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NNTP-Posting-Date: Tue, 28 Aug 2012 03:06:20 -0500
Date: Tue, 28 Aug 2012 01:06:19 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: hashCode
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On 8/27/2012 9:19 PM, markspace wrote:
> On 8/27/2012 6:58 PM, Patricia Shanahan wrote:
>> On 8/27/2012 5:03 PM, markspace wrote:
>> ...
>>> For example, in C, one can always hash based on memory address.  In Java
>>> we don't have that option, so hashcode() takes the place of the
>>> intrinsic property of an address.
>> ...
>>
>> In Java we have System.identityHashCode() which provides an address-like
>> hash code for any object.
>
>
> I think System.identityHashCode() is the (same as the) default
> implementation for Object::hashCode(), yes?

Yes, but it could have been written, with a slightly different
explanation, without putting hashCode() in Object.

>
> So there's a small bit of evidence in support of the idea that
> Object::hashCode() is meant to mimic the idea of just hashing on address.

I don't think you need such indirect evidence:

"As much as is reasonably practical, the hashCode method defined by
class Object does return distinct integers for distinct objects. (This
is typically implemented by converting the internal address of the
object into an integer, but this implementation technique is not
required by the JavaTM programming language.) "

[From the Object API documentation.]

Patricia