Question

I have two arrays that I create like this:

public int GameBoard[][] = new int[30][14];
public int DirectionMap[][] = new int[30][14];

I then initialize the arrays like this:

for (int i = 0; i < GameBoard.length; i++)
{
    for (int j = 0; j < GameBoard[i].length; j++)
    {
        GameBoard[i][j] = 0;
    }
}

... //Same for DirectionMap

When I run the function:

DirectionMap = AStar(GameBoard);

To render the pathfinding map that my units will follow, DirectionMap is correctly set to the values generated based on my GameBoard. However GameBoard is set to the result as well. When I run the application in Debug Mode within Eclipse, I can see that the ID’s of the two arrays are the same. For some reason they seem to be pointing to the memory space. My AStar function does not modify the GameBoard array at all. The only reference to it is int retVal[][] = GameBoard;

My function prototype is public int[][] AStar(int[][] Board); and it returns the int[][] retVal.

I have no idea why I cannot change the values of DirectionMap without GameBoard following. I have never had any issues like this before.

Any ideas are really appreciated. Thanks for your help.

        public int[][] AStar(int[][] Board)
        {
        int retVal[][] = Board;

        //Initialize All Needed Lists
        int width = retVal.length;
        int height = retVal[0].length;
        int goalX = 0;
        int goalY = 0;
        //List<Node> fieldInfo = new ArrayList<Node>(); 

        Node fieldArray[][] = new Node[width][height];

        for (int i = 0; i < fieldArray.length; i++)
        {
            for (int j = 0; j < fieldArray[i].length; j++)
            {
                fieldArray[i][j] = new Node(i, j);
                if (retVal[i][j] == 2)
                {
                    fieldArray[i][j].setOpen(1);
                    fieldArray[i][j].setDirection(10); //Set as target
                    goalX = i;
                    goalY = j;
                }
                if (retVal[i][j] == 1)
                {
                    fieldArray[i][j].setOpen(0);
                    fieldArray[i][j].setDirection(9); //Set as wall
                }
            }
        }

                    //Add AStar Algorithm Here

        for (int i = 0; i < fieldArray.length; i++)
        {
            for (int j = 0; j < fieldArray[i].length; j++)
            {
                if (fieldArray[i][j].getDirection() == 0)
                {
                    //Occurs when node was never reached
                    int dX = i - goalX;
                    int dY = j - goalY;
                    if (dX < 0)
                        dX = -dX;
                    if (dY < 0)
                        dY = -dY;
                    if (dY > dX)
                        fieldArray[i][j].setDirection(1);
                    else
                    {
                        if (i > goalX)
                            fieldArray[i][j].setDirection(7);
                        if (i < goalX)
                            fieldArray[i][j].setDirection(3);
                    }
                }
            }
        }

        for (int i = 0; i < fieldArray.length; i++)
        {
            for (int j = 0; j < fieldArray[i].length; j++)
            {
                retVal[i][j] = fieldArray[i][j].getDirection();
            }
        }

        return retVal;
    }

Answer 1

Remember when you are passing an object to methods you are actually passing a copy of reference. So when you initialise retVal[][] = Board; you actually point Board using another reference retVal. And you are returning the same reference to DirectionMap. Hence same id’s for Board and DirectionMap. Consider array copy instead.