ex4-6.java

public class Animal {
    //private instance variable
    private final String name;

    //constructors
    public Animal(String name) {
        this.name = name;
    }

    public String toString() {
        return "Animal: Animal[name = " + name + "]";
    }
}

//next class

public class Mammal extends Animal {
    //constructors
    public Mammal(String name) {
        super(name);
    }

    @Override
    public String toString() {
        return "Mammal: Mammal[ " + super.toString() + "]";
    }
}

//next class

public class Cat extends Mammal {
    //constructors
    public Cat(String name) {
        super(name);
    }

    public void Greets() {
        System.out.println("Meow");
    }

    @Override
    public String toString() {
        return "Cat: Cat[ " + super.toString() + "]";
    }
}

//next class

public class Dog extends Mammal {
    //constructor

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

    public void Greets() {
        System.out.println("Woof");
    }

    public void Greets2(String name) {
        System.out.println("Woooof");
    }

    @Override
    public String toString() {
        return "Dog: Dog " + super.toString() + "]";
    }
}

//test class

public class testAnimal {
    public static void main(String[] args) {
        //to test animal class
        Animal a1 = new Animal("Rino");

        System.out.println(a1);

        System.out.println();

        //to test mammal class
        Mammal m1 = new Mammal("Dolphin");

        System.out.println(m1);

        System.out.println();

        //to test cat class
        Cat c1 = new Cat("Nyancheng");

        System.out.println(c1);
        c1.Greets();

        System.out.println();

        //to test dog class
        Dog d1 = new Dog("Golden Retriever");
        Dog d2 = new Dog("Husky");

        System.out.println(d1);
        d1.Greets();
        d2.Greets2("Husky");

    }
}