Documentation Comments¶

The javadoc tool uses the documentation comment, if any, that immediately precedes the beginning of the declaration, whether that is an annotation, modifier, or the name being declared. If there are multiple documentation comments before the declaration, only the last one (closest to the declaration) will be used. If there are any documentation comments after the beginning of the declaration, they will be ignored. To check for any extra or misplaced documentation comments, compile your source code with the javac option -Xlint, or more specifically, -Xlint:dangling-doc-comments. Within a source file, you may suppress any warnings generated by these options by using @SuppressWarnings("dangling-doc-comments") on a suitable enclosing declaration.

Conformance¶

The standard doclet does not validate the content of documentation comments for conformance, nor does it attempt to correct any errors in documentation comments. Anyone running javadoc is advised to be aware of the problems that may arise when generating non-conformant output or output containing executable content, such as JavaScript. The standard doclet does provide the DocLint feature to help developers detect common problems in documentation comments; but it is also recommended to check the generated output with any appropriate conformance and other checking tools.

For more details on the conformance requirements for HTML5 documents, see Conformance requirements for authors [https://html.spec.whatwg.org/multipage/introduction.html#conformance-requirements-for-authors] in the HTML5 Specification. For more details on security issues related to web pages, see the Open Web Application Security Project (OWASP) [https://www.owasp.org] page.

Standard javadoc Options¶

The following core javadoc options are equivalent to corresponding javac options. See Standard Options in javac for the detailed descriptions of using these options:

•

--add-modules

•

-bootclasspath

•

--class-path, -classpath, or -cp

•

--disable-line-doc-comments

•

--enable-preview

•

-encoding

•

-extdirs

•

--limit-modules

•

--module

•

--module-path or -p

•

--module-source-path

•

--release

•

--source or -source

•

--source-path or -sourcepath

•

--system

•

--upgrade-module-path

The following options are the core javadoc options that are not equivalent to a corresponding javac option:

-breakiterator

Computes the first sentence of the description in a documentation comment using an instance of java.text.BreakIterator to detect sentence breaks. The rules that are used depend on the current locale: for example, for English, a sentence break occurs after a period, question mark, or exclamation point followed by a space when the next word starts with a capital letter. (This is meant to handle most abbreviations, such as "The serial no. is valid", but will not handle "Mr. Smith".)

-doclet class

Generates output by using an alternate doclet. Use the fully qualified name. This doclet defines the content and formats the output. If the -doclet option isn't used, then the javadoc tool uses the standard doclet for generating the default HTML format. This class must implement the jdk.javadoc.doclet.Doclet interface. The path to this class is defined by the -docletpath option.

-docletpath path

Specifies where to find doclet class files (specified with the -doclet option) and any JAR files it depends on. If the starting class file is in a JAR file, then this option specifies the path to that JAR file. You can specify an absolute path or a path relative to the current directory. If path contains multiple paths or JAR files, then they should be separated with a colon (:) on Linux and macOS, and a semicolon (;) on Windows. This option isn't necessary when the doclet starting class is already in the search path.

-exclude pkglist

Unconditionally, excludes the specified packages and their subpackages from the list formed by -subpackages. It excludes those packages even when they would otherwise be included by some earlier or later -subpackages option.

--expand-requires (transitive|all)

Instructs the javadoc tool to expand the set of modules to be documented. By default, only the modules given explicitly on the command line are documented. Supports the following values:

--help, -help, -h, or -?

Prints a synopsis of the standard options.

--help-extra or -X

Prints a synopsis of the set of extra options.

-Jflag

Passes flag directly to the Java Runtime Environment (JRE) that runs the javadoc tool. For example, if you must ensure that the system sets aside 32 MB of memory in which to process the generated documentation, then you would call the -Xmx option as follows: javadoc -J-Xmx32m -J-Xms32m com.mypackage. Be aware that -Xms is optional because it only sets the size of initial memory, which is useful when you know the minimum amount of memory required.

-locale name

Specifies the locale that the javadoc tool uses when it generates documentation. The argument is the name of the locale, as described in java.util.Locale documentation, such as en_US (English, United States) or en_US_WIN (Windows variant).

-package

Shows only package, protected, and public classes and members.

-private

Shows all classes and members.

-protected

Shows only protected and public classes and members. This is the default.

-public

Shows only the public classes and members.

-quiet

Shuts off messages so that only the warnings and errors appear to make them easier to view. It also suppresses the version string.

