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From: Lew <noone@lewscanon.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Did the sort do anything?
Date: Tue, 17 May 2011 07:19:31 -0400
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Patricia Shanahan wrote:
> Lawrence D'Oliveiro wrote:
>> Patricia  Shanahan wrote:
>>> Lawrence D'Oliveiro wrote:
>>>> Patricia Shanahan wrote:
>>>>> System.identityHashCode(x) does not necessarily return the same as
>>>>> x.hashCode() ...

>>>> It says it does
>>>> <http://developer.android.com/reference/java/lang/System.html#identityHashCode%28java.lang.Object%29>:
>>>>
>>>>
>>>> The hash code returned is the same one that would be returned by the
>>>> method java.lang.Object.hashCode(), whether or not the object's
>>>> class has overridden hashCode().

>>> My sample program output showed both x.hashCode() and
>>> System.identityHashCode(x) for x referencing an Integer. The values were
>>> different, because Integer overrides hashCode.

>> How odd, because the above documentation says otherwise.

> The way I interpret it, and the way it works in practice,

and the way it's documented

> is that System.identityHashCode(x) returns the value that would be returned by
> x.hashCode() if the object referenced by x had inherited the Object
> implementation of hashCode, regardless of whether x in fact uses an
> overridden hash code.

In other words, Laramie, 'x.hashCode()' can be different from 
'Object#hashCode()'.  It's called a "method override", and the point of 
'System.identityHashCode()' is to ignore any possible override of 
'Object#hashCode()' and just use the base version.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg