帮我看看这段代码，运行的时候为什么cpu占用率达到了100%哪里出问题了吗，里面的其他一些类不用管应该就是这段代码出问题了
package Exercise;
import java.awt.*;
import javax.swing.*;
import java.util.*;
import java.awt.event.*;

public class Exercise extends JFrame
{
  public Exercise()
  {
  super("这是一次测试");
  setSize(400,300);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  panel myPanel=new panel();
  addKeyListener(myPanel);
  this.add(myPanel);
   
  }
  public static void main(String[] args)
  {
  Exercise e=new Exercise();  
  e.setVisible(true);
  }
   
}
class panel extends JPanel implements KeyListener
{
  myTank mt=null;
   
  public panel()
  {
  mt=new myTank(100,100);
   
  }
  public void paint(Graphics g)
  {
  super.paint(g);
  this.drawTank(mt.getX(),mt.getY(),g,mt.getType(),0);
   
  if(mt.s!=null)  
  {
   
  g.draw3DRect(mt.s.getX(), mt.s.getY(), 2, 2, false);
  }
   
  }
  public void drawTank(int x,int y,Graphics g,int type,int color)//画坦克（根据坦克的类型画出各种坦克）
  {
  switch(color)
  {  
  case 0:
  g.setColor(Color.red);
  break;
  case 1:
  g.setColor(Color.CYAN);
  break;
  }
  //用switch语句画出
  switch(type)
  {
  case 0:
   
  //向上
  g.fill3DRect(x-10, y-15, 5, 30, false);
  g.fill3DRect(x-5, y-10, 10, 20, false);
  g.fill3DRect(x+5, y-15, 5, 30, false);
  g.drawLine(x, y, x, y-15);
  break;
  case 1:
  //向右
  g.fill3DRect(x-15, y-10, 30, 5, false);
  g.fill3DRect(x-10, y-5, 20, 10, false);
  g.fill3DRect(x-15, y+5, 30, 5, false);
  g.drawLine(x, y, x+15, y);
  break;
  case 2:
  //向下
  g.fill3DRect(x-10, y-15, 5, 30, false);
  g.fill3DRect(x-5, y-10, 10, 20, false);
  g.fill3DRect(x+5, y-15, 5, 30, false);
  g.drawLine(x, y, x, y+15);
  break;
  case 3:
  //向左
  g.fill3DRect(x-15, y-10, 30, 5, false);
  g.fill3DRect(x-10, y-5, 20, 10, false);
  g.fill3DRect(x-15, y+5, 30, 5, false);
  g.drawLine(x, y, x-15, y);
  break;
   
  }
  repaint();
   
  }

  @Override
  public void keyTyped(KeyEvent e) {
  //throw new UnsupportedOperationException("Not supported yet.");
  }

  @Override
  public void keyPressed(KeyEvent e) {
  if(e.getKeyCode()==KeyEvent.VK_W)
  {
  mt.setType(0);
  mt.moveup();
  }else 
  if(e.getKeyCode()==KeyEvent.VK_D)
  {