Parameter a class with type A or B

Question

I am trying to parameter a class with a type that is whether A or B and nothing else.

Something like

final class ChildClass<A | B> extends MotherClass {

This way I can create a ChildClass<A> or a ChildClass<B> but nothing else.

Is it possible in Java?

---

Edit:

I must specify that I am using Java 8 and that I have no control of classes A and B (which are classes of the Android framework I am working with).

Answer 1

Unfortunately is not. Search for term union types in java or java either type.

The most known case of union types in Java is catching multiple exceptions, which is built-in into language, however it would be awful to abuse exceptions for your own types.

Here is also interesting workaround.

Answer 2

With the addition of this JEP, there is a rather interesting way to do it now.

You can create an interface that is sealed:

sealed interface F permits A, B {

    default String name() {
        return "F";
    }
}

add the generic type that is going to be bounded by this interface:

static class WithGenerics<T extends F> {

    private final T t;

    public WithGenerics(T t) {
        this.t = t;
    }

    public void findName() {
        System.out.println(t.name());
    }

}

And finally create the two classes A and B:

static final class A implements F {
    .....
}

static final class B implements F {
   .....
}

And you have effectively said that only A and B can be passed to :

 WithGenerics<A> a = new WithGenerics<>(new A());
 a.findName();

 WithGenerics<B> b = new WithGenerics<>(new B());
 b.findName(); 

because there can be no type C that can potentially implement F.