ImpossibleCast.qhelp

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


<overview>
<p>Some downcasts on arrays will fail at runtime.
An object <code>a</code> with dynamic type <code>A[]</code> cannot be cast to <code>B[]</code>, 
where <code>B</code> is a subtype of <code>A</code>,
even if all the elements of <code>a</code> can be cast to <code>B</code>. 
</p>

</overview>
<recommendation>

<p>Ensure that the array creation expression constructs an array object of the right type.</p>

</recommendation>
<example>

<p>The following example shows an assignment that throws a <code>ClassCastException</code> at runtime.</p>

<sample language="java">String[] strs = (String[])new Object[]{ "hello", "world" };</sample>

<p>To avoid the exception, a <code>String</code> array should be created instead.</p>

<sample language="java">String[] strs = new String[]{ "hello", "world" };</sample>

</example>
<references>


<li>
  Java Language Specification:
  <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-5.html#jls-5.1.6">Narrowing Reference Conversion</a>,
  <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.10.3">Subtyping among Array Types</a>.
</li>


</references>
</qhelp>