I found the problem.
I've forgotten to Launch init() method of my button class

public void  init()
{
Container ct=getContentPane();
tom=new myGraphic();
tom.init();// <-- in fact i got a NullPointer Exception
ct.add(tom);
tom.addMouseListener(this);
}

Now, i think i have another problem, my applet  run correctly with JBuiler 7
appletViewer, but not with Explorers.
I think i have a security problem.