Java: Getting the subclass from a superclass list

Question

i'm new with java and have 2 questions about the following code:

class Animal { }
class Dog extends Animal { }
class Cat extends Animal { }
class Rat extends Animal { }

class Main {
  List<Animal> animals = new ArrayList<Animal>();

  public void main(String[] args) {
    animals.add(new Dog());
    animals.add(new Rat());
    animals.add(new Dog());
    animals.add(new Cat());
    animals.add(new Rat());
    animals.add(new Cat());

    List<Animal> cats = getCertainAnimals( /*some parameter specifying that i want only the cat instances*/ );
  }
}

1) Is there any way to get either the Dog or Cat instances from the Aminal list? 2) If yes, how should i correctly build the getCertainAnimals method?

Answer 1

Animal a = animals.get(i);   

if  (a instanceof Cat)
{
    Cat c = (Cat) a;
} 
else if (a instanceof Dog)
{
    Dog d = (Dog) a;
} 

NB: It will compile if you do not use instanceof, but it will also allow you to cast a to Cat or Dog, even if the a is a Rat. Despite compiling, you will get a ClassCastException on runtime. So, make sure you use instanceof.