java.lang.NullPointerException Error

Hello All,

I know this is a common error with a simple fix but I can't figure out why that Null Pointer Exception error is happening in my code.

Sometimes a second eye helps so if anyone could just look over the following code it would be greatly appreciated :(happy):

Code:

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



public class Lab9Init extends JApplet implements ActionListener
{
       
        private JButton btnAdd, btnClear;
        private JTextField tfTotal, tfQuantity;
        private JLabel lblQuantity, lblTotal;
        private JList lstDisplay;
        private DefaultListModel dlmDisplay;
        private JScrollPane scrollPane;
       
        private ButtonGroup grpGames;
        private JRadioButton radBattlefield3, radSkyrim, radMassEffect;
       

        public void init() {
                        do_gui();
        }//end main
       
        private void do_gui()
        {
                Container c = this.getContentPane();
                c.setLayout(null);
               
                this.setSize(290, 250);
               
                btnAdd = new JButton("Add");
                btnAdd.setBounds(120,190,70,30);
                c.add(btnAdd);
                btnAdd.addActionListener(this);
                this.getRootPane().setDefaultButton(btnAdd);
               
                btnClear = new JButton("Clear");
                btnClear.setBounds(200,190,70,30);
                c.add(btnClear);
                btnClear.addActionListener(this);
               
               
                tfTotal = new JTextField();
                tfTotal.setEditable(false);
                tfTotal.setBounds(180,140,60,30);
                c.add(tfTotal);
                tfTotal.setHorizontalAlignment(SwingConstants.CENTER);
               
                tfQuantity = new JTextField();
                tfQuantity.setBounds(70,190,40,30);
                c.add(tfQuantity);
               
                lblTotal = new JLabel();
                lblTotal.setBounds(110,140,60,30);
                c.add(lblTotal);
                lblTotal.setHorizontalAlignment(SwingConstants.RIGHT);
               
                lblQuantity = new JLabel();
                lblQuantity.setBounds(10, 190, 50, 30);
                c.add(lblQuantity);
                lblQuantity.setHorizontalAlignment(SwingConstants.RIGHT);
               
                grpGames.add(radBattlefield3);
                grpGames.add(radSkyrim);
                grpGames.add(radMassEffect);
               
               
                radBattlefield3 = new JRadioButton(String.format("Battlefield 3 $.2f", COrder.PBATTLEFIELD3), true);
                radBattlefield3.setBounds(10,20,110,30);
                c.add(radBattlefield3);
               
                radMassEffect = new JRadioButton(String.format("Mass Effect $.2f", COrder.PMASSEFFECT));
                radMassEffect.setBounds(10, 60,110,30);
                c.add(radMassEffect);
               
                radSkyrim = new JRadioButton(String.format("Skyrim $.2f",COrder.PSKYRIM));
                radSkyrim.setBounds(10, 100, 100, 30);
                c.add(radSkyrim);
               
               
                dlmDisplay = new DefaultListModel();
                lstDisplay = new JList(dlmDisplay);
               
                scrollPane = new JScrollPane(lstDisplay,
                                JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                                JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);       
                scrollPane.setBounds(120, 10, 150, 120);
                c.add(scrollPane);
                               
        }//end doGui
       
        public void actionPerformed(ActionEvent e)
        {
                if (e.getSource()==btnAdd)do_Add();
                else if (e.getSource()==btnClear)do_Clear();
                else
                        System.exit(0);
               
                       
        }//end actionPerformed
       
private void do_Add(){
dlmDisplay.addElement("Hello World");
}

private void do_Clear(){
dlmDisplay.clear();       
       
}

}//end class

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Critical information: which line throws the NPE?

Ooops thought I included that, sorry.

It's 64 and 22.

Quote:

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Originally Posted by rockintyler

Ooops thought I included that, sorry.

It's 64 and 22.

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OK, on line 64 -- check the variables that could possibly be null (there's only one possibility) . Now check to see if you initialized it before using it.

Thanks for the response.

I forgot to initialize the button group so thanks for giving me an idea what to think about. I'm in a beginning Java course and this is the assignment I'm working on for it.

Quote:

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Originally Posted by rockintyler

Thanks for the response.

I forgot to initialize the button group so thanks for giving me an idea what to think about. I'm in a beginning Java course and this is the assignment I'm working on for it.

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You're welcome. There's more null problems though. Again, look at when you're initializing your variables with regards to when you're adding them to the button group.