This document specifies the form of documentation comments recognized
by the standard doclet for the javadoc
tool in JDK 23, used
to generate HTML documentation for an API.
In the context of the javadoc
tool, the interpretation
of the content of a documentation comment is up to doclet that is used
to process the comment. Other doclets may accept the same syntax as the
standard doclet, or they may support an alternate syntax. However, due
to support in many tools, the syntax supported by the standard doclet
has become a de facto standard.
General Syntax
Documentation comments are stylized comments appearing in source code, near to the declarations that they serve to document.
Documentation comments are recognized only when placed immediately before the declaration of a module, package, class, interface, constructor, method, enum member, or field. In other words, a documentation comment should appear before any annotation, modifier, keyword, identifier, or other Java construct that is part of the declaration.
Documentation comments placed in the body of a method are ignored. Only one documentation comment per declaration statement is recognized.
The overall form of a documentation comment is an initial main description, followed by a series of block tags, which provide additional information about the declaration to which the comment applies. Descriptive text may include inline tags and HTML content, as described below. Leading asterisks at the beginning of each line, and any preceding whitespace, are ignored.
It is possible to have a comment with only block tags and no main description.
For historical reasons, the documentation comment for a package may
instead be provided in a file called package.html in a source
directory for the package. In this case, the documentation comment is
the content of the <body>
tag, and all references to
Java types (for example, in see
tags) must be fully
qualified. The standard doclet also allows additional documentation to
be provided in files such as overview.html. The rules for such
content are the same as for package.html.
Main Description
The main description in a documentation comment is the content from the beginning of the comment, up to the first block tag, if there are any, or to the end of the comment, if there are none. Leading and trailing whitespace is ignored. If there is no such content, the main description is said to be missing.
The main description cannot continue after any block tags.
Examples of a missing main description.
No content before the first block tag:
/** * @param ... * ... */
An empty documentation comment:
/** * */
The first sentence of the main description should be a summary sentence that contains a concise but complete description of the declared entity.
Block Tags
Block tags are of the form @
identifier
content and give additional details to be incorporated into the
generated documentation. Each block tag must appear at the beginning of
a line, ignoring leading asterisks, whitespace characters, and the
initial comment delimiter (/**
). This means you can use the
@
character elsewhere in the text and it will not be
interpreted as the start of a tag. If you want to start a line with the
@
character and not have it be interpreted, then use the
HTML entity @
. The content of a block tag is any
text following the tag up to, but not including, either the next block
tag, or the end of the documentation comment. The content can span
multiple lines.
There can be any number of block tags; some types of tags can be repeated while others cannot.
Inline Tags
Inline tags are of the form {@
identifier
content}
and provide details within the context of
the enclosing description. They may generally appear wherever
descriptive text and HTML is permitted, although some inline tags may
only be used at the beginning of the main description.
Some inline tags may contain free-form text. When such text
explicitly contains braces, the braces must be "balanced", implying an
equal number of appropriately nested left brace and right brace
characters, so that the closing brace of the inline tag can be
determined. No other lexical analysis of the text is performed; in
particular, there is no special consideration of characters like
'
, "
, \
, and @
.
Lines beginning with @
that are enclosed within an
inline tag are not considered as beginning a block tag.
When the text content is HTML, it may be possible to use entities
{
and }
to represent
unbalanced braces.
HTML Content
HTML content is not formally checked, although some tools may provide some amount of checking to help catch common errors.
In order to be able to generate documentation that conforms to the appropriate standards, the following considerations should be taken into account when using HTML constructs in a documentation comment:
HTML constructs should be written in HTML 5.
To support properly structured headings within the pages of generated documentation, headings in the documentation comments for module, package, and type declarations (including nested types) should start at
<h2>
and increase accordingly as needed; likewise, headings in the documentation comments for constructors, methods, fields and other members should start at<h4>
. In standalone HTML files, such as in adoc-files
subdirectory, headings should start at<h1>
.To avoid the possibility of a conflict with the unique identifiers used to identify positions within the generated documentation for the declaration of program elements, the values of user-defined
id
attributes should contain a character (such as-
) that is not a valid character in a Java identifier.
Leading Asterisks
When a documentation comment is read, leading asterisks
(*
) on each line are discarded, and blanks and tabs that
precede the initial asterisks (*
) are also discarded. If
you omit the leading asterisk on a line, then the leading whitespace is
no longer removed so that you can paste code examples directly into a
documentation comment inside a <pre>
tag with its
indentation preserved. Spaces are interpreted by browsers more uniformly
than tabs. Indentation is relative to the left margin (rather than the
separator /**
or <pre>
tag).
Escape Sequences
The following escape sequences are supported wherever text, entities and HTML may appear, to represent characters that would otherwise be inconvenient or difficult to represent:
@@
, to represent@
, to prevent it from being interpreted as part of the introduction of a block or inline tag,@/
, to represent/
, as part of*@/
to represent*/
, to avoid prematurely terminating the enclosing comment,@*
, to represent*
, where it would otherwise be discarded at the beginning of a line.
