<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>If two files share a lot of each other's code then there is a lot of unnecessary code duplication. 
This makes it difficult to make changes in future and makes the code harder to read.</p>

</overview>
<recommendation>
<p>While completely duplicated files are rare, they are usually a sign of a simple oversight. 
Usually the required action is to remove all but one of them. A common exception to this rule may arise  
from generated code that simply occurs in several places in the source tree; the check can be 
adapted to exclude such results.</p>

<p>It is far more common to see duplication of many lines between two files, leaving just a few that 
are actually different. Consider such situations carefully. Are the differences deliberate or 
a result of an inconsistent update to one of the clones? If the latter, then treating the files as 
completely duplicate and eliminating one (while preserving any corrections or new features that 
may have been introduced) is the best course. If two files serve genuinely different purposes but almost 
all of their lines are the same, that can be a sign that there is a missing level of abstraction. Look 
for ways to share the functionality, either by creating a utility class for the common parts or by 
encapsulating the common parts into a new super class of any classes involved.</p>

</recommendation>
<references>

  <li>Elmar Juergens, Florian Deissenboeck, Benjamin Hummel and Stefan Wagner. <em>Do Code Clones Matter?</em>. 2009.</li>

</references>
</qhelp>
