Re: hashCode
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
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