Escape sequences are context-sensitive, and can only be used where the use of the escaped character by itself would have a different syntactic interpretation. In other situations, these character sequences are taken literally, without additional interpretation.
Escape sequences cannot be used in inline tags that contain literal
text; this includes code
, literal
, snippet
, and user-defined tags.
References
References are the constructs in a documentation comment that refer to elements in the surrounding declarations. Depending on the context, they may refer to modules, packages, classes and interfaces, constructors, methods, annotation members, fields, enum members, parameters, record components and the names of exceptions that may be thrown by a method or constructor.
The most general form of a reference is:
- module
/
package.
class#
member
This form is used by the see
, link
and linkplain
tags.
Leading components can be omitted when they can be inferred from the
surrounding context. Trailing components can be omitted when they are
not required. Generally, the reference is evaluated in the scope in
which the documentation comment exists. In particular,
import
statements for the compilation unit are taken into
account when evaluating class and interface names.
The class may be any top-level or nested class or interface.
The member may be any constructor, method, annotation
member, field or enum member, but not a nested class or interface. As in
Java source code, a constructor is identified by using the name of its
class. The name of a constructor or method should normally be followed
by the list of its parameter types, enclosed in parentheses, although
the parameter types and parentheses can be omitted if the method or
constructor is not overloaded and the name is not also that of a field
or enum member in the same class or interface. When a parameter list is
given, whitespace characters may appear between tokens in the parameter
list; whitespace characters may not appear elsewhere in the reference.
When the reference is to a member of the same class as that containing
the documentation comment, all parts of the reference up to and
including the #
may be omitted, although the '#' may be
retained for clarity.
Parameterized types may be used in the class and member parts of the
reference; annotations may not be used anywhere in the reference.
Whitespace characters may occur between tokens within the parameter list
for a constructor or method. A trailing /
can be added to a
name to refer to a module in the presence of a package or class with the
same name.
Note: you cannot refer to the declaration of a specific parameter or record component with this form.
An alternative form is provided to generate references to arbitrary
URI fragments in the generated documentation such as headings in
documentation comments. This form uses a double hash mark
(##
) as separator:
- module
/
package.
class##
fragment
fragment is interpreted as URI fragment within the page documenting the specified program element.
Other tags, such as param
, throws
, and serialField
may only provide
support for the specific kinds of references that are relevant to each
tag. See the description of individual tags for more details.
Method Documentation
A documentation comment for a method declaration must at least provide the following:
the main description,
a
param
tag per method type parameter, if any,a
return
tag for the result, if the return type is notvoid
,a
param
tag per formal parameter, if any,a
throws
tag per exception type, checked or unchecked, in thethrows
clause, if any.
It is an error if any item described in that list is missing from a documentation comment of a method declaration and either of following is true:
- the declaration is not overriding, or
- the declaration is overriding and if the item were provided with an
inheritDoc
tag in its content, it would be an error.
Otherwise, a missing item is considered as if it were provided with
{@inheritDoc}
as its content.
For the purpose of this specification an overriding method
declaration is a method declaration that could be annotated with
@Override
(JLS
9.6.4.4), but is not an accessor method declaration for a record
component.
Method documentation allows inheritance by omission: if a documentation comment for a method declaration provides only some of the items, the rest are assumed to be inherited. For example, if this is provided:
/**
* @param scale a non-zero number
* @throws IllegalArgumentException if scale is 0
*/
@Override
<T> T magnify(int scale, T element) throws MagnificationException
This is assumed:
/**
* {@inheritDoc}
*
* @param <T> {@inheritDoc}
* @param scale a non-zero number
* @param element {@inheritDoc}
* @return {@inheritDoc}
* @throws IllegalArgumentException if scale is 0
* @throws MagnificationException {@inheritDoc}
*/
@Override
<T> T magnify(int scale, T element) throws MagnificationException
However, not all missing items can be inherited. For example, if a
method declares an exception X
that is not documented by
any of the methods that this method overrides, then documentation item
for that exception cannot be inherited and can only be provided by this
method's documentation comment. (Adding or assuming
@throws X {@inheritDoc}
would be an error.) If that item is
not provided, it is considered missing.
(@Override
is only added to these examples to emphasize
that the declarations are overriding; that annotation has no effect on
documentation.)
Note: a documentation comment consisting of a sole
inheritDoc
tag explicitly provides only the main
description of a method:
/**
* {@inheritDoc}
*/
Other items, if any, are inherited by omission.
Note: it's the overriding method, not the overridden method, that determines which items are missing and which aren't.
For example, if an overriding method declares a thrown exception
X
, but that method's documentation comment does not contain
@throws X ...
, then that documentation item is missing. If
an overriding method does NOT declare a thrown exception, even if the
overridden method does, then that documentation item is NOT missing.
This behavior is usually noticed when dealing with unchecked
exceptions. Since unchecked exceptions do not normally appear in the
throws
clause, unless explicitly documented, they will not
be missing. This gives rise to a misconception that the standard doclet
treats checked exceptions differently from unchecked exceptions, which
it does not.
