hg: jdk8/tl/jdk: 7173919: Minor optimization of hashing methods (original) (raw)

Mike Duigou mike.duigou at oracle.com
Thu Jun 14 20:26:40 UTC 2012

On Jun 14 2012, at 09:29 , Ulf Zibis wrote:

Hi Mike,

I like the 1-liner ... :-) int h = hashSeed ^ k.hashCode(); ... but I'm still missing a little comment, what this xor with a hashSeed serves for. Such as brief, as the next following 3 lines about preventing from collisions.

The hashSeed randomizes table order to reduce the value of partial collisions--only full collisions will predictably collide. The comment I think you are looking for is on hashSeed itself.

/**
 * A randomizing value associated with this instance that is applied to
 * hash code of keys to make hash collisions harder to find.
 */

WeakHashMap.hash(Object) could be private too, instead final.

OK. I will probably make it private method though I hate opening an issue just for one keyword.

And last... you have reinserted/left the space after the cast in some occurences. ;-)

Netbeans did actually. I don't do my own source formatting.

Mike

-Ulf Am 14.06.2012 17:27, schrieb mike.duigou at oracle.com: Changeset: 505455116320 Author: mduigou Date: 2012-06-13 16:48 -0700 URL: http://hg.openjdk.java.net/jdk8/tl/jdk/rev/505455116320

7173919: Minor optimization of hashing methods Summary: several minor optimizations to hashing methods used by hash map classes Reviewed-by: dholmes ! src/share/classes/java/util/HashMap.java ! src/share/classes/java/util/Hashtable.java ! src/share/classes/java/util/WeakHashMap.java ! src/share/classes/java/util/concurrent/ConcurrentHashMap.java

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