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config.html
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<!DOCTYPE html>
<!--
| Generated by Apache Maven Doxia Site Renderer 1.11.1 from src/xdocs/config.xml at 2024-04-28
| Rendered using Apache Maven Default Skin
-->
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" />
<title>checkstyle – Configuration</title>
<link rel="stylesheet" href="./css/maven-base.css" />
<link rel="stylesheet" href="./css/maven-theme.css" />
<link rel="stylesheet" href="./css/site.css" />
<link rel="stylesheet" href="./css/print.css" media="print" />
<script type="text/javascript" src="./js/checkstyle.js"></script>
<script type="text/javascript"
src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script type="text/javascript" src="./js/anchors.js"></script>
<script type="text/javascript" src="./js/google-analytics.js"></script>
<link rel="icon" href="./images/favicon.png" type="image/x-icon" />
<link rel="shortcut icon" href="./images/favicon.ico" type="image/ico" />
</head>
<body class="composite">
<div id="banner">
<a href="./" id="bannerLeft" title="Checkstyle"><img src="images/header-checkstyle-logo.png" alt="Checkstyle"/></a><a href="./" id="bannerRight" title="Checkstyle"><img src="images/header-right-ruller.png" alt="Checkstyle"/></a> <div class="clear">
<hr/>
</div>
</div>
<div id="breadcrumbs">
<div class="xright"><a href="" title="toTop">toTop</a> | <span id="publishDate">Last Published: 2024-04-28</span>
| <span id="projectVersion">Version: 10.16.0</span>
</div>
<div class="clear">
<hr/>
</div>
</div>
<div id="leftColumn">
<div id="navcolumn">
<h5>About</h5>
<ul>
<li class="none"><a href="index.html" title="Checkstyle">Checkstyle</a></li>
<li class="none"><a href="releasenotes.html" title="Release Notes">Release Notes</a></li>
<li class="none"><a href="consulting.html" title="Consulting">Consulting</a></li>
<li class="none"><a href="sponsoring.html" title="Sponsoring">Sponsoring</a></li>
</ul>
<h5>Documentation</h5>
<ul>
<li class="expanded"><strong>Configuration</strong>
<ul>
<li class="none"><a href="property_types.html" title="Property Types">Property Types</a></li>
<li class="none"><a href="config_system_properties.html" title="System Properties">System Properties</a></li>
</ul></li>
<li class="expanded"><a href="running.html" title="Running">Running</a>
<ul>
<li class="none"><a href="anttask.html" title="Ant Task">Ant Task</a></li>
<li class="none"><a href="cmdline.html" title="Command Line">Command Line</a></li>
</ul></li>
<li class="expanded"><a href="checks.html" title="Checks">Checks</a>
<ul>
<li class="collapsed"><a href="checks/annotation/index.html" title="Annotations">Annotations</a></li>
<li class="collapsed"><a href="checks/blocks/index.html" title="Block Checks">Block Checks</a></li>
<li class="collapsed"><a href="checks/design/index.html" title="Class Design">Class Design</a></li>
<li class="collapsed"><a href="checks/coding/index.html" title="Coding">Coding</a></li>
<li class="collapsed"><a href="checks/header/index.html" title="Headers">Headers</a></li>
<li class="collapsed"><a href="checks/imports/index.html" title="Imports">Imports</a></li>
<li class="collapsed"><a href="checks/javadoc/index.html" title="Javadoc Comments">Javadoc Comments</a></li>
<li class="collapsed"><a href="checks/metrics/index.html" title="Metrics">Metrics</a></li>
<li class="collapsed"><a href="checks/misc/index.html" title="Miscellaneous">Miscellaneous</a></li>
<li class="collapsed"><a href="checks/modifier/index.html" title="Modifiers">Modifiers</a></li>
<li class="collapsed"><a href="checks/naming/index.html" title="Naming Conventions">Naming Conventions</a></li>
<li class="collapsed"><a href="checks/regexp/index.html" title="Regexp">Regexp</a></li>
<li class="collapsed"><a href="checks/sizes/index.html" title="Size Violations">Size Violations</a></li>
<li class="collapsed"><a href="checks/whitespace/index.html" title="Whitespace">Whitespace</a></li>
</ul></li>
<li class="collapsed"><a href="filters/index.html" title="Filters">Filters</a></li>
<li class="collapsed"><a href="filefilters/index.html" title="File Filters">File Filters</a></li>
<li class="expanded"><a href="style_configs.html" title="Style Configurations">Style Configurations</a>
<ul>
