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Kotlin Comments

A comment is a note written in code for people to read. The compiler ignores every comment.

A comment above code

The note above the println explains that line. Only the greeting reaches the screen.

fun main() {
    // Show a greeting
    println("Hello")
}

A comment after code

The note after the code explains that println line. The shown words are the only output.

fun main() {
    println("Hello again") // Show another greeting
}

A block comment

The block note spans two lines above the println lines. Both shown words still appear in order.

fun main() {
    /* Show two short lines
       Each line shows one word */
    println("First")
    println("Second")
}

Example

fun main() {
    // Show the title
    println("Morning")
    /* Show the next line
       The step shows below this note */
    println("Tea")
}

Key points

  • Use // to start a line comment.
  • A line comment runs to the end of its line.
  • Use /* to open a block comment and */ to close it.
  • A comment can sit above a line of code or after code on the same line.

In this example, a line comment sits above the first println, and that println shows Morning. A block comment sits above the second println, and that println shows Tea. No comment text reaches the screen.

Note

A program with comments gives the same output as the same program without them.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Kotlin Playground

Exercise

What does the compiler do with a comment?