Kotlin Hello World
last modified August 24, 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.
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 article we have created a simple program in Kotlin. The program was built and run with command line tools.
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