Colorchooser - Strange Exceptions in simple code.

[spec8320]

Hi, I have really tough problem I tried to solve it but I cant ... After running this code: I have some exceptions. Line 76 is "Color wybor = Okno.Chooser.getColor();" and I cant understand why its a problem... So I'm looking for help from you guys.

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
import javax.swing.colorchooser.*;

class data
{
	public static boolean zmienna_do_przycisku_chooser = false;
}
class Okno extends JFrame {
 
	// Colorchosser
	public static JColorChooser Chooser;
	// Przycisk colorchoosera
	static JButton przycisk_colorchooser = new JButton();
	ActionListener przycisk_colorchooser_listener = new przycisk_colorchooser();

	private static final long serialVersionUID = 1L;

	public Okno() {
        setSize(1000, 700);
        setTitle("Grafika komputerowa"); 
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
        
        // Dodaje panel
        Panel panel = new Panel();
        add(panel);
        // Przycisk Rysowania
		przycisk_colorchooser.addActionListener(przycisk_colorchooser_listener);
		panel.add(przycisk_colorchooser);
		
        Chooser = new JColorChooser ();
        Chooser.setPreviewPanel(new JPanel());
		panel.add(Chooser);
		Chooser.setVisible(false);
		Chooser.setColor(Color.black);
    }
	
	// Przycisk colorchooser
	public class przycisk_colorchooser implements ActionListener
	{
		public void actionPerformed(ActionEvent e)
		{
			if(data.zmienna_do_przycisku_chooser == false)
			{
				Okno.Chooser.setVisible(true);
				data.zmienna_do_przycisku_chooser = true;
			}
			else
			{
				Okno.Chooser.setVisible(false);	
				data.zmienna_do_przycisku_chooser = false;
			}
			repaint();
		}
	}
}
 
class Panel extends JPanel {
 
    /**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public void paintComponent(Graphics g) {
 
        Graphics2D g2 = (Graphics2D) g;
        // Czyszczenie
        g2.clearRect(0,0,1000,700);
        // Przycisk colorchooser
        Okno.przycisk_colorchooser.setBounds(30,30,100,100);
        Color wybor = Okno.Chooser.getColor();
        Okno.przycisk_colorchooser.setBackground(wybor);
        g2.setPaint(Color.black);
		repaint();
    }
}
 
public class Main {
 
    public static void main(String args[]) {
        Okno okno = new Okno();
    }
}

Exceptions:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Panel.paintComponent(Main.java:76)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintChildren(Unknown Source)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintChildren(Unknown Source)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JLayeredPane.paint(Unknown Source)
	at javax.swing.JComponent.paintChildren(Unknown Source)
	at javax.swing.JComponent.paintToOffscreen(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
	at javax.swing.RepaintManager.paint(Unknown Source)
	at javax.swing.JComponent.paint(Unknown Source)
	at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
	at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
	at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
	at java.awt.Container.paint(Unknown Source)
	at java.awt.Window.paint(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
	at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$000(Unknown Source)
	at java.awt.EventQueue$1.run(Unknown Source)
	at java.awt.EventQueue$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Panel.paintComponent(Main.java:76)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintToOffscreen(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
	at javax.swing.RepaintManager.paint(Unknown Source)
	at javax.swing.JComponent._paintImmediately(Unknown Source)
	at javax.swing.JComponent.paintImmediately(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
	at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$000(Unknown Source)
	at java.awt.EventQueue$1.run(Unknown Source)
	at java.awt.EventQueue$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

[Fubarable]

Your code has many problems not the least of which is over use of statics variables, but your problem is your calling the chooser from within paintComponent before any colors have been chosen and before the chooser has been rendered. You should re-think your design. Perhaps set your color first to a default value, then give the Panel class a Color field and a public setColor(Color color) method. Then have the other class, the one with the color chooser set the Panel's color once a color has been chosen.

[spec8320]

Fubarable as you can see, I'm new in this and I don't understand at all how its work, so if you can give me some advice, or link or simply repair it I will be really glad for you.

[Fubarable]

Again your code has many mistakes, in fact I see that you're trying to set the color of another component from within a paint/paintComponent method:

   public void paintComponent(Graphics g) {
      Graphics2D g2 = (Graphics2D) g;
      g2.clearRect(0, 0, 1000, 700);
      Okno.przycisk_colorchooser.setBounds(30, 30, 100, 100); //You shouldn't be setting bounds 
      Color wybor = Okno.Chooser.getColor();  // or colors of other components in paintComponent
      Okno.przycisk_colorchooser.setBackground(wybor);
      g2.setPaint(Color.black);
      repaint();  // you should never call repaint from within a paintComponent method.
   }

and so that code shouldn't even be in that method. I think that you should start at the beginning, going through the basic Java tutorials here:

Trail: Learning the Java Language (The Java™ Tutorials)

Then when you've got a solid footing in Java, look over the Swing tutorials which you can find here:

Lesson: Using Swing Components (The Java™ Tutorials > Creating a GUI With JFC/Swing)