Inheritance in Java

Explanation

This code defines three classes: students, marks1, and finaltot1, forming a chain of inheritance.

1. students class: This is the base class. It represents a generic student with a student number (sno) and a student name (sname).

   • It has a constructor students(int no, String name) that initializes these two private fields.
   • The dispstud() method prints the student's number and name.

2. marks1 class: This class extends students, meaning it inherits all the public and protected members from the students class.

   • It adds two new fields: mark1 and mark2, which are protected so they can be accessed by its subclasses.
   • Its constructor marks1(int n1, int n2, int sno, String sname) takes parameters for its own marks (n1, n2) and also for the parent students class (sno, sname).
   • Crucially, the first line inside its constructor is super(sno, sname);. This calls the constructor of its immediate parent class (students) to initialize the inherited sno and sname fields.
   • The dispmarks() method prints the two marks.

3. finaltot1 class: This class extends marks1, which in turn extends students. This creates a multilevel inheritance structure.

   • It adds a new private field total.
   • Its constructor finaltot1(int n1, int n2, int no, String name) takes parameters for marks (n1, n2) and student details (no, name).
   • The first line inside its constructor is super(n1, n2, no, name);. This calls the constructor of its immediate parent class (marks1) to initialize mark1, mark2, and then marks1's constructor will call students's constructor to initialize sno and sname.
   • After calling the parent constructor, it calculates total by summing mark1 and mark2. Since mark1 and mark2 are protected in marks1, finaltot1 can directly access them.
   • The disptotal() method prints the calculated total.

4. main method: This is the entry point of the program, located within the finaltot1 class.

   • It creates an object f of the finaltot1 class, passing values for marks (90, 89) and student details (100, "Kirthika") to its constructor.
   • It then calls f.dispstud(), f.dispmarks(), and f.disptotal(). Even though dispstud() is defined in students and dispmarks() in marks1, the finaltot1 object f can access and execute them due to inheritance.

In essence, the code demonstrates how a specialized class (finaltot1) can build upon more general classes (marks1, students) to combine their functionalities and data, while ensuring all parts of an object are correctly initialized through chained constructor calls.

Algorithm

1. Define Base Class (students):

   • Declare private fields sno (student number) and sname (student name).
   • Create a constructor students(int no, String name) to initialize sno and sname.
   • Create a public method dispstud() to print sno and sname.

2. Define Intermediate Subclass (marks1):

   • Declare marks1 to extend students.
   • Declare protected fields mark1 and mark2.
   • Create a constructor marks1(int n1, int n2, int sno, String sname):
     • Call the parent class constructor using super(sno, sname) as the first statement.
     • Initialize mark1 and mark2 with n1 and n2.
   • Create a public method dispmarks() to print mark1 and mark2.

3. Define Final Subclass (finaltot1):

   • Declare finaltot1 to extend marks1.
   • Declare a private field total.
   • Create a constructor finaltot1(int n1, int n2, int no, String name):
     • Call the parent class constructor using super(n1, n2, no, name) as the first statement.
     • Calculate total by summing mark1 and mark2 (which are inherited from marks1).
   • Create a public method disptotal() to print total.

4. Main Program Execution (main method in finaltot1):

   • Create an object f of finaltot1 class, passing initial values for marks, student number, and student name: new finaltot1(90, 89, 100, "Kirthika").
   • Call f.dispstud() to display student details (inherited from students).
   • Call f.dispmarks() to display marks (inherited from marks1).
   • Call f.disptotal() to display the calculated total (from finaltot1 itself).