View source for Javadoc

{{short description|Documentation generator for Java}}
{{how-to|date=August 2023}}
'''Javadoc''' (also capitalized as '''JavaDoc''' or '''javadoc''') is an [[Application programming interface|API]] [[documentation generator]] for the [[Java (programming language)|Java programming language]]. Based on information in Java [[source code]], Javadoc generates documentation formatted as [[HTML]] and other formats via [[Plug-in (computing)|extensions]].<ref>{{cite web |url=http://agile.csc.ncsu.edu/SEMaterials/tutorials/javadoc/ |title=Javadoc |website=agile.csc.ncsu.edu |access-date=12 January 2022 |archive-url=https://web.archive.org/web/20170613233020/http://agile.csc.ncsu.edu/SEMaterials/tutorials/javadoc/ |archive-date=13 June 2017 |url-status=dead}}</ref> Javadoc was created by [[Sun Microsystems]] and is owned by [[Oracle Corporation|Oracle]] today.

The content and formatting of a resulting document are controlled via special [[Markup language|markup]] in source code [[Comment (computer programming)|comments]]. As this markup is [[de facto standard]] and ubiquitous for documenting Java code,<ref>{{cite web|url = http://docs.oracle.com/javase/1.5.0/docs/tooldocs/solaris/javadoc.html|title = javadoc - The Java API Documentation Generator|access-date = 2011-09-30|publisher = [[Sun Microsystems]]}}.</ref> many [[Integrated Development Environment|IDE]]s extract and display the Javadoc information while viewing the source code; often via hover over an associated symbol. Some IDEs, like [[IntelliJ IDEA]], [[NetBeans]] and [[Eclipse (software)|Eclipse]], support generating Javadoc template comment blocks.<ref>[https://www.jetbrains.com/idea/ IntelliJ IDEA], [http://www.netbeans-blog.org/netbeans-ide/generating-javadoc-for-a-project-in-netbeans-ide.html NetBeans] {{Webarchive|url=https://web.archive.org/web/20170405230224/http://www.netbeans-blog.org/netbeans-ide/generating-javadoc-for-a-project-in-netbeans-ide.html |date=2017-04-05 }} and [http://www.eclipse.org/ Eclipse]</ref> The <code>@tag</code> syntax of Javadoc markup has been re-used by other documentation generators, including [[Doxygen]], [[JSDoc]], [https://www.erlang.org/doc/apps/edoc/chapter.html EDoc] and [[HeaderDoc]].

Javadoc supports extension via [[doclets]] and taglets, which allow for generating different output formats and for [[static analysis]] of a [[codebase]]. For example, [[JDiff]] reports changes between two versions of an API.

Although some criticize Javadoc and API document generators in general, one motivation for creating Javadoc was that more traditional (less automated) API documentation is often out-of-date or does not exist due to business constraints such as limited availability of [[API writer|technical writers]].<ref>{{cite web|url=http://www.artima.com/intv/jackpot3.html
|title=Visualizing with JavaDoc
|first1=Bill| last1=Venners| first2=James| last2=Gosling | display-authors=etal | publisher=artima.com
|date=2003-07-08
|access-date=2013-01-19
|quote=When I did the original JavaDoc in the original compiler, even the people close around me pretty soundly criticized it. And it was interesting, because the usual criticism was: a good tech writer could do a lot better job than the JavaDoc does. And the answer is, well, yeah, but how many APIs are actually documented by good tech writers? And how many of them actually update their documentation often enough to be useful?}}</ref> 

Javadoc has been part of Java since its first release, and is often updated with each release of the [[Java Development Kit]].<ref>{{cite web|url = http://www.oracle.com/technetwork/java/javase/documentation/index-137868.html|title = How to Write Doc Comments for the Javadoc Tool|access-date = 2011-09-30|publisher = [[Sun Microsystems]]}}.</ref> 

Javadoc and the source code comments used by Javadoc, do not affect the performance of a Java executable since comments are ignored by the compiler. 

== Markup ==

Javadoc ignores comments unless they are specially marked. A Javadoc comment is marked with an extra asterisk after the start of a multi-line comment: <code>/**</code>. A comment block pertains to the symbol that follows the block. 

An example of a class header block follows:

<syntaxhighlight lang="java">
/**
 * Provides some service
 * @author Jill Smith <address@example.com>
 * @version 1.6
 * @since 1.2
 */
public class Test {}
</syntaxhighlight>

For a method, the first line is a short description of the method. If more detail is warranted, then it may be followed by a longer description in additional paragraphs. Following that are optionally various tags.

Various aspects of HTML as supported via Javadoc. For example <code>&lt;p&gt;</code> denotes a paragraph break.