<li class="none"><a href="google_style.html" title="Google's Style">Google's Style</a></li>
<li class="none"><a href="sun_style.html" title="Sun's Style">Sun's Style</a></li>
</ul></li>
</ul>
<h5>Developers</h5>
<ul>
<li class="expanded"><a href="extending.html" title="Extending Checkstyle">Extending Checkstyle</a>
<ul>
<li class="none"><a href="writingchecks.html" title="Writing Checks">Writing Checks</a></li>
<li class="none"><a href="writingjavadocchecks.html" title="Writing Javadoc Checks">Writing Javadoc Checks</a></li>
<li class="none"><a href="writingfilters.html" title="Writing Filters">Writing Filters</a></li>
<li class="none"><a href="writingfilefilters.html" title="Writing File Filters">Writing File Filters</a></li>
<li class="none"><a href="writinglisteners.html" title="Writing Listeners">Writing Listeners</a></li>
</ul></li>
<li class="none"><a href="contributing.html" title="Contributing">Contributing</a></li>
<li class="expanded"><a href="beginning_development.html" title="Beginning Development">Beginning Development</a>
<ul>
<li class="none"><a href="eclipse.html" title="Eclipse IDE">Eclipse IDE</a></li>
<li class="none"><a href="netbeans.html" title="NetBeans IDE">NetBeans IDE</a></li>
<li class="none"><a href="idea.html" title="IntelliJ IDE">IntelliJ IDE</a></li>
</ul></li>
<li class="none"><a href="apidocs/index.html" title="Javadoc">Javadoc</a></li>
</ul>
<h5>Project Documentation</h5>
<ul>
<li class="collapsed"><a href="project-info.html" title="Project Information">Project Information</a></li>
<li class="collapsed"><a href="project-reports.html" title="Project Reports">Project Reports</a></li>
</ul>
<a href="https://github.com/checkstyle/checkstyle" title="GitHub" class="poweredBy">
<img class="poweredBy" alt="GitHub" src="images/github_logo_social_coding_outlined.png" />
</a>
<a href="https://twitter.com/checkstyle_java/" title="Twitter" class="poweredBy">
<img class="poweredBy" alt="Twitter" src="images/twitter_button.png" />
</a>
<a href="https://stackoverflow.com/questions/tagged/checkstyle" title="Stackoverflow" class="poweredBy">
<img class="poweredBy" alt="Stackoverflow" src="images/stackoverflow.jpeg" />
</a>
<a href="https://groups.google.com/forum/#!forum/checkstyle" title="GoogleGroups" class="poweredBy">
<img class="poweredBy" alt="GoogleGroups" src="images/groups.png" />
</a>
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<img class="poweredBy" alt="JProfiler" src="https://www.ej-technologies.com/images/product_banners/jprofiler_medium.png" />
</a>
</div>
</div>
<div id="bodyColumn">
<div id="contentBox">
<section>
<h2><a name="Content"></a>Content</h2>
<ul>
<li><a href="#Content">Content</a></li>
<li><a href="#Overview">Overview</a></li>
<li><a href="#Modules">Modules</a></li>
<li><a href="#Properties">Properties</a></li>
<li><a href="#Checker">Checker</a></li>
<li><a href="#TreeWalker">TreeWalker</a></li>
<li><a href="#TreeWalker_Checks">TreeWalker Checks</a></li>
<li><a href="#Severity">Severity</a></li>
<li><a href="#tabWidth">tabWidth</a></li>
<li><a href="#Id">Id</a></li>
<li><a href="#Custom_messages">Custom messages</a></li>
<li><a href="#Filters">Filters</a></li>
<li><a href="#Before_Execution_File_Filters">Before Execution File Filters</a></li>
<li><a href="#Audit_Listeners">Audit Listeners</a></li>
<li><a href="#Packages">Packages</a></li>
<li><a href="#Configuration_XML_Structure">Configuration XML Structure</a></li></ul>
</section>
<section>
<h2><a name="Overview"></a>Overview</h2>
<p>
A Checkstyle configuration specifies which <i>modules</i> to
plug in and apply to Java source files. Modules are structured
in a tree whose root is the <i>Checker</i> module. The next
level of modules contains:
</p>
<ul>
<li><i>File Set Checks</i> - modules that take a set of input
files and fire violation messages.</li>
<li><i>Filters</i>
- modules that filter audit events,
including messages, for acceptance.</li>
<li><i>Audit Listeners</i> - modules that report accepted events.</li>
</ul>
<p>
Many checks are submodules of the <i>TreeWalker</i>
File Set Check module. The TreeWalker operates by separately
transforming each of the Java source files into an abstract
syntax tree and then handing the result over to each of its
submodules which in turn have a look at certain aspects of the
tree.
