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Thread: Game of life counter not working

  1. #1
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    Question Game of life counter not working

    I'm running into an issue where my method that should count neighbors gets an array out of bounds error. I have tried a couple of things to fix it, but they've all failed. Any suggestions?

    public static int neighbors(boolean[][] matrix, int row, int col) {
    		int count = 0;
     
    		if (matrix[row][col]) {
    			count++;
    		}
    		if (matrix[row - 1][col]) {
    			count++;
    		}
    		if (matrix[row + 1][col]) {
    			count++;
    		}
    		if (matrix[row][col - 1]) {
    			count++;
    		}
    		if (matrix[row][col + 1]) {
    			count++;
    		}
    		if (matrix[row + 1][col + 1]) {
    			count++;
    		}
    		if (matrix[row + -1][col - 1]) {
    			count++;
    		}
    		if (matrix[row - 1][col + 1]) {
    			count++;
    		}
    		if (matrix[row + 1][col - 1]) {
    			count++;
    		}
     
     
    		return count;
     
    	}

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Game of life counter not working

    gets an array out of bounds error.
    Can you copy the full text of the error message and paste it here? It should show the line number of the statement and the value of the index.

    Also post the code that shows the dimensions of the array.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Game of life counter not working

    This is the error:
    "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8
    at Life.neighbors(Life.java:51)
    at Life.main(Life.java:29)"

    The matrix is determined by the user input:
    boolean[][] matrix = new boolean[userRows][userColumns];

  4. #4
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    Default Re: Game of life counter not working

    "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8
    at Life.neighbors(Life.java:51)
    The statement at line 51 used an index (8) that was past the end of the array. The array had less than 9 elements.
    What statement is at line 51? What variable had the invalid value?
    Remember that the valid indexes for an array range in value from 0 to the size-1. An index of 8 requires at least 9 elements in the array.

    The code that checks the slots at the boundaries (top, right, bottom and left) of the rectangle must be careful to not go over the boundary.
    If you don't understand my answer, don't ignore it, ask a question.

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