Java Generics — Assigning a list of subclass to a list of superclass

Question

I have a basic question regarding assignment of a list of subclass to a list of superclass.

So I have something like the following:

Class B extends          


        

Answer 1

To explain this, let me substitute "B" with Integer and "A" with Number. This is just to make it a little easier to explain.

Class Integer extends Number;

List  iList = new ArrayList();
List  nList = iList // will fail

The reason this would fail is because nList can take any Number -- it can take Integer, it can take Double, or for that matter any subclass of Number. However, this is not true for iList. You cannot add a Double to iList because it accepts only Integer and its subclasses. Hope this helps explain it to you.