Comments and documentation syntax in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the syntax for a single-line comment in Kotlin?

Use two forward slashes // before the comment text. Everything after // on that line is ignored by the compiler.

beginner

How do you write a multi-line comment in Kotlin?

Start with /* and end with */. Everything between these markers is treated as a comment, even if it spans multiple lines.

intermediate

What is the purpose of KDoc in Kotlin?

KDoc is Kotlin's documentation syntax. It helps you write clear explanations for classes, functions, and properties that tools can use to generate documentation.

intermediate

How do you write a KDoc comment for a function in Kotlin?

Use /** ... */ before the function. Inside, you can add descriptions and tags like @param and @return to explain parameters and return values.

advanced

Can you nest multi-line comments in Kotlin?

Yes, Kotlin allows nesting multi-line comments. You can start a new /* ... */ comment inside another multi-line comment.

Which symbol starts a single-line comment in Kotlin?

A /*

B <!--

C #

D //

Single-line comments in Kotlin start with two forward slashes //.

How do you write a multi-line comment in Kotlin?

A /* comment */

B # comment

C <!-- comment -->

D // comment

Multi-line comments in Kotlin start with /* and end with */.

What is the correct way to start a KDoc comment?

A /**

B /*

C //

D <!--

KDoc comments start with /** and end with */.

Which tag is used in KDoc to describe a function parameter?

A @throws

B @return

C @param

D @author

The @param tag describes a function parameter in KDoc.

Can multi-line comments be nested in Kotlin?

A No

B Yes

C Only in single-line comments

D Only in KDoc comments

Kotlin supports nesting multi-line comments inside other multi-line comments.

Explain the different types of comments available in Kotlin and when to use each.

Think about quick notes, longer explanations, and documentation.

Describe how to write a KDoc comment for a function including parameters and return value.

Imagine explaining your function to a friend who will use it.

Practice

1. Which of the following is the correct way to write a single-line comment in Kotlin?

easy

A. /* This is a single-line comment */

B.

C. // This is a single-line comment

D. # This is a single-line comment

Solution

1. Step 1: Identify single-line comment syntax in Kotlin

   Kotlin uses // to start a single-line comment.

2. Step 2: Compare options

   // This is a single-line comment uses //, which is correct. /* This is a single-line comment */ is for multi-line comments. <!-- This is a single-line comment --> is HTML style. # This is a single-line comment is used in some scripting languages but not Kotlin.

3. Final Answer:

   // This is a single-line comment -> Option C

4. Quick Check:

   Single-line comment = // [OK]

Hint: Single-line comments start with // in Kotlin [OK]

Common Mistakes:

• Using /* */ for single-line comments
• Using # or which are not Kotlin comments
• Confusing multi-line and single-line comment syntax

2. Which of the following is the correct syntax for a multi-line comment in Kotlin?

easy

A. /* This is a multi-line comment */

B.

C. /** This is a multi-line comment */

D. // This is a multi-line comment

Solution

1. Step 1: Recall multi-line comment syntax in Kotlin

   Kotlin uses /* ... */ to write multi-line comments.

2. Step 2: Analyze options

   /* This is a multi-line comment */ correctly uses /* ... */. // This is a multi-line comment is single-line comment syntax. /** This is a multi-line comment */ is documentation comment syntax. <!-- This is a multi-line comment --> is HTML comment syntax.

3. Final Answer:

   /* This is a multi-line comment */ -> Option A

4. Quick Check:

   Multi-line comment = /* ... */ [OK]

Hint: Multi-line comments use /* and */ to start and end [OK]

Common Mistakes:

• Using // for multi-line comments
• Confusing documentation comments /** */ with regular multi-line comments
• Using HTML style comments

3. What will be the output of the following Kotlin code?

fun main() {
    // println("Hello")
    println("World")
}

medium

A. Hello
World

B. World

C. Hello

D. No output

Solution

1. Step 1: Understand comment effect on code execution

   The line // println("Hello") is a comment, so it does not run.

2. Step 2: Identify which println runs

   Only println("World") runs, so output is "World".

3. Final Answer:

   World -> Option B

4. Quick Check:

   Commented code does not run = World [OK]

Hint: Commented lines do not execute, only uncommented print runs [OK]

Common Mistakes:

• Thinking commented println runs
• Expecting both lines to print
• Confusing comment syntax and output

4. Identify the error in the following Kotlin code snippet:

fun main() {
    /* This is a comment
    println("Hello")
}

medium

A. No error, code runs fine

B. Incorrect single-line comment syntax

C. Missing quotation marks in println

D. Missing closing */ for multi-line comment

Solution

1. Step 1: Check multi-line comment syntax

   The comment starts with /* but does not have a closing */.

2. Step 2: Understand impact of missing closing comment

   Without closing */, the compiler treats the rest as comment, causing syntax error.

3. Final Answer:

   Missing closing */ for multi-line comment -> Option D

4. Quick Check:

   Multi-line comments must close with */ [OK]

Hint: Always close multi-line comments with */ [OK]

Common Mistakes:

• Forgetting to close multi-line comments
• Confusing single-line and multi-line comment syntax
• Assuming code inside unclosed comment runs

5. Which comment style should you use in Kotlin to write documentation that tools can extract to generate API docs?

hard

A. /** This is a documentation comment */

B. /* This is a documentation comment */

C. // This is a documentation comment

D.

Solution

1. Step 1: Identify documentation comment syntax in Kotlin

   Kotlin uses /** ... */ for documentation comments that tools can parse.

2. Step 2: Compare with other comment types

   // This is a documentation comment is single-line comment syntax. /* This is a documentation comment */ is regular multi-line comment syntax. <!-- This is a documentation comment --> is HTML comment syntax.

3. Final Answer:

   /** This is a documentation comment */ -> Option A

4. Quick Check:

   Documentation comments use /** ... */ [OK]

Hint: Use /** ... */ for documentation comments in Kotlin [OK]

Common Mistakes:

• Using // or /* */ for documentation comments
• Confusing documentation comments with regular comments
• Using HTML comment style by mistake