Hashtable.Entry.hashCode() no longer conforms to Map.Entry.hashCode()

[Mike Duigou]

Good find Neil. 

I have opened JDK-8000955 for this issue along with JDK-8000956 for the Java 7 backport.

The code could be simplified by using Objects.hashCode()

ie.

return Objects.hashCode(key) ^ Objects.hashCode(value);

Any objection to extending the test similar to Collisions.java to test other Map classes?

Mike

On Oct 15 2012, at 18:29 , Neil Richards wrote:

> Hi,
> I notice that the behaviour of java.util.Hashtable.Entry.hashCode() no
> longer conforms to the defined behaviour (in the Java API Javadoc [1])
> for java.util.Map.Entry.hashCode() implementations.
> 
> The code in Hashtable.Entry.hashCode() assumes that the value in
> Hashtable.Entry.hash will always be the same as that for
> Hashtable.Entry.getKey().hashCode() .
> 
> However, since Java bug 7126277 (Alternative String hashing
> implementation), the use of Hashtable.hashSeed, a randomizing factor,
> has been introduced into the calculation of Hashtable.hash().
> 
> It is the result from Hashtable.hash() which ends up stored in the
> Hashtable.Entry.hash field.
> 
> So the assumption made in Hashtable.Entry.hashCode() is no longer valid,
> and the code needs to be corrected, so that it once more complies with
> the Java API defined behaviour.
> 
> 
> I have created a webrev [2] with my suggested fix for this problem,
> together with a simple testcase to demonstrate it.
> 
> (I've also checked the other Map implementations modified by 7126277,
> and verified that the others still conform to the Java API in this
> regard).
> 
> Please review the problem and suggested fix, and let me know your
> thoughts.
> 
> I am not aware of an existing Java bug for this issue. 
> Provided you agree with my analysis, could one be raised to allow the
> fix to be committed?
> 
> Thanks,
> Neil
> 
> [1] http://docs.oracle.com/javase/7/docs/api/java/util/Map.Entry.html#hashCode%28%29
> [2] http://cr.openjdk.java.net/~ngmr/hashtable-entry-hashcode-fix/webrev.00
> 
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