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Kotlin Hello World tutorial

Kotlin Hello World tutorial 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

From the official Github repository, we download Kotlin from the releases link. It comes in a ZIP archive. (Kotlin is built into the IntelliJ IDEA IDE.)

$ unzip kotlin-compiler-1.2.21.zip

We unzip the archive.

$ mv kotlinc ~/bin/

We move the directory into a destination of our choice.

$ export PATH=$PATH:~/bin/kotlinc/bin/

We add the path to the Kotlin compiler to .bashrc or .profile files.

Kotlin Hello World example

The following program prints a simple message to the console.

hello.kt
package com.zetcode

fun main(args: Array<String>) {
    
    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(args: Array<String>) {
    
    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
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. You might also be interested in the related tutorials: Kotlin variables tutorial, Kotlin control flow tutorial, Kotlin read file tutorial, and Kotlin write file tutorial.