Comments in Java

Comments are an essential part of any programming language, including Java. They are used to explain and document code, making it easier to read and maintain. Comments are ignored by the Java compiler, so they do not affect the execution of the program.

Types of Comments

Single-line Comments

Single-line comments start with two forward slashes (//). Everything following // on that line is considered a comment and is ignored by the compiler.

Example

// This is a single-line comment
System.out.println("Hello, world!");  // This is an inline comment

Multi-line Comments

Multi-line comments start with /* and end with */. Everything between these markers is considered a comment and is ignored by the compiler.

Example

/*
 This is a multi-line comment
 that spans multiple lines.
 */
System.out.println("Hello, world!");

Documentation Comments

Documentation comments, also known as Javadoc comments, are used to generate API documentation. These comments start with /** and end with */. They can be used to describe classes, methods, and fields.

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.
     */
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Using Javadoc Comments

Javadoc comments can include special tags that provide additional information. Some commonly used Javadoc tags include:

• @param: Describes a method parameter.
• @return: Describes the return value of a method.
• @throws or @exception: Describes exceptions thrown by a method.
• @see: Provides a reference to another method, class, or field.
• @deprecated: Marks a method, field, or class as deprecated.

Example

/**
 * The Calculator class provides methods to perform basic arithmetic operations.
 */
public class Calculator {
    
    /**
     * Adds two integers.
     * @param a the first integer
     * @param b the second integer
     * @return the sum of a and b
     */
    public int add(int a, int b) {
        return a + b;
    }
    
    /**
     * Subtracts the second integer from the first.
     * @param a the first integer
     * @param b the second integer
     * @return the difference between a and b
     */
    public int subtract(int a, int b) {
        return a - b;
    }
}

Best Practices for Writing Comments

1. Be Clear and Concise: Write comments that are easy to understand. Avoid unnecessary words and jargon.
2. Keep Comments Up-to-date: Ensure comments are updated whenever the code changes to prevent outdated or misleading comments.
3. Avoid Obvious Comments: Do not comment on things that are self-explanatory or trivial.
4. Use Comments to Explain Why, Not What: Explain the reasoning behind a block of code rather than just describing what the code does.
5. Use Documentation Comments for Public APIs: Use Javadoc comments to document public classes, methods, and fields.

Example of Good Comments

/**
 * Returns the maximum of two integers.
 * 
 * @param a the first integer
 * @param b the second integer
 * @return the maximum of a and b
 */
public int max(int a, int b) {
    return (a > b) ? a : b;
}

Example of Bad Comments

// Increment x by 1
x = x + 1; // This is a bad comment because it restates the code