Showing JPanel error

[Fermen]

Why do I get this error? --> Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container

It's ridiculous... I'm just adding a JPanel to a JFrame..or?

Class with JPanel

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
 
public class Stapeldiagram extends JPanel
{
 
    public Stapeldiagram()
    {
 
        this.setBackground(Color.white);
    }
 
    @Override
         public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor(Color.red);
        g.fill3DRect(35, 225-150, 40, 150, true);
        g.draw3DRect(35,225-150,40,150,false);
        g.setColor(Color.green);
        g.fill3DRect(75, 225-100, 40, 100, true);
        g.draw3DRect(75, 225-100, 40, 100,false);
        g.setColor(Color.blue);
        g.fill3DRect(115, 225-190, 40, 190, true);
        g.draw3DRect(115, 225-190, 40,190,false);
    }
}//end class

Class to show the JPanel

import java.awt.Color;
import java.awt.FlowLayout;
import javax.swing.JFrame;
 
 
public class VisaStapel extends JFrame {
 
    Stapeldiagram stip1;
 
    public VisaStapel()
    {
 
        stip1 = new Stapeldiagram();
        add(stip1);
        this.setBackground(Color.white);
    }
 
 
        public static void main(String[] args)
    {
        JFrame f = new JFrame();
        f.setSize(400, 300);
        f.setLocation(100,100);
        f.setTitle("Min JPanel!");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        VisaStapel p = new VisaStapel ();//anropar min JPanel
        f.add(p);
        f.setVisible(true);
    }
 
}

[newbie]

I am making a guess here, so forgive me if I'm incorrect.
I believe it's down to the fact that you're trying to add a JFrame to a JFrame.
Try replacing your JFrame f = new JFrame with:

JFrame f = new VisaStapel ();
then set the size etc of that object.

[Norm]

What line is the error occurring on? You didn't post the full text of the compiler's error message which includes the line and the line number.

[bgroenks96]

VisaStaple p = new VisaStaple();
f.add(p);

Your VisaStaple class extends JFrame. So by trying to add a VisaStaple object to a JFrame you are trying to add a frame to a frame which doesn't work unless you use JInternalFrame.

I really don't know what you are trying to do here. If you want the Staplediagram class's paintComponent product to appear in the JFrame, I would suggest making a simple change:

Staplediagram s = new Staplediagram();
f.add(s);
f.setVisible(true);

I don't know if that was a simple fluke/typo or a major logical error. A bit more context would help.

IF however, that is what you want, that should do it.

[Fermen]

Your VisaStaple class extends JFrame. So by trying to add a VisaStaple object to a JFrame you are trying to add a frame to a frame which doesn't work unless you use JInternalFrame.

I really don't know what you are trying to do here. If you want the Staplediagram class's paintComponent product to appear in the JFrame, I would suggest making a simple change:

Staplediagram s = new Staplediagram();
f.add(s);
f.setVisible(true);

I don't know if that was a simple fluke/typo or a major logical error. A bit more context would help.

IF however, that is what you want, that should do it.

Yes, this change make it work. But it should, according to my instructions work the way I wrote it to. This is the error:

Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container
at java.awt.Container.checkNotAWindow(Container.java: 431)
at java.awt.Container.addImpl(Container.java:1039)
at java.awt.Container.add(Container.java:959)
at javax.swing.JFrame.addImpl(JFrame.java:545)
at java.awt.Container.add(Container.java:365)
at Kap5.VisaStapel.main(VisaStapel.java:35)
Java Result: 1

[Fermen]

Oh, I think I found out the error now. I should have extended my VisaStapel - class with JPanel instead of JFrame...

Thanks for the help everyone