Hello, World

Since the release of C Programming Language, most programming books have begun with a simple “Hello, world” example, and in keeping with tradition, here’s the source code for a Kotlin “Hello, world” example:

fun main(args: Array<String>) {
    println("Hello, world")

Using a text editor, save that source code in a file named Hello.kt.

This code is similar to Java (and Scala), but notice a few things about it:

  • A Kotlin function is declared with the fun keyword
  • Compared to Java, you only have to write println as opposed to System.out.println
  • In Kotlin, functions don’t have to be inside classes, so it’s perfectly legal to put a function like this in a file by itself

A fun thing about Kotlin is that you can easily create a jar file with the kotlinc compiler, so run this command at your command line prompt to compile that source code and create a jar file named Hello.jar:

$ kotlinc Hello.kt -include-runtime -d Hello.jar

Then execute the jar file with this java command:

$ java -jar Hello.jar
Hello, world

Welcome to the Kotlin world!

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