Abstract classes and example of using polymorphism.

Animal.java

public abstract class Animal {

    public abstract void makeSound(); // Force every animals to have sound
}

Cat.java

public class Cat extends DomesticAnimal {

    public Cat(String name) {
        super(name);
    }

    @Override
    public void makeSound() {
        System.out.println("Meou (^-^)");
    }
}

Cow.java

public class Cow extends DomesticAnimal {

    public Cow(String name) {
        super(name);
    }

    @Override
    public void makeSound() {
        System.out.println("Moo.");
    }
}

Dog.java

public class Dog extends DomesticAnimal {

    public Dog(String name) {
        super(name);
    }

    @Override
    public void makeSound() {
        System.out.println("Woof, woof.");
    }
}

DomesticAnimal.java

public abstract class DomesticAnimal extends Animal {

    // Domestic animals should have their names
    protected String name;

    // Name must be assigned in the constructor
    public DomesticAnimal(String name) {
        this.name = name;
    }

    // Name should be retrievable from anywhere
    public String getName() {
        return name;
    }
}

Lion.java

public class Lion extends Animal {

    @Override
    public void makeSound() {
        System.out.println("Lion sound!");
    }
}

Main.java

package ge.tsu.lab4;

public class Main {

    public static void main(String[] args) {

        // Generally all animals
        Animal[] animals = {
                new Cat("Pupu"),
                new Dog("Frufru"),
                new Lion(),
                new Wolf(),
                new Cat("Kiki"),
                new Cow("Milky"),
        };

        for (Animal animal : animals) {
            animal.makeSound();
        }

        // Domestic ones
        DomesticAnimal[] domesticAnimals = {
                (DomesticAnimal) animals[0],
                (DomesticAnimal) animals[1],
                (DomesticAnimal) animals[4],
                (DomesticAnimal) animals[5],
        };

        for (DomesticAnimal domesticAnimal : domesticAnimals) {
            System.out.println(
                    String.format("Domestic animal with name: %s and sound...", domesticAnimal.getName())
            );
            domesticAnimal.makeSound();
        }
    }
}

Wolf.java

public class Wolf extends Animal {

    @Override
    public void makeSound() {
        System.out.println("Wolf sound!");
    }
}