##### Overview

- Download PMD 3.9
- What's new in PMD 3.9
- PMD in the news
- PMD-related products and books
- Best practices
- Future directions
- Similar projects
- Credits
- License
- What does 'PMD' mean?

##### Usage

- Installation
- Command line usage
- Ant task usage
- Maven plugin usage
- IDE plugin usage
- Suppressing warnings
- Finding duplicated code
- JSP support

##### Customizing PMD

- Compiling PMD
- How to write a rule
- Writing XPath rules
- How to make a rule set
- How it works

##### For example

- Run PMD on a Sourceforge project

##### Rule Sets

- Index
- Basic
- Braces
- Code Size
- Clone
- Controversial
- Coupling
- Design
- Finalizers
- Import Statements
- J2EE
- Javabeans
- JUnit Tests
- Logging (Java)
- Logging (Jakarta)
- Migrating
- Naming
- Optimizations
- Strict Exceptions
- Strings
- Sun Security
- Unused Code
- Java Server Pages
- Java Server Faces

##### Project Documentation

- About PMD
- Project Info
- Project Reports
- Development Process

## Finding duplicate code

### Overview

Duplicate code can be hard to find, especially in a large project. But PMD's Copy/Paste Detector (CPD) can find it for you! CPD has been through three major incarnations:

- First we wrote it using a variant of Michael Wise's Greedy String Tiling algorithm (our variant is described here)
- Then it was completely rewritten by Brian Ewins using the Burrows-Wheeler transform
- Finally, it was rewritten by Steve Hawkins to use the Karp-Rabin string matching algorithm.

Each rewrite made it much faster, and now it can process the JDK 1.4 java.* packages in about 4 seconds (on my workstation, at least).

Here's a screenshot of CPD after running on the JDK java.lang package.

Note that CPD works with Java, JSP, C, C++, and PHP code.

CPD is included with PMD, which you can download here. Or, if you have Java Web Start, you can run CPD by clicking here.

Here are the duplicates CPD found in the JDK 1.4 source code.

Here are the duplicates CPD found in the APACHE_2_0_BRANCH branch of Apache (just the `httpd-2.0/server/` directory).

### Ant task

Andy Glover wrote an Ant task for CPD; here's how to use it:

    <target name="cpd">
        <taskdef name="cpd" classname="net.sourceforge.pmd.cpd.CPDTask" />
        <cpd minimumTokenCount="100" outputFile="/home/tom/cpd.txt">
            <fileset dir="/home/tom/tmp/ant">
                <include name="**/*.java"/>
            </fileset>
        </cpd>
    </target>

There's a `ignoreLiterals="true"` option which makes CPD ignore literal value differences when evaluating a duplicate block. This means that `foo=42;` and `foo=43;` will be seen as equivalent. You may want to run PMD with this option off to start with and then switch it on to see what it turns up. There's also a `ignoreIdentifiers="true"` option that does the same thing with identifiers; i.e., variable names, methods names, and so forth. The same guidelines apply. Finally, there's an optional `language="cpp|java|php|ruby"` flag to select the appropriate language; the default language is "java".

Also, you can get verbose output from this task by running ant with the `-v` flag; i.e.:

     ant -v -f mybuildfile.xml cpd

Also, you can get an HTML report from CPD by using the XSLT script in pmd/etc/xslt/cpdhtml.xslt. Just run the CPD task as usual and right after it invoke the Ant XSLT script like this:

    <xslt in="cpd.xml" style="etc/xslt/cpdhtml.xslt" out="cpd.html" />

### Command line usage

To run CPD from the command line, just give it the minimum duplicate size and the source directory:

    $ java net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /usr/local/java/src/java

You can also specify the language:

    $ java net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /path/to/c/source --language cpp

And if you're checking a C source tree with duplicate files in different architecture directories you can skip those using --skip-duplicate-files:

    $ java net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /path/to/c/source --language cpp --skip-duplicate-files

You can also specify a report format - here we're using the XML report:

    $ java net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /usr/local/java/src/java --format net.sourceforge.pmd.cpd.XMLRenderer

The default format is a text report, and there's also a `net.sourceforge.pmd.cpd.CSVRenderer` report.

Note that CPD is pretty memory-hungry; you may need to give Java more memory to run it, like this:

    $ java -Xmx512m net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /usr/local/java/src/java

Suggestions? Comments? Post them here. Thanks!