</p>
<p>
Checkstyle obtains a configuration from an XML document whose
elements specify the configuration's hierarchy of modules and
their properties. You provide a file that contains the
configuration document when you invoke Checkstyle at the <a href="cmdline.html">command line</a>, and when you run a <a href="anttask.html">Checkstyle task</a> in ant. The
documentation directory of the Checkstyle distribution contains
a sample configuration file <i>sun_checks.xml</i> which
configures Checkstyle to check for the Sun coding conventions.
</p>
</section>
<section>
<h2><a name="Modules"></a>Modules</h2>
<p>
A <code>module</code> element in the configuration
XML document specifies a module identified by the element's
<code>name</code> attribute.
</p>
<p>
Here is a fragment of a typical configuration document:
</p>
<div class="source">
<pre>
<module name="Checker">
<module name="JavadocPackage"/>
<module name="TreeWalker">
<module name="AvoidStarImport"/>
<module name="ConstantName"/>
<module name="EmptyBlock"/>
</module>
</module>
</pre></div>
<p>
In this configuration:
</p>
<ul>
<li>
Root module <code>Checker</code> has child
FileSetChecks <code>JavadocPackage</code> and <code>TreeWalker</code>. (Module <a href="checks/javadoc/index.html"> <code>JavadocPackage</code></a> checks that all packages
have package documentation.)
</li>
<li>
Module <code>TreeWalker</code> has submodules
<code>AvoidStarImport</code>, <code>ConstantName</code>,
and <code>EmptyBlock</code>. (Modules <a href="checks/imports/index.html"><code>AvoidStarImport</code></a>, <a href="checks/naming/index.html"><code>ConstantName</code></a>, and <a href="checks/blocks/index.html"><code>EmptyBlock</code></a> check that a Java source
file has no star imports, has valid constant names, and has no
empty blocks, respectively.)
</li>
</ul>
<p>
For each configuration module, Checkstyle loads a class
identified by the <code>name</code> attribute of
the <code>module</code>. There are several rules
for loading a module's class:
</p>
<ol style="list-style-type: decimal">
<li>
Load a class directly according to a package-qualified <code>name</code>, such as loading
class <code>com.puppycrawl.tools.checkstyle.TreeWalker</code> for element:
<div class="source">
<pre>
<module name="com.puppycrawl.tools.checkstyle.TreeWalker"/>
</pre></div>
This is useful for plugging third-party modules into a configuration.
</li>
<li>
Load a class of a pre-specified package, such as loading class
<code>com.puppycrawl.tools.checkstyle.checks.AvoidStarImport</code>
for element
<div class="source">
<pre>
<module name="AvoidStarImport"/>
</pre></div>
Checkstyle applies packages <code>
com.puppycrawl.tools.checkstyle</code>, <code>
com.puppycrawl.tools.checkstyle.filters</code>, and
<code>com.puppycrawl.tools.checkstyle.checks</code>
and its sub-packages (only those included in the Checkstyle
distribution). You can specify other packages in a <a href="#Packages"><i>package names XML document</i></a>
when you invoke Checkstyle at the <a href="cmdline.html">command line</a>, and when you run a <a href="anttask.html">Checkstyle task</a> in ant.
