Try overriding the update function  of Applet:

public void update(Graphics g) {
paint(g);
}

Usually update first clears the display area and then calls paint().

but i dont get the graphics object at the time of calling update .. i
have not used createimage and the getGraphics to store the g..
so i am having problem. Is there any other solution u have

You don't have to call  update yourself, it is done automatically whenever it
is needed. You can force it to be called by calling repaint().

It is explained in more detail at http://newdata.box.sk/bx/java/httoc.html.
Look at
chapters 10 and 11.