mirror of
https://github.com/github/codeql.git
synced 2026-01-05 18:50:23 +01:00
455b840712
For those documents with no obvious new home I've pointed the links to the Internet Archive.
61 lines
1.8 KiB
XML
61 lines
1.8 KiB
XML
<!DOCTYPE qhelp PUBLIC
|
|
"-//Semmle//qhelp//EN"
|
|
"qhelp.dtd">
|
|
<qhelp>
|
|
<overview>
|
|
<p>
|
|
Efferent coupling is the number of outgoing dependencies for each class. In other words, it is the
|
|
number of other classes on which each class depends.
|
|
</p>
|
|
|
|
<p>
|
|
A class that depends on many other classes is quite brittle, because if any of
|
|
its dependencies change, the class itself may have to change as well. Furthermore, the
|
|
reason for the high number of dependencies is often that different parts of
|
|
the class depend on different groups of other classes, so it is common to
|
|
find that classes with high efferent coupling also lack cohesion.
|
|
</p>
|
|
|
|
</overview>
|
|
<recommendation>
|
|
|
|
<p>
|
|
You can reduce efferent coupling by splitting up a class so that each part depends on fewer classes.
|
|
</p>
|
|
|
|
</recommendation>
|
|
<example>
|
|
|
|
<p>In the following example, class <code>X</code> depends on both <code>Y</code> and
|
|
<code>Z</code>.
|
|
</p>
|
|
|
|
<sample src="ClassEfferentCoupling.py" />
|
|
|
|
<p>However, the methods that use <code>Y</code> do not use <code>Z</code>, and the methods
|
|
that use <code>Z</code> do not use <code>Y</code>. Therefore, the class can be split into
|
|
two classes, one of which depends only on <code>Y</code> and the other only on <code>Z</code></p>
|
|
|
|
<sample src="ClassEfferentCouplingGood.py" />
|
|
|
|
<p>
|
|
Although this is a slightly artificial example, this sort of situation
|
|
does tend to occur in more complicated classes,
|
|
so the general technique is quite widely applicable.
|
|
</p>
|
|
|
|
</example>
|
|
<references>
|
|
|
|
|
|
<li>
|
|
IBM developerWorks: <a href="https://web.archive.org/web/20190919085934/https://www.ibm.com/developerworks/library/j-eaed6/">Evolutionary architecture and emergent design: Emergent design through metrics</a>.
|
|
</li>
|
|
<li>
|
|
R. Martin, <em>Agile Software Development: Principles, Patterns and Practices</em>. Pearson, 2011.
|
|
</li>
|
|
|
|
|
|
</references>
|
|
</qhelp>
|