Generics are sometimes confusing. Here is why it gives you an error:

private class Foo<T> {
   protected T doSomething();
}

private class Bar extends Foo<Integer> {
   protected Integer doSomething();
}

foo1 = new Foo<Integer>();
foo2 = new Bar();
foo1.doSomething();
foo2.doSomething();

Erasing the types, the first method will return Object and the second
Integer. Then, foo2's doSomething will become ambiguous in your code.
The return type would become ambiguous because of the cast.

Yes, I know it seems overprotective, but much of generics is like that.

Works for me! Are you using and old or non-Sun compiler?

There are some confusing wildcard situations where you have nesting of
generic types (Foo<Bar<?>>), but this code should not be a problem.

Tom Hawtin