JPanel and JFrame coordinate messed up

Question

I am trying to write a game using JPanle and JFrame. I set up a panel inside a frame. When I paint on the panel with a rectangle size of the panel at 0,0. The rectangle shifts up and left for some pixels. How do I fix this problem? I googled and I saw the insets method, but I don't want to use that calculate my coordinate everytime I draw.

Here are the codes

public class Game extends JFrame{

public Game(){
    this.getContentPane().setPreferredSize(new Dimension(800,600));  
    pane p = new pane();
    this.getContentPane().add(p,BorderLayout.CENTER);
    p.setPreferredSize(new Dimension(800,600));
    pack();
    setResizable(false);
    setVisible(true);


}


public static void main(String[] args){
    new Game();
}

}

---

public class pane extends JPanel{

public pane(){

setDoubleBuffered(false);
setBackground(Color.black);
setPreferredSize( new Dimension(800, 600));

setFocusable(true);
requestFocus(); 
}

@Override
public void paint(Graphics g) {
    g.setColor(Color.white);
    g.fillRect(0, 0, 800, 600);
    g.setColor(Color.black);
    g.fillRect(0, 0, 800, 600);

}
}

screen shot link

Answer 1

Actually there is no shift of your panel, it is located in 0,0. The problem is that the panel actually gets a size of 810,610 instead of 800,600. For some reason (which so far I was unable to find and if somebody has an idea I would love to learn), when you call setResizable(false) on a JFrame , its insets are modified and eventually this leads to your content pane to be bigger than expected (at least on JDK6/Win7). Call setResizable(false) before adding the components and packing the frame, and it works.

Also consider painting a rectangle of the size of your panel ( g.fillRect(0, 0, getWidth(), getHeight()); so that you are sure to fill the entire area, no matter what happens.

Any reason to fill the background with white color and then replace it with black?