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Date: Tue, 29 Dec 2009 06:43:29 +0000 (UTC)
From: "Henri Yandell (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Subject: [jira] Updated: (LANG-574) HashCodeBuilder append(Object) could be
 more efficient
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     [ https://issues.apache.org/jira/browse/LANG-574?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Henri Yandell updated LANG-574:
-------------------------------

    Fix Version/s: 3.0

> HashCodeBuilder append(Object) could be more efficient
> ------------------------------------------------------
>
>                 Key: LANG-574
>                 URL: https://issues.apache.org/jira/browse/LANG-574
>             Project: Commons Lang
>          Issue Type: Improvement
>          Components: lang.builder.*
>    Affects Versions: 2.4
>         Environment: Sun JDK 1.6.0_17
>            Reporter: Anthony Whitford
>            Priority: Minor
>             Fix For: 3.0
>
>
> See:  http://svn.apache.org/viewvc/commons/proper/lang/trunk/src/java/org/apache/commons/lang3/builder/HashCodeBuilder.java?view=markup
> If you use *reflectionHashCode*, you will eventually call *reflectionAppend(Object)* for every field (see lines 859 to 890).  There is a long list of _instanceOf_ checks for the various types of arrays.  My concern is that having an array field is relatively rare, yet the code does 9 if/else checks before computing the _hashCode_ for _one_ element.  I am thinking that it would make a lot of sense to wrap those if/else checks for the various array types in an *isArray* check (see Class.isArray).
> If you look at the JDK source code for *Arrays.deepToString*, you will see that it checks if the class is an array before checking the various types.  Note that since it gets the Class, it doesn't need to execute _instanceOf_ which is likely more expensive...
> I have not done profiling, but I would not be surprised if short circuiting these checks could improve performance by an order of magnitude.  The assumption is that getting the Class of an Object and asking it if it is an array is cheaper than asking _instanceOf_ 9 times.

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