"Extends JFrame" and JPanel?

Question

The following code, as you see below:

public class app extends javax.swing.JFrame implements Runnable {

extends JFrame. But I also need it to extend JPanel, in order to make a transparent JPanel. The problem is that I can't extend both, java throws a mistake:

If I extend JPanel I'm able to make a transparent JPanel, but the program can't run because there's a mistake in a few lines of code (mistake that disappears if I extend JFrame).

However, if I extend JFrame the program will run just fine, but it keeps me away from doing a transparent JPanel. How can I solve this?

What are you trying to make? Perhaps JavaFX would be a better solution for you. — Josh M, Sep 09 '13 at 01:56
I am trying to make a JFrame with a transparent JPanel. But, to do a transparent JPanel I need to extend "JPanel" , but I can't extend it because if I do that, the program doesn't work — Seba Paz, Sep 09 '13 at 01:57

MadProgrammer · Answer 1 · 2013-09-09T11:03:14.737

Basically, create your custom class extending from a JPanel, use setOpaque to false to make it transparent.

Create an instance of JFrame, set it to undecorated and adjust it's opacity separately.

Add the custom panel to the frame...

Example

enter image description here

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.Image;
import java.awt.LayoutManager;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TransparentPanel {

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

    public TransparentPanel() {
        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.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new BorderLayout());
            try {
                BufferedImage img = ImageIO.read(new File("/Users/swhitehead/Dropbox/MegaTokyo/issue459.jpg"));
                final JLabel label = new JLabel(new ImageIcon(img.getScaledInstance(-1, 200, Image.SCALE_SMOOTH)));
                label.setLayout(new CardLayout());

                JPanel menu = new JPanel(new GridBagLayout());
                JButton button = new JButton("Show");
                menu.add(button);

                JPanel transparent = new JPanel(new GridBagLayout());
                transparent.setOpaque(false);
                transparent.add(new JLabel("Look, I'm see through"));

                label.add(menu, "menu");
                label.add(transparent, "transparent");
                CardLayout layout = (CardLayout) label.getLayout();
                layout.show(label, "menu");

                button.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        CardLayout layout = (CardLayout) label.getLayout();
                        layout.show(label, "transparent");
                    }
                });

                add(label);
            } catch (IOException exp) {
                exp.printStackTrace();
            }
        }
    }    
}

Personally, I wouldn't (use design view). Can you give me a little more idea of what you are trying to achieve first... — MadProgrammer, Sep 09 '13 at 02:31
Yes: I have a JFrame with a JLabel that says "MENU". When I click on "MENU" it shows a JPanel with options. I want that JPanel to be transparent — Seba Paz, Sep 09 '13 at 02:43

score 1 · Answer 2 · edited May 23 '17 at 11:52

1

A class can only ever extend one other class, that's why it won't allow you to extend more than 1 class. here is an explanation why that is the case. Perhaps you should try reading this for more information about such window modifications (window transparency and shapes)

If you want specifically a transparent JPanel, perhaps you should look at this answer as it could explain it better than I could.

edited May 23 '17 at 11:52

Community

1
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answered Sep 09 '13 at 02:02

Josh M

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Thanks, but I am looking specifically how to do transparent JPanels – Seba Paz Sep 09 '13 at 02:05
It's useful to me, but the code of that answer extends JPanel, and I can't extend JPanel in my program because the program will not work if I do that. It throws a mistake in some JFrame methods – Seba Paz Sep 09 '13 at 02:15

"Extends JFrame" and JPanel?

2 Answers2