How do you cast a List of supertypes to a List of subtypes?

Question

For example, lets say you have two classes:

public class TestA {}
public class TestB extends TestA{}

I have a method that returns a L

Answer 1

This is possible due to type erasure. You will find that

List x = new ArrayList();
List y = new ArrayList();
x.getClass().equals(y.getClass()); // true

Internally both lists are of type List