Should/does -MyInterface give MyInterface return types?

Question

The variance-overview.pdf says that List<-E> has Object as the return type of the get method. If this is true, I'm disappointed. I'd expect the following to work quite happily: List<-List<*>> myList = buildList();
List<*> elt1 = myList.get(0);There's no obvious reason why Object should be a supertype of List.

Answer 1

I'm still a bit fuzzy about contravariance, but it all depends on what your buildList() method returns. I think this is all legal code:
    List<Object> list1 = new ArrayList<Object>();
    List<List<*>> list2 = new ArrayList<List<*>>();
    list1.add (new Object());
    list2.add (new ArrayList<Integer>());
    List<-List<*>> list3;
    list3 = list2;
    list3 = list1;
    Object o = list3.get(0); // o is not a List!Either of list1, list2 or list3 will accept list.add(new ArrayList<Integer>()) - however at the price that nothing can be guaranteed about the type of the contents of the array (in the second case, the list is only guaranteed to contain Object).
What you want is for your buildList() method to return List<+List<*>>, the variant case (since you are reading from it).
    List<ArrayList<*>> list1 = new ArrayList<ArrayList<*>>();
    List<List<*>> list2 = new ArrayList<List<*>>();
    list1.add (new ArrayList<Integer>());
    list2.add (new ArrayList<Integer>());
    List<+List<*>> list3;
    list3 = list2;
    list3 = list1;
    List<*> o = list3.get(0); // o is a List