</li>
<li>
Apply the above rules to <code>name</code>
concatenated with <code>"Check"</code>,
such as loading class
<code>com.puppycrawl.tools.checkstyle.checks.ConstantNameCheck</code>
for element
<div class="source">
<pre>
<module name="ConstantName"/>
</pre></div>
</li>
</ol>
</section>
<section>
<h2><a name="Properties"></a>Properties</h2>
<p>
Properties of a module control how the module performs its task.
Each module property has a default value, and you are not
required to define a property in the configuration document if
the default value is satisfactory. To assign a non-default
value to a module's property, define a child <code>property</code> element
of the <code>module</code> element in the configuration XML
document. Also provide appropriate <code>name</code> and <code>value</code>
attributes for the <code>property</code> element.
For example, property <code>max</code> of module
<code>MethodLength</code> specifies the maximum
allowable number of lines in a method or constructor, and has
default value <code>150</code>. Here is a
configuration of module <code>MethodLength</code>
so that the check reports methods and constructors with more
than <code>60</code> lines:
</p>
<div class="source">
<pre>
<module name="MethodLength">
<property name="max" value="60"/>
</module>
</pre></div>
<p>
<a href="cmdline.html">Command line</a> properties and ant <a href="anttask.html">Checkstyle task</a> properties apply to the
root <code>Checker</code> module. Also, properties
are inherited in the module hierarchy. These features make it
easy to define one property value that applies to many
modules. For example, the following configuration fragment
specifies that a <code>tabWidth</code> of <code>4</code>
applies to <code>TreeWalker</code> and its submodules:
</p>
<div class="source">
<pre>
<module name="Checker">
<module name="JavadocPackage"/>
<module name="TreeWalker">
<property name="tabWidth" value="4"/>
<module name="AvoidStarImport"/>
<module name="ConstantName"/>
...
</module>
</module>
</pre></div>
<p>
The value of a module property can be specified through
<i>property expansion</i> with the <code>${<i>property_name</i>}</code> notation, where
<code><i>property_name</i></code> is a <a href="cmdline.html">command line</a> property or an ant <a href="anttask.html">Checkstyle task</a> property. For example,
the following configuration document element gives property
<code>headerFile</code> the value of command line
property <code>checkstyle.header.file</code>:
</p>
<div class="source">
<pre>
<module name="Header">
<property name="headerFile" value="${checkstyle.header.file}"/>
</module>
</pre></div>
<p>
You can use property expansion to re-specify a module property
value without changing the configuration document.
</p>
<p>
The property element provides an optional <code>default</code> attribute which is
used when a property in the value cannot be resolved. For example this
configuration snippet from a central configuration file checks
that methods have javadoc, but allows individual projects to
override the severity by specifying their desired value in the
command line property <code>checkstyle.javadoc.severity</code>:
</p>
<div class="source">
<pre>
<module name="JavadocMethod">
<property name="severity"
value="${checkstyle.javadoc.severity}"
default="error"/>
</module>
</pre></div>
<p>
ATTENTION: default value is applied to module property value if at least one expansion
property is not defined.
</p>
<p>
This feature is a great help when setting up a centralized
configuration file (e.g. one file for the whole company) to
lower configuration maintenance costs. Projects that are happy
with the default can simply use that configuration file as is,
but individual projects with special needs have the flexibility
to adjust a few settings to fit their needs without having to
copy and maintain the whole configuration.
</p>
<p>
Apart from the above mentioned properties, there are a few system
properties that changes the way how Checkstyle behaves.
All the system properties can be found at the
<a href="config_system_properties.html">system properties</a> page.
</p>
<p>
You can find information about property types on
<a href="property_types.html">Property Types</a> page.
