KeyEvent doesn' work ....

Hi experts,

   Does anyone know how come my keyevent doesn't work ? many thanks !!!

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

public class Test extends JFrame implements KeyListener, ActionListener{
   
    private int snake_x[] = new int[150] ;
    private int snake_y[] = new int[150] ;
    private int snake_dir[] = new int[150] ;
    private final int Delta_x = 20, Delta_y = 20 ;
   
    private static final int UP = 0 ;
    private static final int RIGHT = 1 ;
    private static final int DOWN = 2 ;
    private static final int LEFT = 3 ;
   
   
     
    private javax.swing.Timer headTimer ;
   
    ImageIcon headImg = new ImageIcon(getClass().getResource("head.gif"));
    /** Creates a new instance of SnakeFrame */
 
    public Test() {
        snake_x[0] = 200 ; snake_y[0] = 200 ; snake_dir[0] = 3 ;
        headTimer = new Timer(400, this);
        headTimer.start();
       
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        setSize(600,600) ;
        show() ;
       
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Test mySnake = new Test() ;
        // TODO code application logic here
    }
   
 
   
    public void paint(Graphics g)
    {
        super.paint(g);
        g.drawImage( headImg.getImage(), snake_x[0], snake_y[0], 20, 20, null) ;  
     }

    public void actionPerformed(ActionEvent e) {
         if ( snake_dir[0] == 0) snake_y[0] -= Delta_y ;
         if ( snake_dir[0] == 1) snake_x[0] += Delta_x ;
         if ( snake_dir[0] == 2) snake_y[0] += Delta_y ;
         if ( snake_dir[0] == 3) snake_x[0] -= Delta_x ;
         repaint() ;
    }
   
    public void keyPressed(KeyEvent e) {
     
           
           if (e.getKeyCode()==KeyEvent.VK_UP) {
             snake_dir[0] = 0 ;
             System.out.println("UP") ;
           }
           else if (e.getKeyCode()==KeyEvent.VK_RIGHT) {
             snake_dir[0] = 1 ;
             System.out.println("RIGHT") ;
           }
           else if (e.getKeyCode()==KeyEvent.VK_DOWN) {
             snake_dir[0] = 2 ;
             System.out.println("DOWN") ;
           }
           else if (e.getKeyCode()==KeyEvent.VK_LEFT) {
             snake_dir[0] = 3 ;
             System.out.println("LEFT") ;
           }      
         
    }
   
    public void keyReleased(KeyEvent e) {
    }
   
    public void keyTyped(KeyEvent e) {
    }
   
}