Kotlin from Scratch in 2025: A Practical Guide for Beginners

Introduction: Why Kotlin is Your Best Choice in 2025

Kotlin is a modern, concise, and safe programming language that has become the standard for Android development in recent years and is actively used in backend, web, and even Data Science. In 2025, Kotlin is not just alive but thriving: Google officially recommends it for Android, JetBrains continues to develop the ecosystem, and the community is growing every day.

If you are a beginner and want to start programming, Kotlin is an ideal choice. It combines the simplicity of Python with the power of Java, while eliminating outdated syntax. In this article, we will break down where to start learning Kotlin in 2025, set up the development environment, write our first programs, and touch on key concepts. No boring theory — just practice.

1. Installation and Environment Setup

Before writing code, you need to prepare your workspace. In 2025, this is done in 10 minutes.

Step 1: Install JDK (Java Development Kit)

Kotlin runs on the Java Virtual Machine (JVM), so first install JDK version 17 or 21 (LTS). Download it from Adoptium or use OpenJDK. Install and verify:

java -version# Output: openjdk version "21.0.1" 2025-01-18

Step 2: Install IntelliJ IDEA Community Edition

The best IDE for Kotlin is IntelliJ IDEA from JetBrains. The Community version is free and includes everything you need. Download it from the official website.

Step 3: Create Your First Project

Open IntelliJ, click New Project, select Kotlin → Console Application. Name the project HelloKotlin and click Finish. Done! Your first project is created.

2. Kotlin Syntax: First Steps

Kotlin is known for its clean and expressive syntax. Let's write the classic Hello, World! program and break it down piece by piece.

Example 1: Hello, World!

fun main() {    println("Hello, Kotlin 2025!")}

What's happening here:

• fun — keyword for declaring a function.
• main() — the entry point of the program. Without it, the code won't run.
• println() — function to output a string to the console.
• The semicolon ; is optional — Kotlin is smart.

Run the code (▶️ button to the left of fun main). You will see the greeting in the console.

Example 2: Variables and Data Types

Kotlin supports two types of variables:

• val — immutable, like a constant.
• var — mutable.

fun main() {    val name = "Alex"  // immutable    var age = 25          // mutable    println("My name is $name, I am $age years old")        age = 26  // works, because it's var    // name = "Peter"  // Error! val cannot be changed}

Notice the string templates: $name and $age — this is inserting variables directly into the string. Very convenient.

Example 3: Conditional Statements

fun main() {    val score = 85    val grade = if (score >= 90) {        "Excellent"    } else if (score >= 75) {        "Good"    } else {        "Needs improvement"    }    println("Your grade: $grade")}

In Kotlin, if is an expression, not a statement. It returns a value, so you can assign the result to a variable.

3. Functions and Null Safety — The Pillars of Kotlin

Two main features of Kotlin that make code safer and shorter.

Functions: Declaration and Parameters

fun greet(name: String, age: Int): String {    r