Exception in thread "main" java.lang.NullPointerException

[Legaly]

Hello, I really hopeless and I feel like this is my last chance to fix that, before I will have to send this to my teacher.
I'm getting this error:
Exception in thread "main" java.lang.NullPointerException
at ui.PanelBatohu.<init>(PanelBatohu.java:33)
at ui.Gui.init(Gui.java:107)
at ui.Gui.<init>(Gui.java:68)
at main.Start.main(Start.java:25)

Legend: Doing graphic interface for this one little java game.
Batoh= Bag(container in game)
zaregistruj pozorovatele(register observer)


first error line is:

[30] public PanelBatohu(Batoh batoh) {
[31] super();
[32] this.batoh = batoh;
[33] batoh.zaregistrujPozorovatele(this);
[34] this.aktualizuj(batoh);
[35]
[36] this.setBorder(BorderFactory.createTitledBorder("V ěci v batohu:"));
[37] this.setVisible(true);
}


second error line is:


[107]panelBatohu = new PanelBatohu(hra.getBatoh());
[108] hlavniOknoFrame.add(panelBatohu, BorderLayout.WEST);[LIST=1]


third error line:

[65]public Gui(Hra hra) {
[66] this.hra = hra;
[67] initMenu();
[68] init();

fourth error line:


[23]public static void main(String[] args) {
[24] if (args.length == 0) {
[25] Gui grafika = new Gui(new Hra());

[dswastik]

You get nullpointerexception when you are calling a method of an object, but the object is holding a null reference, i.e. it has not been initialized with a valid reference. So without looking at your complete code, it's to know what's going wrong.

[Legaly]

Hey, thanks for reaction:)
here's whole code of that class:

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package ui;

import java.net.URL;
import javax.swing.*;
import logika.HerniPlan;
import logika.Batoh;
import logika.Prostor;
import util.ObserverZmenyBatohu;

/**
* Instance třídy PanelBatohu představují panel batohu.
*
* @author
*/
public class PanelBatohu extends JPanel implements ObserverZmenyBatohu {

private Batoh batoh;
private Icon logoIcon;
private String[] oddeleneVeci;

/**
* Konstruktor panelu batohu.
*
* @param inventar logika
*/
public PanelBatohu(Batoh batoh) {
super();
this.batoh = batoh;
batoh.zaregistrujPozorovatele(this);
this.aktualizuj(batoh);

this.setBorder(BorderFactory.createTitledBorder("V ěci v batohu:"));
this.setVisible(true);
}

/**
* Metoda zaregistruje pozorovatele.
*
* @param inventar logika
*/
public void nastaveniBatohu(Batoh batoh) {
this.batoh = batoh;
batoh.zaregistrujPozorovatele(this);
this.aktualizuj(batoh);
}

/**
* Metoda, ve které proběhne aktualizace pozorovatele.
*
* @param aktualniVeci logika
*/
public void aktualizuj(Batoh aktualniVeci) {
this.removeAll();
String veci = aktualniVeci.seznamVeci();
oddeleneVeci = veci.split(" ");

URL umisteniObrazku;
for (int i = 1; i < oddeleneVeci.length; i++) {
umisteniObrazku = this.getClass().getResource("/zdroje/" + oddeleneVeci[i] + ".jpg");
if (umisteniObrazku == null) {
JOptionPane.showMessageDialog(null,
"Soubor s obrázkem nebyl nalezen.",
"Chyba při načítání obrázku", JOptionPane.ERROR_MESSAGE);
} else {
logoIcon = new ImageIcon(umisteniObrazku);
JLabel obrazek = new JLabel(logoIcon);
this.add(obrazek);
}
}
}
}

[Tolls]

Please use [code] tags [/code] (not quote tags) when posting code.

'batoh' is null before even getting into the constructor above.
Your problem lies before that point, probably in the Hra class, since that's where you are getting a Batoh from.

[DarrylBurke]

... but the object is holding a null reference

Variables hold references to objects. Objects don't hold references.

db