How to retain all instances of of a single subclass from a general ArrayList

Question

I'm having a problem and I can't figure out a clean solution.

I have this superclass "Creature" with subclasses "Human" and "Zombie" I have constructed a series of humans and zombies and saved them in an ArrayList Now I want to get the subArrayList that only contains the constructed humans. I thought I could use the "retainAll" but it turns out it doesn't do what I thought it would do.

Any suggestions how to create a new ArrayList with only the objects of subclass Zombie in it?

Answer 1

You can use the instanceof operator. Try this code:

List<Human> humans = new ArrayList<Human>();
for (Creature creature : creatures) {
    if (creature instanceof Human) {
        humans.add((Human) creature);
    }
}