From Class extends X?> to X

I am currently working on some reflexion stuff and I'm just a beginner at it.

I got this :

List<X> list;
Set<Class<? extends X>> set;

And I want to do something like this :

for (Class<? extends X> classx : set) list.add(classx);

But i couldn't find anything on how to achieve it. Can someone help me?