Javadoc


Javadoc is a documentation generator created by Sun Microsystems for the Java language for generating API documentation in HTML format from Java source code. The HTML format is used for adding the convenience of being able to hyperlink related documents together.
The "doc comments" format used by Javadoc is the de facto industry standard for documenting Java classes. Some IDEs, like IntelliJ IDEA, NetBeans and Eclipse, automatically generate Javadoc HTML. Many file editors assist the user in producing Javadoc source and use the Javadoc info as internal references for the programmer.
Javadoc also provides an API for creating doclets and taglets, which allows users to analyze the structure of a Java application. This is how JDiff can generate reports of what changed between two versions of an API.
Javadoc does not affect performance in Java as all comments are removed at compilation time. Writing comments and Javadoc is for better understanding the code and thus better maintaining it.

History

Javadoc was an early Java language documentation generator. Prior to the use of documentation generators it was customary to use technical writers who would typically write only standalone documentation for the software, but it was much harder to keep this documentation in sync with the software itself.
Javadoc has been used by Java since the first release, and is usually updated upon every new release of the Java Development Kit.
The @field syntax of Javadoc has been emulated by documentation systems for other languages, including the cross-language Doxygen, the JSDoc system for JavaScript, and Apple's HeaderDoc.

Technical architecture

Structure of a Javadoc comment

A Javadoc comment is set off from code by standard multi-line comment tags /* and */. The opening tag, has an extra asterisk, as in /**.
  1. The first paragraph is a description of the method documented.
  2. Following the description are a varying number of descriptive tags, signifying:
  3. # The parameters of the method
  4. # What the method returns
  5. # Any exceptions the method may throw
  6. # Other less-common tags such as @see

    Overview of Javadoc

The basic structure of writing document comments is to embed them inside
/**... */. The Javadoc is written next to the items
without any separating newline. Note that any import statements must precede the class declaration. The class declaration usually
contains:

// import statements
/**
* @author Firstname Lastname

* @version 1.6
* @since 1.2
*/
public class Test

For methods there is a short, concise, one line description to
explain what the item does. This is followed by a longer
description that may span multiple paragraphs. The details
can be explained in full here. This section is
optional. Lastly, there is a tag section to list the accepted input
arguments and return values of the method. Note that all of the
Javadoc is treated as HTML so the multiple paragraph sections
are separated by a "<p>" paragraph break tag.

/**
* Short one line description.
*


* Longer description. If there were any, it would be
* here.
*


* And even more explanations to follow in consecutive
* paragraphs separated by HTML paragraph breaks.
*
* @param variable Description text text text.
* @return Description text text text.
*/
public int methodName

Variables are documented similarly to methods with the exception that
part is omitted. Here the variable contains only the short
description:

/**
* Description of the variable here.
*/
private int debug = 0;

Note that it is not recommended to define multiple variables in a single documentation comment. This is because Javadoc reads each variable and places them separately to the generated HTML page with the same documentation comment that is copied for all fields.

/**
* The horizontal and vertical distances of point
*/
public int x, y; // AVOID

Instead, it is recommended to write and document each variable separately:

/**
* The horizontal distances of point.
*/
public int x;
/**
* The vertical distances of point.
*/
public int y;

Table of Javadoc tags

Some of the available Javadoc tags are listed in the table below:
Tag & ParameterUsageApplies toSince
@author John SmithDescribes an author.Class, Interface, Enum
Represents the relative path to the generated document's root directory from any generated page.Class, Interface, Enum, Field, Method
@version versionProvides software version entry. Max one per Class or Interface.Class, Interface, Enum
@since since-textDescribes when this functionality has first existed.Class, Interface, Enum, Field, Method
@see referenceProvides a link to other element of documentation.Class, Interface, Enum, Field, Method
@param name descriptionDescribes a method parameter.Method
@return descriptionDescribes the return value.Method
@exception classname description
@throws classname description		Describes an exception that may be thrown from this method.Method
@deprecated descriptionDescribes an outdated method.Class, Interface, Enum, Field, Method
Copies the description from the overridden method.Overriding Method1.4.0
Link to other symbol.Class, Interface, Enum, Field, Method
Identical to, except the link's label is displayed in plain text than code font.Class, Interface, Enum, Field, Method
Return the value of a static field.Static Field1.4.0
Formats literal text in the code font. It is equivalent to .Class, Interface, Enum, Field, Method1.5.0
Denotes literal text. The enclosed text is interpreted as not containing HTML markup or nested javadoc tags.Class, Interface, Enum, Field, Method1.5.0
Used in the doc comment for a default serializable field.Field
Documents the data written by the writeObject or writeExternal methods.Field, Method
Documents an ObjectStreamField component.Field

Examples

An example of Javadoc to document a method follows. Notice that spacing and number of characters in this example are as conventions state.

/**
* Validates a chess move.
*
*

Use to move a piece.
*
* @param fromFile file from which a piece is being moved
* @param fromRank rank from which a piece is being moved
* @param toFile file to which a piece is being moved
* @param toRank rank to which a piece is being moved
* @return true if the move is valid, otherwise false
* @since 1.0
*/
boolean isValidMove
/**
* Moves a chess piece.
*
* @see java.math.RoundingMode
*/
void doMove