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

The simple answer to your question is that the library designer wanted to give the maximum flexibility to the user of the library; this method signature for example allows you to do something like this:

List ints = Arrays.asList(1,2,3);
Comparator numberComparator = ...;

Collections.sort(ints, numberComparator);

Using the wildcard prevents you from being forced to use a Comparator; the fact that the language requires a wildcard to be specified by the library designer enables him or her to either permit or restrict such use.