🚀 go-pugleaf

Witam
Napisalem taki maly programik w ktorym po kliknieciu buttonu OK
pojawiaja sie dodatkowy zolty kwadrat. Po przyslonieciu i odslonieciu
tego okna jakims innym oknem np mozilla zostaje tlo ale kwadrat znika.
Pytanie jest takie: jak to zrobic zeby ten kwadrat nie zniknal ?
Dzieki za wszelkie sugestie

Ponizej kod programu:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;


class PaintBackground extends JPanel {

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D)g;
        setBackground(Color.BLACK);
        g2d.setColor(Color.RED);
        g2d.drawRect(60,60,150,150);
    }
}

class CreateGUI implements MouseListener {
    JFrame frame = null;
    JPanel panel = new JPanel();
    JButton button = null;

    final static int sizeX = 400;
    final static int sizeY = 400;
    final static int locX = 10;
    final static int locY = 10;

    public CreateGUI() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(sizeX,sizeY);
        frame.setLocation(locX,locY);

        Container cont = frame.getContentPane();
        cont.setLayout(new BorderLayout());
        button = new JButton("OK");
        button.addMouseListener(this);
        cont.add(button, BorderLayout.NORTH);
        panel.setLayout(new BorderLayout());
        panel.add(new PaintBackground(), BorderLayout.CENTER);
        cont.add(panel, BorderLayout.CENTER);

        frame.setVisible(true);
    }

    public void mouseClicked(MouseEvent e) {}
    public void mousePressed(MouseEvent e) {
        Graphics g = panel.getGraphics();
        g.setColor(Color.YELLOW);
        g.drawRect(40,40,90,90);
        panel.revalidate();
    }
    public void mouseReleased(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
}

public class RunApp {
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            public void run() {
                new CreateGUI();
            }
        };
        EventQueue.invokeLater(runnable);
    }
}