public class TestAnimal {
    public static void main(String[] args) {
        Animal dog = new Dog();
        Animal cat = new Cat();

        dog.makeSound();
        cat.makeSound();

        // 向下转型调用游泳方法
        if (dog instanceof Swimmable) {
            Swimmable swimmable = (Swimmable) dog;
            swimmable.swim();
        }
    }
}