MagicConstantsString.qhelp

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


<overview>
<p>A <em>magic string</em> is a string literal (for example, <code>"SELECT"</code>,
<code>"127.0.0.1"</code>) that is used in the middle of a block of code without
explanation. It is considered bad practice to use magic strings because:</p>

<ul>
<li>A string in isolation can be difficult for other programmers to understand.
</li>
<li>It can be difficult to update the code if the requirements change. For example, if the magic 
string represents a protocol, changing the protocol means that you must change
every occurrence of the protocol.
</li>
</ul>

</overview>
<recommendation>

<p>Assign the magic string to a new named constant, and use this instead. This overcomes the two problems
with magic strings:</p>

<ul>
<li>A named constant (such as <code>SMTP_HELO</code>) is more easily understood by other programmers.
</li>
<li>Using the same named constant in many places makes the code much easier to
update if the requirements change, because you have to update the string in only one place.
</li>
</ul>

</recommendation>
<example>

<p>The following example shows a magic string <code>username</code>. This should be replaced by a new
named constant, as shown in the fixed version.</p>

<sample src="MagicConstantsString.java" />

</example>
<references>


<li>
R. C. Martin, <em>Clean Code: A Handbook of Agile Software Craftsmanship</em>, &sect;17.G25. Prentice Hall, 2008.
</li>


</references>
</qhelp>