Including Multi-Line Code Examples in Javadoc Comments (Java, HTML, Javadoc)

In Java, Javadoc comments are special comments used to document classes, methods, fields, and other program elements. These comments are processed by the Javadoc tool to generate API documentation in HTML format.

When you need to illustrate the usage of a method or class with code snippets, you can include those snippets within your Javadoc comments. This enhances the clarity and usefulness of your documentation.

Methods to Include Multi-Line Code

There are two primary approaches to incorporate multi-line code examples in Javadoc comments:

1. Using the <pre> Tag (HTML Preformatted Text):

   • Enclose your code snippet within <pre> and </pre> tags.
   • This preserves the original formatting of the code, including indentation and line breaks.

   /**
    * Calculates the factorial of a number.
    *
    * @param n The non-negative integer for which to calculate the factorial.
    * @return The factorial of n.
    * @throws IllegalArgumentException if n is negative.
    *
    * <pre>
    * public static long factorial(int n) {
    *   if (n < 0) {
    *     throw new IllegalArgumentException("n must be non-negative");
    *   }
    *
    *   long result = 1;
    *   for (int i = 2; i <= n; i++) {
    *     result *= i;
    *   }
    *   return result;
    * }
    * </pre>
    */
   

Choosing the Right Method

• If you prioritize exact formatting preservation, use the <pre> tag.
• If simplicity is your main concern and formatting isn't critical, use the {@code} tag.

Additional Considerations

• While <pre> tags preserve formatting, they can introduce extra whitespace in the generated HTML documentation.
• For complex code examples, consider using a separate code block outside the Javadoc comment and referencing it within the comment using a link. This helps keep the Javadoc comment more concise and readable.

/**
 * This method reverses a given string.
 *
 * @param str The string to be reversed.
 * @return The reversed string.
 *
 * <pre>
 * public static String reverseString(String str) {
 *   StringBuilder sb = new StringBuilder();
 *   for (int i = str.length() - 1; i >= 0; i--) {
 *     sb.append(str.charAt(i));
 *   }
 *   return sb.toString();
 * }
 * </pre>
 */

This example preserves the indentation and line breaks within the code snippet.

Example 2: Using {@code} Tag (Simpler but Might Lose Formatting)

/**
 * This method checks if a number is even.
 *
 * @param num The number to check.
 * @return True if the number is even, false otherwise.
 *
 * {@code
 * public static boolean isEven(int num) {
 *   return num % 2 == 0;
 * }
 * }
 */

1. Linking to External Code Blocks:

   • If your code example is lengthy or complex, consider placing it in a separate code block outside the Javadoc comment. This helps keep the Javadoc comment concise and easier to read.
   • Within the comment, use a link (preferably HTML anchor tag <a> with href) to reference the external code block.
   • This approach is beneficial for organizing large code snippets and enhancing readability of the Javadoc comment itself.

2. Code Comments within Code Snippet (Limited Usefulness):

   • Java supports single-line comments (//) and multi-line comments (/* */) within the code itself.
   • While technically possible to include comments within the code snippet included in the Javadoc comment, this approach is generally not recommended.
   • It can create confusion and clutter, especially if the code you're documenting already has comments. This method might be considered for very specific scenarios where you need to highlight a particular line or section within the included code snippet.

3. Javadoc Tools with Advanced Formatting (Third-Party):

   • Some third-party Javadoc tools offer advanced formatting options for code examples. These tools might allow more control over indentation, syntax highlighting, and other aspects of the code presentation within the generated documentation.
   • However, this approach introduces additional dependencies and might not be suitable for all projects. It's important to evaluate the trade-offs before using a third-party tool.