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Re: hashCode

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  Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-odu-this> - 2012-08-13 19:38 +0000

#17853 — Re: hashCode

  To: Robert Klemme
From: "Arne Vajhoj" <arne.vajhoj@1:261/38.remove-nlb-this>

  To: Robert Klemme
From: Arne Vajhoj <arne@vajhoej.dk>

On 8/12/2012 11:06 AM, Robert Klemme wrote:
> On 11.08.2012 01:27, Arne Vajhoj wrote:
>> On 8/10/2012 6:22 PM, bob smith wrote:
>>> On Friday, August 10, 2012 11:34:28 AM UTC-5, Eric Sosman wrote:
>>>> On 8/10/2012 11:47 AM, bob smith wrote:
>>>>> Is it always technically correct to override the hashCode function
>>>>> like so:
>>>>>     @Override
>>>>>     public int hashCode() {
>>>>>         return 1;
>>>>>     }
>>>>> Would it be potentially better if that was Object's implementation?
>>>>
>>>>       Define "better."
>>>
>>> Better in the sense that you would never HAVE to override hashCode.
>>>
>>> Now, there are cases where you HAVE to override it, or your code is
>>> very broken.
>>
>> It is not broken.
>>
>> It will perform poorly in many cases.
>
> Well, I would go as far as to say that it will perform poorly in all
> cases where hashCode() is actually needed

More or less.

>                                        - and that makes it broken.

This thread started about whether it is correct. The term correct has a very 
specific meaning in programming and that always return 1 code is correct.

Now you talk about broken. If broken means not good, then you are right. If 
broken means not correct, then you are wrong. I suspect that broken is not very 
well defined.

> The whole idea of hashing is based on the fact that the hash code
> _somehow_ represents the item to be hashed.  If all items have the same
> constant hash code there is no point in hashing at all.  So while it
> does work, it does not work as intended.

It disable the entire hashing functionality and a HashMap get characteristics 
of ArrayList.

But the code should actually work.

Arne

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