--show-members value

Specifies which members (fields, methods, or constructors) are documented, where value can be any of the following:

--show-module-contents value

Specifies the documentation granularity of module declarations, where value can be api or all.

--show-packages value

Specifies which module packages are documented, where value can be exported or all packages.

--show-types value

Specifies which types (classes, interfaces, etc.) are documented, where value can be any of the following:

-subpackages subpkglist

Generates documentation from source files in the specified packages and recursively in their subpackages. This option is useful when adding new subpackages to the source code because they are automatically included. Each package argument is any top-level subpackage (such as java) or fully qualified package (such as javax.swing) that doesn't need to contain source files. Arguments are separated by colons on all operating systems. Wild cards aren't allowed. Use -sourcepath to specify where to find the packages. This option doesn't process source files that are in the source tree but don't belong to the packages.

-verbose

Provides more detailed messages while the javadoc tool runs. Without the -verbose option, messages appear for loading the source files, generating the documentation (one message per source file), and sorting. The -verbose option causes the printing of additional messages that specify the number of milliseconds to parse each Java source file.

--version

Prints version information.

-Werror

Reports an error if any warnings occur.

Note that if a Java source file contains an implicitly declared class, then that class and its public, protected, and package members will be documented regardless of the options such as --show-types, --show-members, -private, -protected, -package, and -public. If --show-members is specified with value private or if -private is used then all private members of an implicitly declared class will be documented too.

Extra javadoc Options¶

Note: The additional options for javadoc are subject to change without notice.

The following additional javadoc options are equivalent to corresponding javac options. See Extra Options in javac for the detailed descriptions of using these options:

•

--add-exports

•

--add-reads

•

--patch-module

•

-Xmaxerrs

•

-Xmaxwarns

Standard Options for the Standard Doclet¶

The following options are provided by the standard doclet.

--add-script file

Adds file as an additional JavaScript file to the generated documentation. This option can be used one or more times to specify additional script files.

--add-stylesheet file

Adds file as an additional stylesheet file to the generated documentation. This option can be used one or more times to specify additional stylesheets included in the documentation.

--allow-script-in-comments

Allow JavaScript in documentation comments, and options whose value is html-code.

-author

Includes the text of any author tags in the generated documentation.

-bottom html-code

Specifies the text to be placed at the bottom of each generated page. The text can contain HTML tags and white space, but when it does, the text must be enclosed in quotation marks. Use escape characters for any internal quotation marks within text.

-charset name

Specifies the HTML character set for this document. The name should be a preferred MIME name as specified in the IANA Registry, Character Sets [http://www.iana.org/assignments/character-sets].

-d directory

Specifies the destination directory where the javadoc tool saves the generated HTML files. If you omit the -d option, then the files are saved to the current directory. The directory value can be absolute or relative to the current working directory. The destination directory is automatically created when the javadoc tool runs.

-docencoding name

Specifies the encoding of the generated HTML files. The name should be a preferred MIME name as specified in the IANA Registry, Character Sets [http://www.iana.org/assignments/character-sets].

-docfilessubdirs

Enables deep copying of doc-files directories. Subdirectories and all contents are recursively copied to the destination. For example, the directory doc-files/example/images and all of its contents are copied. Use the -excludedocfilessubdir option to restrict the subdirectories to be copied.

-doctitle html-code

Specifies the title to place near the top of the overview summary file. The text specified in the title tag is placed as a centered, level-one heading directly beneath the navigation bar. The title tag can contain HTML tags and white space, but when it does, you must enclose the title in quotation marks. Additional quotation marks within the title tag must be escaped. For example, javadoc -doctitle "<b>My Library</b><br>v1.0" com.mypackage.

-excludedocfilessubdir name1,name2...

Excludes any subdirectories with the given names when recursively copying doc-files subdirectories. See -docfilessubdirs. For historical reasons, : can be used anywhere in the argument as a separator instead of ,.

-footer html-code

This option is no longer supported and reports a warning.

-group name p1,p2...

Group the specified packages together in the Overview page. For historical reasons, : can be used as a separator anywhere in the argument instead of ,.

-header html-code

Specifies the header text to be placed at the top of each output file. The header is placed to the right of the navigation bar. The header can contain HTML tags and white space, but when it does, the header must be enclosed in quotation marks. Use escape characters for internal quotation marks within a header. For example, javadoc -header "<b>My Library</b><br>v1.0" com.mypackage.

