memory allocation for upcasting in java

Question

Considering these classes:

public class Animal{

}

public class Dog extends Animal{

}

public AnimalTest(){
    public static void main(String[] args){
       Dog d = new Dog();
       Animal a = d;
   }
}

my question is since I performed an upcasting on Animal a = d;does it consume a new memory allocation on the machine or does it use the memory allocated to the Dog d = new Dog();

Answer 1

Animal a = d;

a is just a reference and the reference's memory is allocated in method stack(or jvm stack, not heap).

That is when invoke the method main, JVM will allocate a stack which contains the reference's space.

Answer 2

The Actual object or its memory footprint is not affected. just a new reference to the object is created. The only difference is that the reference a can only call methods or access attributes that was available in the Super Class Animal.

Answer 3

Implicit upcasting really helps in Runtime polymorphism/ method overriding when we have multiple child classes of a parent class. Here, instead of creating reference variables of each child class for referring to the child class object, we can have a single reference variable that is of parent class type in order to save the extra memory allocation for each reference variable in stack memory.