Board.java

    public boolean validMove(String move) {
        if (tryParse(move)) { // Checks if string can be parsed
            int cellIndex = (new Integer(move) - 1);
            int totalCellsCount = rows * rows;
            return (cellIndex >= 0) && (cellIndex < totalCellsCount) && isOpen(cellIndex); // Checks if parsed value is valid based on game board
        } else {
            return false;
        }
    }
    
    private static boolean tryParse(String input) {
        if (input.length() > 0) {  // Checks for empty string
            try {
                new Integer(input);  // Checks if valid number
                return true;
            } catch (NumberFormatException e) {
                return false;
            }
        } else {
            return false;
        }
    }