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https://issues.apache.org/jira/browse/SOLR-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13003675#comment-13003675
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Dawid Weiss commented on SOLR-2410:
-----------------------------------
It's because there's a bug -- PriorityQueue declares a generic array:
protected T[] heap;
but assigns an Object[] to it in:
heap = (T[]) new Object[heapSize]; // T is unbounded type, so this
unchecked cast works always
this is true only if heap is not exposed outside the class (and is the pattern
used in JDK's ArrayDeque<E>, for example). Unfortunately the compiler will
insert casts if you have a subclass with a narrowed generic type to ensure the
array is indeed of proper type. The solution is to:
1) allocate arrays of real component type (impossible if you don't know it in
advance or don't have an existing array or its component). Example: Google
Guava's ObjectArrays.newArray, as here:
http://guava-libraries.googlecode.com/svn/tags/release08/javadoc/com/google/common/collect/ObjectArrays.html#newArray(java.lang.Class,
int)
2) cast superclass's array to (Object[]) first, then cast to the concrete
component type. Here:
(CacheEntry<K,V>) ((Object[]) heap)[1];
3) Declare PriorityQueue's internal array as Object[] and provide a getter that
casts components to (T)?
> ConcurrentLRUCache can throw class cast exception
> -------------------------------------------------
>
> Key: SOLR-2410
> URL: https://issues.apache.org/jira/browse/SOLR-2410
> Project: Solr
> Issue Type: Bug
> Affects Versions: 4.0
> Reporter: Yonik Seeley
> Fix For: 4.0
>
>
> ConcurrentLRUCache throws a class cast exception.
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