Moving ball across the boundry

 import java.applet.*;   
 import java.awt.Color;  
 import java.awt.Graphics;  
 import java.util.logging.Level;  
 import java.util.logging.Logger;  
 public class Moveball extends Applet implements Runnable{  
   public int x=1,y=0;  
   public void init(){  
     Thread t=new Thread(this);  
     t.start();  
   }  
   public void run(){  
     while(true){  
       try {  
        if(x<300 && y==0)x=x+1;  
        if(x==300 && y<150)y++;  
        if(y==150 && x>0)x=x-1;  
        if(x==0 && y<=150)y=y-1;  
        Thread.sleep(3);  
        repaint();  
        } catch (InterruptedException ex) {  
           Logger.getLogger(Moveball.class.getName()).log(Level.SEVERE, null, ex);  
         }  
     }  
   }  
   public void paint(Graphics g){  
       setBackground(Color.BLUE);  
       setForeground(Color.GREEN);  
       g.drawOval(x, y, 50, 50);  
   }    
 }  

Using applet to demonstrate the wind

 import java.applet.Applet;  
 import java.awt.Dimension;  
 import java.awt.Graphics;  
 public class Wind extends Applet implements Runnable{  
   int Theta;  
   int x11=0,y11=0,x12=0,y12=0,x21=0,y21=0,x22=0,y22=0;  
   @Override  
   public void run() {  
     while(true){  
       Dimension d=getSize();  
       x11=150+(int)(100*Math.cos(Math.toRadians(Theta)));  
       y11=150+(int)(100*Math.sin(Math.toRadians(Theta)));  
       x12=150+(int)(100*Math.cos(Math.toRadians(Theta+180)));  
       y12=150+(int)(100*Math.sin(Math.toRadians(Theta+180)));  
       x21=150+(int)(100*Math.cos(Math.toRadians(Theta+90)));  
       y21=150+(int)(100*Math.sin(Math.toRadians(Theta+90)));  
       x22=150+(int)(100*Math.cos(Math.toRadians(Theta+270)));  
       y22=150+(int)(100*Math.sin(Math.toRadians(Theta+270)));  
       Theta++;  
       try{  
         Thread.sleep(3);  
         repaint();  
       }  
       catch(Exception e){  
       }  
     }  
   }  
   @Override  
   public void init(){  
     Thread t1=new Thread(this);  
     t1.start();  
   }  
   @Override  
   public void paint(Graphics g){  
     g.drawLine(x11,y11,x12,y12);  
     g.drawLine(x21,y21,x22,y22);  
   }  
 }  

OUTPUT