I just wish to know if it is possible to do subtotals in a list component? If so, is it like using a variable and putting the reset type as 'Group' and putting the expression?
There are many limitations of List component (calculations, return values, headers and footers, ...). See section "13.1.3 List Component Issues" in ireport-ultimate-guide.
Try to use subreport instead list. It is more suited for computation on a subset of data