java.lang.NullPointerException | try to get value from another class array

Question

I'm working on a game with a friend right now and I got some problems by implementing a save feature to the game. But I keep getting NullPointerExceptions every time I try to get a specific value from an array.

SaveGame.java:

public class SaveGame {
    static int newValue;
    //unnecessary stuff hidden...

    public static void SaveGame() {
        //The class which uses getTokenPositionList()
    }

    //Saves the positioning of the tokens within a String
    static String getTokenPositionList() {
        String tokenPositionList = "";
        for (int row = 0; row < 10; row++) {
            for (int col = 0; col < 10; col++) {
                tokenPositionList = tokenPositionList + KodeKs.KodeKsData.getKodeKsData(row, col);
            }
        }
        return tokenPositionList;
    }  // end getTokenPositionList()
}

KodeKs.java:

public class KodeKs extends JPanel {
    public KodeKs() {
        //lots of unessecary stuff hidden
        public static class KodeKsData {
            public static int[][] board;
            public KodeKsData() {
                board = new int[10][10];
                setUpGame();
            }
            public static int getKodeKsData(int row, int col) {
                return board[row][col];

            }
            //more stuff hidden
        }
    }
}

And this is the error-code I get when running this stuff:

> Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
>     at KodeKs$KodeKsData.getKodeKsData(KodeKs.java:597)     at
> SaveGame.getTokenPositionList(SaveGame.java:61)     at
> SaveGame.SaveGame(SaveGame.java:33)     at
> KodeKsToolBar$3.actionPerformed(KodeKsToolBar.java:48)  at
> javax.swing.AbstractButton.fireActionPerformed(Unknown Source)  at
> javax.swing.AbstractButton$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.dispatchEventImpl(Unknown Source)   at
> java.awt.EventQueue.access$200(Unknown Source)  at
> java.awt.EventQueue$3.run(Unknown Source)   at
> java.awt.EventQueue$3.run(Unknown Source)   at
> java.security.AccessController.doPrivileged(Native Method)  at
> java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown
> Source)     at
> java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown
> Source)     at java.awt.EventQueue$4.run(Unknown Source)    at
> java.awt.EventQueue$4.run(Unknown Source)   at
> java.security.AccessController.doPrivileged(Native Method)  at
> java.security.ProtectionDomain$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)

What line is 597 in KodeKsData?

Justin Jasmann
– Justin Jasmann

2013-10-16 02:17:46 +00:00
Commented Oct 16, 2013 at 2:17 — Justin Jasmann
– Justin Jasmann, Commented Oct 16, 2013 at 2:17

Iłya Bursov · Accepted Answer · 2013-10-16 02:52:02Z

1

You have declared board array, but init it only in constructor, which is not called for static method call, declare it like:

public static int[][] board = new int[10][10];

also, consider - during static function call method "setupGame" is not called, is it expected?

edited Oct 16, 2013 at 2:52

answered Oct 16, 2013 at 2:20

Iłya Bursov

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1 Comment

Jeroen Vannevel Over a year ago

Or use the static initializer static { board = new int[10][10]; }

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