Question

Out of mere curiosity, is it possible to assign a variable to two types?

Since I don’t have my technical terms straight in this matter, let me clarify a bit. Normally you would have a static and dynamic type:

Animal a = new Dog();

Where the dynamic type has to inherit the static type:

public class Dog extends Animal {...}

But is it possible to ensure that the dynamic type extends/implements multiple types?

So that the Dog has to extend the Animal-class and implement an interface?

I’d imagine something like:

Animal [implements Happy] a = new Dog();

I’m quite sure it’s just crazy talk, but is it possible? And if not, what’s the closest alternative?

I’m thinking this only would be relevant in cases of ensuring a variable is of an interface you made yourself and a class that you cannot edit.

One way I can think of is determining it runtime by casting it every time you use it:

try {
    @SuppressWarnings("unused")
    Animal a = (Happy) new Dog();
} catch (ClassCastException e) {
    //Is not of type Happy
}

//Using a method from the Happy-interface
try {
    ((Happy)a).smile();
} catch (ClassCastException e) {
    //Is not of type Happy
}

Answer 1

No, it is not possible directly. You can think of some workarounds like:

abstract class HappyAnimal extends Animal implements Happy

And then use that type. Of course your classes must extend HappyAnimal, it won’t work if they extend Animal and implement Happy directly.