Hello, World Program is a basic Simple First program or application to code and learn any new programming language.

It just displays the hello world string to the console.

This post shows how to write a Hello World application in Kotlin Programming language.

How do you write Hello World in Kotlin?

The following are steps to run the Kotlin class from the command line.

  • Open Text editor
  • Create a helloworld.kt file and copy the below code, save the file
fun main(args: Array<String>) {
    println("Hello World.")
}
  • Open terminal, compile helloworld.kt file using kotlin compiler (kotlinc)
kotlinc helloworld.kt

Generates class files

  • Run kotlin helloworld.class command.

  • It prints the Hello World. to the console.

Kotlin Hello World example program

here is an example program to print Hello World to the console.

package com.w3schoolsio;
/*
* Hello.kt
* Kotlin Hello World Example
*/
fun main(args: Array<String>) {
    println("Hello World. Welcome")
}

The program contains the following components.

  • comments

Comments are useful text about the line of code that is ignored by the compiler. Comments can be single or multi-line comments.

/*
* Hello.kt
* Kotlin Hello World Example
*/
  • the main function It is a function and entry point for the Kotlin application. func is a keyword in Kotlin. The main function takes an array of strings from the command line.
  fun main(args : Array<String>) {
    }
  • println statement

println() is a function that prints the string inside double quotes to a standard output stream such as a console with an insertion new line.

How to compile and run the Kotlin application

kotlinc is a kotlin compiler used to compile and execute a program

kotlinc helloworld.kt

It generates helloworld.class in the com/w3schoolsio folder.

To run

kotlin com/w3schoolsio/helloworld.class
Hello World. Welcome

How to Package as a JAR file in Kotlin?

Below are steps to generate a self-executable jar file and execute from the terminal in Kotlin. You have written a program, compiled and executed the program in the command line. In real-time, You make the Kotlin program as a JAR file and run the program.

For example, here is an example to read command line arguments

fun main(args: Array<String>) {
    println("command line arguments " + args[0])
}

Following execute the Kotlin compiler command with the -include-runtime option package and generate an executable jar file.

kotlinc helloworld.kt -include-runtime -d helloworld.jar

Next, Run the program from the executable jar by supplying command line arguments.

java -jar helloworld.jar john

It is similar to running a Java executable jar file and Output

command line arguments john

How do I run a JAR file from the command line?

  • Create a helloworld.kt file in a Text editor and copy the below code, save the file
fun main(args: Array<String>) {
    println("Hello World.")
}
  • Open terminal, compile helloworld.kt file using kotlin compiler (kotlinc)
kotlinc helloworld.kt
  • Following kotlin compiler command with -include-runtime option package and generates class files and package as an executable jar file.
kotlinc helloworld.kt -include-runtime -d helloworld.jar

Next, execute the jar file the program from the executable jar by supplying command line arguments.

java -jar helloworld.jar john