How to use paint method to draw in many componets.

Question

Hi!
I have code like this:
public class MainPanel extends JPanel{
   JPanel p1;
   JPanel p2;
   public MainPanel(){
       super(new BorderLayout());
       p1 = new JPanel();
       p2 = new JPanel();
       add(p1 , BorderLayout.Center);
       add(p2 , BorderLayout. West);
       setVisible(true);
@Override
    protected void paintComponent(Graphics g) {
       g.setColor(Color.red);
       g.fillrect(10,10,10,10);
}This code is onle an example. Supose, this code will paint black rectangle on "main panel" to which p1 and p2 are added. What should i do to be able to paint this rectangle on p1 or p2 without creating separate classes in which i will override paintComponents() method for p1 and p2. I would like to avoid creating separete classes for each panels. Is there any way to do that using one paint Components method. Thanks in advance for all respone.

Answer 1

(where's Darryl when you need him?)Erm, Pete, since when did I become an expert lol?
Lost my hard disk, its been hiccuping for a couple of weeks now. I'm running on an old 20 GB PATA with a 5GB c drive. No IDE, no offline Javadoc. I'll get a HDD in the morning, but I hope I can spin up the old disk at least once and recover the last week's "work" ... just fun stuff actually.
Why does this code draw rectangles just for split second?repaint() (and consequently paint(), paintComponent() and other painting methods) may be called by the system any time it is detected that the component needs to be repainted. Since you do not have a override for paintComponent, it will perform its default painting and paint the entire component, wiping out your rectangle.
For persistent drawing on a JPanel or JComponent I know only one way: override paintComponent. If you need to avoid this, you could go with morgalr's suggestion to use JLabel.
For this you would draw the triangle/rectangle/whatever to a BufferedImage, then call label.setIcon with a new ImageIcon constructed from the BufferedImage.
Also, avoid obtaining a Graphics reference via getGraphics. During the lifetime of a visible component, various different Graphics references may be passed into the paintComponent method, so the reference you obtain may not be current. getGraphics can also return null.
luck, db