Debugging Game of Life, Java

Question

I am trying to reproduce the Game of Life but I've a bug. Cells are born according to design, but they don't die. This confuses me because my strategy for killing cells is the same as for giving birth to them. Here is a segment of the console output, 'x' represents living cells, '-' represents dead cells.

---------
---------
---------
---xx----
----x----
----x----
----xx---
---------
---------

---------
---------
---------
---xx----
----xx---
---xx----
----xx---
---------
---------

---------
---------
---------
---xxx---
----xx---
---xx----
---xxx---
---------
---------

And the relevant piece of code:

public class Life {

final static int WIDTH = 9, HEIGHT = 9;

void start(){

    // scanning input file

    char[][][] board =  new char[WIDTH][HEIGHT][maxAllowedGenerations];
    board = getInitialBoard(initialBoardString, maxAllowedGenerations, board);

    for (int generation = 1; generation < maxAllowedGenerations; generation++){
        for (int y = 0; y < HEIGHT; y++)
            for (int x = 0; x < WIDTH; x++){

                int numberOfNeighbours = getNumberOfNeighbours(x, y, generation - 1 , board);

                if (board[x][y][generation - 1] == '-' && numberOfNeighbours == 3)
                    board[x][y][generation] = 'x';

                else if (board[x][y][generation - 1] == 'x' && numberOfNeighbours < 2)
                    board[x][y][generation] = '-';

                else board[x][y][generation] = board[x][y][generation - 1];


                if (board[x][y][generation] == 'x')
                    ui.place(x, y, LifeUserInterface.ALIVE);
                else
                    ui.place(x, y, LifeUserInterface.DEAD);

                out.print(board[x][y][generation]);
            }
            out.println();
        }
    }
    out.println("Max number of generations reached");
    System.exit(0);             
}

Answer 1

Found two bugs! One of them was impossible for you to spot because I didn't post the code in which it was contained: I am a cell at [x][y][g]. I was considering [x][y][g - 1] to be a neighbour, but that is of course me! I am not my own neighbour.

The other bug was a bit embarrasing actually. I had left out rule number 2... >.<

I also realize I should have posted the rules of the Game of Life instead of assuming that you all know them or that you would bother researching them. It's a bit late now of course, but I'll post them anyway in case you are interested. Also, I really reccomend the wiki article for anyone interested in self-organization.

Rules:

1. Live cells with < 2 live neighbours die, as if by loneliness.
2. Live cells with > 3 live neighbours die, as if by overpopulation.
3. Live cells with 2 || 3 live neighbours survive to the next generation.
4. Dead cells with 3 live neighbours are revived, as if by reproduction.

Thank you for all input!

Answer 2

I agree with @elyashiv - if you change char[][][] board to SomeEnum[][][] board, with SomeEnum defined with values LIVE_CELL and DEAD_CELL that would make things much more readable.

Also, there is no such thing as an empty character ''. An empty String is simply a String with zero length (ie no characters), but '' makes no sense. You could use null, but then you'd have to move away from the primitive char declaration and use Character instead since primitives can't be null.

That said, much better to use enums to represent the data. If you want, you can even make your enum look like this so you can represent your X and empty characters like so:

public enum SomeEnum {
    LIVE_CELL("X"),
    DEAD_CELL("");

    public final displayString;

    SomeEnum(String displayString) {
        this.displayString = displayString;
    }    
}

Then for your display you could reference SomeEnum.LIVE_CELL.displayString in your code