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From: Jim Janney <jjanney@shell.xmission.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: hashCode
Date: Fri, 31 Aug 2012 09:56:48 -0600
Organization: more research is needed
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Eric Sosman <esosman@ieee-dot-org.invalid> writes:

> On 8/31/2012 11:08 AM, Jim Janney wrote:
>> Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> writes:
>>
>>> On 31/08/2012 03:43, Eric Sosman allegedly wrote:
>>>> On 8/30/2012 6:52 PM, Daniele Futtorovic wrote:
>>>> [...]
>>>> As an example of why a hasher might want access to a strictly-private
>>>> field, I offered String: [...]
>>>
>>> Imposing that classes should expose all information "relevant" (says
>>> who??) to hashing is utter rubbish IMNSHO.
>>
>> Objects that compare equal must hash to the same value.  It follows that
>> if the hash function uses a value, so must the comparison method.
>
>     Since java.lang.String had already been mentioned, it's sort
> of too bad you didn't look at it before posting.  Had you done so,
> you'd have found that [1] hashCode() uses the private field `hash'
> and [2] equals() does not.

If you want to play gotcha, it's sort of too bad you don't read this
newsgroup more often.  I pointed out the use of the private field some
time ago, when we were discussing immutable classes.

If you'd rather argue on the actual issues, a cached result is not extra
information.  The hashCode method in String doesn't return anything that
can't be computed from publically available information.

-- 
Jim Janney