Guide to Commenting Out Multiple Lines in Java

Understanding How to Comment Out Multiple Lines in Java

Java, one of the most popular programming languages, provides various tools and methods to manage and organize code effectively. Commenting is a crucial part of coding in Java, allowing developers to annotate parts of the codebase for clarity and to disable execution of code blocks without deleting them. This guide will cover different methods to comment out multiple lines in Java, helping both novice and experienced programmers manage their coding projects more conveniently.

Why Commenting is Important?

Before diving into the specifics, let’s understand the importance of commenting in programming:

  • Documentation: Comments provide insights into what a specific part of code does, especially in complex algorithms.
  • Maintenance: Well-commented code is easier to update or modify by anyone, especially in team environments.
  • Debugging: Commenting out sections of code helps in isolating problematic code segments without removing them.

Methods for Commenting Out Multiple Lines in Java

In Java, there are primarily two ways to comment out multiple lines: using block comments and using single-line comments repeatedly. Each method has its own appropriate use-cases, which we will explore below.

1. Using Block Comments

Block comments, also known as multi-line comments, are used to comment out large blocks of code quickly. The syntax for block comments in Java is as follows:

   Code to be commented 
   More code to be commented

This method is highly effective for disabling many lines of code with just a couple of delimiters. Here’s how you use block commenting effectively:

  • Begin with /* to start commenting.
  • End with */ to stop commenting. Everything between these markers will be considered a comment.

Example of block commenting:

int a = 50;
int b = 30;
int sum = a + b;

This snippet effectively prevents multiple lines of Java code from being compiled and executed by enclosing them in block comment markers.

2. Using Single-Line Comments Repeatedly

A single-line comment starts with // and comments out everything from the symbol to the end of the line. This method is useful for temporarily disabling specific lines or adding brief notes. However, you can use single-line comments for multiple lines consecutively:

// int a = 50;
// int b = 30;
// int sum = a + b;
// System.out.println(sum);

This approach gives you the flexibility to uncomment individual lines by removing the // marker, which can be particularly useful during debugging or when adjusting parts of your code gradually.

When to Use Each Commenting Method?

Choosing when to use block comments over single-line comments depends on your specific scenario:

  • Use block comments when you need to disable large blocks of code quickly without the intention of selectively enabling some lines from the commented section.
  • Use single-line comments when you anticipate the need to turn some lines back on individually or when adding explanations adjacent to each line of code.

Best Practices for Commenting Code in Java

While commenting out code is helpful, it’s essential to follow best practices to keep your codebase clean and understandable:

  • Keep comments updated: As you change your code, update the comments to reflect the changes.
  • Avoid commenting obvious code: Only comment code that does complex operations or where the logic isn’t immediately apparent.
  • Use comments to explain ‘why’ not ‘what’: Your code should already be self-explanatory for what it does; use comments to explain why a particular approach was taken.

Conclusion and Final Recommendations

Commenting multiple lines of code in Java is straightforward but needs careful consideration to maintain code readability and ease of maintenance. Here’s a quick recommendation based on different scenarios:

  • For large projects: Use block comments to handle big chunks of code that you want to disable for an extended period.
  • For debugging: Use single-line comments to selectively toggle specific lines during troubleshooting.
  • For code review and collaboration: Consider using both, but keep comments clear and relevant to help other developers understand your thought process.


Can I nest comments in Java?
No, Java does not support nested commenting. Nesting block comments can lead to compilation errors.

Is there a keyboard shortcut to comment out multiple lines in Java in most IDEs?
Yes, most Java IDEs like Eclipse or IntelliJ IDEA provide shortcuts to comment out multiple lines. Typically, it’s Ctrl + / or Cmd + / depending on your operating system.

Should I comment out code that is no longer in use?
It’s generally better to delete code that is no longer used to keep the codebase clean. Use version control systems to keep a history of changes instead.

What should I include in a comment?
Comments should include explanations of complex logic, reasons for specific implementation choices, and any information relevant to future revisions or other developers.

How do comments impact the performance of Java applications?
Comments do not affect the runtime performance of Java applications as they are ignored at compile time.

We encourage you to ask questions, post comments, or share your experiences regarding using comments in Java programming. Your insights are valuable to us and can help improve the usefulness of this guide.