Your First Kotlin Program

The main() Function

Every runnable Kotlin program needs an entry point function called main, marked with the fun keyword. When you run the compiled program, execution starts at the first line inside main's curly braces.

Example: The main() Function

fun main() {
    println("Hello from main()")
}

Printing Hello, World

The classic first program in any language prints a greeting to the screen. In Kotlin, println("Hello, World!") does exactly that, sending the text to standard output followed by a newline.

Note: println adds a newline after the text; print does not.

Example: Printing Hello, World

fun main() {
    println("Hello, World!")
}

Understanding the Syntax

Curly braces { } mark the start and end of the function body, and each statement inside typically sits on its own line. Unlike some languages, Kotlin does not require a semicolon at the end of each line.

Example: Understanding the Syntax

fun main() {
    println("Curly braces group statements together")
    println("No semicolon needed at the end of a line")
}

Compiling and Running

Save the code in a file such as Hello.kt, then compile it with kotlinc Hello.kt -include-runtime -d hello.jar and run the result with java -jar hello.jar to see the output printed in your terminal.

Example: Compiling and Running

fun main() {
    println("Saved as Hello.kt, compiled, then run")
}