2 replies to this topic

[John Jang]

I read a really good post about up and downcasting on this forum:
http://forum.codecal...owncasting.html

But my question is, why do you want to cast?
(referring to the link I posted up there)
if all cats can perform animal methods, why would you want to upcast a cat to an animal in first place?

p.s: wasn't sure where to post...

[An Alien]

Found a really good tutorial on this. I don't know this so I'm currently reading it.
http://forum.codecal...owncasting.html

[wim DC]

You want to cast because you will have to write less code. Take the example of Cat and Dog who extend Animal. Now you have another class Cage (how cruel ^^). Cage can hold both dog and cat. Without casting your Cage class will look like:

public class Cage{

  private Cat cat;

  private Dog dog;


  public void addCat(Cat cat){

     this.cat = cat;

  }


  public void addDog(Dog dog){

    this.dog = dog;

  }

}

While with casting you can just do

public class Cage{

  private Animal animal;

  

  public void addAnimal(Animal animal){

    this.animal = animal;

  }

}

Also with generics, like an ArrayList, you can't put a Dog AND a cat in an ArrayList.

ArrayList<Dog, Cat> myPets = new ArrayList<>(); //Won't work

That's not possible. You can however decide to put Animal in the arrayList, and then both dog and cat can be added:

ArrayList<Animal> myPets = new ArrayList<>();

myPets.add(new Cat());

myPets.add(new Dog());

...


Cat cat = (Cat) myPets.get(0);

Dog dog = (Dog) myPets.get(1);