</p>
</section>
<section>
<h2><a name="Checker"></a>Checker</h2>
<a name="Checker_Description"></a><section id="Checker_Description">
<h3><a name="Description"></a>Description</h3>
<p>Since Checkstyle 3.0</p>
<p>
All configurations have root module <code>Checker</code>. <code>Checker</code>
contains:
</p>
<ul>
<li><i>File Set Check</i> children: modules that check sets of
files.</li>
<li><i>Filter</i> children: modules that filter audit
events.</li>
<li><i>File Filter</i> children: modules that filter files
for Checkstyle to process.</li>
<li><i>Audit Listener</i> children: modules that report
filtered events.</li>
</ul>
<p>
<code>Checker</code> also defines properties that are
inherited by all other modules of a configuration.
</p>
</section>
<a name="Checker_Properties"></a><section id="Checker_Properties">
<h3><a name="Properties"></a>Properties</h3>
<div class="wrapper">
<table border="0" class="bodyTable">
<tr class="a">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
<th>since</th>
</tr>
<tr class="b">
<td align="left">basedir</td>
<td>Base directory name; stripped off in messages about files</td>
<td><a href="property_types.html#String">String</a></td>
<td><code>null</code></td>
<td>3.0</td>
</tr>
<tr class="a">
<td align="left">cacheFile</td>
<td>Caches information about files that have checked OK; used
to avoid repeated checks of the same files</td>
<td><a href="property_types.html#File">File</a></td>
<td><code>null</code> (no cache file)</td>
<td>6.16</td>
</tr>
<tr class="b">
<td align="left">charset</td>
<td>Name of the file charset</td>
<td><a href="property_types.html#String">String</a></td>
<td><code>UTF-8</code></td>
<td>5.0</td>
</tr>
<tr class="a">
<td align="left">fileExtensions</td>
<td>File extensions that are accepted</td>
<td><a href="property_types.html#String.5B.5D">String[]</a></td>
<td><code>all files</code></td>
<td>6.3</td>
</tr>
<tr class="b">
<td align="left">haltOnException</td>
<td>Whether to stop execution of Checkstyle if a single file produces any kind of
exception during verification</td>
<td><a href="property_types.html#boolean">boolean</a></td>
<td><code>true</code></td>
<td>7.4</td>
</tr>
<tr class="a">
<td align="left">localeCountry</td>
<td>Locale country for messages</td>
<td><a href="property_types.html#String">String</a> (either
the empty string or an uppercase ISO 3166 2-letter code)</td>
<td>default locale country for the Java Virtual Machine</td>
<td>3.0</td>
</tr>
<tr class="b">
<td align="left">localeLanguage</td>
<td>Locale language for messages</td>
<td><a href="property_types.html#String">String</a> (either
the empty string or a lowercase ISO 639 code)</td>
<td>default locale language for the Java Virtual Machine</td>
<td>3.0</td>
</tr>
<tr class="a">
<td align="left">severity</td>
<td>The default severity level of all violations</td>
<td><a href="property_types.html#SeverityLevel">SeverityLevel</a></td>
<td><code>error</code></td>
<td>3.1</td>
</tr>
<tr class="b">
<td align="left">tabWidth</td>
<td>Number of expanded spaces for a tab character (<code>'\t'</code>); used in
messages and Checks that print violations on files with tabs</td>
<td><a href="property_types.html#int">int</a></td>
<td><code>8</code></td>
<td>8.19</td>
</tr>
</table>
</div>
</section>
<a name="Checker_Metadata"></a><section id="Checker_Metadata">
<h3><a name="Metadata"></a>Metadata</h3>
<p>
This tag is used to keep metadata in the Checkstyle configuration file.
This information is ignored by Checkstyle. This may be useful if you want
to store plug-in specific information or any other information in the config
file.
</p>
<p>
To avoid name clashes between different tools/plug-ins you are <b>strongly</b>
encouraged to prefix all names with your domain name. For example, use the
name "com.mycompany.parameter" instead of "parameter".
<br />
Prefixes
<code>com.puppycrawl.</code>,
<code>net.sourceforge.checkstyle.</code>,
<code>org.checkstyle.</code>
are reserved for Checkstyle.
