ComplexCondition.qhelp

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


<overview>
<p>In general, very complex conditions are difficult to write and read, and increase the chance
of defects.</p>

</overview>
<recommendation>

<p>Firstly, a condition can often be simplified by changing other parts of the
code to initialize variables more consistently. For example, is
there a semantic difference between <code>id</code> being <code>null</code> and
having zero-length? If not, choosing one sentinel value and using it
consistently simplifies most uses of that variable.</p>

<p>Secondly, extracting part of a condition into a Boolean-valued method can simplify the condition
and also allow code reuse, with all its benefits.</p>

<p>Thirdly, assigning each subcondition of the condition to a local variable, and then using the variables in 
the condition instead can simplify the condition.</p>

</recommendation>
<example>

<p>The following example shows a complex condition found
in a real program used by millions of people. The condition is so confusing that even the programmer 
who wrote it is not sure if he got it right (see the <code>TODO</code> comment).</p>

<sample src="ComplexCondition.java" />

<p>The condition can be simplified by extracting parts of the condition into Boolean-valued methods.
These methods are then used in the condition.</p>

<sample src="ComplexConditionGood.java" />

</example>
<references>


<li>
R. C. Martin, <em>Clean Code: A Handbook of Agile Software Craftsmanship</em>, &sect;17.G28. Prentice Hall, 2008.
</li>
<li>
S. McConnell, <em>Code Complete: A Practical Handbook of Software Construction</em>. Microsoft Press, 2004.
</li>


</references>
</qhelp>