// for double buffering to prevent flicker 
      // memory image 
      Image offScreenImage; 
      // graphics context
      Graphics offScreen; 

     // Called when the applet needs to be painted 
     // calls the flicker free updating system 
     public void paint (Graphics g) { 
          update(g); 
     } // end of paint 

     // Draw the applet without flicker 
     // Use synchronized 
     public synchronized void update(Graphics g) { 
          // get the size of the applet 
          int xW = size().width ; 
          int xH = size().height ; 

          if ((xW != aW) || (xH != aH) || (offScreen == null)) { 
               // initialise the double buffering screen 
               try { 
                    offScreenImage = createImage (xW, xH); 
                    offScreen = offScreenImage.getGraphics (); 
               } catch (Exception e) { 
                    offScreen = null; 
               } 
               aW = xW ; 
               aH = xH ; 

               // get Image size 
               iW = img.getWidth(this) ; 
               iH = img.getHeight(this) ; 
          } 

          if ((offScreen!=null) && b) { 
               paintApplet(offScreen); 
               g.drawImage(offScreenImage,0,0,this); 
          }  else 
               paintApplet(g); 
     } // end of update 

     // Draw applet 
     public void paintApplet(Graphics g) {  
            g.setColor(Color.white ) ; 
          g.fillRect(0, 0, aW, aH) ; 
          g.drawImage(img, xPos, yPos, this) ; 
            g.setColor(Color.red ) ; 
            g.drawString("double buffer : " + b, 10, yPos) ; 
     }