instanceof keyword usage

Question

Is using the instanceof keyword against the essence of object oriented programming? I mean is it a bad programming practice? I read somewhere that us

Answer 1

It's discouraged because people might use it to do something like this:

if( myAnimal instanceof Dog )
    ((Dog)myAnimal).bark();
else( myAnimal instanceof Cat )
    ((Cat)myAnimal).meow();

Instead, Animal should have a speak() method which Dog and Cat inherit. In proper OOP with polymorphism and dynamic binding, you would then simply do

myAnimal.speak();

However, there are some instances in which you must use instanceof to determine the specific type of an object. Perhaps you have a list of Animals in your house and the only ones you want to take out for a walk() are the Dogs. In that case you would iterate through your list and only walk() the dogs.