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https://issues.apache.org/jira/browse/LUCENE-2953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13003852#comment-13003852
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Dawid Weiss commented on LUCENE-2953:
-------------------------------------
There seems to be no consensus on how to deal with generic arrays. Even the JDK
has two different implementations -- one in ArrayDeque (uses T[]), the other in
ArrayList (uses Object[]). Creating an array of a given component type is (can
be?) more costly than keeping an array Object[] because it needs to be done via
call to Array.newArray (haven't checked though). Theoretically having a
concrete-type array should speed up iterators (because no additional casts are
needed), but I don't think this is the case.
In fact, I just wrote a simple Caliper benchmark that compares these
(attached), my results show the runtime times is nearly identical (probably
within stddev).:
{noformat}
0% Scenario{vm=java, trial=0, benchmark=Generic, size=1000000} 8985430.93 ns;
σ=257329.28 ns @ 10 trials
33% Scenario{vm=java, trial=0, benchmark=GenericSubclass, size=1000000}
8989486.27 ns; σ=207151.20 ns @ 10 trials
67% Scenario{vm=java, trial=0, benchmark=Object, size=1000000} 8767324.34 ns;
σ=218235.97 ns @ 10 trials
benchmark ms linear runtime
Generic 8.99 =============================
GenericSubclass 8.99 ==============================
Object 8.77 =============================
vm: java
trial: 0
size: 1000000
{noformat}
> PriorityQueue is inheriently broken if subclass attempts to use "heap"
> w/generic T bound to anything other then "Object"
> ------------------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-2953
> URL: https://issues.apache.org/jira/browse/LUCENE-2953
> Project: Lucene - Java
> Issue Type: Bug
> Reporter: Hoss Man
> Attachments: LUCENE-2953.patch
>
>
> as discovered in SOLR-2410 the fact that the protected "heap" variable in
> PriorityQueue is initialized using an Object[] makes it impossible for
> subclasses of PriorityQueue to exist and access the "heap" array unless they
> bind the generic to Object.
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