Okay, so this is due to a subtle semantic difference.
List
This is the raw type of List, which equates to T being of type Object. So it's the same as saying:
List
Now, the Compiler knows for a fact, that whatever happens, this is a subclass of type Object. And if you do..
List myList = new ArrayList();
myList.add(new Object());
It will work fine! This is because Object is the same or it is some derivation of the type.
List
This is literally a list of unknown (Java Docs). We don't even know that the subclass of the things in here are of type Object. In fact, the ? type is an unknown type all on its own. It has nothing to do with Object! This is why when you try and do..
List myList = new ArrayList();
myList.add(new Object());
You get a compile time error!
