ZetCode

Kotlin Hello World

last modified January 10, 2023

This article shows how to create a Hello World program in Kotlin.

Kotlin is a statically-typed programming language that runs on the Java virtual machine.

Kotlin was created by JetBrains. Kotlin is and object-oriented and functional programming language. Kotlin was designed to be a pragmatic, concise, safe, and interoperable programming language.

Installing Kotlin compiler

We install the Kotlin compiler with SDKMAN. 

$ sdk install kotlin

SDKMAN is a tool for managing parallel versions of multiple Software Development Kits on most Unix based systems. 

$ kotlin -version
Kotlin version 1.6.21-release-334 (JRE 17.0.3+6-LTS)

We check the version.

Kotlin Hello World example

The following program prints a simple message to the console.

hello.kt
package com.zetcode

fun main() {

    println("Hello, World!")
}

The Kotlin source files have .kt extension. Note that in Kotlin we do not have to use semicolons. 

package com.zetcode

A source file may start with a package declaration. Packages are use to organize types. Unlike Java, Kotlin does not require the packages to match the directory structure; however, it is good practice to do so. 

fun main() {

    println("Hello, World!")
}

The main function is an entry point to the program. A function is declared with the fun keyword. In Kotlin, we do not have to put a function into a class. The println function prints a message to the console. The main function takes an array of strings as a parameter. Notice that in Kotlin the types follow the variable names after a colon character.

Compiling Kotlin program

We are going to compile and run the program from the command line. 

$ kotlinc hello.kt

With the kotlinc compiler, we compile the source. 

$ ls com/zetcode/
HelloKt.class

The compiler creates a HelloKt.class in the com/zetcode subfolder. 

$ kotlin com/zetcode/HelloKt.class 
Hello World!

We run the program with the kotlin tool.

Packaging Kotlin program

Next we are going to show how to package a Kotlin program into a Java JAR file. 

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

With the -include-runtime option, we include Kotlin runtime into the resulting JAR file. 

$ java -jar hello.jar
Hello, World!

We run the program with java tool.

In this tutorial, we have created a simple program in Kotlin. The program was built and run with command line tools.

List all Kotlin tutorials.