DuplicateAnonymous.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>


<overview>
<p>Anonymous classes are a common way of creating implementations of an interface
or abstract class whose functionality is
really only needed once. Duplicating the definition of an anonymous class in several
places is usually a sign that refactoring is necessary.</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>Introduce a concrete class
that contains the definition just once, and replace the anonymous classes with instances
of this concrete class.</p>

</recommendation>
<example>

<p>In the following example, the definition of the class <code>addActionListener</code> is duplicated for 
each button that needs to use it. A better solution is shown that defines just one class, 
<code>MultiplexingListener</code>, which is used by each button.</p>

<sample src="DuplicateAnonymous.java" />

</example>
<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>