Handling Multilevel Constructors – super Keyword

In Java, when dealing with multilevel inheritance and constructors, the `super` keyword plays a crucial role. The `super` keyword is used to call the constructor of the immediate superclass from within the subclass constructor. This is essential for initializing the inherited members of the superclass before initializing the members of the subclass.

Let's illustrate how `super` keyword is used to handle multilevel constructors:

class Animal {

    String type;

    Animal(String type) {

        this.type = type;

        System.out.println("Animal constructor called");

    }

    void eat() {

        System.out.println("Animal is eating");

    }

}

class Dog extends Animal {

    String breed;

    Dog(String type, String breed) {

        super(type); // Calling superclass constructor

        this.breed = breed;

        System.out.println("Dog constructor called");

    }

    void bark() {

        System.out.println("Dog is barking");

    }

}

class Labrador extends Dog {

    String color;

    Labrador(String type, String breed, String color) {

        super(type, breed); // Calling superclass constructor

        this.color = color;

        System.out.println("Labrador constructor called");

    }

    void playFetch() {

        System.out.println("Labrador is playing fetch");

    }

}

public class Main {

    public static void main(String[] args) {

        Labrador labrador = new Labrador("Canine", "Golden Retriever", "Golden");

        labrador.eat();       // Inherited method from Animal

        labrador.bark();      // Inherited method from Dog

        labrador.playFetch(); // Specific to Labrador

    }

}

In this example:

- The `Animal` class has a constructor that initializes the `type` of animal.

- The `Dog` class extends `Animal` and has its own constructor that initializes the `breed` of dog.

- The `Labrador` class extends `Dog` and has its own constructor that initializes the `color` of the Labrador.

- Each subclass constructor uses `super()` to call the constructor of its immediate superclass.

- This ensures that the constructors of all classes in the hierarchy are invoked properly, initializing the state of each object.

By using the `super` keyword, we ensure that constructors are called in the correct order in the multilevel inheritance hierarchy, allowing for proper initialization of inherited members and avoiding inconsistencies in object state.