Question

In theory, the input paramters in a subclass method should be equivaent to or less restrictive than the input parameters of the superclass (contravariant).

What I want to do is basically create a class A that has a generic binding <T extends SomeType>, but then create a subclass B, with no generic binding (should allow any type) <T>:

    class A<T extends SomeType> {....}

    class B<T> extends A<T extends SomeType> { ..... }

Is this even possible in java or ever right from a theoretic point of view?

Answer 1

No, that isn’t correct. Consider a method declared in A that returns T:

abstract class A<T extends SomeType> {

    abstract T foo();
}

An object statically typed as A would be expected to conform to the bounds declared by that class:

A<?> a = ...;
SomeType someObject = a.foo();

But then if B does away with those bounds:

abstract class B<T> extends A<T> { }

class C extends B<String> {

    @Override
    String foo() {
        return "foo";
    }
}

We have chaos:

A<?> a = new C();
SomeType someObject = a.foo(); // ???