Why generic type is not applicable for argument extends super class for both?

Question

Here is the problem that I have been being tried to find the solution.

We have two class definitions. One of two extends other one.

    class T{}         


        

Answer 1

There are boundary rules defined for Java Generics when using WildCards

  **extends Wildcard Boundary**

List means a List of objects that are instances of the class T, or subclasses of T (e.g. TT). This means a Read is fine , but insertion would fail as you dont know whether the class is Typed to T

**super Wildcard Boundary**

When you know that the list is typed to either T, or a superclass of T, it is safe to insert instances of T or subclasses of T (e.g.TT ) into the list.

In your example , you should use "super"