🎯 Object-Oriented Programming (OOP)

📂 Topics Covered

File	Description	Status
Basic	OOP Fundamentals	✅ Done

🎯 Four Pillars of OOP

1. Encapsulation

class BankAccount {
  #balance = 0;  // Private field

  deposit(amount) {
    this.#balance += amount;
  }

  getBalance() {
    return this.#balance;
  }
}

2. Abstraction

// Hide complex implementation
class EmailService {
  send(to, subject, body) {
    // Complex SMTP logic hidden
    this.#connect();
    this.#authenticate();
    this.#sendEmail(to, subject, body);
  }
}

3. Inheritance

class Animal {
  speak() { console.log("Sound"); }
}

class Dog extends Animal {
  speak() { console.log("Bark!"); }
}

4. Polymorphism

class Shape {
  area() { throw "Override this"; }
}

class Circle extends Shape {
  constructor(r) { this.r = r; }
  area() { return Math.PI * this.r ** 2; }
}

class Rectangle extends Shape {
  constructor(w, h) { this.w = w; this.h = h; }
  area() { return this.w * this.h; }
}

SOLID Principles

Principle	Description
S - Single Responsibility	One class = One job
O - Open/Closed	Open for extension, closed for modification
L - Liskov Substitution	Subclass should be substitutable for parent
I - Interface Segregation	Many specific interfaces > One general
D - Dependency Inversion	Depend on abstractions, not concretions

📚 Resources

Last Updated: March 2026