An example of a method header block follows:

<syntaxhighlight lang="java">
/**
 * One-line description
 * <p>
 * Longer description. If there were any, it would be here.
 * <p>
 * And even more explanation to follow in consecutive
 * paragraphs separated by paragraph break.
 *
 * @param variableName Description...
 * @return Description...
 */
public int methodName(...) { ... }
</syntaxhighlight>

Variables can also be documented. For example:

<syntaxhighlight lang="java">
/**
 * Description of the variable here
 */
private int debug = 0;
</syntaxhighlight>

A more complete example follows:

<syntaxhighlight lang="java">
/**
 * Validates a chess move
 *
 * <p>Use {@link #doMove(int fromFile, int fromRank, int toFile, int toRank)} 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(int fromFile, int fromRank, int toFile, int toRank) { ... }

/**
 * Moves a chess piece
 *
 * @see java.math.RoundingMode
 */
void doMove(int fromFile, int fromRank, int toFile, int toRank) { ... }
</syntaxhighlight>

== Markdown ==
From Java 23 onwards, Javadoc supports the [[Markdown]] standard CommonMark on comment lines that start with <code>///</code> instead of the older multiline format. <ref>https://openjdk.org/jeps/467</ref>

== Doclets ==
A Doclet program works with Javadoc to select which content to include in the documentation, format the presentation of the content and create the file that contains the documentation.<ref>{{cite web | url=https://docs.oracle.com/javase/8/docs/technotes/guides/javadoc/doclet/overview.html | title=Doclet Overview }}</ref> A Doclet is written in Java and uses the {{Javadoc:SE|jdk/javadoc/doclet|name=Doclet API|module=jdk.javadoc}},

The {{Javadoc:SE|jdk/javadoc/doclet|StandardDoclet|module=jdk.javadoc}}[https://docs.oracle.com/javase/9/javadoc/javadoc-command.htm#JSJAV-GUID-04BFA924-7C45-4E9C-91D1-0B77D97E65AB] included with Javadoc generates [[API]] documentation as frame-based [[HTML]] files. Other Doclets are available on the web {{Citation needed|reason=Is this still true today?|date=December 2017}}, often for free. These can be used to:
* Create other types of documentation (non-API)
* Output to a format other than HTML; such as [[PDF]]
* Output as HTML with additional features such as a search or with embedded [[Unified Modeling Language|UML]] diagrams generated from the Java classes

== Tags ==
{{Update|section|inaccurate=yes|reason=Should be updated according to the [https://docs.oracle.com/en/java/javase/21/docs/specs/javadoc/doc-comment-spec.html official documentation]|date=November 2023}}
Some of the available Javadoc tags<ref>[https://docs.oracle.com/en/java/javase/13/docs/specs/javadoc/doc-comment-spec.html JavaSE 13 Documentation Comment Specification]</ref> are listed in the table below:

{| class="wikitable"
!Syntax
!Usage
!Applies to
!Since
|-
|'''@author''' ''name''|| Identifies the author such as "Pat Smith" || Class, Interface, Enum ||
|-
|{'''@docRoot'''}
|Represents the relative path to the generated document's root directory from any generated page
|Class, Interface, Enum, Field, Method
|
|-
|'''@version''' ''version''|| Version information || Module, Package, Class, Interface, Enum ||
|-
|'''@since''' ''since-text''|| Describes when this functionality first existed || Class, Interface, Enum, Field, Method||
|-
|'''@see''' ''reference''|| Links to other element of documentation || Class, Interface, Enum, Field, Method||
|-
|'''@param''' ''name description''|| Describes a method parameter || Method||
|-
|'''@return''' ''description''|| Describes the return value || Method||
|-
|'''@exception''' ''classname description''<br />'''@throws''' ''classname description''|| Describes an exception that may be thrown from this method|| Method||
|-
|'''@deprecated''' ''description''|| Marks the method as outdated || Class, Interface, Enum, Field, Method||
|-
|{'''@inheritDoc'''}||Copies the description from the overridden method||Overriding Method||1.4.0
|-
|{'''@link''' ''<var>reference</var>''}||Link to other symbol||Class, Interface, Enum, Field, Method||
|-
|{'''@linkplain''' ''<var>reference</var>''}
|Identical to {@link}, except the link's label is displayed in plain text than code font
|Class, Interface, Enum, Field, Method
|
|-
|{'''@value''' ''#STATIC_FIELD''}|| Return the value of a static field||Static Field||1.4.0
|-
|{'''@code''' ''literal''}|| Formats literal text in the code font; equivalent to '''<code>{@literal}</code>''' || Class, Interface, Enum, Field, Method||1.5.0
|-
|{'''@literal''' ''literal''}|| Denotes literal text; the enclosed text is interpreted as not containing HTML markup or nested javadoc tags || Class, Interface, Enum, Field, Method||1.5.0
|-
|{'''@serial''' ''literal''}
|Denotes a default serializable field
|Field
|
|-
|{'''@serialData''' ''literal''}
|Denotes data written by the writeObject( ) or writeExternal( ) methods
|Field, Method
|
|-
|{'''@serialField''' ''literal''}
|Denotes an ObjectStreamField component
|Field
|
|}

== See also ==
* [[Comparison of documentation generators]]
* [[.NET documentation comments|.NET XML documentation comments]]

== References ==
{{Reflist}}

== External links ==
* [https://docs.oracle.com/en/java/javase/13/javadoc/javadoc.html Java Platform, Standard Edition Javadoc Guide]
* [https://www.jcp.org/en/jsr/detail?id=260 JSR 260] Javadoc Tag Technology Update [[Java Specification Request]] (defines new Javadoc tags)
* [https://web.archive.org/web/20130927133806/https://today.java.net/pub/a/today/2004/08/26/ashkelon.html Improve on Javadoc with ashkelon]
* [https://javadoc.allimant.org/ Various Java documentations converted to Windows Help format]

[[Category:Free documentation generators]]
[[Category:Source code documentation formats]]
[[Category:Java development tools]]