public class Animal {
    void talk() { throw new Error("what animal am I?"); }

    class Cat extends Animal {
        void talk() { System.out.println("meow"); }
    }
    class Cow extends Animal {
        void talk() { System.out.println("moooh"); }
    }
    class Dog extends Animal {
        void talk() { System.out.println("wuff"); }
    }

    /* This is the function that's interesting.
     * How does the compiler generate the call to a.talk?
     */
    static void letAnimalTalk(Animal a) {
        a.talk();
    }

    public static void main(String []av) {
        letAnimalTalk(new Cat());
        letAnimalTalk(new Cow());
        letAnimalTalk(new Dog());
    }
}