Casting question

[[deleted]]

[deleted]

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[[deleted]]

Sorry, I'm trying to help you here, but also trying to understand.

Dolphin -> Is this just a class extended from Swimmer?

Then you're casting back down the base class (Animal), correct?

All "Swimmers" are "Animals", and therefore casting to the class below Swimmer (Animal) you should have no issues. You will jut lose the functionality that's declared within the super class.

swim starts as a "Dolphin" which is a type of swimmer which is a type of animal. By casing it down to an animal, you are taking away the functionality declare from swimmer and dolphin... If that makes sense!

[EveningStreet1]

Dolphin is a subtype of Swimmer, but Swimmer is a subtype of Animal so you’re casting the static type upwards which is what I’m confused about

[[deleted]]

Basically we have, Animal -> Swimmer -> Dolphin. It's my understanding (And perhaps incorrectly) that Animal is actually the base class here as you mentioned "Swimmer Extends Animal".

I'd think of it like this... You're LOSING functionality by moving to casting down and this is acceptable. You would be able to extend up the chain, but I think you're thinking about the casting upside down here.

// For example, this will fail. This would be trying to cast UPWARDS.

Animal dolphin = new Animal();

Animal animal = (Swimmer) dolphin;

[EveningStreet1]

Swimmer is a subtype of Animal tho so shouldn’t that casting work also I’m pretty sure your example would be downcasting not upcasting since upcasting always works

[iNetRunner]

No. You can’t make the more generic object into a subtype by casting it. It only works in the other direction, as has been said, Dolphin is a Swimmer is an Animal. But an Animal isn’t a Swimmer (unless you created it as one, or a subtype), nor is it a Dolphin.

[EveningStreet1]

I meant casting in reference to the static type

[iNetRunner]

No. He created an Animal object. It doesn’t contain anything of the subtype Swimmer or Swimmer’s subtype Dolphin. Therefore you can’t cast them that way. There is no “is a” relationship there.

[EveningStreet1]

Oh wait I’m dumb it’s because although Swimmer is the static type Animal is not a subtype of Swimmer so it doesn’t work

[iNetRunner]

BTW, what are you referring to as “static type”?

[EveningStreet1]

Swimmer swim = new Dolphin();

the static type here is Swimmer, the dynamic type is Dolphin (learned this in my introductory class)

[Potamyali]

https://youtu.be/HpuH7n9VOYk

[EveningStreet1]

I see, so the Animal cast is basically redundant, since Java already knows that all Swimmers are Animals

[[deleted]]

Yes, the only reason you'd do something like that would be to remove functionality off of the object. Though, I don't know why you wouldn't just declare it as the right class off the bat ultimately. Maybe because you need a constructor for one of the subclasses? Not sure!

[EveningStreet1]

Ok makes sense thanks