-helpfile filename

Specifies a file containing the text that will be displayed when the HELP link in the navigation bar is clicked. If this option is not given, the javadoc tool creates a default page that will be used.

-html5

This option is a no-op and is just retained for backwards compatibility.

--javafx or -javafx

Enables JavaFX functionality. This option is enabled by default if the JavaFX library classes are detected on the module path.

-keywords

Adds HTML keyword <meta> tags to the generated file for each class. These tags can help search engines that look for <meta> tags find the pages. Most search engines that search the entire Internet don't look at <meta> tags, because pages can misuse them. Search engines offered by companies that confine their searches to their own website can benefit by looking at <meta> tags. The <meta> tags include the fully qualified name of the class and the unqualified names of the fields and methods. Constructors aren't included because they are identical to the class name. For example, the page for the class String includes these keywords:

-link url

Creates links to existing javadoc generated documentation of externally referenced classes. The url argument is the absolute or relative URL of the directory that contains the external javadoc generated documentation. You can specify multiple -link options in a specified javadoc tool run to link to multiple documents.

--link-modularity-mismatch (warn|info)

Specifies whether external documentation with wrong modularity (e.g. non-modular documentation for a modular library, or the reverse case) should be reported as a warning (warn) or just a message (info). The default behavior is to report a warning.

-linkoffline url1 url2

This option is a variation of the -link option. They both create links to javadoc generated documentation for externally referenced classes. You can specify multiple -linkoffline options in a specified javadoc tool run.

--link-platform-properties url

Specifies a properties file used to configure links to platform documentation.

-linksource

Creates an HTML version of each source file (with line numbers) and adds links to them from the standard HTML documentation. Links are created for classes, interfaces, constructors, methods, and fields whose declarations are in a source file. Otherwise, links aren't created, such as for default constructors and generated classes.

--main-stylesheet file or -stylesheetfile file

Specifies the path of an alternate stylesheet file that contains the definitions for the CSS styles used in the generated documentation. This option lets you override the default. If you do not specify the option, the javadoc tool will create and use a default stylesheet. The file name can be any name and isn't restricted to stylesheet.css. The --main-stylesheet option is the preferred form.

-nocomment

Suppresses the entire comment body, including the main description and all tags, and generate only declarations. This option lets you reuse source files that were originally intended for a different purpose so that you can produce skeleton HTML documentation during the early stages of a new project.

-nodeprecated

Prevents the generation of any deprecated API in the documentation. This does what the -nodeprecatedlist option does, and it doesn't generate any deprecated API throughout the rest of the documentation. This is useful when writing code when you don't want to be distracted by the deprecated code.

-nodeprecatedlist

Prevents the generation of the file that contains the list of deprecated APIs (deprecated-list.html) and the link in the navigation bar to that page. The javadoc tool continues to generate the deprecated API throughout the rest of the document. This is useful when your source code contains no deprecated APIs, and you want to make the navigation bar cleaner.

--no-fonts

Prevents inclusion of font files in the generated documentation. This can be useful if the documentation uses a custom stylesheet which does not use the default fonts.

-nohelp

Omits the HELP link in the navigation bar at the top of each generated page.

-noindex

Omits the index from the generated documents. The index is produced by default.

-nonavbar

Prevents the generation of the navigation bar and header. The -nonavbar option has no effect on the -bottom option. The -nonavbar option is useful when you are interested only in the content and have no need for navigation, such as when you are converting the files to PostScript or PDF for printing only.

--no-platform-links

Prevents the generation of links to platform documentation. These links are generated by default.

-noqualifier name1,name2...

Excludes the list of qualifiers from the output. The package name is removed from places where class or interface names appear. For historical reasons, : can be used anywhere in the argument as a separator instead of ,.

-nosince

Omits from the generated documentation the Since sections derived from any since tags.

-notimestamp

Suppresses the time stamp, which is hidden in an HTML comment in the generated HTML near the top of each page. The -notimestamp option is useful when you want to run the javadoc tool on two source bases and compare them, because it prevents time stamps from causing a difference (which would otherwise be a difference on every page). The time stamp includes the javadoc tool release number.

-notree

Omits the class and interface hierarchy pages from the generated documents. These are the pages you reach using the TREE link in the navigation bar. The hierarchy is produced by default.

--override-methods (detail|summary)

Documents overridden methods in the detail or summary sections. The default is detail.

-overview filename

Specifies that the javadoc tool should retrieve the content for the overview documentation from the file specified by filename and place it on the Overview page (overview-summary.html). If the filename is a relative path, it is evaluated relative to the current working directory.