In fact, a similar behavior might be replicated with checked
exceptions. Consider a method that declares two checked exceptions
X
and Y
, such that X
is a
supertype of Y
. If an overriding method declares
X
but not Y
, then @throws Y ...
won't be missing.
Overriding Methods in Classes and Interfaces
When a method declaration overrides a method in the superclass or an extended superinterface, the standard doclet generates the subheading "Overrides" in the documentation for the overriding method.
When a method declaration in a class overrides a method in an interface, the standard doclet generates the subheading "Specified by" in the documentation for the overriding method.
In both cases, a link to the overridden method is included.
Standard Tags
The following sections describe the standard block and inline tags supported by the standard doclet.
Note: The standard doclet also supports user-defined tags conforming to the same general syntactic rules.
author
@author
name-text
Adds an "Author" entry with the specified name text to the generated
documents when the -author
option is used. A documentation
comment can contain multiple author
tags. You can specify
one name per author
tag or multiple names per tag. In the
former case, the standard doclet inserts a comma (,
) and a
space between names. In the latter case, the entire text is copied to
the generated document without being parsed. Therefore, you can use
multiple names per line if you want a localized name separator other
than a comma.
Introduced in JDK 1.0.
code
{@code
text}
Equivalent to <code>{@literal
text
}</code>
.
Displays text in code font without interpreting the text as
HTML markup or nested Javadoc tags. This enables you to use regular
angle brackets (<
and >
) instead of the
HTML entities (<
and >
) in
documentation comments, such as in parameter types
(<Object>
), inequalities (3 < 4
), or
arrows (->
). For example, the documentation comment text
{@code A<B>C}
displayed in the generated HTML page
unchanged as A<B>C
. This means that the
<B>
is not interpreted as bold and is in code font.
If you want the same functionality without the code font, then use the
literal
tag.
Introduced in JDK 1.5.
deprecated
@deprecated
deprecated-text
This tag is used in conjunction with the @Deprecated
annotation to indicate that this API should no longer be used (even
though it may continue to work). The standard doclet moves deprecated
text ahead of the main description, placing it in italics and preceding
it with a bold warning.
The first sentence of deprecated text should tell the user when the
API was deprecated and what to use as a replacement. The standard doclet
copies the first sentence to the summary section and index. Subsequent
sentences can also explain why it was deprecated. You should include a
link
tag that points to the replacement API.
Introduced in JDK 1.0.
docRoot
{@docRoot}
Represents the relative path to the generated document's (destination) root directory from any generated page. This tag is useful when you want to include a file, such as a copyright page or company logo, that you want to reference from all generated pages. Linking to the copyright page from the bottom of each page is common.
The docRoot
tag can be used both on the command line and
in a documentation comment. The tag is valid in all documentation
comments: overview, module, package, class, interface, constructor,
method and field, including the text portion of any tag (such as the
return
, param
and deprecated
tags).
For example, on the command line, where the header, footer, or bottom are defined:
javadoc -bottom '<a href="{@docRoot}/copyright.html">Copyright</a>'.
When you use the {@docRoot}
tag this way in a make file,
some makefile programs require a special way to escape for the brace
{}
characters. For example, the Inprise MAKE version 5.2
running on Windows requires double braces: {{@docRoot}}
. It
also requires double (rather than single) quotation marks to enclose
arguments to options such as the -bottom
option (with the
quotation marks around the href
argument omitted).
For example, in a documentation comment:
/**
* See the <a href="{@docRoot}/copyright.html">Copyright</a>.
*/
This tag is needed because the generated documents are in
hierarchical directories, as deep as the number of subpackages. The
expression <a href="{@docRoot}/copyright.html">
resolves to <a href="../../copyright.html">
for
java/lang/Object.java and
<a href="../../../copyright.html">
for
java/lang/ref/Reference.java.
Introduced in JDK 1.3.
exception
@exception
exception-name description
This tag is equivalent to the throws
tag, which is now the recommended
form.
Introduced in JDK 1.0.
hidden
@hidden
Hides a program element from the generated API documentation. This tag may be used when it is not otherwise possible to design the API in a way that such items do not appear at all.
Introduced in JDK 9.
index
{@index
word description}
{@index "
phrase"
description}
Declares that a word or phrase, together with an optional short description, should appear in the index files generated by the standard doclet. The index entry will be linked to the word or phrase that will appear at this point in the generated documentation. The description may be used when the word or phrase to be indexed is not clear by itself, such as for an acronym.
Introduced in JDK 9.
inheritDoc
{@inheritDoc}
{@inheritDoc
supertype}
Indicates that a method documentation comment part that contains this tag is the same as that of the overridden method in a superclass or superinterface, which is either determined automatically or specified.
It is an error if the overridden method is missing the corresponding part.
This tag enables you to write more general comments higher up the inheritance hierarchy and to write around the inherited parts.
This tag is valid only in these places in a documentation comment of an overriding declaration of a method:
- the main description,
- the description of
param
,return
, andthrows
tags.
If the corresponding part of the overridden method's documentation
comment itself uses an inheritDoc
tag, then that tag is
processed first. (This might be applied recursively as required.)
