Inheritance with generics + collection + method = question

I have some problem with generics and collection. Java support generics only at compilation level. So we can't use case B.

{
    foo(开发者_StackOverflownew HashSet<I>());  //case A
    foo(new HashSet<C>());  //case B: wrong
}
void foo(Set<I> set){}
class C implements I{}
interface I {}

So how we can use function foo with Set< C > parameter?

Thanks.

By changing the signature of Foo:

void foo(Set<? extends I> set){}

You won't be able to add values to the set within foo, but you'll be able to iterate over them or check for containment.

Jon Skeet is right. If you did need to add something, however, you could write a generic function

public <T extends I> void foo2(Set<T> set, T added){set.add(added);}