<br />
Example:
</p>
<div class="source">
<pre>
<module name="Checker">
<metadata name="com.myproject.cs-version" value="4.4"/>
<metadata name="com.myproject.cs-version.desc" value="legacy config"/>
...
</module>
</pre></div>
</section>
<a name="Checker_Examples"></a><section id="Checker_Examples">
<h3><a name="Examples"></a>Examples</h3>
<p>
For example, the following configuration fragment specifies base
directory <code>src/checkstyle</code>, cache file <code>target/cachefile</code> and German
locale for all modules:
</p>
<div class="source">
<pre>
<module name="Checker">
<property name="basedir" value="src/checkstyle"/>
<property name="cacheFile" value="target/cachefile"/>
<property name="localeCountry" value="DE"/>
<property name="localeLanguage" value="de"/>
<module name="JavadocPackage"/>
<module name="TreeWalker">
...
</module>
</module>
</pre></div>
<p>
To configure a <code>Checker</code> so that it
handles files with the <code>ISO-8859-5</code> charset:
</p>
<div class="source">
<pre>
<module name="Checker">
<property name="charset" value="ISO-8859-5"/>
...
</module>
</pre></div>
<p>
To configure a <code>Checker</code> so that it
handles files with the <code>java, xml, properties</code> extensions:
</p>
<div class="source">
<pre>
<module name="Checker">
<property name="fileExtensions" value="java, xml, properties"/>
...
</module>
</pre></div>
<p>
To configure a <code>Checker</code> so that it doesn't stop execution on an
<code>Exception</code> and instead prints it as a violation:
</p>
<div class="source">
<pre>
<module name="Checker">
<property name="haltOnException" value="false"/>
...
</module>
</pre></div>
<p>
To configure a <code>Checker</code> so that it
handles files with any extension:
</p>
<div class="source">
<pre>
<module name="Checker">
<property name="fileExtensions" value="null"/>
...
</module>
</pre></div>
<p>OR</p>
<div class="source">
<pre>
<module name="Checker">
<property name="fileExtensions" value=""/>
...
</module>
</pre></div>
</section>
<a name="Checker_Example_of_Usage"></a><section id="Checker_Example_of_Usage">
<h3><a name="Example_of_Usage"></a>Example of Usage</h3>
<ul>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%20path%3A**%2Fgoogle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+Checker">
Google Style</a>
</li>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%20path%3A**%2Fsun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+Checker">
Sun Style</a>
</li>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Aconfig%20path%3A**%2Fcheckstyle-checks.xml+repo%3Acheckstyle%2Fcheckstyle+Checker">
Checkstyle Style</a>
</li>
</ul>
</section>
<a name="Checker_Package"></a><section id="Checker_Package">
<h3><a name="Package"></a>Package</h3>
<p> com.puppycrawl.tools.checkstyle </p>
</section>
</section>
<section>
<h2><a name="TreeWalker"></a>TreeWalker</h2>
<a name="TreeWalker_Description"></a><section id="TreeWalker_Description">
<h3><a name="Description"></a>Description</h3>
<p>Since Checkstyle 3.0</p>
<p>
File Set Check <code>TreeWalker</code> checks
individual Java source files and defines properties that are
applicable to checking such files.
</p>
</section>
<a name="TreeWalker_Properties"></a><section id="TreeWalker_Properties">
<h3><a name="Properties"></a>Properties</h3>
<div class="wrapper">
<table border="0" class="bodyTable">
<tr class="a">
<th>name</th>
<th>description</th>
<th>type</th>
<th>default value</th>
<th>since</th>
</tr>
<tr class="b">
<td align="left">fileExtensions</td>
<td>File type extension to identify Java files. Setting this
property is typically only required if your Java source code
is preprocessed before compilation and the original files do
not have the extension <code>.java</code></td>
<td><a href="property_types.html#String.5B.5D">String[]</a></td>
<td><code>.java</code></td>
<td>3.0</td>
</tr>
</table>
</div>
</section>
<a name="TreeWalker_Examples"></a><section id="TreeWalker_Examples">
<h3><a name="Examples"></a>Examples</h3>
<p>
For example, the following configuration fragment specifies
<code>TreeWalker</code> a <code>tabWidth</code> of <code>4</code>:
</p>
<div class="source">
<pre>
<module name="Checker">
<module name="TreeWalker">
<property name="tabWidth" value="4"/>
...
