​

class LandAnimal { public void crying() { System.out.println("육지동물"); } }

class Cat extends LandAnimal { public void crying() { System.out.println("냐옹냐옹"); } }

class Dog extends LandAnimal { public void crying() { System.out.println("멍멍"); } }

class Sparrow { public void crying() { System.out.println("짹짹"); } } 

​

class AnimalList<T> {

    ArrayList<T> al = new ArrayList<T>();

    public static void cryingAnimalList(AnimalList<? extends LandAnimal> al) {

        LandAnimal la = al.get(0);

        la.crying();

    }

    void add(T animal) { al.add(animal); }

    T get(int index) { return al.get(index); }

    boolean remove(T animal) { return al.remove(animal); }

    int size() { return al.size(); }

}

​

public class prog {

    public static void main(String[] args) {

        AnimalList<Cat> catList = new AnimalList<Cat>();

        catList.add(new Cat());

        AnimalList<Dog> dogList = new AnimalList<Dog>();

        dogList.add(new Dog());

        AnimalList.cryingAnimalList(catList);

        AnimalList.cryingAnimalList(dogList);

    }

}