Let m
be a method declaration in a class or interface
T
. If the documentation comment for m
contains
an inheritDoc
tag then the superclass or superinterface
(whose overridden method this tag will use the corresponding part of) is
determined as follows:
- If the tag has the form
{@inheritDoc S}
, then the superclass or superinterface isS
. It is an error, ifm
does not override fromT
a method inS
. - If the tag has the form
{@inheritDoc}
, then the superclass or superinterface is determined using automatic supertype search. It is an error if the automatic search cannot determine it.
Automatic Supertype Search
The search for the supertype is performed in two phases: the
recursive phase, then the final phase. For simplicity, the search starts
from S
, where S = T
, although there's nothing
to be found in T
(otherwise, the search would not be
required). When starting from S
, where S = T
,
the first condition always breaks into "otherwise" because a method does
not override itself (JLS
8.4.8.1).
Recursive phase
If S
declares a method that T.m
overrides,
then S
is a supertype, otherwise:
If S
is a class that has a direct superclass (JLS
8.1.4) that is not java.lang.Object
, then the recursive
phase of the search is applied to that superclass. If that application
has not found a supertype, then:
If S
has direct superinterfaces (JLS
8.1.5), then the recursive phase of the search is applied to each of
those superinterfaces, in the order that they are listed in the
extends
(if S
is a class) or
implements
(if S
is an interface) clause,
until the supertype found or superinterfaces are exhausted.
Final phase
If the recursive phase of search has not found the supertype, then
one final attempt is made to see if java.lang.Object
is the
supertype. If T
is a class and m
overrides a
method in java.lang.Object
, or T
is an
interface and m
's signature is override-equivalent to the
signature of a public method in java.lang.Object
(JLS
8.4.2), then java.lang.Object
is the supertype.
Otherwise, the search has not found the supertype.
Note: The search is performed in two phases so as to not prematurely
consider java.lang.Object
as the supertype. Sometimes
java.lang.Object
provides overly general documentation for
its public methods (such as equals
, hashCode
,
toString
) when more specific documentation is
available.
For example, consider this schematic hierarchy:
interface A
interface B extends A
interface C
class D implements B, C
interface E
class F extends D implements E
The automatic supertype search traverses that hierarchy in the following
order: F
, D
, B
, A
,
C
, E
, java.lang.Object
.
Note: The source file for an inherited method must be on the source path for the documentation comment to be available for copy. Neither the class nor its package needs to be passed in on the command line.
Introduced in JDK 1.4; accepts an optional argument since JDK 22.
link
{@link
reference label}
Inserts an inline link with a visible text label that points to the
documentation for the specified module, package, class, or member name
of a referenced class. This tag is valid in all documentation comments:
overview, module, package, class, interface, constructor, method and
field, including the description part of any tag, such as the
return
, param
and deprecated
tags.
This tag is similar to the third form of the see
tag. The main difference is that the
link
tag generates an inline link rather than placing the
link in the "See Also" section. The link
tag begins and
ends with braces to separate it from the rest of the inline text. If you
need to use the right brace (}
) inside the label, then use
the HTML entity notation }
.
There is no limit to the number of link
tags allowed in
a sentence.
For example, here is a comment that refers to the
getComponentAt(int, int)
method:
Use the {@link #getComponentAt(int, int) getComponentAt} method.
From this code, the standard doclet generates the following HTML (assuming it refers to another class in the same package):
Use the <a href="Component.html#getComponentAt(int,int)">getComponentAt</a> method.
The previous line appears on the web page as:
Use the getComponentAt method.
Introduced in JDK 1.2.
linkplain
{@linkplain
reference label}
Behaves the same as the link
tag, except the link label
is displayed in plain text rather than code font. Useful when the label
is plain text. For example,
Refer to {@linkplain #add() the overridden method}.
is displayed as:
Refer to the overridden method.
Introduced in JDK 1.4.
literal
{@literal
text}
Displays text without interpreting the text as HTML markup or nested
Javadoc tags. This enables you to use angle brackets (<
and >
) instead of the HTML entities
(<
and >
) in documentation
comments, such as in parameter types (<Object>
),
inequalities (3 < 4
), or arrows (->
).
For example, the documentation comment text
{@literal A<B>C}
displays unchanged in the generated
HTML page in your browser, as A<B>C
. The
<B>
is not interpreted as bold (and it is not in code
font). If you want the same functionality with the text in code font,
then use the code
tag.
Introduced in JDK 1.5.
param
@param
parameter-name description@param
<
type-parameter-name>
description
Adds a parameter with the specified parameter name followed by the
specified description to the "Parameters" section. The description may
continue onto multiple lines. This tag is valid only in a documentation
comment for a method, constructor, or class. The parameter name can be
the name of a parameter in a method or constructor, or the name of a
type parameter of a class, method, or constructor. Use angle brackets
(< >
) around such a parameter name to indicate the
use of a type parameter.
