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Thread: Problem with CardLayout

  1. #1
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    Default Problem with CardLayout

    Hey guys I'm trying to make a GUI which can navigate through JTextAreas when a Next or Previous button is pushed. I'm using CardLayout to switch between the JTextArea. I can get the program to compile but every time I push the next or previous button I always get a NullPointerException. I don't know why the CardLayout object is null in the next and previous methods and its making me really confused. Any help is appreciated thx guys!

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

    /**
    *The AsciiCanvas class creates the text area for the ascii animation
    */

    public class AsciiCanvas extends JTextArea
    {
    private JPanel jp1;
    private JPanel jp2;
    private JPanel jp3;
    private JPanel jp4;
    private JPanel jp5;
    private JPanel jp6;
    private JPanel jp7;
    private JPanel jp8;
    private JPanel jp9;
    private JPanel jp10;
    private JTextArea text1;
    private JTextArea text2;
    private JTextArea text3;
    private JTextArea text4;
    private JTextArea text5;
    private JTextArea text6;
    private JTextArea text7;
    private JTextArea text8;
    private JTextArea text9;
    private JTextArea text10;

    private JPanel cardPanel;
    private CardLayout cl;
    private int currentCard = 1;

    private JFileChooser fc;


    public AsciiCanvas()
    {
    Font mono = new Font("Monospaced", Font.PLAIN, 12);

    cardPanel = new JPanel();
    CardLayout cl = new CardLayout();
    cardPanel.setLayout(cl);


    JTextArea text1 = new JTextArea();
    JTextArea text2 = new JTextArea();
    JTextArea text3 = new JTextArea();
    JTextArea text4 = new JTextArea();
    JTextArea text5 = new JTextArea();
    JTextArea text6 = new JTextArea();
    JTextArea text7 = new JTextArea();
    JTextArea text8 = new JTextArea();
    JTextArea text9 = new JTextArea();
    JTextArea text10 = new JTextArea();



    JPanel jp1 = new JPanel();
    JPanel jp2 = new JPanel();
    JPanel jp3 = new JPanel();
    JPanel jp4 = new JPanel();
    JPanel jp5 = new JPanel();
    JPanel jp6 = new JPanel();
    JPanel jp7 = new JPanel();
    JPanel jp8 = new JPanel();
    JPanel jp9 = new JPanel();
    JPanel jp10 = new JPanel();

    jp1.add(text1);
    jp2.add(text2);
    jp3.add(text3);
    jp4.add(text4);
    jp5.add(text5);
    jp6.add(text6);
    jp7.add(text7);
    jp8.add(text8);
    jp9.add(text9);
    jp10.add(text10);

    cardPanel.add(jp1, "1");
    cardPanel.add(jp2, "2");
    cardPanel.add(jp3, "3");
    cardPanel.add(jp4, "4");
    cardPanel.add(jp5, "5");
    cardPanel.add(jp6, "6");
    cardPanel.add(jp7, "7");
    cardPanel.add(jp8, "8");
    cardPanel.add(jp9, "9");
    cardPanel.add(jp10, "10");

    setBorder(BorderFactory.createTitledBorder("Animat ion here"));
    setFont(mono);

    fc = new JFileChooser();
    }


    public void Next()
    {
    if(currentCard < 10)
    {

    currentCard +=1;
    cl.show(cardPanel, "" + (currentCard));
    }


    }

    public void Previous()
    {
    if(currentCard > 1)
    {
    currentCard -= 1;
    cl.show(cardPanel, "" + (currentCard));


    }
    }




    Error Message*******

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at AsciiCanvas.Next(AsciiCanvas.java:108)
    at AsciiArt$btnOneListener.actionPerformed(AsciiArt.j ava:72)
    at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed (AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed (DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultB uttonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.jav a:6504)
    at javax.swing.JComponent.processMouseEvent(JComponen t.java:3321)
    at java.awt.Component.processEvent(Component.java:626 9)
    at java.awt.Container.processEvent(Container.java:222 9)
    at java.awt.Component.dispatchEventImpl(Component.jav a:4860)
    at java.awt.Container.dispatchEventImpl(Container.jav a:2287)
    at java.awt.Component.dispatchEvent(Component.java:46 86)
    at java.awt.LightweightDispatcher.retargetMouseEvent( Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(C ontainer.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Conta iner.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.jav a:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2713 )
    at java.awt.Component.dispatchEvent(Component.java:46 86)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.j ava:707)
    at java.awt.EventQueue.access$000(EventQueue.java:101 )
    at java.awt.EventQueue$3.run(EventQueue.java:666)
    at java.awt.EventQueue$3.run(EventQueue.java:664)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPri vilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPri vilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:680)
    at java.awt.EventQueue$4.run(EventQueue.java:678)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPri vilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java: 677)
    at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:128)
    at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:117)
    at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:113)
    at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:105)
    at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:90)


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Problem with CardLayout

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at AsciiCanvas.Next(AsciiCanvas.java:108)
    There is a variable with a null value at line 108. Look at that line, find the null variable and backtrack in the code to see why that variable does not have a valid value.
    Use println to print out the variables' values to see which variable is null.

    Please Edit your post and wrap your code with[code=java]<YOUR CODE HERE>[/code] to get highlighting
    If you don't understand my answer, don't ignore it, ask a question.

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