Java利用多线程编程实现一个正在旋转的地球

import java.applet.*;
import java.awt.*;
import java.util.*;
public class Eearth extends Applet  implements Runnable {
  Thread clockThread;
  //for(int r=40;r>0;r=r-10){
  double r=Math.PI/8;
  public void start(){
    if(clockThread==null){
      clockThread=new Thread(this,"Clock");
      clockThread.start();
    }
  }
  public void run(){
    while(clockThread!=null){
      repaint();
      try{
        clockThread.sleep(100);
      }catch(InterruptedException e){}
    }
  }
  public void paint(Graphics g)
  {
    for(double angle=0;angle<2*Math.PI;)//周长为零 周长小于2π
    {
      g.drawString("*", (100+(int)(50*Math.sin(r)*Math.sin(angle))),100+(int)(50*Math.cos(angle)));
    //画图 这里是参数方程 x=a+rcosθ   y=b+rsinθ
      angle+=(Math.PI/20.0);//Math.PI 圆周率 这里是打印多少个* 
    }
    r=r+Math.PI/8;
  }
  public void stop(){
    clockThread.stop();
    clockThread=null;
  }
}