Comments

Learn single-line (//) and multi-line (/* */) comments.

Why write comments?

Comments are text that Java ignores but explains the code to humans. Comments help you remember what code does later and help others understand it.

A single-line comment starts with //. Everything from the sign to the end of the line is a comment:

// This is a comment
System.out.println("Hello");

A multi-line comment is wrapped in /* */. A documentation comment /** */ is used for the javadoc tool.

Exercise Add a comment and println

Print Welcome to the screen with println. Add a // Greeting message comment above it.

Show example solution

// Greeting message
System.out.println("Welcome");

When should you write comments?

Comments are best used to explain why code is written a certain way. But instead of commenting every line, it is better to pick descriptive variable and method names.

A good comment explains the step of a complex calculation, the reason for an external dependency, or why a hack is needed. A bad comment just repeats what the code does line by line.

Documentation comments (/** */) are written for public methods and classes; javadoc generates HTML docs from them.

Test yourself

Complete the comment line

// This line is a ____

Show answer

// This line is a comment

Which of these is a valid comment?
- // Greeting message //
- // Greeting message
- ** Greeting message **
- /* Greeting message
Show answer

// Greeting message — A single-line comment starts with //.
Match the comment types

//

Single line
/* */

Multi-line
/** */

Documentation
javadoc

Doc tool

Next lesson: Class skeleton

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