Comments

Learn to write // and /* */ comments in Kotlin.

Comments: // and /* */

Comments are notes the Kotlin compiler ignores. Single-line comments start with // and run to the end of the line. Block comments start with /* and end with */; they can span multiple lines.

Comments explain code; they do not affect the compiled output. Clear names and short comments keep code readable.

// a single-line comment
/* this is
   a block
   comment */

KDoc /** */

Kotlin offers a special comment form called KDoc for documentation. KDoc starts with /** and ends with */; it can hold tags like @param and @return.

Functions with KDoc show up as tooltips in the IDE. So when you use a library, you easily see what a function does.

/**
 * Sums two numbers.
 * @param a the first number
 * @param b the second number
 * @return the sum
 */
fun add(a: Int, b: Int): Int = a + b

Exercise Add a comment

Complete this code: a fun main() with a println("Hello Kotlin") inside. Add a single-line comment before println; the comment must start with // and contain a short note.

Show example solution

fun main() {
    // start
    println("Hello Kotlin")
}

Test yourself

Which is a single-line comment?
- # a comment
- 
- -- a comment
- // a comment
Show answer

// a comment — A line starting with // is a single-line comment.

Complete the comment

println("Hello") ____ a comment

Show answer

println("Hello") // a comment

Comments: match the terms

//

Single line
/* */

Block comment
/** */

KDoc
#

Invalid

Next lesson: String templates

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