Java Tutorial - Java Comments

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Comments in source provide information about the source code. It is a good practice to write comments to document the source code

There are three types of comment supported in Java.

1. Single-line,
2. Multiline and
3. Documentation comment.

Single-line comment

Java single line comment starts from // and ends till the end of that line.

public class Main {
  // This is a single line comment.
  public static void main(String[] argv) {
  }

}

Multiline comment

Java multiline comment is between /* and */. Everything from /* through */ is ignored by the compiler.

public class Main {
  /* This /*w  ww.  ja v a2 s.c o m*/
     is 
     a
     Multiline 
     comment.
  */
  public static void main(String[] argv) {
  }

}

Java documentation comment(Javadoc)

Javadoc Documentation comment is used to produce an HTML file that documents your program. In short we usually call Java documentation comment javadoc.

A Javadoc comment occupies one or more lines of source code. The documentation comment begins with a /** and ends with a */. Everything from /** through */ is ignored by the compiler.

The following example demonstrates a Javadoc comment:

/** 
* Application entry point 
* 
* @param args array of command-line arguments passed to this method 
*/ 
public static void main(String[] args) 
{ 
// TODO code application logic here 
}

This example begins with a Javadoc comment that describes the main() method. /** and */ contains a description of the method, which could include HTML tags such as <p>, <code> and /</code>, and the @param Javadoc tag (an @-prefixed instruction).

The following list identifies several commonly used tags:

• @author identifies the source code's author.
• @deprecated identifies a source code entity that should no longer be used.
• @param identifies one of a method's parameters.
• @see provides a see-also reference.
• @since identifies the software release where the entity first originated.
• @return identifies the kind of value that the method returns.

The following code has more documentation comments

/**/*w  w  w. ja v a  2s. c o m*/
 * A simple class for introducing a Java application.
 * 
 * @author yourName
 */
public class HelloWorld {
  /**
   * Application entry point
   * 
   * @param args
   *          array of command-line arguments passed to this method
   */
  public static void main(String[] args) {
    System.out.println("Hello, world!");
  }
}

We can extract these documentation comments into a set of HTML files by using the JDK's javadoc tool, as follows:

javadoc command defaults to generating HTML-based documentation for public classes and public/protected members of these classes.

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