public Test(){
setSize(200,200);
setVisible(true);
btn=new Button("test");
btn.addActionListener(this);
add(btn);
}

public void actionPerformed(ActionEvent ae){
repaint();
btn.setBackground(Color.YELLOW);
}

public void paint(Graphics g2){
if(im==null){
im=btn.createImage(getWidth(),getHeight());
g=im.getGraphics();
}
g.setColor(c);
g.fillOval(50,50,220,220);
g2.drawImage(im,0,0,this);
}