public class AnimalTest {
    public static void main(String[] args) {
        Animal[] animals = new Animal[2];
        animals[0] = new Dog();
        animals[1] = new Cat();

        for (Animal a : animals) {
            a.makeSound();
            if (a instanceof Swimmable) {
                ((Swimmable) a).swim();
            }
        }

        System.out.println("\n--- Testing individual Dog ---");
        Dog dog = new Dog();
        dog.makeSound();
        dog.swim();

        System.out.println("\n--- Testing individual Cat ---");
        Cat cat = new Cat();
        cat.makeSound();
    }
}