To spell this out so it's a bit more obvious, given a Thing at head of a list, you could have: - a List<Thing> - a List<ThingSuperclass> - a List<?

To spell this out so it's a bit more obvious, given a Thing at head of a list, you could have: - a List<Thing> - a List<ThingSuperclass> - a List<? extends Thing> - a List<? super ThingSubclass> - a List<IThing> - a List<ILiterallyAnyImplementedIFace> - a List<IHaventForgottenInterfacesCanExtendOthers> - a List<Object> - a List<I'm probably forgetting some possibilities> And you have no way of knowing which it is. So yes, it's a boundary, which is significantly more than nothing. But far less useful than it feels like at first.