Game of Life malfunctioning java

Question

Me and my research partner at school have trouble with our assignment about Conway's Game Of Life.

Our program is malfunctioning and looking at the code I see nothing wrong with our code and when looking at the error message and even the debug function I still cannot find out why it's malfunctioning.

The error message is as follows:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 36 at nl.ru.ai.exercise6.tryout.nextGeneration(tryout.java:84) at nl.ru.ai.exercise6.tryout.evolve(tryout.java:138) at nl.ru.ai.exercise6.tryout.main(tryout.java:27)

When using the debug function it says that there is a problem in line 84, nextUniverse[i][j] = Cell.DEAD; Can somebody maybe please look at our code and specify why our code doesn't work at that particular point. I know our code is very long, but we're still

public static void main(String[] args) throws IOException {
    System.out.print("Enter input file:");
    Scanner scanner = new Scanner(System.in);
    String fileName = scanner.nextLine();
    System.out.print("For how many generations do you want your program to run?");
    for (int row = 0; row < 40; row++) {
        for (int col = 1; col < 60; col++) {
    int numberEvolve = scanner.nextInt();
    Cell[][] universe = readUniverseFile(fileName);
    showUniverse(universe);
    evolve(universe, numberEvolve, 2, fileName, row, col);}}
}

static Cell[][] readUniverseFile(String fileName) throws IOException {
    Cell[][] universe = new Cell[40][60];
    try {
        BufferedReader in = new BufferedReader(new FileReader(fileName));

        try {
            for (int i = 0; i <= 39; i++) {
                String line = in.readLine();
                if (line == null) {
                    throw new IllegalArgumentException("Input file does not contain 40 lines");
                }
                if (line.length() != 60) {
                    throw new IllegalArgumentException(
                            "Input file contains a line which doesn't contain 60 characters");
                }
                for (int j = 0; j < 60; j++) {
                    if (line.charAt(j) == '*') {
                        universe[i][j] = Cell.LIVE;
                    } else if (line.charAt(j) == '.') {
                        universe[i][j] = Cell.DEAD;
                    } else if (line.charAt(j) != '.') {
                        throw new IllegalArgumentException("Input file contains invalid character");
                    } else if (line.charAt(j) != '*') {
                        throw new IllegalArgumentException("Input file contains invalid character");
                    }

                }
            }
            in.close();
        } catch (FileNotFoundException e) {
            throw new IllegalArgumentException("Input file could not be found");
        }

    } catch (FileNotFoundException e) {
        throw new IllegalArgumentException("Input file could not be found");
    }
    return universe;
}

private static void showUniverse(Cell[][] universe) {
    for (int row = 0; row <= 39; row++) {
        for (int col = 0; col <= 59; col++) {
            updateScreen(row, col, universe[row][col]);
        }
    }
}

private static Cell[][] nextGeneration(Cell[][] universe, String fileName, int row, int col) throws IOException {   
            Cell[][] nextUniverse = new Cell[row][col];
            for (int i = 1; i <= 38; i++) {
                for (int j = 1; j <= 58; j++) {
                    int livingNeighbours = numberLivingNeighbours(universe);
                    if (universe[i][j] == Cell.LIVE) {
                        if (livingNeighbours < 2 || livingNeighbours > 3) {
                            nextUniverse[i][j] = Cell.DEAD;
                        } else {
                            nextUniverse[i][j] = Cell.LIVE;
                        }
                    } else {
                        if (livingNeighbours == 3) {
                            nextUniverse[i][j] = Cell.LIVE;
                        }
                    }

                }
            }
    return nextUniverse;
}

private static int numberLivingNeighbours(Cell[][] universe) {
    int numberLivingNeighbours = 0;
    for (int row = 1; row < 39; row++) {
        for (int col = 1; col < 59; col++) {
            if (universe[row + 1][col] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row + 1][col - 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row + 1][col + 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row][col - 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row][col + 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row - 1][col] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row - 1][col - 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            }
            if (universe[row - 1][col + 1] == Cell.LIVE) {
                numberLivingNeighbours++;
            } else {
                numberLivingNeighbours--;
            }
        }
    }
    return numberLivingNeighbours;
}

private static void evolve(Cell[][] universe, int numberEvolve, int generationTime, String fileName, int row, int col) throws IOException {
    for (int i = 0; i < numberEvolve; i++) {
        showUniverse(universe);
        sleep(generationTime);
        universe = nextGeneration(universe, fileName, row , col);
    }
}

2

Really, a programming geniuses? – TDG Oct 21 '16 at 07:42

score 0 · Answer 1 · answered Oct 21 '16 at 07:52

for (int row = 0; row < 40; row++) {
    for (int col = 1; col < 60; col++) {
      int numberEvolve = scanner.nextInt();
      Cell[][] universe = readUniverseFile(fileName);
      showUniverse(universe);
      evolve(universe, numberEvolve, 2, fileName, row, col);
    }
}

Here you call evolve() the first time with row = 0 and col = 1 These values are passed to nextGeneration() there:

universe = nextGeneration(universe, fileName, row , col);

There you call Cell[][] nextUniverse = new Cell[row][col]; (Remember, it's 0 and 1)

Then you start an iteration with fixed values i and j:

for (int i = 1; i <= 38; i++) {
  for (int j = 1; j <= 58; j++) {

And as soon as you call nextUniverse[i][j] = Cell.DEAD; with values i/j greater than 0/1 you get an ArrayOutOfBoundsException, cause your array size depends on the row/col input, but your iteration with i and j goes up to 38/58.

Happy fixing :)

score 0 · Answer 2 · answered Oct 21 '16 at 08:06

On the first iteration of your for loops in the main method, row is 0 and col is 1

22 for (int row = 0; row < 40; row++) {
23     for (int col = 1; col < 60; col++) {
24         int numberEvolve = scanner.nextInt();
25         Cell[][] universe = readUniverseFile(fileName);
26         showUniverse(universe);
           // On the first iteration, row is 0 and col is 1 when calling evolve() method
27         evolve(universe, numberEvolve, 2, fileName, row, col);}}

After which, nextGeneration() is called with the variables row = 0 and col = 1

134 private static void evolve(Cell[][] universe, int numberEvolve, int generationTime, String fileName, int row, int col) throws IOException {
135     for (int i = 0; i < numberEvolve; i++) {
136         showUniverse(universe);
137         sleep(generationTime);
            // In the method nextGeneration(), row is 0 and col is 1
138         universe = nextGeneration(universe, fileName, row , col);
139     }
140 }

Next, you create an object called nextUniverse with the size of Cell[0][1]
However, you tried to access nextUniverse[38][58] in line 84 and hence a NullPointerException is thrown.

Basically, you cannot access nextUniverse[38][58] as the size of nextUniverse is [0][1]

77 private static Cell[][] nextGeneration(Cell[][] universe, String fileName, int row, int col) throws IOException {   
       // nextUniverse has a size of [0][1]
78     Cell[][] nextUniverse = new Cell[row][col];
79     for (int i = 1; i <= 38; i++) {
80         for (int j = 1; j <= 58; j++) {
81             int livingNeighbours = numberLivingNeighbours(universe);
82             if (universe[i][j] == Cell.LIVE) {
83                 if (livingNeighbours < 2 || livingNeighbours > 3) {
                       // Attempted to store values into nextUniverse[38][58]
84                     nextUniverse[i][j] = Cell.DEAD;

Game of Life malfunctioning java

2 Answers2