Java泛型：做什么 <? extends Interface <?> &gt;是什么意思？

Question

Further to a previous post I'm hope someone can help clarify/confirm my understanding of the following java generics statements, and offer some input as to what the final one means:

If:

Class<abc> className = x

means to assign x of type abc to Class variable className

And:

Class<? extends IAbc> className = x

means to assigns x which implements interface IAbc to Class variable className

What does:

Class<? extends IAbc<?>> className = x

mean?

Answer 1

That just means that IAbc is itself a generic type IAbc<T> , you're asking for a Class object representing some implementation of some parameterization of IAbc but you don't know (or care?) which.

More interesting would be something like

Class<? extends IAbc<? extends Number>>

which would accept any class that implements IAbc<Number> , IAbc<Integer> , IAbc<Double> , etc.