GameOfLife.java

import java.util.Scanner;   // for user input

public class GameOfLife {

    /**
    *   Program: GameOfLife.java
    *   Purpose: Implement Conway's Game of Life, using examples
    *   Creator: Chris Clarke
    *   Created: 02.10.2012
    *   Modified: 19.10.2012
    */

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n=0;
        System.out.print("Example 1, 2, 3 or 4? ");
        try {
            n = Integer.parseInt(scan.nextLine());
        } catch (NumberFormatException e) {
            System.out.println("Must be 1, 2, 3 or 4!");
            System.exit(1);
        }
        clearBoard();
        setUpExample(n);
        printBoard();
        while (true) {
            System.out.print("Press Enter to continue (x to exit)...");
            String s = scan.nextLine();
            if (s.toLowerCase().startsWith("x")) break;
            board = applyRules();
            printBoard();
        } // while
    } // main

    public static void clearBoard() {
        for (int i = 0; i < NUMBER_OF_ROWS; i++) {
            for (int j = 0; j < NUMBER_OF_COLUMNS; j++) {
                board[i][j] = false;
            } // for j
        } // for i
    } // clearBoard

    public static void example1() {
        board[2][2] = true;
        board[2][3] = true;
        board[3][2] = true;
        board[3][3] = true;
        board[5][10] = true;
        board[5][11] = true;
        board[5][12] = true;
        board[4][9] = true;
        board[4][10] = true;
        board[4][11] = true;
        board[8][20] = true;
        board[8][21] = true;
        board[9][20] = true;
        board[9][21] = true;
        board[10][22] = true;
        board[10][23] = true;
        board[11][22] = true;
        board[11][23] = true;
    } // example1

    public static void example2() {
        board[3][12] = true;
        board[3][13] = true;
        board[3][14] = true;
        board[4][11] = true;
        board[4][12] = true;
        board[4][13] = true;
        board[7][2] = true;
        board[7][3] = true;
        board[8][1] = true;
        board[8][4] = true;
        board[9][2] = true;
        board[9][3] = true;
        board[10][10] = true;
        board[10][11] = true;
        board[10][12] = true;
    } // example2

    public static void example3() {
        board[5][5] = true;
        board[5][6] = true;
        board[5][7] = true;
        board[5][9] = true;
        board[6][5] = true;
        board[7][8] = true;
        board[7][9] = true;
        board[8][6] = true;
        board[8][7] = true;
        board[8][9] = true;
        board[9][5] = true;
        board[9][7] = true;
        board[9][9] = true;
    } // example3

    public static void example4() {
        for (int i=2; i<=4; i++) {
            board[8][i] = true;
        }
        board[9][4] = true;
        board[10][2] = true;
    } // example4

    public static void setUpExample(int x) {
        switch (x) {
            case 1  :   example1(); break;
            case 2  :   example2(); break;
            case 3  :   example3(); break;
            case 4  :   example4(); break;
            default :   System.out.println("Error");
                    System.exit(1);
        } // switch
    } // setUpExample

    public static void printBoard() {
        for (int i=0; i<20; i++) System.out.println();  // make space

        for (int i = 0; i < NUMBER_OF_ROWS; i++) {
            for (int j = 0; j < NUMBER_OF_COLUMNS; j++) {
                if (board[i][j]) {
                    System.out.print("*");
                } else {
                    System.out.print(".");
                } // if
            } // for j
            System.out.println();
        } // for i
    } // printBoard

    public static int countLiveNeighbours(int i, int j) {
        int n = 0;

        if (i>0) {              // up
            if (board[i-1][j]) {
                n++;
            }
            if (j>0) {          // up & left
                if (board[i-1][j-1]) {
                    n++;
                }
            }
            if (j < NUMBER_OF_COLUMNS-1) {  // up & right
                if (board[i-1][j+1]) {
                    n++;
                }
            }
        }

        if (i < NUMBER_OF_ROWS-1) {     // down
            if (board[i+1][j]) {
                n++;
            }
            if (j>0) {          // down & left
                if (board[i+1][j-1]) {
                    n++;
                }
            }
            if (j < NUMBER_OF_COLUMNS-1) {  // down & right
                if (board[i+1][j+1]) {
                    n++;
                }
            }
        }

        if (j>0) {              // left
            if (board[i][j-1]) {
                n++;
            }
        }

        if (j < NUMBER_OF_COLUMNS-1) {      // right
            if (board[i][j+1]) {
                n++;
            }
        }

        return n;
    } // countLiveNeighbours

    public static boolean isAlive(boolean alive, int n) {
        if (alive) {
            if (n<2) {
                return false;
            } else if (n<=3) {
                return true;
            } else {
                return false;
            }
        } else {
            if (n==3) {
                return true;
            } else {
                return false;
            }
        } // if (alive)
    } // isAlive

    public static boolean[][] applyRules() {
        boolean[][] newBoard = new boolean[ NUMBER_OF_ROWS][ NUMBER_OF_COLUMNS];
        for (int i = 0; i < NUMBER_OF_ROWS; i++) {
            for (int j = 0; j < NUMBER_OF_COLUMNS; j++) {
                int n = countLiveNeighbours(i, j);
                newBoard[i][j] = isAlive(board[i][j], n);
            } // for j
        } // for i

        return newBoard;
    } // applyRules

    static final int NUMBER_OF_ROWS = 22;
    static final int NUMBER_OF_COLUMNS = 27;
    static boolean[][] board = new boolean[ NUMBER_OF_ROWS][ NUMBER_OF_COLUMNS];
} // class