Groups > comp.lang.java.programmer > #17800

Re: hashCode

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From	"Arne Vajhøj" <�� høj@1:261/38.remove-nlb-this>
Subject	Re: hashCode
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  To: Lew
From: "=?UTF-8?B?QXJuZSBWYWpow7hq?=" <=?utf-8?b?qxjuzsbwywpow7hq?=@1:261/38.rem
ove-m2z-this>

  To: Lew
From: =?UTF-8?B?QXJuZSBWYWpow7hq?= <arne@vajhoej.dk>

On 8/11/2012 7:34 PM, Lew wrote:
> Jan Burse wrote:
>> Maybe it would make sense to spell out what the contract
>> for hashCode() is. Well the contract is simply, the
>> following invariant should hold:
>>
>>     /* invariant that should hold */
>>     if a.equals(b) then a.hashCode()==b.hashCode()
>
> True, but if you read the specification for 'hashCode()' fully, that is
> not the entire contract, only the compiler-enforceable part of it.
>
> The entire specification requires that as much as feasible, the 'Object'
> implementation distinguish distinct instances, and that the method
> generally support 'HashMap', which promises O(1) 'get()' and 'put()'
> with a "proper" (i.e., compliant) 'hashCode()'.

Two wrong statements.

It says that the method is defined to support HashMap

And HashMap does not guarantee O(1) with a correct hashCode - it guarantee that 
for one that return good distributed values.

Arne

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Thread

Re: hashCode "Lew" <lew@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
  Re: hashCode "Lew" <lew@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
  Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
    Re: hashCode "Lew" <lew@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000

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