How to Comment in Java: Syntax and Examples

In Java, you can add comments using // for single-line comments, /* ... */ for multi-line comments, and /** ... */ for documentation comments. Comments are ignored by the computer and help explain your code to others or yourself.

Syntax

Java supports three types of comments:

• Single-line comment: Starts with // and continues to the end of the line.
• Multi-line comment: Starts with /* and ends with */, can span multiple lines.
• Documentation comment: Starts with /** and ends with */, used to generate documentation.

java

// This is a single-line comment

/*
 This is a multi-line comment
 It can span several lines
*/

/**
 * This is a documentation comment
 * It is used by tools like Javadoc
 */

Example

This example shows all three comment types in a simple Java program that prints a message.

java

public class CommentExample {
    public static void main(String[] args) {
        // Print a greeting message
        System.out.println("Hello, world!");

        /*
         This is a multi-line comment.
         It explains that the program ends here.
        */
    }

    /**
     * This method is not used but shows a documentation comment.
     * @return A greeting string
     */
    public static String greet() {
        return "Hello!";
    }
}

Output

Hello, world!

Common Pitfalls

Common mistakes when commenting in Java include:

• Forgetting to close multi-line comments, which causes errors.
• Using // for multi-line comments instead of /* ... */.
• Placing comments inside string literals, which does not create a comment.

java

// Wrong: multi-line comment not closed
/* This comment starts but never ends */

// Right: properly closed multi-line comment
/* This comment starts and ends properly */

Quick Reference

Comment Type	Syntax	Use Case
Single-line	// comment text	Short notes or explanations on one line
Multi-line	/* comment text */	Longer explanations spanning multiple lines
Documentation	/** comment text */	Generate API docs with Javadoc tool

Key Takeaways

Use // for single-line comments to explain brief points.

Use /* ... */ for multi-line comments to explain longer ideas.

Use /** ... */ for documentation comments to create API docs.

Always close multi-line comments properly to avoid errors.

Comments do not affect program execution but improve code readability.