Java generics - restrict child class object stored in parent class argument

I have classes Parent and (Child extends Parent). Also I have classes A and (B extends A).

Have the following code setup:

class Parent {
  method (A a) {
    //some actions
  }
}

class Child extends Parent {
 method (B b) {
   super.method(b)
   // some additional actions
 }
}

Let's say we have the following:

Parent p = new Parent();
Child c = new Child();
A a = new A();
B b = new B();

The requirement is the following:

p.method(a); // success
p.method(b); //RunTimeException

c.method(a); //RunTimeException
c.method(b); //success

The primary problem here is c.method(a) and p.method(b) works successfully.

Is it possible to achieve this behavior using generics? Any suggestion is appreciated.

Thanks.

Solution

You can always throw RuntimeExceptions as you wish, but you should not, you most likely want to have a compiler error instead!? And then the question is: why? A Child is a Parent, and everything you can call on the parent should also work on the child, see the L in SOLID.

You might be able to achieve this with generics by using a

class Parent<T> { 
    void method (T t) { ... }
}

class Child<T> extends Parent<T> {
    void somethingElse () { ... }
}

and then

Parent<A> p = new Parent<>();
Child<B> c = new Child<>();
A a = new A();
B b = new B();

p.method(a); // works
p.method(b); // compiler error

c.method(a); // compiler error
c.method(b); // works

But at that point the Child<B> is something completely different compared to the Parent<A> and the Parent p = c; that would have worked previously is no longer valid / available.