-serialwarn

Reports compile-time warnings for missing @serial tags. By default, Javadoc reports no serial warnings. Use this option to display the serial warnings, which helps to properly document default serializable fields and writeExternal methods.

--since release(,release)*

Generates documentation for APIs that were added or newly deprecated in the specified releases.

--since-label text

Specifies the text to use in the heading of the "New API" page. This may contain information about the releases covered in the page, e.g. "New API in release 2.0", or "New API since release 1".

--snippet-path snippetpathlist

Specifies the search paths for finding files for external snippets. The snippetpathlist can contain multiple paths by separating them with the platform path separator (; on Windows; : on other platforms.) The standard doclet first searches the snippet-files subdirectory in the package containing the snippet, and then searches all the directories in the given list.

-sourcetab tab-length

Specifies the number of spaces each tab uses in the source.

--spec-base-url url

Specifies the base URL for relative URLs in @spec tags, to be used when generating links to any external specifications. It can either be an absolute URL, or a relative URL, in which case it is evaluated relative to the base directory of the generated output files. The default value is equivalent to {@docRoot}/../specs.

-splitindex

Splits the index file into multiple files, alphabetically, one file per letter, plus a file for any index entries that start with non-alphabetical symbols.

-tag name:locations:header

Specifies a custom tag with a single argument. For the javadoc tool to spell-check tag names, it is important to include a -tag option for every custom tag that is present in the source code, disabling (with X) those that aren't being output in the current run. The colon (:) is always the separator. To include a colon in the tag name, escape it with a backward slash (\). The -tag option outputs the tag heading, header, in bold, followed on the next line by the text from its single argument. Similar to any block tag, the argument text can contain inline tags, which are also interpreted. The output is similar to standard one-argument tags, such as the @return and @author tags. Omitting a header value causes the name to be the heading. locations is a list of characters specifying the kinds of declarations in which the tag may be used. The following characters may be used, in either uppercase or lowercase:

-taglet class

Specifies the fully qualified name of the taglet used in generating the documentation for that tag. Use the fully qualified name for the class value. This taglet also defines the number of text arguments that the custom tag has. The taglet accepts those arguments, processes them, and generates the output.

-tagletpath tagletpathlist

Specifies the search paths for finding taglet class files. The tagletpathlist can contain multiple paths by separating them with the platform path separator (; on Windows; : on other platforms.) The javadoc tool searches all subdirectories of the specified paths.

-top html-code

Specifies the text to be placed at the top of each output file.

-use

Creates class and package usage pages. Includes one Use page for each documented class and package. The page describes what packages, classes, methods, constructors, and fields use any API of the specified class or package. Given class C, things that use class C would include subclasses of C, fields declared as C, methods that return C, and methods and constructors with parameters of type C. For example, you can look at the Use page for the String type. Because the getName method in the java.awt.Font class returns type String, the getName method uses String and so the getName method appears on the Use page for String. This documents only uses of the API, not the implementation. When a method uses String in its implementation, but doesn't take a string as an argument or return a string, that isn't considered a use of String. To access the generated Use page, go to the class or package and click the USE link in the navigation bar.

-version

Includes the text of any version tags in the generated documentation. This text is omitted by default. Note: To find out what version of the javadoc tool you are using, use the --version option (with two hyphens).

-windowtitle title

Specifies the title to be placed in the HTML <title> tag. The text specified in the title tag appears in the window title and in any browser bookmarks (favorite places) that someone creates for this page. This title should not contain any HTML tags because a browser will not interpret them correctly. Use escape characters on any internal quotation marks within the title tag. If the -windowtitle option is omitted, then the javadoc tool uses the value of the -doctitle option for the -windowtitle option. For example, javadoc -windowtitle "My Library" com.mypackage.

Extra Options for the Standard Doclet¶

The following are additional options provided by the standard doclet and are subject to change without notice. Additional options are less commonly used or are otherwise regarded as advanced.

--date date-and-time

Specifies the value to be used to timestamp the generated pages, in ISO 8601 [https://www.iso.org/iso-8601-date-and-time-format.html] format. The specified value must be within 10 years of the current date and time. It is an error to specify both -notimestamp and --date. Using a specific value means the generated documentation can be part of a reproducible build [https://reproducible-builds.org/]. If the option is not given, the default value is the current date and time. For example:

--legal-notices (default|none|directory)

Specifies the location from which to copy legal files to the generated documentation. If the option is not specified or is used with the value default, the files are copied from the default location. If the argument is used with value none, no files are copied. Every other argument is interpreted as directory from which to copy the legal files.

