# Duplicate Code Checks

There are many trade-offs when writing a duplicate code detection tool. Some of the conflicting goals are:

- Fast
- Low memory usage
- Avoid false alarms
- Support multiple/arbitrary languages
- Support Fuzzy matches (comments, whitespace, linebreaks, variable renaming, etc.)

Note that there are brilliant commercial implementations of duplicate code detection tools. One that is particularly noteworthy is Simian from RedHill Consulting, Inc.

Simian is reasonably priced (free for noncommercial projects) and includes a Checkstyle plugin. We encourage all users of Checkstyle to evaluate Simian as an alternative to the Checks we offer in our distribution.

The following table summarizes the characteristics of the available Checkstyle plugins for duplicate code detection:

Name | Speed | Memory Usage | False Alarms | Supported languages | Fuzzy matches
--- | --- | --- | --- | --- | ---
StrictDuplicateCode | Medium | Very Low | Possible but very unlikely | any language | No
Simian | Very high | Low | Possible but very unlikely | many languages, including Java and C/C++/C# | Limited support

## StrictDuplicateCode

Performs a line-by-line comparison of all code lines and reports duplicate code, i.e. a sequence of lines that differ only in indentation. All import statements in Java code are ignored, any other line - including javadoc, whitespace lines between methods, etc. - is considered (which is why the check is called strict).

#### Properties

name | description | type | default value
--- | --- | --- | ---
min | how many lines must be equal to be considered a duplicate | int | 12

#### Examples

To configure the check:

    <module name="StrictDuplicateCode"/>

To configure the check so that it allows larger equivalent blocks:

    <module name="StrictDuplicateCode">
        <property name="min" value="15"/>
    </module>

#### Package

com.puppycrawl.tools.checkstyle.checks.duplicates

#### Parent Module

Checker

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Copyright © 2002-2003 Oliver Burn. All rights Reserved.