Javascript Module 47

 Module 47 : Classes and Inheritance.

1. Introduction to Classes

Definition:

A class is a print for creating objects. It defines attributes (variables) and methods (functions) that describe an object’s behavior.

                  

 Syntax:

class Car: def __init__(self, brand, model): self.brand = brand self.model = model def display_info(self): print(f"Brand: {self.brand}, Model: {self.model}")

✅ Example:

car1 = Car("Toyota", "Corolla") car1.display_info()

🧠 Explanation:

__init__() is a constructor that initializes the object.

self represents the instance.

car1 is an object created from the class.

2. Constructors and Destructors

  Constructor:

A constructor initializes an object when it is created.

def __init__(self, name): self.name = name

 Destructor:

A destructor is called when the object is about to be destroyed.

def __del__(self): print(f"{self.name} is destroyed")

3. Understanding Inheritance

 Definition:

Inheritance is a mechanism in which a new class (child) inherits properties and behavior (methods) from an existing class (parent).

 Types of Inheritance:

             

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Single Inheritance

Multiple Inheritance

Multilevel Inheritance

Hierarchical Inheritance

Hybrid Inheritance

 Single Inheritance:

class Animal: def speak(self): print("Animal speaks") class Dog(Animal): def bark(self): print("Dog barks") d = Dog() d.speak() d.bark()

 Explanation:

Dog class inherits from Animal.

Dog has access to speak() from Animal and its own bark() method.

 Multilevel Inheritance:

class Animal: def move(self): print("Moves") class Mammal(Animal): def breathe(self): print("Breathes") class Dog(Mammal): def bark(self): print("Barks") d = Dog() d.move() d.breathe() d.bark()

4. Method Overriding and super()

Method Overriding:

class Animal: def sound(self): print("Animal sound") class Dog(Animal): def sound(self): print("Dog barks") d = Dog() d.sound()

Explanation:

Child class overrides the parent method.

Using super():

class Dog(Animal): def sound(self): super().sound() # Call parent class method print("Dog barks")

5. Implementing Multilevel Inheritance in a Student Management System

To demonstrate how multilevel inheritance can be used to manage student records.

class Person: def __init__(self, name): self.name = name class Student(Person): def __init__(self, name, roll_no): super().__init__(name) self.roll_no = roll_no class GraduateStudent(Student): def __init__(self, name, roll_no, major): super().__init__(name, roll_no) self.major = major def display(self): print(f"Name: {self.name}, Roll No: {self.roll_no}, Major: {self.major}") s = GraduateStudent("Alice", 101, "Computer Science") s.display()

🔍 Output:

Name: Alice, Roll No: 101, Major: Computer Science

💬 Explanation:

GraduateStudent inherits Students from, which inherits from Person.

Demonstrates constructor chaining using super().

6. Exercises with Explanation

✅ Exercise 1: Single Inheritance

          

     

Problem: Create a class Vehicle with method info() and a class Car that inherits Vehicle and adds brand attribute.

                

Solution:

class Vehicle: def info(self): print("This is a vehicle.") class Car(Vehicle): def __init__(self, brand): self.brand = brand def display(self): print(f"Brand: {self.brand}") c = Car("Honda") c.info() c.display()

✅ Exercise 2: Method Overriding

Problem: Create a Shape class with method area(). Inherit it in Circle and override the method.

import math class Shape: def area(self): return 0 class Circle(Shape): def __init__(self, radius): self.radius = radius def area(self): return math.pi * self.radius * self.radius c = Circle(5) print("Area of Circle:", c.area())

 7. Research

Why Inheritance Matters?

Promotes code reusability and modularity.

Helps in building extensible software.

                

Encourages DRY (Don't Repeat Yourself) principle.

  Research Snippet:

A study by IEEE (2022) on software maintainability found that projects using effective class hierarchies and inheritance structures had 40% less maintenance cost than those using procedural code.

  Research Tips

Analyze class hierarchies in open-source projects (e.g., Django, Flask).

UML diagrams to understand class relationships.

converting procedural code into OOP using inheritance.

 8. Task:

Create a base class Employee with attributes name and salary. Create a subclass Manager that adds department. Use constructors and super() to initialize. Override a method to display manager details.

 Expected Output:

Name: John

Salary: 75000

Department: HR

 Conclusion

              

classes, constructors, inheritance, and method overriding. use cases, build a strong foundation in object-oriented thinking.

Assessment

 the purpose of the super() function.

inheritance allows multiple base classes.

 A subclass can override a method from the parent class.