Example of a type parameter of a class:
/**
* @param <E> Type of element stored in a list
*/
public interface List<E> extends Collection<E> { ... }
Example of parameters, including type parameters, of a method:
/**
* @param string the string to be converted
* @param type the type to convert the string to
* @param <T> the type of the element
* @param <V> the value of the element
*/
<T, V extends T> V convert(String string, Class<T> type) { ... }
When an inheritDoc
tag is used
in the description of a method formal or type parameter, the
corresponding part of the overridden method documentation is matched
using the parameter's position, not the parameter's name (JLS
8.4.2 and JLS
8.4.4).
For example, consider the following method declaration:
/**
...
* @param scale a non-zero number
...
* @param <T> the type of the element being magnified
...
*/
<T> T magnify(int scale, T element) throws MagnificationException
Then as far as the documentation inheritance is concerned, these two comments are equivalent:
/**
...
* @param s {@inheritDoc}
* @param e {@inheritDoc}
...
* @param <E> {@inheritDoc}
*/
@Override
<E> E magnify(int s, E e) throws MagnificationException
/**
...
* @param scale {@inheritDoc}
* @param element {@inheritDoc}
...
* @param <T> {@inheritDoc}
*/
@Override
<T> T magnify(int scale, T element) throws MagnificationException
If parameter names differ, care should be taken when inheriting such parameter documentation because that parameter name might be referred to from elsewhere both in the overridden and overriding methods.
Introduced in JDK 1.0.
provides
@provides
service-type description
This tag may only appear in the documentation comment for a module declaration, and serves to document an implementation of a service provided by the module. The description may be used to specify how to obtain an instance of this service provider, and any important characteristics of the provider.
Introduced in JDK 9.
return
@return
description{@return
description}
As a block tag, adds a "Returns" section with the given description, providing details about the values that may be returned by the method.
As an inline tag, provides content for the first sentence of a
method's main description, and a "Returns" section, as if
"@return
description" were also present. In the
default English locale, the first sentence is Returns
description .
This tag is valid only in a documentation comment for a method. As an inline tag, it may only occur at the beginning of a method's main description.
When inheriting documentation, either form of a return
tag can be used:
/**
* {@return {@inheritDoc}}
...
*/
<T> T magnify(int scale, T element) throws MagnificationException
/**
...
* @return {@inheritDoc}
*/
<T> T magnify(int scale, T element) throws MagnificationException
Introduced as a block tag in JDK 1.0, and as an inline tag in JDK 16.
see
Adds a "See Also" heading with a link or text entry that points to a
reference. A documentation comment can contain any number of
see
tags, which are all grouped under the same heading. The
see
tag has three variations. The form to reference other
program elements is the most common. This tag is valid in all
documentation comments. For inserting an inline link within a sentence
to a package, class, or member, use a link
tag.
@see
"
string"
Adds a text entry for string. No link is generated. The string may be a reference to information which is not available by URL. The standard doclet distinguishes this from the other cases by searching for a double quotation mark (
"
) as the first character.@see
<a href="
url">
label</a>
Adds a link as defined by the url. The URL may be a relative or absolute URL. The standard doclet distinguishes this from other cases by searching for a less-than symbol (
<
) as the first character.@see
reference labelAdds a link with a visible text label that points to the documentation for the specified program element that is referenced.
reference can refer to any valid program element. If this element is in the documented classes, then the standard doclet creates a link to it.
To create links to external referenced classes, use the
-link
option. External referenced classes are classes that are not passed into thejavadoc
tool on the command line. Links in the generated documentation to external referenced classes are called external references or external links. For example, if you run the standard doclet on only thejava.awt
package, then any class injava.lang
, such asObject
, is an external referenced class. Use the-link
and-linkoffline
options to link to external referenced classes. The source comments of external referenced classes are not available to thejavadoc
command run.Use either of the other two
see
tag forms to refer to the documentation of a name that does not belong to a referenced class.label is text to be used as the link label and is optional for references to program elements. If no label is provided for an element reference, a default is generated, based on the target of the reference. Use the label when you want the text to be different from the auto-generated text. For references to URI fragments a label must be provided. The label can contain whitespace characters.
If the content of the label appears to be a phrase, and not just a possibly-abbreviated form of a reference to the target link, the link will be displayed in plain font; otherwise, the link will be displayed in monospace font.
Introduced in JDK 1.0.
serial
@serial
field-description@serial
include@serial
exclude
Used in the documentation comment for a default serializable field. See Documenting Serializable Fields and Data for a Class.
See also Oracle's Criteria for Including Classes in the Serialized Form Specification.
An optional field description should explain the meaning of the field and list the acceptable values. When needed, the description can span multiple lines. The standard doclet adds this information to the serialized form page.
If a serializable field was added to a class after the class was made serializable, then a statement should be added to its main description to identify at which version it was added.
The include
and exclude
arguments identify
whether a class or package should be included or excluded from the
serialized form page. They work as follows:
A public or protected class that implements
Serializable
is included unless that class (or its package) is marked with the@serial exclude
tag.A private or package-private class that implements
Serializable
is excluded unless that class (or its package) is marked with the@serial include
tag.
For example, the javax.swing
package is marked with the
@serial exclude
tag in package-info.java
. The
public class java.security.BasicPermission
is marked with
the @serial exclude
tag. The package-private class
java.util.PropertyPermissionCollection
is marked with the
@serial include
tag.
