IteratorRemoveMayFail.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
The <code>remove</code> method of the <code>Iterator</code> interface is an optional operation.
It is not supported by iterators on unmodifiable collections, or iterators on lists constructed
by the <code>Arrays.asList</code> method. Invoking <code>remove</code> on such an iterator
will lead to an <code>UnsupportedOperationException</code>.
</p>

</overview>
<recommendation>

<p>
If a collection is meant to be modified after construction, use a modifiable collection type such as
<code>ArrayList</code> or <code>HashSet</code>.
</p>

</recommendation>
<example>

<p>
In the following example, the constructor <code>A(Integer...)</code> initializes the field
<code>A.l</code> to <code>Arrays.asList(is)</code>. While the type of lists returned by
<code>Arrays.asList</code> supports element updates through the <code>set</code> method, it
does not support element removal. Hence the call to <code>iter.remove</code> on line 20 must
fail at runtime.
</p> 

<sample src="IteratorRemoveMayFail.java" />

<p>
To avoid this failure, copy the list returned by <code>Arrays.asList</code> into a newly
created <code>ArrayList</code> like this:
</p>

<sample src="IteratorRemoveMayFailGood.java" />

</example>
<references>


<li>Mark Needham: <a href="https://dzone.com/articles/java-fooled">Java: Fooled by java.util.Arrays.asList</a>.</li>


</references>
</qhelp>