--no-frames

This option is no longer supported and reports a warning.

-Xdoclint

Enables recommended checks for problems in documentation comments.

-Xdoclint:flag,flag,...

Enables or disables specific checks for different kinds of issues in documentation comments.

-Xdoclint/package:[-]packages

Enables or disables checks in specific packages. packages is a comma separated list of package specifiers. A package specifier is either a qualified name of a package or a package name prefix followed by *, which expands to all subpackages of the given package. Prefix the package specifier with - to disable checks for the specified packages.

-Xdocrootparent url

Replaces all @docRoot items followed by /.. in documentation comments with url.

Groups¶

The checks performed by DocLint are organized into groups. The warnings and errors in each group can be enabled or disabled with command-line options, or suppressed with @SuppressWarnings annotations.

The groups are as follows:

•

accessibility --- Checks for issues related to accessibility. For example, no alt attribute specified in an <img> element, or no caption or summary attributes specified in a <table> element.

•

html --- Detects common high-level HTML issues. For example, putting block elements inside inline elements, or not closing elements that require an end tag.

•

missing --- Checks for missing documentation comments or tags. For example, a missing comment on a class declaration, or a missing @param or @return tag in the comment for a method declaration.

•

reference --- Checks for issues relating to the references to Java API elements from documentation comment tags. For example, the reference in @see or {@link ...} cannot be found, or a bad name is given for @param or @throws.

•

syntax --- Checks for low-level syntactic issues in documentation comments. For example, unescaped angle brackets (< and >) and ampersands (&) and invalid documentation comment tags.

Suppressing Messages¶

DocLint checks for and recognizes two strings that may be present in the arguments for an @SuppressWarnings annotation.

•

doclint

•

doclint:LIST

where LIST is a comma-separated list of one or more of accessibility, html, missing, reference, syntax.

The names in LIST are the same group names supported by the command-line -Xdoclint option for javac and javadoc. (This is the same convention honored by the javac -Xlint option and the corresponding names supported by @SuppressWarnings.)

The names in LIST can equivalently be specified in separate arguments of the annotation. For example, the following are equivalent:

•

@SuppressWarnings("doclint:accessibility,missing")

•

@SuppressWarnings("doclint:accessibility", "doclint:missing")

When DocLint detects an issue in a documentation comment, it checks for the presence of @SuppressWarnings on the associated declaration and on all lexically enclosing declarations. The issue will be ignored if any such annotation is found containing the simple string doclint or the longer form doclint:LIST where LIST contains the name of the group for the issue.

Note: as with other uses of @SuppressWarnings, using the annotation on a module or package declaration only affects that declaration; it does not affect the contents of the module or package in other source files.

All messages related to an issue are suppressed by the presence of an appropriate @SuppressWarnings annotation: this includes errors as well as warnings.

Note: It is only possible to suppress messages. If an annotation of @SuppressWarnings("doclint") is given on a top-level declaration, all DocLint messages for that declaration and any enclosed declarations will be suppressed; it is not possible to selectively re-enable messages for issues in enclosed declarations.

Comparison with downstream validation tools¶

DocLint is a utility built into javac and javadoc that checks the content of documentation comments, as found in source files. In contrast, downstream validation tools can be used to validate the output generated from those documentation comments by javadoc and the standard doclet.

Although there is some overlap in functionality, the two mechanisms are different and each has its own strengths and weaknesses.

•

Downstream validation tools can check the end result of any generated documentation, as it will be seen by the end user. This includes content from all sources, including documentation comments, the standard doclet itself, user-provided taglets, and content supplied via command-line options. Because such tools are analyzing complete HTML pages, they can do more complete checks than can DocLint. However, when a problem is found in the generated pages, it can be harder to track down exactly where in the build pipeline the problem needs to be fixed.

•

DocLint checks the content of documentation comments, in source files. This makes it very easy to identify the exact position of any issues that may be found. DocLint can also detect some semantic errors in documentation comments that downstream tools cannot detect, such as missing comments, using an @return tag in a method returning void, or an @param tag describing a non-existent parameter. But by its nature, DocLint cannot report on problems such as missing links, or errors in user-provided custom taglets, or problems in the standard doclet itself. It also cannot reliably detect errors in documentation comments at the boundaries between content in a documentation comment and content generated by a custom taglet.