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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: hashCode
Date: Fri, 31 Aug 2012 17:55:32 +0200
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Xref: csiph.com comp.lang.java.programmer:18477

On 31.08.2012 17:38, Eric Sosman wrote:
> 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.

Well, Jim's wording may not be correct to the last bit but the message 
is still true: String's hash member just caches the hash code derived 
from the characters of the String.  And obviously equals() must compare 
the characters.  So basically both recur to the same underlying data.

Cheers

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/