Inheritance with generics + collection + method = question

Question

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

{
    foo(new 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.

Jon Skeet · Accepted Answer · 2010-11-15 19:51:48Z

4

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.

answered Nov 15, 2010 at 19:51

Jon Skeet

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Comments

ILMTitan · Accepted Answer · 2010-11-15 21:50:27Z

1

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);}

answered Nov 15, 2010 at 21:50

ILMTitan

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