Comments

Comments are notes you leave in your code for yourself and others. The computer ignores them completely, but they make your code way easier to understand later.

Single-line comments with //

Everything after // on a line is treated as a comment.

fun main() {
  // This is a single-line comment
  println("Comments are invisible to the machine")
  // println("This line won't run because it's commented out")
}
    

Multi-line comments with /* */

Use these when you need more than one line of explanation.

fun main() {
  /*
    This is a multi-line comment.
    You can write as much as you want here.
    None of it will affect the program.
  */
  println("See? No problem.")
}
    

KDoc — documenting your code /** */

For functions and classes, Kotlin has a special documentation comment format called KDoc. It starts with /** and uses @param and @return tags to describe what your code does.

/**
 * Calculates the square of a number.
 * @param x the number to square
 * @return x multiplied by itself
 */
fun square(x: Int): Int {
  return x * x
}

fun main() {
  println(square(5))
}
    

Most IDEs will show these docs when you hover over the function name.