Inheritance in Java

Explanation

This Java code demonstrates the concept of multi-level inheritance, a fundamental principle of Object-Oriented Programming (OOP). It models a simple student record system where information is progressively added and processed across different classes that inherit from one another.

Let's break it down step by step:

1. students Class (Base Class):

   • This is the most basic class. It represents a generic student with two pieces of information: sno (student number) and sname (student name).
   • These fields are declared private, meaning they can only be accessed directly within the students class itself, promoting encapsulation.
   • It provides two public methods: setstud() to set the student's number and name, and putstud() to display this information.

2. marks Class (Derived Class - Level 1):

   • This class extends students, meaning it inherits all the public and protected members (fields and methods) from the students class. So, a marks object inherently "is a" students object and can access setstud() and putstud().
   • It adds new functionality specific to marks: mark1 and mark2. These are declared protected, which means they are accessible within the marks class itself, by any class that extends marks (like finaltot), and within the same package. This choice is crucial for the next level of inheritance.
   • It provides setmarks() to set the two marks and putmarks() to display them.

3. finaltot Class (Derived Class - Level 2):

   • This class extends marks, which means it inherits from marks, and indirectly from students (since marks extends students). This is the "multi-level" aspect.
   • An object of finaltot therefore has access to methods and protected fields from students (like setstud, putstud) and from marks (like setmarks, putmarks, mark1, mark2).
   • It adds its own specific field total (declared private) and methods:
     • calc(): This method calculates the total by adding mark1 and mark2. It can access mark1 and mark2 directly because they were declared protected in the marks class.
     • puttotal(): Displays the calculated total.
   • main Method: This is the entry point of the program.
     • finaltot f = new finaltot();: An object f of the finaltot class is created.
     • f.setstud(7,"Nathan");: The object f calls the setstud() method, which it inherited from the students class, to set the student's number and name.
     • f.setmarks(80,81);: The object f calls the setmarks() method, inherited from the marks class, to set the two marks.
     • f.calc();: The object f calls its own calc() method to compute the total.
     • f.putstud();, f.putmarks();, f.puttotal();: Finally, the object f calls various display methods (inherited from students and marks, and its own) to print all the collected and calculated information to the console.

In essence, the code builds up a complete student record piece by piece, demonstrating how a specialized class (finaltot) can utilize and extend the functionalities of more general classes (students and marks) through inheritance.

Algorithm

The program follows a hierarchical approach to manage student data and calculate their total marks using multi-level inheritance.

1. Define Base Class (students):

   • Declare private fields for student number (sno) and name (sname).
   • Provide public methods (setstud, putstud) to set and display these details.

2. Define Intermediate Derived Class (marks):

   • Extend the students class to inherit student details.
   • Declare protected fields for two marks (mark1, mark2).
   • Provide public methods (setmarks, putmarks) to set and display these marks.

3. Define Final Derived Class (finaltot):

   • Extend the marks class to inherit student details and marks.
   • Declare a private field for the total marks (total).
   • Provide a public method (calc) to calculate total by summing mark1 and mark2 (which are accessible due to protected access).
   • Provide a public method (puttotal) to display the calculated total.
   • Include the main method to execute the program logic.

4. Program Execution in main method:

   • Create an object of the finaltot class.
   • Use the finaltot object to call the setstud method (inherited from students) to assign a student number and name.
   • Use the finaltot object to call the setmarks method (inherited from marks) to assign two marks.
   • Use the finaltot object to call its own calc method to compute the total marks.
   • Use the finaltot object to call the putstud method (inherited from students) to display student details.
   • Use the finaltot object to call the putmarks method (inherited from marks) to display the marks.
   • Use the finaltot object to call its own puttotal method to display the calculated total.