Kotlin Classes and Objects: The Core of Object-Oriented Programming 🚀

Imagine you're a car manufacturer 🚗. You want to create multiple cars with similar properties but different details like color, model, and speed.

Instead of building each car from scratch, you design a blueprint (a class) and use it to create different cars (objects).

This is exactly how classes and objects work in Kotlin!

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📌 In this blog, we’ll explore:

✅ What are Classes and Objects? 🤔
✅ Defining a Class in Kotlin 🏗️
✅ Creating Objects from a Class 🚗
✅ Class Constructors (Primary & Secondary) 🔨
✅ Properties and Methods 🛠️
✅ Visibility Modifiers 🔒
✅ Data Classes for Easy Modeling 📊
✅ Real-World Applications 🌍

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1️⃣ What are Classes and Objects? 🤔

📌 A class is a blueprint for creating objects. It defines:

• Properties (variables) 🏷️
• Methods (functions) ⚙️

📌 An object is an instance of a class.

💡 Example Analogy:

• 🏠 Class → Blueprint of a house.
• 🏡 Object → A real house built from that blueprint.

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2️⃣ Defining a Class in Kotlin 🏗️

🔹 Simple Class Definition

class Car {
    var brand: String = "Toyota"
    var speed: Int = 0

    fun accelerate() {
        speed += 10
        println("The car is now going at $speed km/h")
    }
}

✅ This defines a Car class with two properties (brand, speed) and a method (accelerate()).

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3️⃣ Creating Objects from a Class 🚗

🔹 Creating an Object

val myCar = Car()  // Creating an instance of Car
println(myCar.brand)  // Output: Toyota

myCar.accelerate()  // Output: The car is now going at 10 km/h

✅ Each object gets its own copy of the properties and methods!

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4️⃣ Class Constructors (Primary & Secondary) 🔨

🔹 Primary Constructor (Short & Clean)

class Car(val brand: String, var speed: Int) {
    fun accelerate() {
        speed += 10
        println("$brand is now going at $speed km/h")
    }
}

val car1 = Car("Tesla", 0)
car1.accelerate()  // Output: Tesla is now going at 10 km/h

✅ No need to declare brand and speed separately. The constructor does it!

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🔹 Secondary Constructor (Extra Initialization)

class Car {
    var brand: String
    var speed: Int

    constructor(brand: String, speed: Int) {
        this.brand = brand
        this.speed = speed
    }
}

✅ Use secondary constructors when additional setup is needed.

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5️⃣ Properties and Methods 🛠️

🔹 Adding More Methods

class Car(val brand: String, var speed: Int) {
    
    fun accelerate() {
        speed += 10
        println("$brand is now going at $speed km/h")
    }

    fun brake() {
        speed -= 10
        println("$brand slowed down to $speed km/h")
    }
}

val car = Car("Honda", 50)
car.accelerate()  // Output: Honda is now going at 60 km/h
car.brake()  // Output: Honda slowed down to 50 km/h

✅ Objects interact with their own properties and methods!

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6️⃣ Visibility Modifiers 🔒

📌 Control who can access properties and methods.

Modifier	Access Level
public	Default. Accessible from anywhere.
private	Accessible only inside the class.
protected	Accessible inside the class and subclasses.
internal	Accessible within the same module.

🔹 Example: Using private

class BankAccount(private var balance: Double) {
    
    fun deposit(amount: Double) {
        balance += amount
        println("Deposited $$amount. New balance: $$balance")
    }

    fun withdraw(amount: Double) {
        if (amount <= balance) {
            balance -= amount
            println("Withdrew $$amount. Remaining balance: $$balance")
        } else {
            println("Insufficient funds!")
        }
    }
}

val account = BankAccount(1000.0)
account.deposit(500.0)  // Output: Deposited $500.0. New balance: $1500.0
account.withdraw(2000.0)  // Output: Insufficient funds!

✅ balance is private, so it can’t be modified directly from outside.

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7️⃣ Data Classes for Easy Modeling 📊

📌 Used for holding data with built-in toString(), equals(), and copy().

🔹 Example:

data class User(val name: String, val age: Int)

val user1 = User("Alice", 25)
println(user1)  // Output: User(name=Alice, age=25)

val user2 = user1.copy(age = 30)
println(user2)  // Output: User(name=Alice, age=30)

✅ No need to manually define toString() or equals().

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8️⃣ Real-World Applications 🌍

🔹 1. Modeling a Student System

class Student(val name: String, var grade: Int) {
    
    fun promote() {
        grade += 1
        println("$name is now in grade $grade!")
    }
}

val student = Student("John", 10)
student.promote()  // Output: John is now in grade 11!

✅ Used in schools and universities to manage student details.

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🔹 2. Creating a Simple Inventory System

class Product(val name: String, var price: Double) {
    
    fun applyDiscount(discount: Double) {
        price -= price * (discount / 100)
        println("New price of $name: $$price")
    }
}

val laptop = Product("Laptop", 1000.0)
laptop.applyDiscount(10.0)  // Output: New price of Laptop: $900.0

✅ Used in e-commerce and retail systems.

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🔟 Conclusion: Object-Oriented Power in Kotlin 🎯

✅ Classes act as blueprints for objects.
✅ Objects are created from classes and have properties & methods.
✅ Constructors simplify object creation.
✅ Visibility modifiers protect data.
✅ Data classes are useful for modeling data.

💡 Now, go ahead and create your own Kotlin classes! 🚀

💬 What would you like to model using Kotlin classes? Let me know in the comments! ⬇️😊