HashCodeBuilder append(Object) could be more efficient
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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
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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