memory allocation for upcasting in java

问题

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();

回答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.

回答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.

来源：https://stackoverflow.com/questions/21374682/memory-allocation-for-upcasting-in-java