Exception in thread "AWT-EventQueue-0"

[jaszczomp]

Hello!
I have a problem with my java application.

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

public class main
{
	public static Pole text = new Pole("0");
	public static Przycisk plus = new Przycisk("+");
	public static Przycisk minus = new Przycisk("-");
	public static Przycisk dimen = new Przycisk("/");
	public static Przycisk multi = new Przycisk("*");
	public static Przycisk is = new Przycisk("=");
	
	public int l[];
	public int i = 0;
	public int w = 0;
	
	public static void main(String[] args)
	{
		Okno calc = new Okno("Kalkulator");
		
		Panel p1 = new Panel();
		Panel p2 = new Panel();
		Panel p3 = new Panel();
		
		calc.add(p1);
		calc.add(p2);
		calc.add(p3);
		
		Akcja dodaj = new Akcja_p();
		Akcja odejmij = new Akcja_o();
		Akcja mnoz = new Akcja_m();
		Akcja dziel = new Akcja_d();
		Akcja wynik = new Akcja_w();
		
		plus.addActionListener(dodaj);
		minus.addActionListener(odejmij);
		dimen.addActionListener(dziel);
		multi.addActionListener(mnoz);
		is.addActionListener(wynik);
		
		p1.add(text);
		p2.add(plus);
		p2.add(minus);
		p2.add(dimen);
		p2.add(multi);
		p3.add(is);
		
		calc.setVisible(true);
	}
}

class Okno extends JFrame
{
	Okno(String title)
	{
		setTitle(title);
		setSize(240, 320);
		
		setLayout(new GridLayout(3,1));
	}
}

class Panel extends JPanel
{
	Panel()
	{
		
	}
}

class Przycisk extends JButton
{
	Przycisk(String text)
	{
		setText(text);
	}
}

class Pole extends JTextField
{
	Pole(String def)
	{
		setColumns(15);
		setText(def);
	}
}

class Akcja implements ActionListener
{
	main m = new main();

	public void actionPerformed(ActionEvent e)
	{
		
	}
}

class Akcja_p extends Akcja
{
	public void actionPerformed(ActionEvent e)
	{
		m.l[m.i] = Integer.parseInt(main.text.getText());
		
		m.w = m.w + m.l[m.i];
		
		main.text.setText(Integer.toString(m.w));
		
		m.i++;
	}
}

class Akcja_o extends Akcja
{
	public void actionPerformed(ActionEvent e)
	{
		
	}
}

class Akcja_m extends Akcja
{
	public void actionPerformed(ActionEvent e)
	{
		
	}
}

class Akcja_d extends Akcja
{
	public void actionPerformed(ActionEvent e)
	{
		
	}
}

class Akcja_w extends Akcja
{
	public void actionPerformed(ActionEvent e)
	{
		main.text.setText(Integer.toString(m.w));
	}
}

After "compiling" this code, and launching app, i get following exception in console output:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Akcja_p.actionPerformed(main.java:104)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
	at java.awt.Component.processMouseEvent(Unknown Source)
	at javax.swing.JComponent.processMouseEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(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)

I haven't any idea, what mean this exception, i cannot see any bugs in my app. I'm still learning Java.

[Norm]

at Akcja_p.actionPerformed(main.java:104)

Look at line 104 in your program.
Which object reference on that line is null?
Then figure out where it should be set to some value and set it.
If you don't see which is null, add a System.out.println() for each object reference in line 104.
For example if the statement is: a.b.c(x) , you need to see if a or b is null:
System.out.println("a=" + a + ", b=" + b);

[jaszczomp]

when i add system.out.blah.blah, i don't get any values in console output :/

[Norm]

Then your code where the println() are located is NOT executing.
Add more println()s so you see where the code is executing. Keep adding them until you see output on the console.