A serial
tag at the class level overrides any
serial
tag at the package level.
Introduced in JDK 1.2.
serialData
@serialData
data-description
Uses the data description value to document the types and order of
data in the serialized form. This data includes the optional data
written by the writeObject
method and all data (including
base classes) written by the Externalizable.writeExternal
method.
The serialData
tag can be used in the documentation
comment for the readObject
, writeObject
,
readExternal
, writeExternal
,
readResolve
, and writeReplace
methods.
Introduced in JDK 1.2.
serialField
@serialField
field-name field-type field-description
Documents an ObjectStreamField
component of the
serialPersistentFields
member of a
Serializable class
. Use one serialField
tag
for each ObjectStreamField
component.
Introduced in JDK 1.2.
since
@since
since-text
Adds a "Since" heading with the specified since-text value
to the generated documentation. The text has no special internal
structure. This tag is valid in any documentation comment: overview,
module, package, class, interface, constructor, method, or field. This
tag means that this change or feature has existed since the software
release specified by the since-text value, for example:
@since 1.5
.
For Java platform source code, the since
tag indicates
the version of the Java platform API specification, which is not
necessarily when the source code was added to the reference
implementation. Multiple since
tags are allowed and are
treated like multiple author
tags.
You could use multiple tags when the program element is used by more
than one API.
Introduced in JDK 1.1.
snippet
{@snippet
attributes}
{@snippet
attributes :
body}
Includes a fragment, or "snippet", of example code in the generated documentation. The code may be provided inline within the tag by specifying a body and/or in an external file, specified in the attributes. Within the content, markup tags can be placed in line comments to identify regions within the text and instruct how to present the text in these regions.
Additional details about the snippet can be given as
attributes, in the form of
name=
value pairs, placed after the
initial tag name. An attribute name is always a simple identifier. An
attribute value may be an identifier, unsigned integer, or enclosed in
either single or double quote characters; no escape characters are
supported. An attribute value and the preceding =
may be
omitted when the presence of the attribute name is sufficient.
Attributes are separated from the tag name and from each other by
whitespace characters, such as space and newline.
A snippet may specify an id
attribute, which can be used
to identify the snippet in both the API and the generated HTML, and
which may be used to create a link to the snippet. In the generated
HTML, the id will be placed on the outermost element that is generated
to represent the snippet.
Code fragments are typically Java source code, but they may also be
fragments of properties files, source code in other languages, or plain
text. A snippet may specify a lang
attribute, which
identifies the kind of content in the snippet. For an inline snippet,
the default value is java
. For an external snippet, the
default value is derived from the extension of the name of the file
containing the snippet's content.
Inline snippets
An inline snippet contains the content of the snippet within the tag itself.
The content of the snippet, which is included in the generated
documentation, is the text between the first newline after the colon
(:
) and the closing curly brace (}
).
There is no need to escape characters such as <
,
>
, and &
with HTML entities, nor is
there any need to escape documentation comment tags.
Surrounding whitespace is stripped from the content using String::stripIndent.
There are two limitations on the content of inline snippets:
The character sequence
*/
cannot be used anywhere within the content, because the*/
would terminate the enclosing documentation comment. This includes use of/* ... */
comments, or within a//
comment, or within string literals, such as those used to represent regular expressions. This restriction applies to all content in documentation comments; it is not specific to thesnippet
tag.The content of an inline snippet can only contain balanced pairs of curly-brace characters. The overall inline tag is terminated by the first right brace that matches the opening brace. This restriction applies to all inline tags; it is not specific to the
snippet
tag.
External snippets
An external snippet refers to a separate class or file that contains the content of the snippet.
In an external snippet the colon, newline, and subsequent content can be omitted.
Unlike inline snippets, external snippets have no limitations on
their content. In particular, they may contain /* ... */
comments.
The location of the external code can be specified either by class
name, using the class
attribute, or by a short relative
file path, using the file
attribute. In either case the
file can be placed in a package hierarchy rooted in a
snippet-files
subdirectory of the directory containing the
source code with the snippet
tag. Alternatively, the file
can be placed on an auxiliary search path, specified by the
--snippet-path
option to the javadoc
tool. The
use of snippet-files
subdirectories is similar to the use
of doc-files
subdirectories for auxiliary documentation
files.
The file for an external snippet may contain multiple regions, to be referenced in different snippet tags, appearing in different parts of the documentation.
Hybrid snippets
A hybrid snippet is both an internal snippet and an external snippet. It contains the content of the snippet within the tag itself, for the convenience of anyone reading the source code for the class being documented, and it also refers to a separate file that contains the content of the snippet.
It is an error if the result of processing a hybrid snippet as an inline snippet does not match the result of processing it as an external snippet.
Markup tags
Markup tags define regions within the content of a snippet. They also control the presentation of the content, for example highlighting parts of the text, modifying the text, or linking to elsewhere in the documentation. They can be used in internal, external, and hybrid snippets.
Markup tags begin with @
name, followed by any
required arguments. They are placed in //
comments (or the
equivalent in other languages or formats), so as not to unduly interfere
with the body of the source code, and also because
/* ... */
comments cannot be used in inline snippets. Such
comments are referred to as markup comments.
