Game of Life, method doesnt work

问题

I'm not sure if I am turning mad but this is what my problem is:

I programm Game of Life and have a "countalive" method which counts how many surrounding fields are alive.

    public int countalive(Board board, int yaxis, int xaxis) { //defekt

    int living = board.getfields()[yaxis - 1][xaxis - 1] + board.getfields()[yaxis - 1][xaxis] + board.getfields()[yaxis - 1][xaxis + 1] + 
            board.getfields()[yaxis][xaxis - 1] + board.getfields()[yaxis][xaxis + 1] + board.getfields()[yaxis + 1][xaxis - 1] +
            board.getfields()[yaxis + 1][xaxis] + board.getfields()[yaxis + 1][xaxis + 1];
    return living;
}

This method seems to work perfectly fine. But when i do this

 public Board evolve(Board board) {
    Board tmpboard = board;
    System.out.println(countalive(board, 1, 3));  //I test with this. SHOULD AND IS 2!!
    int aliveneighbours = 0;
    for (int i = 1; i < board.getfields().length - 1; i++) {
        for (int j = 1; j < board.getfields()[i].length - 1; j++) {
            System.out.print("i = " +i);
            System.out.print("j = " +j +" ");
            aliveneighbours = countalive(board, i, j);
            System.out.println(aliveneighbours);

            if (aliveneighbours == 3) {
                tmpboard.getfields()[i][j] = 1;
            } else if (aliveneighbours < 2 || aliveneighbours > 3) {
                tmpboard.getfields()[i][j] = 0;
            }
        }
        System.out.println("");
    }
    return tmpboard;
}

I get this in the console:

2
i = 1j = 1 1
i = 1j = 2 1
i = 1j = 3 1
i = 1j = 4 1
i = 1j = 5 0
...

even though i = 1 and j =3 should be 2 and not 1. As you see the the method countalive(board, 1, 3) works but in the for loop it gives me a different result. Can you find my error?

回答1:

You are changing the aliveness of cells during the iteration. What you need to do is to have a separate array for the next generation and update that based on this generation, then swap them once you have completely looked at the current generation.

来源：https://stackoverflow.com/questions/25832120/game-of-life-method-doesnt-work