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

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

Answer 2

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!