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From: Jim Janney <jjanney@shell.xmission.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: hashCode
Date: Fri, 31 Aug 2012 09:08:16 -0600
Organization: Pan-Pacific Grand Prix
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Eric Sosman <esosman@ieee-dot-org.invalid> writes:

> On 8/30/2012 6:52 PM, Daniele Futtorovic wrote:
>> On 29/08/2012 20:49, Eric Sosman allegedly wrote:
>>> On 8/29/2012 2:06 PM, Daniel Pitts wrote:
>>>> On 8/28/12 5:02 PM, markspace wrote:
>>>>> On 8/28/2012 4:33 PM, Daniel Pitts wrote:
>>>>>>
>>>>>> interface Hasher<Type> {
>>>>>>      int hash(Type t);
>>>>>
>>> The difficulty is that an external Hasher would have no access to
>>> private fields (...)
>>
>> This.
>
>     ?
>
> 	package deal;
> 	public class ToBeHashed {
> 	    private int noGettersForMeThanks;
> 	    ...
> 	}
>
> 	package express;
> 	Hasher<ToBeHashed> hasher = new Hasher<ToBeHashed>() {
> 	    public int hashCode(ToBeHashed obj) {
> 	        // How do you obtain the value of
> 	        // obj.noGettersForMeThanks
> 	        // if that would be useful?
> 	    }
> 	    ...
> 	}
>
> As an example of why a hasher might want access to a strictly-private
> field, I offered String: How could a Hasher<String> (outside String
> itself) use String's private `hash' element?  (And before you say
> "Give String a getHash() method," ponder what hashCode() does.)

I have, and I don't see a problem.  String can define hashCode(), and
hashCodeIgnoreCase(), and hashCode(Locale), if those turn out to be
useful things to do for that particular class (String is an exceptional
class in several ways).  The objection is to building hashCode() into
the Object hierarchy and hard-coding its use in HashMap.  A separate
interface would allow more flexibility.

-- 
Jim Janney