Introduction to Kotlin: Where to Start in 2025

Introduction to Kotlin: Where to Start in 2025

Kotlin is a modern, statically typed programming language that is rapidly gaining popularity among developers worldwide. In 2025, it has firmly established itself as the primary language for Android development (official Google support), and is also actively used for backend, desktop applications, and even web development. If you have decided to start your journey in IT or expand your technology stack, Kotlin will be an excellent choice. In this article, we will break down where to start learning Kotlin in 2025 and show simple code examples.

Why Kotlin in 2025?

Kotlin was created by JetBrains and first introduced in 2016. In recent years, it has come a long way. Here are the key reasons why you should choose Kotlin right now:

• Full compatibility with Java: Kotlin runs on the Java Virtual Machine (JVM) and can use all existing Java libraries. This means you don't lose access to a huge ecosystem.
• Concise and safe syntax: Kotlin code is on average 30-40% shorter than equivalent Java code. At the same time, the language eliminates many common errors (for example, NullPointerException).
• Multiplatform (KMP): With Kotlin Multiplatform, you can write shared code for Android, iOS, web, and desktop. This is a trend in 2025.
• Active community and jobs: The demand for Kotlin developers is steadily growing, especially in mobile development and fintech.

Installation and Environment Setup

To start writing in Kotlin, you will need to install several tools. The easiest way is to use IntelliJ IDEA Community Edition (free version from JetBrains).

Step-by-step instructions:

1. Download and install IntelliJ IDEA from the official JetBrains website.
2. Make sure you have Java Development Kit (JDK) version 17 or higher installed. Kotlin is fully compatible with modern JDKs.
3. When creating a new project, select the "Kotlin" template and configure the build tool (Gradle or Maven).
4. For a quick start, you can use the online compiler Kotlin Playground directly in your browser (play.kotlinlang.org).

Example of a simple "Hello, World!" program in Kotlin:

fun main() {    println("Hello, Kotlin world!")}

Run this code — and you will see the greeting in the console. Congratulations, the first step is done!

Kotlin Syntax Basics

Kotlin is a language that combines the best of object-oriented and functional programming. Let's look at the basic constructs you will need first.

Variables: val and var

Kotlin has two keywords for declaring variables:

• val — an immutable reference (analogous to final in Java). The value cannot be changed after assignment.
• var — a mutable reference. The value can be changed.

val name = "Anna"  // immutablevar age = 25       // mutableage = 26           // OK// name = "Olga"  // Compilation error

Functions

Functions are declared using the keyword fun. Kotlin supports functions with expressions and default values:

fun sum(a: Int, b: Int): Int {    return a + b}

// Shorthand notation (single-expression function)fun multiply(x: Int, y: Int) = x * y

fun main() {    println(sum(5, 3))      // 8    println(multiply(4, 2)) // 8}

Conditional Expressions and when

Instead of the cumbersome switch, Kotlin uses when — a more powerful and flexible operator: