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Thread: Null Pointer Exception

  1. #1
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    Default Null Pointer Exception

    Well I just started coding in Java with seperate files and classes, and I believe this is an organization problem;

    SOOOO I have 3 files:
    All have 1 class and methods.

    Here's one
    public class runprogram {
     
    public static void main(String[] args) {
     
    runprogram run = new runprogram();
    run.runprogram();
    }
    public void runprogram(){
    GetDataMethods f = new GetDataMethods();
    Cell cell = new Cell();
    cell.assignvalues();
    System.out.println(cell.cellarray[4].value);
    }
    }
     
     
    }

    Here's the other
    public class Cell {
    int value;
    int xloc;
    int yloc;
    int possiblevalues[];
    Cell[] cellarray = new Cell[81];
    //Prints out values of Cell
    public void assignvalues(){
    	GetDataMethods g = new GetDataMethods();
    	Cell one = new Cell();
    		int currentnumber = 0;
    		for (int row = 0; row <= 8; row++)
    		{
    		     for(int col = 0; col <= 8; col++)
    		     {
    		    	 int x = 0;
    		    	 currentnumber = g.newboard[row][col];
    		    	  one.cellarray[x] = new Cell();
    		         System.out.println(one.cellarray[x].value=currentnumber);
    		         x++;
     
    		     	}
    		     }
    		}
    	 }

    And here's my last one
    This one has alot more methods I posted only the relevant part of it.


    public class GetDataMethods {
    	int emptycells[];
    	//The Sudoku
        int[][] newboard = {{0,0,0,0,6,0,0,0,9},
                            {0,6,0,0,0,0,3,0,1},
                            {2,0,0,0,0,9,8,0,0},
                            {1,9,6,0,0,2,0,0,8},
                            {0,0,0,3,0,8,0,0,0},
                            {8,0,0,9,0,0,1,7,5},
                            {0,0,1,7,0,0,0,0,4},
                            {6,0,7,0,0,0,0,8,0},
                            {4,0,0,0,9,0,0,0,0}};
    //The Possible Values
    public int possibilityboard[][];
    int value;
    }
    That's all dandy, however, I get a null pointer exception error if I try using the method assignvalues from Cell class, the file Cell, out side of file Cel.
    Any idea what I'm doing wrong?

    Basically, why do I get a nullpointer in runprogram?
    Last edited by MysticDeath; October 23rd, 2009 at 03:00 PM.


  2. #2
    Administrator copeg's Avatar
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    Default Re: Null Pointer Exception

    Not sure if this is the exact solution, but in the loops within assignvalues(), you are always assigning a value to one.cellarray[0] (you reset x to zero with every look). So if you ever try to access one of the other memebers of the cellarray array - such as you are in runprogram - you will get a null pointer exception. Try moving int x = 0 outside the for loops
    Last edited by copeg; October 23rd, 2009 at 04:31 PM.

  3. #3
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    Default Re: Null Pointer Exception

    Never mind I solved it;
    Remove the decleration of Cell in the file were the objects are created, then simply in the runprogram declare a new instance of the class, and call the method assignvalues.
    Last edited by MysticDeath; October 24th, 2009 at 03:11 PM.

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