Q:

Type mismatch: cannot convert from List> to List>?

Here's code:
List<SelectOption<String>> validMemberList = ValidDataUtil.getValidMemberType();

Can anyone tell me :
How can convert the List<SelectOption<Integer>> to List<SelectOption<String>> ?

A:

How can convert the List<SelectOption<Integer>> to List<SelectOption<String>> ?

You can't, directly. You can loop through the first and use toString on each of the integers to build the second, though.

