Introduction to Kotlin

Kotlin is a statically-typed language that runs on the same JVM Java does, and is Google's preferred language for Android development.

Example: a minimal Kotlin program

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

Hello, world!

Kotlin can call any existing Java code directly, but with more concise syntax — fun main() needs no wrapping class the way Java's public class Main { public static void main(...) } does. Kotlin also catches a lot of "null" errors at compile time instead of at runtime: a variable's type has to explicitly allow null (written String? instead of just String) before it's even permitted to hold one, which prevents an entire, very common category of Java crash from happening in the first place.