Why is SomeClass<? super T> not equivalent to SomeClass in Java generic types?

Question

I noticed the specificaition for Collections.sort:

public static  void sort(List list, Comparator c)

Why

Answer 1

It's obvious to you that, in the case of Comparator, any ancestor of T would work. But the compiler doesn't know that class Comparator functions like that - it just needs to be told whether it should allow or .

Viewed another way, yes it's true that any Comparator of an ancestor would work in this case - and the way the library developer says that is to use .