java/w6/Main.java

abstract class Animal {
    abstract void makeSound();
}

interface Swimmable {
    void swim();
}

class Dog extends Animal implements Swimmable {
    public void makeSound() {
        System.out.println("Woof!");
    }

    public void swim() {
        System.out.println("Dog is swimming!");
    }
}

class Cat extends Animal {
    public void makeSound() {
        System.out.println("Meow!");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myDog = new Dog();
        Animal myCat = new Cat();

        myDog.makeSound();
        myCat.makeSound();

        if (myDog instanceof Swimmable) {
            ((Swimmable) myDog).swim();
        }
    }
}