Difference between <? super T> and <? extends T> in Java [duplicate]

Answer 1

The generic wildcards target two primary needs:

Reading from a generic collection Inserting into a generic collection There are three ways to define a collection (variable) using generic wildcards. These are:

List           listUknown = new ArrayList();
List listUknown = new ArrayList();
List listUknown = new ArrayList();

List means a list typed to an unknown type. This could be a List, a List, a List etc.

List means a List of objects that are instances of the class A, or subclasses of A (e.g. B and C). List means that the list is typed to either the A class, or a superclass of A.

Read more : http://tutorials.jenkov.com/java-generics/wildcards.html