import java.util.*;
import java.lang.*;
import java.io.*;

// The main method must be in a class named "Main".
class Main {
    public static void main(String[] args) {
        
        Dog dog = new Dog();
        Cat cat = new Cat();
        dog.eat();
        cat.eat();
        
        Owner owner = new Owner();
        owner.feed(dog);
        owner.feed(cat);
    }
}

interface IAnimal {
    public void eat();    
}

class Dog implements IAnimal {
    public void eat() {
        System.out.println("Dog eats.");
    }
}

class Cat implements IAnimal {
    public void eat() {
        System.out.println("Cat eats.");
    }
}

class Owner {
    public void feed(IAnimal animal) {
       animal.eat();
    }
}