WhitespaceContradictsPrecedence.qhelp

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


<overview>
<p>
Nested expressions where the spacing around operators suggests a different
grouping than that imposed by the Java operator precedence rules are problematic:
they could indicate a bug where the author of the code misunderstood the precedence
rules. Even if there is no a bug, the spacing could be confusing to people who
read the code.
</p>

</overview>
<recommendation>

<p>
Make sure that the spacing around operators reflects operator precedence, or use parentheses to
clarify grouping.
</p>

</recommendation>
<example>

<p>
Consider the following piece of code for allocating an array:
</p>
<pre>
    int[] buf = new int[capacity + capacity>>1];
</pre>
<p>
Here, the spacing around <code>+</code> and <code>&gt;&gt;</code> suggests the grouping
<code>capacity + (capacity&gt;&gt;1)</code>, that is, the allocated array should be 50% larger than
the given capacity.
</p>
<p>In fact, however, <code>+</code> has higher precedence than <code>&gt;&gt;</code>, so
this code allocates an array of size <code>(capacity + capacity) &gt;&gt; 1</code>, which is
the same as <code>capacity</code>.
</p>

</example>
<references>


<li>
  J. Bloch and N. Gafter, <em>Java Puzzlers: Traps, Pitfalls, and Corner Cases</em>, Puzzle 35. Addison-Wesley, 2005.
</li>


</references>
</qhelp>