多角形を動かす範囲を設定したいのですが…。

多角形をKeyListenerで動かす範囲を設定 したいのですがどうすればいいでしょうか。 import java.awt.Color; import java.awt.Graphics; import java.awt.Polygon; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import javax.swing.JFrame; import javax.swing.JPanel; public class JavaGame2 { public static void main(String age[]) { JFrame frame = new JFrame(); frame.setTitle("テスト"); frame.setSize(400, 400); frame.setLocation(1000, 200); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); MyPanel panel = new MyPanel(); frame.add(panel); frame.setVisible(true); } } class MyPanel extends JPanel implements KeyListener{ private Ziki ziki; public MyPanel() { setBackground(Color.black); ziki = new Ziki(); addKeyListener(this); setFocusable(true); } protected void paintComponent(Graphics g) { super.paintComponent(g); ziki.draw(g); } public void keyPressed(KeyEvent e) { int key = e.getKeyCode(); switch(key) { case KeyEvent.VK_UP : ziki.moveUpZiki(); break; case KeyEvent.VK_RIGHT :ziki.moveRightZiki(); break; case KeyEvent.VK_DOWN : ziki.moveDownZiki(); break; case KeyEvent.VK_LEFT : ziki.moveLeftZiki(); break; }repaint(); } public void keyReleased(KeyEvent e){} public void keyTyped(KeyEvent e){} } class Ziki { private Polygon p; public Ziki() { int[] xpoints = {240,260,250}; int[] ypoints = {260,260,240}; p = new Polygon(xpoints,ypoints,xpoints.length); } void draw(Graphics g) { g.fillPolygon(p); } public void moveLeftZiki() { for (int i=0; i < p.xpoints.length; i++ ) { p.xpoints[i] -= 5; } } public void moveRightZiki() { for (int i=0; i < p.xpoints.length; i++ ) { p.xpoints[i] +=5; } } public void moveUpZiki() { for (int i=0; i < p.ypoints.length; i++ ) { p.ypoints[i] -= 5; } } public void moveDownZiki() { for (int i=0; i < p.ypoints.length; i++ ) { p.ypoints[i] += 5; } } }