How to make more than one panel transparent?

Question

Implementing the answer of this issue, i managed to make a panel transparent. However, in order to organize the way I want, I wanted to use more JPanels, with different layout managers.

But when I do that, they don’t get transparent. How could I do that ?

Example of the problem:

The image is just this blue sky, this gray/white background, is of the component.

When I use a single panel:

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;

public class Teste {

    public Teste() {
        JWindow jWindow = new JWindow();
        jWindow.setBackground(new Color(0, 0, 0, 0));
        jWindow.setContentPane(new Pane());
        jWindow.pack();
        jWindow.setVisible(true);
        jWindow.setLocationRelativeTo(null);
    }

    class Pane extends JPanel {

        private BufferedImage leaf;

        public Pane() {
            //setLayout(new BorderLayout());

            JPanel borderPainel = new JPanel();
            borderPainel.setLayout(new BorderLayout());
            JPanel gridPainel = new JPanel();
            gridPainel.setLayout(new GridLayout(2, 1));

            gridPainel.add(new JLabel("Label 01"));
            gridPainel.add(new JLabel("Label 02"));

            borderPainel.add(gridPainel, BorderLayout.SOUTH);
            add(borderPainel);

            try {
                leaf = ImageIO.read(getClass().getResource("/imagens/icon.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }

            gridPainel.setOpaque(false);
            borderPainel.setOpaque(false);
            //setOpaque(false);

        }

        @Override
        public Dimension getPreferredSize() {
            return leaf == null ? new Dimension(200, 200) : new Dimension(leaf.getWidth(), leaf.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (leaf != null) {
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.drawImage(leaf, 0, 0, this);
                g2d.dispose();
            }
        }
    }

    public static void main(String[] args) {
        JFrame.setDefaultLookAndFeelDecorated(true);
        new Teste();
    }
}

Answer 1

I made 3 changes to the code:

• altered JWindow for JFrame, since you are working with the swing API, use components of this API and not the awt;

• I’ve warned you several times in other posts, but I warn you again: ALWAYS dispatch graphical application of this API to the Event-Dispatch-thread;

• I just cracked the line setOpaque(false); which makes the JFrame see-through as well.

The code went like this:

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

import javax.imageio.ImageIO;

public class PainelTransparenteTest {

    public PainelTransparenteTest() {
        JFrame jWindow = new JFrame();
        jWindow.setBackground(new Color(0, 0, 0, 0));
        jWindow.setContentPane(new Pane());
        jWindow.pack();
        jWindow.setVisible(true);
        jWindow.setLocationRelativeTo(null);
    }

    class Pane extends JPanel {

        private BufferedImage leaf;

        public Pane() {
            //setLayout(new BorderLayout());

            JPanel borderPainel = new JPanel();
            borderPainel.setLayout(new BorderLayout());
            JPanel gridPainel = new JPanel();
            gridPainel.setLayout(new GridLayout(2, 1));

            gridPainel.add(new JLabel("Label 01"));
            gridPainel.add(new JLabel("Label 02"));

            borderPainel.add(gridPainel, BorderLayout.SOUTH);
            add(borderPainel);

            try {
                //leaf = ImageIO.read(getClass().getResource("/imagens/icon.png"));
                leaf = ImageIO.read(new URL("https://i.stack.imgur.com/i5lmv.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }

            gridPainel.setOpaque(false);
            borderPainel.setOpaque(false);
            setOpaque(false);

        }

        @Override
        public Dimension getPreferredSize() {
            return leaf == null ? new Dimension(200, 200) : new Dimension(leaf.getWidth(), leaf.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (leaf != null) {
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.drawImage(leaf, 0, 0, this);
                g2d.dispose();
            }
        }
    }

    public static void main(String[] args) {
        JFrame.setDefaultLookAndFeelDecorated(true);
       SwingUtilities.invokeLater(() ->  new PainelTransparenteTest());
    }
}

And the result:

The trick here was to set up for that main screen(the JFrame in this case) is not opaque either, hence it will follow the background of the internal components. So it was enough to uncomment the informed line.