怎样实现KeyHandler的keyReleased方法

import javax.swing.*;import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;public class Sketch
{
  public static void main(String[] args)  {
   SketchFrame frame=new SketchFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.show() ;
  }  }  class SketchFrame extends JFrame
  {
    public SketchFrame()
    {
      setTitle("PlafTest");
       setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
      SketchPanel panel=new SketchPanel();
       Container contentPane=getContentPane();
       contentPane.add(panel);    }    public static final int DEFAULT_WIDTH=300;
     public static final int   DEFAULT_HEIGHT =200;
  } class SketchPanel extends JPanel
  {
    public SketchPanel()
    {
      last = new Point2D.Double(100, 100);
      lines = new ArrayList();
      KeyHandler listener = new KeyHandler();
     addKeyListener(listener);
      setFocusable(true);
    }
       public void add(int dx,int dy)
      {
         Point2D end=new Point2D.Double(last.getX()+dx,last.getY()+dy);
         Line2D line=new Line2D.Double(last,end);
         lines.add(line);
         repaint();
       last=end;
      }      public void paintrComponent(Graphics g)
      {
        super.paintComponent(g);
        Graphics2D g2=(Graphics2D)g;      for(int i=0;i<lines.size();i++)
         g2.draw((Line2D)lines.get(i));      }      private Point2D last;
      private ArrayList lines;      private static final int  SAMLL_INCREMENT=1;
      private static final int   LARGE_INCREMENT=5;     private class KeyHandler implements KeyListener
      {
        public void KeyPressed(KeyEvent event)
       {
          int keyCode=event.getKeyCode();
          int d;
          if(event.isShiftDown())
            d=LARGE_INCREMENT;
            else
              d=SAMLL_INCREMENT;             if(keyCode==KeyEvent.VK_LEFT) add(-d,0);
             else if(keyCode==KeyEvent.VK_RIGHT) add(d,0);
              else if(keyCode==KeyEvent.VK_UP) add(0,-d);
                else if(keyCode==KeyEvent.VK_DOWN) add(0,d);
        }
       
        
         //怎样实现
        public void keyReleased(KeyEvent event)
        {}
        public void keyTyped(KeyEvent event)
        {
           char keyChar=event.getKeyChar();
           int d;
           if(Character.isUpperCase(keyChar))
           {
             d=LARGE_INCREMENT;
             keyChar=Character.toLowerCase(keyChar);
           }
           else
             d= SAMLL_INCREMENT;             if(keyChar=='h') add(-d,0);
             else if(keyChar=='l') add(d,0);
              else if(keyChar=='k') add(0,-d);
               else if(keyChar=='j') add(0,d);        }
      }  }