(gè)getKeyCode只會(huì)返回0呢？

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class q09 extends JFrame
{
    private int x=150,y=150,index=0;
    private line []l;
    public q09() 
    {
        huaban p1=new huaban();
        add(p1);
        l=new line[100];
        p1.setFocusable(true);
        p1.addKeyListener(new KeyAdapter() 
        {
            public void keyTyped(KeyEvent e) 
            {
                System.out.println(e.getKeyCode());
                //如果能從getKeyCode中得到鍵的常量符號(hào)的話，下面就還有代碼。
            }
        });
    }
    class line
    {
        private int sx,sy,VK,px,py;
        public line(int VK) 
        {
            sx=x;
            sy=y;    
            px=x;
            py=y;
            switch(VK)
            {
                case KeyEvent.VK_UP:py+=10;
                case KeyEvent.VK_DOWN:py-=10;
                case KeyEvent.VK_LEFT:px-=10;
                case KeyEvent.VK_RIGHT:px+=10;
            }
            x=px;
            y=py;
        }
    }
    public static void main(String[] args) 
    {
        JFrame frame=new q09();
        frame.setTitle("q09");
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setSize(300,300);
        frame.setVisible(true);
    }
    class huaban extends JPanel
    {
        protected void paintComponent(Graphics g) 
        {
            super.paintComponent(g);
            for(int i=0;i<index;i++)
                g.drawLine(l[i].sx, l[i].sy,l[i].px,l[i].py);
        }
    }
}