java - Set JFrame background transparent but show contents

Question

I'm looking for some solution to turn an opaque, null JFrame background to transparent (no Translucent) but showing swing components like buttons containers etc... here a example.

Default JFrame

Something like, HERE disable the background

Answer 1

This is a simple two step process...

First, you need to make a transparent frame...

JFrame frame = new JFrame("Testing");
frame.setUndecorated(true);
frame.setBackground(new Color(0, 0, 0, 0));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);

For every component you want to be see through, you need to make sure that it's set to be transparent, for example...

public class TestPane extends JPanel {

    public TestPane() {
        setOpaque(false);
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.insets = new Insets(4, 4, 4, 4);
        add(new JLabel("Product"), gbc);
        gbc.gridy++;
        add(new JLabel("Company"), gbc);
        gbc.gridy++;
        add(new JLabel("Phone"), gbc);

        gbc.gridx++;
        gbc.gridy = 0;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        add(new JTextField(10), gbc);
        gbc.gridy++;
        add(new JComboBox(), gbc);
        gbc.gridy++;
        add(new JTextField(10), gbc);

        JPanel buttons = new JPanel();
        buttons.setOpaque(false);
        buttons.add(new JButton("Add"));
        buttons.add(new JButton("Update"));
        buttons.add(new JButton("Delete"));
        gbc.gridx = 0;
        gbc.gridy++;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        add(buttons, gbc);

        gbc.gridy++;
        JPanel filler = new JPanel();
        filler.setBorder(new CompoundBorder(new LineBorder(Color.BLACK), new EmptyBorder(10, 10, 10, 10)));
        add(filler, gbc);

        gbc.gridy++;
        gbc.fill = GridBagConstraints.BOTH;
        add(new JScrollPane(new JTable(new DefaultTableModel(new String[]{"Product", "Company", "Phone"}, 0))), gbc);

    }

}

And a runnable example...

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.CompoundBorder;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;
import javax.swing.table.DefaultTableModel;

public class Test {

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

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setUndecorated(true);
                frame.setBackground(new Color(0, 0, 0, 0));
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setOpaque(false);
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.insets = new Insets(4, 4, 4, 4);
            add(new JLabel("Product"), gbc);
            gbc.gridy++;
            add(new JLabel("Company"), gbc);
            gbc.gridy++;
            add(new JLabel("Phone"), gbc);

            gbc.gridx++;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.HORIZONTAL;
            add(new JTextField(10), gbc);
            gbc.gridy++;
            add(new JComboBox(), gbc);
            gbc.gridy++;
            add(new JTextField(10), gbc);

            JPanel buttons = new JPanel();
            buttons.setOpaque(false);
            buttons.add(new JButton("Add"));
            buttons.add(new JButton("Update"));
            buttons.add(new JButton("Delete"));
            gbc.gridx = 0;
            gbc.gridy++;
            gbc.fill = GridBagConstraints.HORIZONTAL;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            add(buttons, gbc);

            gbc.gridy++;
            JPanel filler = new JPanel();
            filler.setBorder(new CompoundBorder(new LineBorder(Color.BLACK), new EmptyBorder(10, 10, 10, 10)));
            add(filler, gbc);

            gbc.gridy++;
            gbc.fill = GridBagConstraints.BOTH;
            add(new JScrollPane(new JTable(new DefaultTableModel(new String[]{"Product", "Company", "Phone"}, 0))), gbc);

        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.dispose();
        }

    }

}

This is also a great way take "fake" a translucent frame...

public class TestPane extends JPanel {

    //...

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(getBackground());
        g2d.setComposite(AlphaComposite.SrcOver.derive(0.5f));
        g2d.fillRect(0, 0, getWidth(), getHeight());
        g2d.dispose();
    }

}