Java cast child to parent

Question

Class Lion extends Animal.

Here is my code:

Animal a = new Animal();
Lion b = new Lion();
Animal c = (Animal) b;

Animal[] arr = { a, b, c };

for (int i = 0; i < arr.length; i++) {
    System.out.println(arr[i].getClass().getName());
    arr[i].run();
}

The result is:

test2.Animal

Animal Run...

test2.Lion

Lion Run...

test2.Lion

Lion Run...

From the example seems that "c" is a "Lion", not an "Animal". Why is that happening?

Answer 1

From the example seems that "c" is a "Lion", not an "Animal". Why is that happening?

Because c is a Lion:

Lion b = new Lion();   // Creates a Lion
Animal c = (Animal) b; // Refers to the Lion through an Animal variable

Now, c is an Animal-typed reference to a Lion object. The object is still a Lion, it's just the reference to it is limited to Animal stuff. So when you ask that object what its class is (not what your interface to it is in the c variable / third entry in your array), it tells you it's a Lion.

This is exactly like this situation:

Map m = new HashMap();

The m reference is typed Map and so you can only use it to access the things the Map interface defines, but the object it's referring to is a HashMap instance.

Answer 2

A cast doesn't make the referenced object change its type, it just restricts itself to the methods of the supertype. You couldn't cast a Banana to an Animal for these reasons.

The cast in your line

Animal c = (Animal) b;

happens automatically anyways. You just need to specify your cast when you downcast:

Animal a = new Dog();
Dog d = (Dog) a;

But both a and d still point to a Dog in the heap and will thus use the instance methods of the Dog class if they override the methods of the Animal class. In other words, a is a Dog, but as long as it is declared as (or typecast to) an Animal, it can only use Animal methods.

Answer 3

You are invoking getClass.

Method invocation resolves at runtime, hence it prints Lion and not Animal.