Multiple markup tags can be placed in the same markup comment. The
markup tags apply to the source line containing the comment unless the
comment is terminated with a colon (:
), in which case it is
as if the tags were present on the immediately following line. The
latter syntax may be useful if the markup comment is particularly long,
or if the syntactic format of the content of a snippet does not permit
comments to appear on the same line as non-comment source. Markup
comments do not appear in the generated output.
Because some other systems use meta-comments similar to markup
comments, comments that begin with @
followed by an
unrecognized name are ignored as markup comments and will appear in the
generated output. If the name is recognized, but there are subsequent
errors in the markup comment, then an error is reported. The generated
output in such cases is undefined, with respect to the output generated
from the snippet.
Regions
A region is an optionally-named range of lines that identifies the text to be displayed by a snippet. They also define the scope of actions such as highlighting or modifying the text.
The beginning of a region is marked by either
@start region=
name, or- an
@highlight
,@replace
, or@link
tag that specifiesregion
orregion=
name. You can omit the name if it is not needed by the matching@end
tag.
The end of a region is marked by @end
or
@end region=
name. If a name is given then the tag
ends the region started with that name. If no name is given then the tag
ends the most recently started region that does not already have a
matching @end
tag.
There are no constraints on the regions created by different pairs of
matching @start
and @end
tags. Regions can
even overlap, although we do not expect such usage to be common.
Highlighting
@highlight
— highlight text within a line or regionsubstring
— the literal text to be highlightedregex
— a regular expression for the text to be highlightedregion
— a region to define the scope in which to find the text to be highlightedtype
— the type of highlighting, such asbold
,italic
, orhighlighted
To highlight content on a line or in a range of lines, use
@highlight
followed by arguments that specify the scope of
the text to be considered, the text within that scope to be highlighted,
and the type of the highlighting.
If region
or region=
name is
specified then the scope is that region, up to the corresponding
@end
tag. Otherwise, the scope is just the current
line.
To highlight each instance of a literal string within the scope,
specify the string with substring=
string where
string can be an identifier or text enclosed in single or
double quotes. To highlight each instance of text matched by a regular
expression within the scope, use regex=
string. If
neither of these attributes are specified then the entire scope is
highlighted.
The type of highlighting can be specified with the type
parameter. Valid type names are bold
, italic
,
and highlighted
. The name of the type is converted to a CSS
class name whose properties can be defined in the system stylesheet or
overridden in a user-defined stylesheet.
Modifying the displayed text
@replace
— replace text within a line or regionsubstring
— the literal text to be replacedregex
— a regular expression for the text to be replacedregion
— a region to define the scope in which to find the text to be replacedreplacement
— the replacement text
It is often convenient to write the content of a snippet as code that
can be accessed and validated by external tools, but to display it in a
form that does not compile. For example, it may be desirable to include
import
statements for illustrative purposes along with code
that uses the imported types. Or, it may be desirable to display code
with an ellipsis or some other marker to indicate that additional code
should be inserted at that point. This can be done by replacing parts of
the content of the snippet with some replacement text.
To replace some text with replacement text, use @replace
followed by arguments that specify the scope of the text to be
considered, the text within that scope to be replaced, and the
replacement text.
If region
or region=
name is
specified then the scope is that region, up to the corresponding
@end
tag. Otherwise, the scope is just the current
line.
To replace each instance of a literal string within the scope,
specify the string with substring=
string where
string can be an identifier or text enclosed in single or
double quotes. To replace each instance of text matched by a regular
expression within the scope, use regex=
string. If
neither of these attributes are specified then the entire scope is
replaced.
Specify the replacement text with the replacement
parameter. If a regular expression is used to specify the text to be
replaced then $
number or
$
name can be used to substitute groups found in
the regular expression, as defined by String::replaceAll.
To delete text, use @replace
with an empty replacement
string. To insert text, use @replace
to replace some no-op
text placed where the replacement text should be inserted. The no-op
text might be a '//' marker, or an empty statement (;
).
Linking text
@link
— link text within a line or regionsubstring
— the literal text to be linkedregex
— a regular expression for the text to be linkedregion
— a region to define the scope in which to find the text to be linkedtarget
— the target of the link, expressed in one of the forms suitable for alink
tagtype
— the type of link: one oflink
(the default) orlinkplain
To link text to declarations elsewhere in the API, use
@link
followed by arguments that specify the scope of the
text to be considered, the text within that scope to be linked, and the
target of the link.
If region
or region=
name is
specified then the scope is that region, up to the corresponding
@end
tag. Otherwise, the scope is just the current
line.
To link each instance of a literal string within the scope, specify
the string with substring=
string where
string can be an identifier or text enclosed in single or
double quotes. To link each instance of text matched by a regular
expression within the scope, use regex=
string. If
neither of these attributes are specified then the entire scope is
linked.
Specify the target with the target
parameter. The form
of its value is the same as used by the standard inline
link
tag.
