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Groups > comp.lang.java.programmer > #17693

Re: hashCode

From "Lew" <lew@1:261/38.remove-pjg-this>
Subject Re: hashCode
Message-ID <50269FCF.56640.calajapr@time.synchro.net> (permalink)
Newsgroups comp.lang.java.programmer
References <50269FCE.56638.calajapr@time.synchro.net>
Date 2012-08-11 18:17 +0000
Organization tds.net

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  To: bob smith
From: Lew <lewbloch@gmail.com>

bob smith wrote:
> Eric Sosman wrote:
>> bob smith wrote:
>>> Is it always technically correct to override the hashCode function like so:

It complies with the contract for 'hashCode()'. Is that all it takes to be 
correct?

>>> Would it be potentially better if that was Object's implementation?

Would what be better if what were Object's implementation of what?

>>      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.

No.

No matter what 'Object''s 'hashCode()' implementation were, it would need to be 
overridden when you want value equality instead of object identity for
'equals()'.

See Joshua Bloch's seminal work /Effective Java/, which has items that pertain 
to this.

Bottom line: 'hashCode()', 'equals()', and when present, 'compareTo()' must be 
consistent.

'toString()' should be consistent with those.

As long as 'hashCode()' fulfills the contract, your code will work - 
functionally. But a bad
'hashCode()' could and likely will noticeably affect performance. There is more
to correctness
than mere functional conformance.

--
Lew

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hashCode "bob smith" <bob.smith@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
  Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
    Re: hashCode "markspace" <markspace@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
      Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
        Re: hashCode "rossum" <rossum@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
  Re: hashCode "Eric Sosman" <eric.sosman@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
    Re: hashCode "bob smith" <bob.smith@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
      Re: hashCode "Lew" <lew@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
          Re: hashCode "Lew" <lew@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
            Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
              Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
                Re: hashCode "Eric Sosman" <eric.sosman@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
                Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Eric Sosman" <eric.sosman@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Lew" <lew@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
          Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Robert Klemme" <robert.klemme@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
          Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
            Re: hashCode "Robert Klemme" <robert.klemme@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
              Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-fzq-this> - 2012-08-20 18:58 +0000
              Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-fzq-this> - 2012-08-20 18:58 +0000
      Re: hashCode "Patricia Shanahan" <patricia.shanahan@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Joshua Cranmer" <joshua.cranmer@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
        Re: hashCode "Patricia Shanahan" <patricia.shanahan@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
          Re: hashCode "Eric Sosman" <eric.sosman@1:261/38.remove-6fd-this> - 2012-08-12 20:00 +0000
            Re: hashCode "Patricia Shanahan" <patricia.shanahan@1:261/38.remove-6fd-this> - 2012-08-12 20:00 +0000
          Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000
        Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
  Re: hashCode "Roedy Green" <roedy.green@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
    Re: hashCode "Lew" <lew@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
      Re: hashCode "Roedy Green" <roedy.green@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Joerg Meier" <joerg.meier@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
          Re: hashCode "Mike Winter" <mike.winter@1:261/38.remove-ya-this> - 2012-08-11 19:19 +0000
        Re: hashCode "Peter Duniho" <peter.duniho@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "rossum" <rossum@1:261/38.remove-ya-this> - 2012-08-11 19:19 +0000
    Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
      Re: hashCode "Eric Sosman" <eric.sosman@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
        Re: hashCode "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
  Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
    Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-pjg-this> - 2012-08-11 18:17 +0000
    Re: hashCode "Lew" <lew@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Lew" <lew@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
        Re: hashCode "Lew" <lew@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
    Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Jan Burse" <jan.burse@1:261/38.remove-m2z-this> - 2012-08-12 18:58 +0000
      Re: hashCode "Lew" <lew@1:261/38.remove-6fd-this> - 2012-08-12 20:00 +0000
        Re: hashCode "Arne Vajhøj" <������
høj@1:261/38.remove-nlb-this> - 2012-08-13 18:36 +0000

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