</module>
</module>
</pre></div>
<p>
To integrate Checkstyle with BEA Weblogic Workshop 8.1:
</p>
<div class="source">
<pre>
<module name="Checker">
<module name="TreeWalker">
<property name="fileExtensions" value="java,ejb,jpf"/>
...
</module>
</module>
</pre></div>
<p>
To configure <code>TreeWalker</code> so that it
handles files with the <code>java</code> extension:
</p>
<div class="source">
<pre>
<module name="TreeWalker">
<property name="fileExtensions" value="java"/>
...
</module>
</pre></div>
<p>
To configure <code>TreeWalker</code> so that it
handles files with any extension:
</p>
<div class="source">
<pre>
<module name="TreeWalker">
<property name="fileExtensions" value="null"/>
...
</module>
</pre></div>
<p>OR</p>
<div class="source">
<pre>
<module name="TreeWalker">
<property name="fileExtensions" value=""/>
...
</module>
</pre></div>
</section>
<a name="TreeWalker_Example_of_Usage"></a><section id="TreeWalker_Example_of_Usage">
<h3><a name="Example_of_Usage"></a>Example of Usage</h3>
<ul>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%20path%3A**%2Fgoogle_checks.xml+repo%3Acheckstyle%2Fcheckstyle+TreeWalker">
Google Style</a>
</li>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Asrc%2Fmain%2Fresources%20path%3A**%2Fsun_checks.xml+repo%3Acheckstyle%2Fcheckstyle+TreeWalker">
Sun Style</a>
</li>
<li>
<a class="externalLink" href="https://github.com/search?q=path%3Aconfig%20path%3A**%2Fcheckstyle-checks.xml+repo%3Acheckstyle%2Fcheckstyle+TreeWalker">
Checkstyle Style</a>
</li>
</ul>
</section>
<a name="TreeWalker_Package"></a><section id="TreeWalker_Package">
<h3><a name="Package"></a>Package</h3>
<p> com.puppycrawl.tools.checkstyle </p>
</section>
<a name="TreeWalker_Parent_Module"></a><section id="TreeWalker_Parent_Module">
<h3><a name="Parent_Module"></a>Parent Module</h3>
<p> <a href="config.html#Checker">Checker</a> </p>
</section>
</section>
<section>
<h2><a name="TreeWalker_Checks"></a>TreeWalker Checks</h2>
<p>
The <code>TreeWalker</code> module creates a syntax
tree for a Java source file and invokes its submodules, called
<i>Checks</i>, during a walk, or traversal, of the nodes of
the tree. Every node of the syntax tree has a token. A visit to
a node during the traversal triggers all Checks that are
configured for its token. For example, if Check
<code>MethodLength</code> has been configured as a
submodule of <code>TreeWalker</code>, then a visit
to a node with a method or a constructor definition token
triggers <code>MethodLength</code> to check the
number of lines of the node's code block.
</p>
<p>
Some Checks, such as <code>FileLength</code> and
<code>LineLength</code>, apply directly to the
source file and do not involve tokens of the syntax tree. Other
Checks are associated with configurable sets of tokens that
trigger the Checks. For example, this element configures Check
<code>MethodLength</code>:
</p>
<div class="source">
<pre>
<module name="MethodLength"/>
</pre></div>
<p>
The default token set for <code>MethodLength</code>
is <code>{METHOD_DEF, CTOR_DEF}</code>, method
definition and constructor definition tokens, so <code>TreeWalker</code> invokes
<code>MethodLength</code> whenever it visits a node with a <code>METHOD_DEF</code>
or a <code>CTOR_DEF</code> token.
</p>
<p>
You specify the trigger tokens for a Check with property <code>tokens</code>. The value
of <code>tokens</code> is a list that denotes a subset of the Check's tokens, as in the
following element that configures Check <code>MethodLength</code> to check the number
of lines of methods only: