Introduction and Setup

What is Kotlin?

Kotlin is a modern programming language that runs on the JVM. It is concise, type-safe, and works smoothly with Java. You can use Kotlin for backend services, Android apps, cross-platform projects, and more.

The current stable version is Kotlin 2.4.x with the K2 compiler. The K2 compiler is faster and gives better error messages than the old compiler.

Install the Tools

You need two things:

1. JDK 17 or later — Kotlin compiles to JVM bytecode
2. IntelliJ IDEA (Community Edition is free) or Android Studio

Download IntelliJ IDEA from jetbrains.com/idea. It comes with Kotlin built in. No separate Kotlin installation needed.

To verify your setup, open IntelliJ IDEA and create a new Kotlin project:

1. Click New Project
2. Select Kotlin → JVM Application
3. Set the JDK to 17 or later
4. Click Create

Your First Kotlin Program

Open the generated Main.kt file and replace the content:

fun main() {
    val name = "Kotlin"
    println("Hello, $name!")
}

Click the green play button next to main() to run it.

Project Structure

Diagram: A typical Kotlin/JVM project layout with source, test, and build files.

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Key Terms

• .kt — Kotlin source file extension
• fun — keyword to declare a function
• val — read-only variable (preferred)
• var — mutable variable (use only when needed)
• $variable — string template, inserts a variable value into a string

Kotlin vs Java Quick Reference

What Next?

You have Kotlin running. The next step is learning variables, data types, and null safety — the feature that makes Kotlin different from Java.