Question

JAVA TIC TAC TOE - please help me correct my code

Write a program that will allow two players to play a game of TIC TAC TOE.

1. When the program starts, it will display a tic tac toe board as below

|    1       |   2        |   3

|    4       |   5        |   6

                |    7      |   8        |   9

2. The program will assign X to Player 1, and O to Player    The program will ask Player 1, to select a position where they would like to mark.

Player will enter values 1-9.

For Example

When the game starts, if player 1 selects 2. The program will redraw the board with position 2 marked as X.

|    1       |   X        |   3

|    4       |   5        |   6

                |    7      |   8        |   9

                Player 2 enters 6, the boards is redrawn as below

|    1       |   X        |   3

|    4       |   5        | O

                |    7      |   8        |   9

3. The program will alternate moves between Player 1 and Player 2 until the game is tied or won.

If the game is won, display the game winner, and ask the user if they want to play again. If yes, restart the game. If not quit the game.

4. After each move, the board should be drawn to display the position where the move was marked.

5. If a position is marked, X or O, the player is not allowed to select the same position again
6. Winner
   1. Game is won if each row or each column has the same mark.
   2. Game is won if diagonal rows have the same mark.

You must create a class object called board with methods and attributes when implementing this game. All methods should be defined within the class object.

Error message I am getting after first input

Exception in thread "main" java.lang.NullPointerException
   at JavaProgramICards/ticTacToe.Board.checkSpace(Board.java:42)
   at JavaProgramICards/ticTacToe.Main.main(Main.java:27)

package ticTacToe;

public class Board {

   private static char[][] board;

   public void initBoard(char[][] board) {
       System.out.println("New Tic Tac Toe Board \n Good Luck!");
       int a = 1;
       for (int i = 0; i < 3; i++)
           for (int j = 0; j < 3; j++) {
               board[i][j] = (char) (a + '0');
               a++;
           }
   }

  
   public void printBoard(char[][] board) {
       for (int i = 0; i < 3; i++) {
           for (int j = 0; j < 3; j++) {
               System.out.print(" | " + board[i][j]);
           }
           System.out.print(" |\n");
       }

   }

   public boolean checkSpace(int space) {

       if (space > 0 && space <= 9) {
           int i = (space - 1) / 3;
           int j = (space - 1) % 3;

           if (board[i][j] == 'X' || board[i][j] == 'O')
               return false;
           else
               return true;
       }
       return false;

   }

   public void place(int space, char input) {
       int i = (space - 1) / 3;
       int j = (space - 1) % 3;
       board[i][j] = input;
   }

   public boolean isWinner() {

       for (int i = 0; i < 3; i++) {
           if (board[i][0] == board[i][1] && board[i][1] == board[i][2])
               return true;

       }

       for (int j = 0; j < 3; j++) {
           if (board[0][j] == board[1][j] && board[1][j] == board[2][j])
               return true;

       }
       if ((board[0][0] == board[1][1] && board[1][1] == board[2][2])
               || (board[2][0] == board[1][1] && board[1][1] == board[0][2]))
           return true;

       else
           return false;

   }
}

package ticTacToe;

import java.util.Scanner;
import ticTacToe.Board;

class Main {
   public static void main(String[] args) {
       char[][] board2 = new char[3][3];
       Board board = new Board();
       Scanner scan = new Scanner(System.in);
       board.initBoard(board2);
       board.printBoard(board2);
       int turns = 0;
       while (true) {

           while (true) {
               System.out.print("Player 1: Enter your move (choose an available number 1-9) ");
               int space = scan.nextInt();
               if (board.checkSpace(space)) {
                   board.place(space, 'X');
                   board.printBoard(board2);
                   turns += 1;
                   break;
               } else {
                   System.out.println("There already is an X or O marker already there");
               }
           }
           if (board.isWinner()) {
               System.out.println("Woo, Player 1 Wins!");
               break;
           }
           if (turns == 9) {
               System.out.println("Awh it's a draw!");
               break;
           }

           while (true) {
               System.out.print("Player 2: Enter your move (choose an available number 1-9) ");
               int space = scan.nextInt();
               if (board.checkSpace(space)) {
                   board.place(space, 'O');
                   board.printBoard(board2);
                   turns += 1;
                   break;
               } else {
                   System.out.println("There already is an X or O marker already there");
               }
           }
           if (board.isWinner()) {
               System.out.println("Alright, alright alright! Player 2 wins!");
               break;
           }
       }

