Java Generics (Wildcards)

Question

I have a couple of questions about generic wildcards in Java:

1. What is the difference between List and List

Answer 1

Generic wildcards are created to make methods that operate on Collection more reusable.

For example, if a method has a parameter List, we can only give List to this method. It is a waste for this method's funtion under some circumstances：

1. If this method only reads objects from List, then we should be allowed to give List to this method. (Because A-sub IS a A)
2. If this method only inserts objects to List, then we should be allowed to give List to this method. (Because A IS a A-super)