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Kotlin Class and Objects Tutorial: Learn Object-Oriented Programming in Kotlin

Introduction to Kotlin Classes and Objects

In this Kotlin tutorial, we’ll delve into the essential concepts of object-oriented programming (OOP) using Kotlin. We’ll cover the basics of classes and objects, constructors, properties, and methods.

Classes in Kotlin

A class in Kotlin is a blueprint for creating objects. It encapsulates data for the object and methods to operate on that data. Here’s how you define a class in Kotlin:

class MyClass {
    // Properties
    var myProperty: String = "Hello"

    // Method
    fun myMethod() {
        println("Method invoked")

Creating Objects

To create an object of a class in Kotlin, you simply use the new keyword followed by the class name, as shown below:

val myObject = MyClass()


In Kotlin, constructors are defined using the constructor keyword. If there are no annotations or visibility modifiers, the constructor keyword can be omitted.

class Person constructor(firstName: String, lastName: String) {
    // Properties
    var fullName = "$firstName $lastName"

Properties and Methods

Properties in Kotlin are declared using either val (immutable) or var (mutable) keywords. Methods are declared inside the class and can be called on objects of that class.

class Rectangle {
    var length: Int = 0
    var width: Int = 0

    fun calculateArea(): Int {
        return length * width

Access Modifiers

Kotlin supports the following access modifiers: public (default), private, protected, internal. You can control the visibility of classes, properties, and methods using these modifiers.

Example: Using Classes and Objects

Let’s create a simple example to demonstrate the usage of classes and objects in Kotlin:

fun main() {
    val rectangle = Rectangle()
    rectangle.length = 5
    rectangle.width = 3
    println("Area of the rectangle: ${rectangle.calculateArea()}")


In this Kotlin tutorial, we’ve covered the fundamentals of classes and objects. You’ve learned how to create classes, objects, constructors, properties, and methods in Kotlin. Object-oriented programming is a powerful paradigm, and Kotlin provides concise syntax to work with classes and objects effectively. Start building your Kotlin applications using these concepts!

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