a setOpaque(false) JPanel is not transparent

[imorio]

These classes should create a 400X400 window showing a blue circle on a red background. Problem: they show a blue circle on a grey (empty?) background.

public class test {
	public static void main(String[] args)
	{
		new testWindow();
	}
}

import javax.swing.JFrame;

public class testWindow extends JFrame{
	private JFrame f=new JFrame();
	public testWindow()
	{
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.add(new background());
		forground p=new forground();
		p.setOpaque(false);
		f.add(p);
		f.pack();
		f.setVisible(true);
	}
}

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JPanel;


public class background extends JPanel
{
	public background()
	{
		
	}
	public Dimension getPreferredSize()
	{
		return new Dimension (400,400);
	}
	public void paint(Graphics g)
	{
		super.paintComponents(g);
		g.setColor(Color.red);
		g.fillRect(0,0,400,400);
	}
}

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JPanel;


public class forground extends JPanel{
	public forground()
	{
		
	}
	public void paint(Graphics g)
	{
		super.paintComponents(g);
		g.setColor(Color.blue);
		g.fillOval(50,50,100,100);
	}
	public Dimension getPreferredSize()
	{
		return new Dimension (400,400);
	}
}

Can anyone show me how to make the "forground" JPanel transparent? As this is a simple compilable version of my bigger program, painting both the background and the forground in one JPanel doesn't help me.

[Michael Dunn]

your main problem is here

f.add(new background());
then
f.add(p);

look up how borderLayout works, to see what needs to be added to what

public void paint(Graphics g)
	{
		super.paintComponents(g);

yuk!

try

//public void paint(Graphics g)
public void paintComponent(Graphics g)
	{
	      //super.paintComponents(g);
                super.paintComponent(g);//singular

[imorio]

Ok, So I changed the code to

import java.awt.BorderLayout;
import javax.swing.JFrame;

public class testWindow extends JFrame{
	private JFrame f=new JFrame();
	public testWindow()
	{
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setLayout(new BorderLayout());
		f.add(new background(), BorderLayout.CENTER);
		forground p=new forground();
		p.setOpaque(true);
		f.add(p, BorderLayout.CENTER);
		
		f.pack();
		f.setVisible(true);
	}
}

And I've changed the "super.paintComponents(g);" to "super.paintComponent(g);". However the output is still the same. Note that I want the 2 JPanels to be displayed on top of each other and that any part of the forground JPanel that isn't painted, the background shows through. So that the result is a blue circle on a red background.

[Fubarable]

I think that when adding two components BorderLayout.CENTER, the second one completely obscures the first, regardless of the second's opaque setting. I believe that a JLayeredPane may suit your purposes better.

[Michael Dunn]

> Note that I want the 2 JPanels to be displayed on top of each other

OverlayLayout panel to contain the 2 panels,
then add the overlayLayoutPanel to BorderLayout.CENTER

can't see why adding foregroundPanel to backgroundPanel,
then adding backgroundPanel to CENTER wouldn't also work
the way you want

[imorio]

> Note that I want the 2 JPanels to be displayed on top of each other

OverlayLayout panel to contain the 2 panels,
then add the overlayLayoutPanel to BorderLayout.CENTER

can't see why adding foregroundPanel to backgroundPanel,
then adding backgroundPanel to CENTER wouldn't also work
the way you want

I can't see that either, all I can see that it doesn't.

Using JLayeredPane, I think it should be something like this:

import java.awt.BorderLayout;

import javax.swing.JFrame;
import javax.swing.JLayeredPane;

public class testWindow extends JFrame{
	private JFrame f=new JFrame();
	private JLayeredPane p=new JLayeredPane();
	public testWindow()
	{
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setLayout(new BorderLayout());
		p.addImpl(new background(), BorderLayout.CENTER, 0);
		forground d=new forground();
		d.setOpaque(false);
		p.addImpl(d, BorderLayout.CENTER, -1);

		p.add(new background(), BorderLayout.CENTER);
		f.pack();
		f.setVisible(true);
	}
}

However these lines gives problems: "p.addImpl(d, BorderLayout.CENTER, -1);" and "p.addImpl(d, BorderLayout.CENTER, -1);".
I looked at the API, send in the right parameters (I think), added it to the JFrame, but it says it isn't visible. When I run it anyway, this error occurs:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
	The method addImpl(Component, Object, int) from the type JLayeredPane is not visible
	The method addImpl(Component, Object, int) from the type JLayeredPane is not visible

	at testWindow.<init>(testWindow.java:13)
	at test.main(test.java:5)

[Fubarable]

If you're going to use JLayeredPanes, you'd best read the tutorials as you don't appear to be using it correctly.

[imorio]

If you're going to use JLayeredPanes, you'd best read the tutorials as you don't appear to be using it correctly.

I read this tutorial: Java Platform SE 6. However my problems remain. Based on the source code found in that tutorial I removed my forground and background classes and rewrote my testWindow class to:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;

public class testWindow extends JFrame{
	private JFrame f=new JFrame();
	private JLayeredPane p=new JLayeredPane();
	public testWindow()
	{
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setLayout(new BorderLayout());
		p.setPreferredSize(new Dimension(400, 400));
		p.add(createBackground(), new Integer(0));
		p.add(createForground(), new Integer(-1));

		p.add(new background(), BorderLayout.CENTER);
		f.setPreferredSize(new Dimension(400,400));
		f.setVisible(true);
	}
	public JLabel createBackground()
	{
		JLabel label=new JLabel();
		label.setVerticalAlignment(JLabel.TOP);
		label.setHorizontalAlignment(JLabel.CENTER);
		label.setBackground(Color.red);
		label.setBounds(0,0,400,400);
		label.setOpaque(true);
		return label;
	}
	public JLabel createForground()
	{
		JLabel label=new JLabel();
		label.setVerticalAlignment(JLabel.TOP);
		label.setHorizontalAlignment(JLabel.CENTER);
		label.setBackground(Color.blue);
		label.setBounds(50,50,100,100);
		label.setOpaque(true);
		return label;
	}
}

However this just creates a window with minimal size and when I enlarge the window, it is empty. This is odd because I setPreferredSize twice and add everything to the JFrame as I think I should. This is very frustrating, because debugging only leads me to conclude that the things I want to appear don't appear.

[Fubarable]

1) Where do you add your JLayeredPane to the JFrame?
2) What is new background() supposed to do?
3) If your JLabels are opaque, how does one see through them?
4) What are you trying to do when you add something to a JLayeredPane BorderLayout.CENTER?

Luck

[imorio]

Thanks, it works now!! You were right, I didn't add the JLayeredPane... But now everything works better then expected. Repainting the JPanel automaticly update's the GUI. Now I can finally continue with my program. Thanks again for answering my question, when in retrospect I looked really stupid.