Question

What are comments? Describe the various comments used in Java.

Short answer

Comments in Java are used for code documentation and consist of single-line (//), multi-line (/* */), and documentation comments (/ ** */).

Step-by-step solution

Understanding Comments

Comments are notes written in the source code to explain what the code does. They are ignored by the compiler and are used to make the code more understandable to humans.

Single-line Comments

In Java, single-line comments start with two forward slashes (//). Everything after this symbol on the same line is ignored by the compiler. For example: ```java // This is a single-line comment int x = 10; // Initialize x to 10 ```

Multi-line Comments

For comments that span multiple lines, Java uses a slash followed by an asterisk (/*) to start the comment and ends with an asterisk followed by a slash (*/). Everything between these symbols is considered a comment. For example: ```java /* This is a multi-line comment */ int y = 20; ```

Documentation Comments

Java supports documentation comments, which start with a slash followed by two asterisks (/ **), and end with an asterisk followed by a slash (*/). These comments can be used to produce HTML documentation and are placed above classes, methods, or fields. For example: ```java /** * Main class for the program */ public class Main { /** * Main method of the program * @param args Command-line arguments */ public static void main(String[] args) { } } ```

Key concepts

Single-line Comments

In Java, single-line comments are used to add short explanations or notes within your code. They help someone reading your code understand its purpose without diving into the logic. To add a single-line comment, you begin with two forward slashes (`//`). Anything following these slashes on the same line will be treated as a comment and ignored during the program's execution.

Single-line comments are typically used to quickly explain a portion of code or annotate variables and logic. This is the simplest form of commenting because it occupies only one line, making your code clearer and more readable.

For instance, you might have a line like this: ```java // Initialize the counter variable int counter = 0; ``` In this example, the comment explains that the variable `counter` is initialized, which can be very helpful when revisiting the code or when others are trying to understand your logic. Remember, a well-commented code is often easier to maintain.

Multi-line Comments

Multi-line comments in Java are essential when you need to add descriptions or notes that extend beyond a single line. They allow you to comment out larger sections of code, which can be incredibly useful for disabling code during the debugging process or while explaining complex logic.

To create a multi-line comment, you start with a `/*` and end with a `*/`. Everything in between these markers is treated as a comment and disregarded by the compiler. Here’s an example of using multi-line comments: ```java /* * This section of code initializes * the variables required to calculate * the area of a rectangle. */ int length = 5; int breadth = 10; ``` Multi-line comments are ideal for providing detailed explanations without cluttering your code with single-line comments on every line. By using this method, you can maintain readability while ensuring all necessary information is conveyed.

Documentation Comments

Java's documentation comments are unique as they allow developers to generate HTML-based documentation directly from their code. These comments help create a bridge between human-readable documents and the codebase, which is exceedingly useful for larger, collaborative projects.

To write a documentation comment, you begin with `/**` and end with `*/`. They are often used to describe class structures, methods, or variables, and can include special tags for further detailing. For example: ```java /** * This class handles user authentication * Uses hashing to secure user passwords. */ public class Authenticator { } ``` One of the standout features is the use of tags within these comments. Tags like `@param`, `@return`, and `@throws` allow developers to specify details about method parameters, return values, and exceptions. Here's a method example with tags: ```java /** * Signs in the user with the provided username and password. * * @param username the user's login name * @param password the user's password * @return true if sign in is successful * @throws AuthenticationException if the login fails */ public boolean signIn(String username, String password) throws AuthenticationException { } ``` Documentation comments are essential for creating comprehensive guides directly from code, ensuring that documentation stays up to date with the codebase.