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<overview>

<p>When most of the lines in one file have corresponding "similar" lines in one or more other

files, the files themselves are regarded as <em>mostly similar</em>. Two lines are defined as

similar if they are either identical or contain only very minor differences.</p>

<p>Code duplication in general is highly undesirable for a range of reasons. The artificially

inflated amount of code is more difficult to understand, and sequences of similar but subtly different lines

can mask the real purpose or intention behind them. Also, there is always a risk that only one

of several copies of the code is updated to address a defect or add a feature.</p>

</overview>

<recommendation>

<p>Consider whether the differences are

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 all but 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. Can some of the shared code be extracted into

methods (perhaps with additional parameters, to cover the differences in behavior)? Should it

be moved into a utility class or file that is accessible to all current implementations, or

should a new level of abstraction be introduced?</p>

</recommendation>

<references>

<li>E. Juergens, F. Deissenboeck, B. Hummel, S. Wagner.

<em>Do code clones matter?</em> Proceedings of the 31st International Conference on

Software Engineering,

485-495, 2009.</li>

</references>

</qhelp>