Migrated more documentation.
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Oliver Burn
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<title>Duplicate Code Checks</title>
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<link rel="stylesheet" type="text/css" href="mystyle.css"/>
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</head>
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<body>
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<!-- The header -->
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<table border="0" width="100%" summary="header layout">
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<tr>
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<td><h1>Duplicate Code Checks</h1></td>
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<td align="right"><img src="logo.png" alt="Checkstyle Logo"/></td>
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</tr>
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</table>
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<!-- content -->
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<table border="0" width="100%" cellpadding="5" summary="body layout">
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<tr>
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<!--Left menu-->
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<td class="menu" valign="top">
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<ul>
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<li>
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<a href="#StrictDuplicateCode">StrictDuplicateCode</a>
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</li>
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</ul>
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</td>
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<!--Content-->
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<td class="content" valign="top" align="left">
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There are many trade-offs when writing a duplicate code detection tool.
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Some of the conflicting goals are:
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<ul>
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<li>Fast</li>
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<li>Low memory usage</li>
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<li>Avoid false alarms</li>
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<li>Support multiple/arbitrary languages</li>
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<li>Support Fuzzy matches (comments, whitespace, linebreaks, variable renaming, etc.)</li>
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</ul>
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</p>
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<p>
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Note that there are brilliant commercial implementations of duplicate code
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detection tools. One that is particularly noteworthy is
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<a href="http://www.redhillconsulting.com.au/products/simian/">Simian</a>
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from RedHill Consulting, Inc.
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</p>
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<p>
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Simian is reasonably priced (free for noncommercial projects)
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and includes a Checkstyle plugin.
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We encourage all users of Checkstyle to evaluate Simian as an
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alternative to the Checks we offer in our distribution.
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</p>
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<p>
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The following table summarizes the characteristics of the available
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Checkstyle plugins for duplicate code detection:
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<table width="100%" border="1" cellpadding="5" class="body">
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<tr class="header">
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<th>Name</th>
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<th>Speed</th>
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<th>Memory Usage</th>
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<th>False Alarms</th>
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<th>Supported languages</th>
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<th>Fuzzy matches</th>
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</tr>
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<tr>
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<td>StrictDuplicateCode</td>
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<td>Medium</td>
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<td>Very Low</td>
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<td>Possible but very unlikely</td>
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<td>any language</td>
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<td>No</td>
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</tr>
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<tr>
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<td>Simian</td>
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<td>Very high</td>
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<td>Low</td>
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<td>Possible but very unlikely</td>
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<td>many languages, including Java and C/C++/C#</td>
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<td>Limited support</td>
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</tr>
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</table>
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</p>
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<a name="StrictDuplicateCode"></a><h2>StrictDuplicateCode</h2>
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<p class="body">
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Performs a line-by-line comparison of all code lines and reports
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duplicate code, i.e. a sequence of lines that differ only in indentation.
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All import statements in Java code are ignored, any other line -
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including javadoc, whitespace lines between methods, etc. - is considered
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(which is why the check is called <em>strict</em>).
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</p>
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<h4>Properties</h4>
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<table width="100%" border="1" cellpadding="5" class="body">
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<tr class="header">
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<th>name</th>
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<th>description</th>
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<th>type</th>
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<th>default value</th>
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</tr>
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<tr>
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<td>min</td>
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<td>how many lines must be equal to be considered a duplicate</td>
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<td><a href="property_types.html#int">int</a></td>
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<td><span class="default">12</span></td>
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</tr>
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<tr>
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<td>charset</td>
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<td>name of the file charset</td>
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<td><a href="property_types.html#string">String</a></td>
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<td>System property "file.encoding"</td>
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</tr>
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</table>
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<h4>Examples</h4>
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<p class="body">
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To configure the check:
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</p>
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<pre class="body">
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<module name="StrictDuplicateCode"/>
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</pre>
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<p class="body">
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To configure the check so that it allows larger equivalent blocks:
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</p>
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<pre class="body">
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<module name="StrictDuplicateCode">
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<property name="min" value="15"/>
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</module>
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</pre>
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<p class="body">
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To configure the check so that it handles files with the <span class="code">UTF-8</span>
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charset:
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</p>
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<pre class="body">
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<module name="StrictDuplicateCode">
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<property name="charset" value="UTF-8"/>
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</module>
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</pre>
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<h4>Package</h4>
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<p class="body">
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com.puppycrawl.tools.checkstyle.checks.duplicates
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</p>
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<h4>Parent Module</h4>
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<p class="body">
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<a href="config.html#checker">Checker</a>
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</p>
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</td>
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</tr>
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</table>
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<hr />
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<div><a href="index.html">Back to the Checkstyle Home Page</a></div>
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<p class="copyright">
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Copyright © 2002-2004 Oliver Burn. All rights Reserved.
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</p>
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</body>
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</html>
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