Putting Rectangle On top of Frame With Multiple Panels

Question

Ok, I can't Figure out how place a Black Rectangle that Covers The whole Frame, while the frame contains 3 panels (for example).
Here is what I tried to do.
import javax.swing.*;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
* @author Sammy
public class TestEngine {
private JPanel pnl;
  private Graphics g;
    private JPanel pnl1;
    private JPanel pnl2;
   public static void main(String[] args) {
   TestEngine test =  new TestEngine();
            test.gui();
   public void gui (){
       JFrame frame = new JFrame("Aurora Engine -- 1.0 Test  ");
       frame.setSize(400, 400);
       frame.setVisible(true);
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       frame.setLocationRelativeTo(null);
       pnl = new JPanel();
       pnl1 = new JPanel();
       pnl2 = new JPanel();
    frame.add(pnl);
    frame.add(pnl);
    frame.add(pnl2);
    g = frame.getGraphics();
    Graphics2D g2 = (Graphics2D) g;
            g2.drawRect(0, 0, pnl.getWidth(), pnl.getHeight());
            g2.setColor(Color.BLACK);
            g2.fillRect(1, 1, pnl.getWidth(), pnl.getHeight());
        frame.paint(g2);
}

Answer 1

1. Don't do any custom painting in a top level window. Use a JComponent or JPanel.
2. Never never never use getGraphics in custom painting. Use an override to a painting method.
how place a Black Rectangle that Covers The whole Frame, while the frame contains 3 panels (for example).Place the 3 panels in a parent panel with a paint() override that invokes the super implementation and then draws the rectangle. For example:import java.awt.*;
import javax.swing.*;
public class OvalOverlay {
  public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        new OvalOverlay().makeUI();
  public void makeUI() {
    JPanel outer = new JPanel(new GridLayout(2, 2)) {
      @Override
      public void paint(Graphics g) {
        super.paint(g);
        g.setColor(Color.RED);
        g.fillOval(50, 50, getWidth() - 100, getHeight() - 100);
    Color[] backgrounds = {Color.YELLOW, Color.GREEN, Color.CYAN, Color.ORANGE};
    for (Color background : backgrounds) {
      JPanel inner = new JPanel();
      inner.setBackground(background);
      outer.add(inner);
    JFrame frame = new JFrame();
    frame.add(outer);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}db