Declared type vs Object type

Question

So I am confused about Declared vs Object types. For example: Animal creature = new Mammal( new Vertebrate) I know that the declared type is Animal, but what would the object type be? Mammal or Vertebrate?

Your example is really bad, why would the `Mammal` constructor take a `Vertebrate` parameter? Not to mention your syntax is wrong there, so I suggest not coming up with your own examples. Read some good tutorials instead. — Kayaman, Apr 28 '22 at 06:59
I am confused, the above isn't valid java syntax. Do you mean `Animal creature = new Mammal( new Vertebrate())`? If so, yes, it is Mammal. Note that the `new Vertebrate()` also creates a new object, but that is directly passed to the constructor of the Mammal class, that is all there is to this. — GhostCat, Apr 28 '22 at 07:00
Does this answer your question? [Difference Between Object Type and Reference Type](https://stackoverflow.com/questions/16730109/difference-between-object-type-and-reference-type) — justanotherguy, Apr 28 '22 at 07:03

score 1 · Answer 1 · answered Apr 28 '22 at 07:01

Here's a thumb rule:

Declared type is whatever is on the left and side of the =, while object type is whatever is after the new keyword. In your case, declared type would be Animal, whereas object type would be Mammal. Vertebrae does not play any role here apart from calling the parameterised ctor of Mammal class.

Thumb Definitions:

Object Type: Whatever class' ctor you use to instantiate an object
Declared Type: Whatever the storage class of the variable you declare to be

score 0 · Answer 2 · answered Apr 28 '22 at 07:12

As others have said Mammal, you can verify this by printing out .getClass()

public static void main(String[] args) {
    Animal mammal = new Mammal(new Vertebrate());
    Animal animal = new Animal();

    System.out.println(mammal.getClass());
    System.out.println(animal.getClass());

    if (mammal instanceof Animal) {
      System.out.println("mammal is animal");
    }
    if (mammal instanceof Mammal) {
      System.out.println("mammal is mammal");
    }
    if (animal instanceof Animal) {
      System.out.println("animal is animal");
    }
    if (animal instanceof Mammal) {
      System.out.println("animal is mammal");
    }
  }

output:

class Scratch$Mammal
class Scratch$Animal
mammal is animal
mammal is mammal
animal is animal

Declared type vs Object type

2 Answers2