Object-Oriented Programming (OOPS) Lecture Notes

Introduction

• Purpose: Cover OOPS from scratch to advanced level for interview preparation, internships, and college exams
• Importance: Major companies ask OOP questions in tech interviews; strong OOP understanding is crucial
• Content: Theory concepts, definitions, practical examples, code implementation, and 30 MCQs for practice

Object-Oriented Programming (OOP)

• Definition: A programming paradigm that uses objects and classes
• Practical Implementation: Makes real-life scenarios easier to represent in code
• Examples: Using libraries (vector, string, stack) in C++ STL implemented via OOP concepts

Key Terms

• Class: Blueprint of objects; tells how objects should look like (Attributes and Methods)
• Object: Instance of a class; real-world entities converted into code objects
• Attributes (Properties): Data stored in objects (e.g., name, department, salary)
• Methods: Functions inside a class

Example: Teacher Class

• Attributes: name, department, subject, salary
• Methods: changeDepartment, calculateTax
• Implementation: C++ code snippets to define Teacher class and use it to create objects

Access Modifiers

• Private: Accessible only within the class
• Public: Accessible from outside the class
• Protected: Accessible within the class and derived classes
• Practical Use: Use access modifiers to implement data hiding and encapsulation

Example: Teacher Class with Access Modifiers

• Attributes: name (public), department (public), subject (public), salary (private)
• Setter Method: To modify private attributes
• Getter Method: To access private attributes

Encapsulation

• Definition: Wrapping data and methods in a single unit (class)
• Purpose: Data hiding and protecting sensitive information, providing necessary access
• Example: Teacher class with private salary, public setter and getter methods

Inheritance

• Definition: Mechanism where a class derives properties and behavior from another class
• Types of Inheritance:
  • Single: One parent class to one child class
  • Multi-level: Chain of inheritance (e.g., Person -> Student -> GraduateStudent)
  • Multiple: One child class from multiple parent classes
  • Hierarchical: Multiple child classes from one parent class
  • Hybrid: Combination of multiple and hierarchical inheritance
• Access Specifiers with Inheritance:
  • Public Inheritance
  • Protected Inheritance
  • Private Inheritance

Example: Classes Demonstrating Inheritance

• Person -> Student: Public inheritance from Person class (name, age) to Student class (roll number)
• Person -> Teacher: Public inheritance from Person class (name, age) to Teacher class (subject, salary)

Polymorphism

• Definition: Ability for a function or object to take on multiple forms
• Types:
  • Compile-time (e.g., Function overloading, Operator overloading)
  • Run-time (e.g., Function overriding, Virtual functions)
• Function Overloading: Multiple functions with the same name but different parameters
• Function Overriding: Child class re-implements a function from the parent class

Example: Polymorphism

• Function Overloading: Different show() methods for int and char
• Function Overriding: Child class's getInfo() method overloading the parent class's method
• Virtual Functions: Functions expected to be overridden in derived classes

Abstract Classes

• Definition: Blueprint for other classes; cannot be instantiated
• Pure Virtual Functions: Functions with no definition, must be overridden in derived classes
• Usage: Provide a base class for other classes to derive from

Example: Shape Class

• Abstract Class: Shape with a pure virtual function draw()
• Derived Classes: Circle, Square classes implementing the draw function

Constructors

• Types: Default, Parameterized, Copy
• Copy Constructor: Copies properties from one object to another
• Deep Copy vs Shallow Copy: Important when dealing with dynamic memory

Destructors

• Purpose: De-allocate memory; inverse of constructor
• Default Destructor: Provided by compiler
• Custom Destructor: Needed when handling dynamic memory

Static Keyword

• Usage: Used with variables and methods
• Static Variables: Lifetime across the entire execution of the program
• Static Methods: Called on the class rather than instances
• Static Objects: Persist for the lifetime of the program

Example: Static Members and Methods

• Static Variable: Shares a single variable among all objects of a class
• Static Method: Class method instead of an instance method

Friend Functions and Friend Classes

• Usage: Provides special access to private members of a class
• Friend Function: Non-member function with access to private data
• Friend Class: Another class which can access private data

Summary

• Review definitions, concepts, and examples
• Apply OOPS concepts in practical scenarios and code
• Solve given MCQs to strengthen understanding