The main function

Learn the fun main(args: Array<String>) structure.

The main function

In Kotlin, the main function is where a program starts. Its simplest form is fun main(); it takes no parameters. To access command-line arguments, use the signature fun main(args: Array<String>).

Here args is an array of strings; each argument given with the program is read as args[0], args[1], and so on. If the program is run with no arguments, args.size is zero.

Exercise Print args

Write a fun main(args: Array<String>). Print the array length with println(args.size).

Show example solution

fun main(args: Array<String>) {
    println(args.size)
}

Which main signature?

Kotlin 2.x has two common main signatures: fun main() and fun main(args: Array<String>). Use the first for simple programs and the second when you need command-line arguments.

Whichever you choose, the program's entry point is always a function named main. IntelliJ IDEA supports both forms.

Test yourself

Complete the signature

fun main(args: Array<String____>) { }

Show answer

fun main(args: Array<String>>) { }

What is args an instance of?
- Int
- Boolean
- Array<String>
- Char
Show answer

Array<String> — args is an Array<String>; that is, an array of strings.
Match the concepts

main

Entry point
args

Command-line arguments
Array<String>

Array type
println

Output

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