Introduced in JDK 18.
spec
- @spec URL title
Identifies an external specification in terms of its URL and title. The URL may be absolute or relative. Relative URLs will be evaluated against a "base URL".
All tags specifying the same URL must provide the same corresponding title; conversely, tags with different URLs must have different titles.
Introduced in JDK 20.
summary
{@summary
text}
Identify the summary of an API description, as an alternative to the default policy to identify and use the first sentence of the API description. The tag only has significance when used at the beginning of a main description. In all cases, the tag is rendered by simply rendering its content.
Introduced in JDK 10.
systemProperty
{@systemProperty
property-name}
Identify property-name as the name of a system property. The
name should be a "dotted identifier". In particular, it must not contain
whitespace characters, or characters such as }
. No other
content is permitted in the tag; the possibility of additional content
is reserved for future use. The tag can be used in all documentation
comments.
Introduced in JDK 12.
throws
@throws
exception-name description
Adds an exception with the specified name followed by the specified description to the "Throws" section of a Method or Constructor detail.
exception-name should refer to an exception that might be thrown by the method, and should either be the name of an exception class or a type variable. This tag is valid only in the documentation comment for a method or constructor.
A documentation comment may use multiple throws
tags for
the same or different exceptions. If such a comment is then targeted by
an inheritDoc
tag, it copies all exceptions of that kind
into the "Throws" section.
Note: an unchecked exception class may be omitted from the
throws
clause, and so won't be considered missing in a
method documentation. To inherit a description of such an exception, add
a corresponding throws
tag with an inheritDoc
tag in its description.
To ensure that all checked exceptions are documented, when a
throws
tag does not exist for an exception in the
throws
clause, the standard doclet adds that exception to
the generated output (with no description) as if it were documented with
the throws
tag.
The exception
tag is equivalent
to this tag, although using a throws
tag is now
recommended.
Introduced in JDK 1.2.
uses
@uses
service-type description
This tag may only appear in the documentation comment for a module declaration, and serves to document that a service may be used by the module. The description may be used to specify the characteristics of the service that may be required, and what the module will do if no provider for the service is available.
Introduced in JDK 9.
value
{@value
format field-reference}
Displays the value of a static field with a compile-time constant value.
The format string may be omitted, in which case a default format will
be used, appropriate to the type of the field. If the format string is
given, it must either begin with a percent character (%) or be enclosed
in double-quote characters ("). It must contain exactly one percent
character. The string must conform to the definition of a format string,
as specified in the documentation for java.util.Formatter
.
The conversion specified in the format string must be appropriate for
the type of the constant value.
When the value
tag is used without a
field_reference argument in the documentation comment of a
static field, it displays the value of that constant:
/**
* The value of this constant is {@value}.
*/
public static final String SCRIPT_START = "<script>"
When used with a field-reference
argument in any documentation comment, the value
tag
displays the value of the specified constant:
/**
* Evaluates the script starting with {@value #SCRIPT_START}.
*/
public String evalScript(String script) {}
Introduced in JDK 1.4; format added in JDK 20.
version
@version
version-text
Adds a "Version" subheading with the specified version-text
value to the generated documents when the -version option is used. This
tag is intended to hold the current release number of the software that
this code is part of, as opposed to the since
tag, which
holds the release number where this code was introduced. The
version-text value has no special internal structure.
A documentation comment can contain multiple version
tags. When it makes sense, you can specify one release number per
version
tag or multiple release numbers per tag. In the
former case, the standard doclet inserts a comma (,
) and a
space between the names. In the latter case, the entire text is copied
to the generated document without being parsed. Therefore, you can use
multiple names per line when you want a localized separator other than a
comma.
Introduced in JDK 1.0.
Where Tags Can Be Used
The following table summarizes which tags can be used in which contexts.
Tag | Module | Package | Type | Constructor | Method | Field | Other |
---|---|---|---|---|---|---|---|
author |
✓ | ✓ | ✓ | ✓ | |||
code |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
deprecated |
✓ | ✓ | ✓ | ✓ | ✓ | ||
docRoot |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
exception |
✓ | ✓ | |||||
hidden |
✓ | ✓ | ✓ | ||||
index |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
inheritDoc |
✓ | ||||||
link |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
linkplain |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
literal |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
param |
✓ | ✓ | ✓ | ||||
provides |
✓ | ||||||
return |
✓ | ||||||
see |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
serial |
✓ | ✓ | ✓ | ||||
serialData |
* | ||||||
serialField |
* | ||||||
since |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
snippet |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
summary |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
systemProperty |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
throws |
✓ | ✓ | |||||
uses |
✓ | ||||||
value |
✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
version |
✓ | ✓ | ✓ | ✓ |
Notes:
- Methods includes members of annotation interfaces.
- Fields includes members of enum classes.
- Other includes the Overview page, which is not tied to any
declaration, and HTML files in
doc-files
subdirectories of a package directory. The Overview page is typically specified with an option to thejavadoc
command. - The
serialData
tag can only be used in the documentation comment for thereadObject
,writeObject
,readExternal
,writeExternal
,readResolve
andwriteReplace
methods. - The
serialField
tag can only be used in the documentation comment for theserialPersistentFields
field.