Java program to animate ball or moving ball using frame

import java.awt.*; import java.awt.event.*; import java.applet.*; public class movball extends Frame implements Runnable { int x,y;   Thread t;   boolean flag;   public movball()   { x=0;     y=250;     addWindowListener(new mwa(this));     t=new Thread(this);     t.start();     flag=false;   }   public void run()   { for(;;)     { try       { repaint();         x++;         Thread.sleep(100);       }       catch(InterruptedException e)       {       }       if(flag)         break;     }   }   public void paint(Graphics g)   { g.drawOval(x,y,30,30);   }   public static void main(String s[])   { movball b=new movball();     b.setSize(new Dimension(1000,600));     b.setTitle("Running Ball");     b.setVisible(true);   } } class mwa extends WindowAdapter { movball a;   public mwa(movball f)   { a=f;   }   public void windowClosing(WindowEvent e)   { a.flag=true;     a.t=null;     System.exit(0);   } } Output