Kotlin in 2026: Your First Lines of Code

Kotlin has rapidly ascended as a preferred language for modern software development, particularly for Android, offering conciseness and safety that traditional languages often lack. If you’re looking to enhance your development toolkit and embrace a language designed for the future, getting started with Kotlin is a smart move that will pay dividends. But how do you actually begin writing your first lines of code and building real-world applications?

1. Install IntelliJ IDEA Community Edition

The first step in your Kotlin journey is selecting the right Integrated Development Environment (IDE). While other options exist, I firmly believe IntelliJ IDEA Community Edition from JetBrains is non-negotiable for anyone serious about Kotlin. It’s the gold standard, offering unparalleled support for the language, superior code completion, and powerful refactoring tools. Don’t even think about VS Code for serious Kotlin work; it’s like bringing a knife to a gunfight when you need a full-fledged IDE.

To get it, navigate to the JetBrains website and download the latest Community Edition. As of 2026, we’re typically on version 2026.1 or newer. The installation process is straightforward: run the executable, accept the defaults, and let it do its magic. I always recommend letting it create desktop shortcuts for easy access.

Pro Tip: While the Ultimate Edition offers more features for web and enterprise development, the Community Edition is completely free and more than sufficient for all your Kotlin and Android development needs. Save your money for a good mechanical keyboard instead.

Common Mistake: Installing an older version or a different IDE like Eclipse. While theoretically possible, you’ll fight against missing features, subpar tooling, and a less intuitive experience. This isn’t a place to cut corners; start strong.

2. Configure Your Java Development Kit (JDK)

Kotlin compiles to JVM bytecode, which means you need a Java Development Kit (JDK) installed on your system. Even though you’re writing Kotlin, the JVM is its runtime. I’ve found that JDK 17 or higher provides the best compatibility and performance for modern Kotlin projects. You can download the latest LTS (Long Term Support) version from Adoptium (formerly AdoptOpenJDK), which provides free, open-source builds.

Once downloaded, install the JDK. On Windows, this usually involves running an installer. On macOS, it might be a .dmg file. After installation, you’ll want to ensure your system’s PATH environment variable includes the JDK’s bin directory. This allows your command line to find the java and javac commands. I’ve had clients in the past struggle with mysterious “command not found” errors simply because their PATH wasn’t set correctly. A quick check involves opening your terminal or command prompt and typing java -version. You should see output indicating your installed JDK version.

Pro Tip: IntelliJ IDEA often bundles a JDK or can automatically detect and download one for you. When you first launch IDEA, it might prompt you to configure a JDK. If it does, let it handle it; it’s usually the easiest way. However, having a system-wide JDK is good practice for other tools.

3. Create Your First Kotlin Project in IntelliJ IDEA

Now for the exciting part: creating your first project! Launch IntelliJ IDEA. You’ll be greeted by a welcome screen. Select “New Project”.

In the New Project wizard:

1. On the left pane, choose “Kotlin”.
2. On the right pane, select the “JVM | IDEA” template. This creates a simple Kotlin project that runs on the Java Virtual Machine.
3. For “Name”, enter MyFirstKotlinApp.
4. For “Location”, choose a directory where you want to store your projects (e.g., ~/Projects/Kotlin/MyFirstKotlinApp).
5. For “JDK”, ensure it points to your installed JDK 17+ (IntelliJ IDEA typically auto-detects this).
6. Click “Create”.

IntelliJ IDEA will then set up your project structure. You’ll see a src folder, and inside it, a Main.kt file. This is where your Kotlin code will live. The IDE will also configure Gradle or Maven for dependency management, though for a simple “Hello, World!” project, you won’t need to interact with it much yet.

Pro Tip: Get familiar with the project structure. The .idea folder contains IDE-specific settings, src is for source code, and out or build will hold your compiled classes. Understanding this basic layout makes debugging and project management much easier down the line.

Common Mistake: Choosing the “Android” template prematurely. While Kotlin is fantastic for Android, starting with a simple JVM project isolates you from Android-specific complexities, allowing you to focus purely on Kotlin syntax and concepts first.

4. Write and Run “Hello, World!”

Open the Main.kt file in your newly created project. You’ll likely see some boilerplate code already there, probably a main function. If not, type this in:

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

This is your classic “Hello, World!” program. fun main() is the entry point of your application, and println() prints the enclosed string to the console. Notice the lack of semicolons – a small but welcome syntactic sugar in Kotlin.

To run it, look for the green “play” icon next to the fun main() declaration in the gutter of the editor. Click it and select “Run ‘MainKt'”. Alternatively, you can go to Run > Run ‘MainKt’ from the top menu. A “Run” tool window will appear at the bottom of your screen, displaying the output:

Hello, Kotlin World!

