Question

I want to write a method that gets an object of the same type as argument, but to declare it in the base class, but I don’t want it to accept other object that derived from same base.

For example, I have the class Animal, and I want to write a method sonOf(Animal a), but I don’t want someone to do something like that:

Animal bolt = new Dog();
Animal mittens = new Cat();

bolt.sonOf(mittens);

I think a generics is needed, but I’m not sure how to use it correctly.

Thank You.

Answer 1

Hm. You could try, for example:

abstract class Animal<T extends Animal<T>> {
    abstract void sonOf(T son);
}

final class Dog extends Animal<Dog> {
    void sonOf(Dog dog) { ... }
}

final class Cat extends Animal<Cat> {
    void sonOf(Cat cat) { ... }
}

Then you get

final Cat mom = new Cat();
final Cat child = new Cat();

child.sonOf(mom);

final Dog dad = new Dog();
child.sonOf(dad);          // "The method sonOf(Cat) in the type Cat is not applicable for the arguments (Dog)"