Why use a wild card capture helper method?

Question

Referring to : Wildcard Capture Helper Methods

It says to create a helper method to capture the wild card.

public void foo(List i) {
    fo         


        

Answer 1

In this particular case it's because the List.set(int, E) method requires the type to be the same as the type in the list.

If you don't have the helper method, the compiler doesn't know if ? is the same for List and the return from get(int) so you get a compiler error:

The method set(int, capture#1-of ?) in the type List is not applicable for the arguments (int, capture#2-of ?)

With the helper method, you are telling the compiler, the type is the same, I just don't know what the type is.

So why have the non-helper method?

Generics weren't introduced until Java 5 so there is a lot of code out there that predates generics. A pre-Java 5 List is now a List so if you were trying to compile old code in a generic aware compiler, you would have to add these helper methods if you couldn't change the method signatures.