Process finished with exit code 0

Congratulations! You’ve just written and executed your first Kotlin program. This confirms your environment is correctly configured and ready for more complex tasks.

Pro Tip: Experiment! Change the string inside println(), add another println() call, or even try declaring a simple variable like val name = "Alice" and printing it. This immediate feedback loop is crucial for learning.

5. Explore the Kotlin REPL

One of my favorite features for quickly testing Kotlin snippets is the REPL (Read-Eval-Print Loop). It’s an interactive console where you can type Kotlin code line by line and see the results instantly, without needing to compile and run a full project. This is invaluable for trying out new syntax, testing library functions, or just playing around.

To access the REPL in IntelliJ IDEA, go to Tools > Kotlin > Kotlin REPL. A new tool window will open, usually at the bottom or side. You can type expressions directly into it:

println("What's up, Kotlin?")

Press Enter, and you’ll see the output immediately below your input. You can also define variables and functions:

val message = "Learning Kotlin is fun!"
println(message.toUpperCase()) // Note: toUpperCase() is deprecated in favor of toUpper() in newer Kotlin versions

The REPL is fantastic for rapid prototyping and understanding how certain language constructs behave. I use it constantly when I’m exploring new features or trying to remember a specific function signature. It’s like a scratchpad for your code, and I tell every junior developer I mentor to use it extensively.

Case Study: Last year, our team at InnovateTech Solutions (a fictional but representative software consultancy) was migrating a legacy Java module to Kotlin. We needed to quickly prototype several data transformation functions to handle a complex JSON structure. Instead of building out full unit tests for each small function, I used the Kotlin REPL. I could paste in sample JSON, parse it, apply transformations, and immediately see the output. This iterative approach, powered by the REPL, allowed us to validate over 20 transformation rules in just two days, saving an estimated week of development time compared to our usual TDD (Test-Driven Development) cycle for such small, isolated logic. The ability to instantly evaluate expressions with real data was a game-changer for that specific task.

6. Learn Basic Kotlin Syntax and Concepts

With your environment set up, it’s time to dive into the language itself. Kotlin’s syntax is famously concise and expressive. Here are some fundamental concepts you’ll want to grasp immediately:

• Variables: Use val for immutable (read-only) variables and var for mutable (changeable) variables. Always prefer val when possible for safer code.
• Data Types: Kotlin has intuitive types like Int, Double, Boolean, String, etc. Type inference often means you don’t need to explicitly declare types.
• Functions: Defined with the fun keyword. Functions can have parameters and return values.
• Null Safety: One of Kotlin’s standout features! It helps eliminate NullPointerExceptions. Types are non-nullable by default; to allow nulls, you append a ? to the type (e.g., String?).
• Control Flow: Standard if/else, when (a more powerful switch statement), for loops, and while loops.
• Classes and Objects: Kotlin is object-oriented. You’ll learn about defining classes, properties, methods, and constructors.

A well-structured tutorial on the official Kotlin website is an excellent resource for this. I always direct my new hires there. Don’t try to memorize everything at once; focus on understanding the core principles and how they differ from other languages you might know.

Pro Tip: Practice small code challenges. Websites like Exercism.org offer structured exercises that help solidify your understanding of syntax and common programming patterns in Kotlin. Doing these regularly is far more effective than just reading documentation.

Common Mistake: Jumping straight into complex frameworks like Spring Boot or Android development without a solid grasp of core Kotlin. This inevitably leads to frustration when you encounter language-specific errors or patterns you don’t understand.

7. Explore Official Documentation and Community Resources

The official Kotlin documentation (kotlinlang.org) is an invaluable, authoritative resource. It’s meticulously maintained and provides comprehensive guides, language references, and examples. I cannot stress enough how important it is to treat this as your primary source of truth.

Beyond the official docs, engage with the vibrant Kotlin community. Forums, Stack Overflow, and Discord channels dedicated to Kotlin are excellent places to ask questions, share knowledge, and learn from others’ experiences. There are also numerous high-quality blogs and online courses that dive deeper into specific aspects of Kotlin development, from coroutines to multiplatform projects.

Pro Tip: Follow prominent Kotlin developers and advocates on social media (e.g., LinkedIn). They often share insights, best practices, and news about the language that can keep you informed and inspired. I’ve personally learned several optimization tricks from these informal channels.

Common Mistake: Relying solely on outdated tutorials or forum posts. The Kotlin language evolves, and what was best practice two years ago might be deprecated or superseded by a better approach today. Always cross-reference with official documentation.

Starting with Kotlin is a journey that begins with setting up your environment and then steadily building your understanding of its powerful features. By following these steps, you’ll establish a strong foundation for developing robust and efficient applications. The key is consistent practice and an eagerness to explore the language’s capabilities.