📝 What You’ll Learn

• What OOP is and why it's used
• How to create classes and objects
• Concepts like encapsulation, inheritance, and polymorphism
• Real-world analogies to understand OOP better

🧠 What is OOP?

Object-Oriented Programming is a style of programming based on the concept of "objects" — like real-world entities.

Java is built entirely around OOP.

Think of a class as a blueprint, and an object as an actual item built from it.

🧰 Creating a Class

public class Car {
    String color;
    int speed;

    void drive() {
        System.out.println("Driving at " + speed + " km/h");
    }
}

This is a blueprint of a Car. It has attributes (color, speed) and a behavior (drive()).

🛠️ Creating Objects

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car();  // create an object
        myCar.color = "Red";
        myCar.speed = 60;

        myCar.drive();  // Output: Driving at 60 km/h
    }
}

🧱 Encapsulation

Encapsulation = data hiding. Use private variables and public getters/setters:

public class BankAccount {
    private double balance;

    public void deposit(double amount) {
        balance += amount;
    }

    public double getBalance() {
        return balance;
    }
}

🧬 Inheritance

Inheritance = a class can inherit fields and methods from another class.

class Animal {
    void speak() {
        System.out.println("Some sound");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Bark!");
    }
}

🎭 Polymorphism

Polymorphism = the same method name can behave differently depending on the object.

class Animal {
    void sound() {
        System.out.println("Some sound");
    }
}

class Cat extends Animal {
    void sound() {
        System.out.println("Meow");
    }
}

Animal myAnimal = new Cat();
myAnimal.sound();  // Output: Meow

👥 Constructors

Special methods used to initialize objects.

public class Person {
    String name;

    Person(String n) {
        name = n;
    }
}

🔍 Example: Simple Class

public class Student {
    String name;
    int age;

    void introduce() {
        System.out.println("Hi, I'm " + name);
    }

    public static void main(String[] args) {
        Student s = new Student();
        s.name = "Alice";
        s.age = 20;
        s.introduce();  // Output: Hi, I'm Alice
    }
}

📘 Recap

• OOP helps organize code using objects and classes
• Key concepts: encapsulation, inheritance, polymorphism
• Java is a fully OOP language — master this to build real-world apps