Introduction to Kotlin

What is Kotlin?

Kotlin is a modern, statically-typed programming language created by JetBrains. It first appeared in 2011, reached 1.0 in 2016, and in 2017 Google announced first-class support for Kotlin on Android — making it the preferred language for Android development in 2019.

Kotlin is concise, null-safe, and fully interoperable with Java. It runs on the Java Virtual Machine (JVM) but also compiles to native binaries, JavaScript, and WebAssembly, which makes it a true multiplatform language.

flowchart TB
    SRC["Kotlin source (.kt)"]

    SRC --> JVM["Kotlin/JVM<br/>(server, Android, desktop)"]
    SRC --> NAT["Kotlin/Native<br/>(iOS, embedded, CLI)"]
    SRC --> JS["Kotlin/JS<br/>(web frontends)"]
    SRC --> WASM["Kotlin/Wasm<br/>(WebAssembly)"]

    JVM --> ANDROID["Android apps"]
    JVM --> SERVER["Backend services"]
    NAT --> IOS["iOS / native apps"]

Why Kotlin?

Feature	What it means for you
Concise	Less boilerplate than Java — data classes, type inference, no semicolons
Null safety	The type system separates nullable (String?) from non-null (String), eliminating most NullPointerExceptions at compile time
Java interop	Call Java from Kotlin and Kotlin from Java seamlessly; adopt it gradually in existing projects
Coroutines	First-class, structured concurrency for asynchronous code without callback hell
Multiplatform	Share business logic across Android, iOS, web, and backend
Tooling	Built by the makers of IntelliJ IDEA, so IDE support is excellent

A first taste

Here is the same idea in Java and Kotlin so you can see the difference in style:

// Java
public class Greeter {
    public String greeting(String name) {
        return "Hello, " + name + "!";
    }
}

// Kotlin
fun greeting(name: String): String = "Hello, $name!"

Kotlin infers types where it can, supports top-level functions (no class required), and uses string templates ($name) for interpolation.

You do not need to know Java to learn Kotlin. This guide assumes only basic programming familiarity. Where Kotlin improves on Java, we will point it out.

Where this guide goes

• Parts 1–2 get you set up and teach the core syntax.
• Parts 3–5 cover object-oriented and functional programming.
• Part 6 introduces coroutines for concurrency.
• Parts 7–8 build real Android apps, from foundations to advanced architecture.
• Part 9 ties everything together with capstone projects.

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Next: Setting Up Your Environment