Comments are non-executable lines of text used to annotate and document code. They provide explanations, notes, or descriptions to aid understanding and maintenance of the code. They serve as documentation for other developers or for the original coder when revisiting the code after some time. Comments are ignored by the compiler and do not affect the execution of the program.

Types of Comments

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

Single Line Comments

They start with // and extend to the end of the line. They are used for short, inline comments or annotations.

// This is a single-line comment
int x = 10; // Initializing variable x

Multi-Line Comments

They start with /* and end with */. They can span multiple lines and are used for longer comments or commenting out large blocks of code. Anything between these two comment symbols is ignored by the compiler.

/*
 * This is a multi-line comment.
 * It can span multiple lines and is useful for longer explanations.
 */

Documentation Comments

They start with /** and end with */. They are used to generate documentation automatically using tools like Javadoc. They typically precede classes, methods, or fields and provide detailed documentation about their purpose, parameters, return values, etc.

/**
 * This is a documentation comment for a class.
 * It provides detailed information about the class.
 */
public class MyClass {
    /**
     * This is a documentation comment for a method.
     * It explains the purpose, parameters, and return value of the method.
     * @param x The first parameter
     * @param y The second parameter
     * @return The sum of x and y
     */
    public int add(int x, int y) {
        return x + y;
    }
}

Best Practices for Using Comments:

1. Be Descriptive: Write comments that explain the intent behind the code, rather than describing what the code does.
2. Keep Comments Updated: Maintain comments to reflect changes in code. Outdated comments can be misleading.
3. Avoid Redundancy: Write comments that add value. Avoid duplicating information that is already clear from the code itself.
4. Use Javadoc for Public APIs: Document public classes, methods, and fields using Javadoc comments to generate API documentation automatically.
5. Keep Comments Concise: Write clear and concise comments. Long-winded comments can be overwhelming and difficult to maintain.
6. Comment Where Necessary: Focus on commenting code sections that are complex, non-obvious, or may require explanation. Avoid over-commenting simple or self-explanatory code.

Does bytecode/.class file contains comments added by programmers? No, comments are not included in the class files.