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