JamMaster :
I have encountered this class in code that I'm maintaining:
new GenericFutureListener<Future<? super Void>>() {...}
I'm having a really hard time understanding what this means. A Future containing a type that is either Void or its superclass - Object. So why not just write Future<Object>?
Jorn Vernee :
It looks like this is being created to conform to some generic type like GenericFutureListener<Future<? super T>>, which is not flexible enough to allow for GenericFutureListener<Future<Void>> alone.
For instance if you have something like this:
class GenericFutureListener<T> {}
public static <T> void m(GenericFutureListener<Future<? super T>> p) {
...
}
m(new GenericFutureListener<Future<? super Void>>() {}); // works,
m(new GenericFutureListener<Future<Void>>() {}); // does not work
Passing in just a GenericFutureListener<Future<Void>> is not allowed.