Use the JPanel's graphics to draw something

Question

I get a Jpanel's Graphcis g and use g to paint something,
g.drawRect(......),
the rectangle show on the JPanel , but it was clear when I resize the JPanel
or switch between applications. I think I can override the paintComponent()
method to let the image keep on it. I want to know: Is there some component
I can get its' graphics like JPanel and whatever I painted on use it can not
be clear?
BTW, I want to try some small game programming, anyone know some BEAutiful
component package?

Answer 1

the rectangle show on the JPanel , but it was clear when I resize the JPanelThe reason your painting clears when you resize your window (or min/maximize) is because you will need to
tell your program to repaint the scene after anything happens to the window. The best thing to do is create
a thread to constantly call your paint routines so that even when the painting clears, it is repainted
immediately.
Is there some component I can get its' graphics like JPanel and whatever I painted on use it can not
be clear?I'm afraid not, all components behave this way. You don't have to worry if you use a thread for painting
(a thread for painting is infact one of several standards for rendering). Here is some code:
public void startPainting(){
   Thread paintTimer = new Thread(
      new Runnable(){
         public void run(){
            try{
                Thread.sleep(delay);
            }catch(InterruptedException e) {break;}
            repaint();
   paintTimer.start();
}[\code]