   }

}

Answer 1

thanks for the question, I have fixed the null pointer error but still the program was not working as expected, I have fine tuned the classes and its working as expected, please find the updated two classes.

thank you !

===============================================================================

package ticTacToe;

public class Board {
    private char[][] board;

    public Board() {

        char[][] temp = {{'1', '2', '3'}, {'4', '5', '6'}, {'7', '8', '9'}};
        board = temp;

    }

    public void initBoard(char[][] board) {
        System.out.println("New Tic Tac Toe Board \n Good Luck!");
        int a = 1;
        for (int i = 0; i < 3; i++)
            for (int j = 0; j < 3; j++) {
                board[i][j] = (char) (a + '0');
                a++;
            }
    }

    public void printBoard() {
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                System.out.print(" | " + board[i][j]);
            }
            System.out.println();

        }
    }

    public boolean checkSpace(int space) {
        if (space > 0 && space <= 9) {
            int i = (space - 1) / 3;
            int j = (space - 1) % 3;
            if (board[i][j] == 'X' || board[i][j] == 'O')
                return false;
            else
                return true;
        }
        return false;
    }

    public void place(int space, char input) {
        int i = (space - 1) / 3;
        int j = (space - 1) % 3;
        board[i][j] = input;

    }

    public boolean isWinner() {
        for (int i = 0; i < 3; i++) {
            if (board[i][0] == board[i][1] && board[i][1] == board[i][2] && (board[i][0] == 'X' || board[i][0] == 'O')) {

                return true;
            }

        }
        for (int j = 0; j < 3; j++) {
            if (board[0][j] == board[1][j] && board[1][j] == board[2][j] && (board[0][j] == 'X' || board[0][j] == 'O')) {

                return true;
            }

        }

      if ((board[0][0] == board[1][1] && board[1][1] == board[2][2] && (board[0][0] == 'X' || board[0][0] == 'O'))
                || (board[2][0] == board[1][1] && board[1][1] == board[0][2] && (board[2][0] == 'X' || board[2][0] == 'O'))) {

            return true;
        } else
            return false;
    }
}

===============================================================================

package ticTacToe;

import java.util.Scanner;



class Main {

    public static void main(String[] args) {



        Board board = new Board();

        Scanner scan = new Scanner(System.in);



        board.printBoard();

        int turns = 0;

        while (true) {

            while (true) {

                System.out.print("Player 1: Enter your move (choose an available number 1-9) ");

                int space = scan.nextInt();

                if (board.checkSpace(space)) {

                    board.place(space, 'X');

                    board.printBoard();

                    turns += 1;

                    break;

                } else {

                    System.out.println("There already is an X or O marker already there");

                }

            }

            if (board.isWinner()) {

                System.out.println("Woo, Player 1 Wins!");

                break;

            }

            if (turns == 9) {

                System.out.println("Awh it's a draw!");

                break;

            }

            while (true) {

                System.out.print("Player 2: Enter your move (choose an available number 1-9) ");

                int space = scan.nextInt();

                if (board.checkSpace(space)) {

                    board.place(space, 'O');

                    board.printBoard();

                    turns += 1;

                    break;

                } else {

                    System.out.println("There already is an X or O marker already there");

                }

            }

            if (board.isWinner()) {

                System.out.println("Alright, alright alright! Player 2 wins!");

                break;

            }

        }

    }

}

===============================================================================

thanks a lot !