How to apply comments in Java

Comments in Java are a crucial part of writing clear, understandable, and maintainable code. They allow you to annotate your code with explanations or notes, which can be helpful for yourself or others who read your code in the future. Comments are ignored by the Java compiler, so they do not affect the execution of your program.

Java supports three types of comments:

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

1. Single-Line Comments

Single-line comments are used for brief explanations or notes about a specific line or block of code. They begin with // and extend to the end of the line.

Example:

public class Main {
    public static void main(String[] args) {
        // This is a single-line comment
        System.out.println("Hello, World!"); // This prints Hello, World! to the console
    }
}

In the example above, the comment // This is a single-line comment explains that the following line prints a message to the console. The comment after the System.out.println statement provides additional context about what that line does.

2. Multi-Line Comments

Multi-line comments are used when you need to write longer explanations or comments that span multiple lines. These comments begin with /* and end with */.

Example:

public class Main {
    public static void main(String[] args) {
        /*
         * This is a multi-line comment.
         * It can span multiple lines.
         * It is useful for providing detailed explanations.
         */
        System.out.println("Hello, World!");
    }
}

In this example, the multi-line comment provides a detailed explanation spanning several lines. This type of comment is particularly useful for documenting more complex sections of your code.

3. Documentation Comments

Documentation comments, also known as “doc comments,” are a special type of comment used to generate external documentation for your code. These comments start with /** and end with */. They are typically placed before classes, methods, or fields and can include tags for more detailed descriptions.

Example:

/**
 * The Main class implements an application that
 * simply prints "Hello, World!" to the standard output.
 */
public class Main {
    /**
     * This is the main method which makes use of the println method.
     * @param args Unused.
     * @return Nothing.
     */
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

In this example, the documentation comment above the Main class provides a summary of the class’s purpose. The documentation comment above the main() method describes the method and includes a @param tag for the method’s parameters and a @return tag for the return value, even though main() doesn’t return anything.

When you use a tool like Javadoc, these comments are extracted to generate HTML documentation for your code, which is useful for other developers who use your classes and methods.

Why Use Comments?

• Clarity: Comments can make your code easier to understand by explaining what your code does, why you made certain decisions, or how a particular algorithm works.
• Maintenance: Well-commented code is easier to update and maintain. If you or someone else needs to make changes to the code in the future, comments can provide valuable context.
• Collaboration: When working on a team, comments help other developers understand your code more quickly, which can lead to more efficient collaboration.

Best Practices for Writing Comments

• Be concise: Comments should be clear and to the point. Avoid unnecessary verbosity.
• Keep comments up-to-date: Ensure that comments accurately reflect the code they describe. Outdated comments can be misleading.
• Avoid obvious comments: Don’t state the obvious. For example, don’t comment int x = 5; with // Declare an integer variable x and assign it the value 5. The code is already self-explanatory.

Summary

In this chapter, you’ve learned about the different types of comments in Java—single-line, multi-line, and documentation comments. Comments are an essential tool for writing readable, maintainable, and well-documented code. By using comments effectively, you can make your Java programs easier to understand and maintain, both for yourself and for others who may work with your code in the future.