Java Comments - Single-line, Multi-line, and Documentation Comments

Comments in Java

Every great codebase tells a story — not just through what it does, but through how clearly it’s explained.

Comments don’t affect how a program runs. Instead, they help other people (and your future self) understand, maintain, and debug the code more easily.

You can use comments to:

• Clarify complex logic
• Mark sections for future improvement
• Disable parts of the code temporarily
• Generate documentation (JavaDoc)

Types of Comments in Java

Java supports three main types of comments:

1. Single-line Comments
2. Multi-line Comments
3. Documentation Comments

1. Single-line Comments

These are used for short explanations or notes.

// This is a single-line comment
System.out.println("Hello, World!"); // Print statement

Here is a simple example, where we use single line comments when doing addition of two numbers.

public class AdditionExample {
    public static void main(String[] args) {
        // Declare two integer variables and assign values
        int num1 = 10;
        int num2 = 20;

        // Add the two numbers and store the result in sum
        int sum = num1 + num2;

        // Print the result to the console
        System.out.println("The sum is: " + sum);
    }
}

Hello, World!

Explanation: The lines starting with // are ignored by the compiler. Only the System.out.println() line executes and prints the output.

2. Multi-line Comments

Multi-line Comments are used when you want to explain something in more than one line. These can also be used to temporarily disable blocks of code during testing or debugging.

/* This is a multi-line comment.
   It can span several lines.
   Useful for detailed notes or explanations. */
System.out.println("Multi-line comment demo");

Multi-line comment demo

Note: Everything between /* and */ is ignored by the compiler.

3. Documentation Comments (JavaDoc)

Specially formatted comments used to generate official documentation. These comments are placed just before class, method, or field declarations.

/**
 * This class demonstrates JavaDoc comments.
 * @author Mallikarjuna
 * @version 1.0
 */
public class Example {

    /**
     * This method prints a greeting.
     * @param name The name to greet
     */
    public void greet(String name) {
        System.out.println("Hello, " + name);
    }
}

Usage Tip: Use the javadoc tool to generate HTML documentation from JavaDoc comments:

javadoc Example.java

Best Practices for Commenting in Java

• Write comments that add value—don't repeat the code.
• Keep them up-to-date. Outdated comments can mislead developers.
• Use comments to explain "why" more than "what".
• Avoid cluttering your code with excessive comments—clarity is key.

Common Mistakes to Avoid while Writing Comments

• Using comments to excuse bad code. Refactor instead.
• Leaving debug comments in production code.
• Overusing JavaDoc for private/internal methods that don’t need documentation.