Jawaharlal Nehru Technological University Hyderabad B.Tech II Year OBJECT ORIENTED PROGRAMMING THROUGH JAVA Previous Question Paper (September - 2021 - R16)

Multilevel inheritance in Java is a process where a class is derived from a class which is also derived from another class, i.e., a class has more than one parent class. The super keyword is a reference variable used to refer to the immediate parent class object, allowing subclasses to invoke overridden methods or access hidden members of the superclass.

The following program demonstrates a three-level hierarchy: Grandparent → Parent → Child.

class Grandparent {
    void display() {
        System.out.println("Grandparent class method");
    }
}

class Parent extends Grandparent {
    void display() {
        super.display(); // Invoking Grandparent method
        System.out.println("Parent class method");
    }
}

class Child extends Parent {
    void display() {
        super.display(); // Invoking Parent method
        System.out.println("Child class method");
    }
}

public class MultilevelDemo {
    public static void main(String[] args) {
        Child obj = new Child();
        obj.display();
    }
}

Key Concepts:

• Inheritance Hierarchy: The Child class inherits properties from Parent, which in turn inherits from Grandparent.
• Method Overriding: Each class provides a specific implementation of the display() method.
• Super Keyword: Used within the display() method of the subclass to explicitly call the overridden method of the immediate superclass, ensuring that the entire chain of execution is maintained.
• Execution Flow: When obj.display() is called, the Child class invokes super.display(), which triggers the Parent class method, which then triggers the Grandparent class method, resulting in a sequential output of all three levels.