Kotlin: Hello World program

 ‘.kt’ is the extension for kotlin files. Create a file ‘HelloWorld.kt’ with below content.

HelloWorld.kt

fun main(args:Array<String>){
 println("Hello World")
}

Keyword ‘fun’ is used to define a function.

‘main’ is the main function of the application. Program execution starts from here.

args:Array<String>

In Kotlin variable name is declared first, followed by the type. In above case, args is variable of type array of strings.

println("Hello World")

Above statement prints the message ‘Hello World’ to the console. As you see, unlike java, Kotlin statements do not end with ‘;’.

Compile HelloWorld.kt
Open command prompt and type the command ‘kotlinc HelloWorld.kt’.

C:\Users\Krishna\Documents\Study\Kotlin\Programs>kotlinc HelloWorld.kt

C:\Users\Krishna\Documents\Study\Kotlin\Programs>dir
 Volume in drive C is OSDisk
 Volume Serial Number is 1034-4F6F

 Directory of C:\Users\Krishna\Documents\Study\Kotlin\Programs

09/02/2017  11:18 AM    <DIR>          .
09/02/2017  11:18 AM    <DIR>          ..
09/02/2017  11:09 AM                57 HelloWorld.kt
09/02/2017  11:18 AM               980 HelloWorldKt.class
09/02/2017  11:18 AM    <DIR>          META-INF
               2 File(s)          1,037 bytes
               3 Dir(s)  63,190,188,032 bytes free

As you see the output of dir command, you can observe, kotlin generates ‘HelloWorldKt.class’ and a META-INF directory.

Run HelloWorld.kt
You can run the HelloWorldkt file using ‘kotlin HelloWorldKt’ command.

C:\Users\krishna\Documents\Study\Kotlin\Programs>kotlin HelloWorldKt
Hello World

Creating and run jar

You can also create a jar file and run the jar file using java launcher.

Use the command ‘kotlinc HelloWorld.kt -include-runtime -d HelloWorld.jar

‘ to create a jar file.

The ‘include-runtime’ option tells kotlin compiler, include kotlin run time in HelloWorld.jar file.

C:\Users\Krishna\Documents\Study\Kotlin\Programs>kotlinc HelloWorld.kt -include-runtime -d HelloWorld.jar

C:\Users\Krishna\Documents\Study\Kotlin\Programs>dir
 Volume in drive C is OSDisk
 Volume Serial Number is 1034-4F6F

 Directory of C:\Users\Krishna\Documents\Study\Kotlin\Programs

09/02/2017  11:24 AM    <DIR>          .
09/02/2017  11:24 AM    <DIR>          ..
09/02/2017  11:24 AM           869,262 HelloWorld.jar
09/02/2017  11:09 AM                57 HelloWorld.kt
               2 File(s)        869,319 bytes
               2 Dir(s)  63,401,816,064 bytes free

Once the jar file is created, you can call the jar file, just like how you run other jar files. Use the command ‘java -jar HelloWorld.jar’

C:\Users\Krishna\Documents\Study\Kotlin\Programs>java -jar HelloWorld.jar
Hello World

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