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Groups > comp.lang.java.programmer > #17654
| From | Lew <lewbloch@gmail.com> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: hashCode |
| Date | 2012-08-10 12:45 -0700 |
| Organization | http://groups.google.com |
| Message-ID | <feb852c5-c9aa-439a-94eb-339c5e213ccf@googlegroups.com> (permalink) |
| References | <563f186a-edb3-4311-ae48-3af7decfce2c@googlegroups.com> <qgna285gdrh2ckdr3f7ct2sp9bneaamo94@4ax.com> |
Roedy Green wrote:
> bob smith wrote, quoted or indirectly quoted someone
> who said :
>
>> @Override
> > public int hashCode() {
> > return 1;
> > }
>
> that's about the worst possible hashCode function.
Normally that's correct, but it's conceivable that one might do it for
some hackish reason. In most situations where one might do such
an override as this, one would do better not to override hashCode().
> See http://mindprod.com/jgloss/hashcode.html for tips on how to write
> good ones.
The default of assembling it via the mix-in of attribute hash codes
using the Knuth constants is usually good enough.
h(object) = Sum(i ∈ 0.. n-1) of ( attribute[i] * pow(31, n - 1 - i) );
or
public static int calculateHash(Foo arg) {
int h = 0;
for ( each attribute of Foo that contributes to 'equals()' )
{
h = 31 * h + attribute.hashCode();
}
return h;
}
http://en.wikipedia.org/wiki/Hash_function
http://en.wikipedia.org/wiki/Java_hashCode()
http://en.wikipedia.org/wiki/Java_hashCode()#Java
--
Lew
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hashCode bob smith <bob@coolfone.comze.com> - 2012-08-10 08:47 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-10 12:13 -0400
Re: hashCode markspace <-@.> - 2012-08-10 10:13 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-10 13:38 -0400
Re: hashCode rossum <rossum48@coldmail.com> - 2012-08-11 10:36 +0100
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-10 12:34 -0400
Re: hashCode bob smith <bob@coolfone.comze.com> - 2012-08-10 15:22 -0700
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-10 15:32 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-10 19:30 -0400
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 16:24 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:15 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:29 -0400
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-11 22:43 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:54 -0400
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 21:46 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-12 16:53 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-12 17:00 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-10 19:27 -0400
Re: hashCode Robert Klemme <shortcutter@googlemail.com> - 2012-08-12 17:06 +0200
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-12 16:59 -0400
Re: hashCode Robert Klemme <shortcutter@googlemail.com> - 2012-08-13 19:17 +0200
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-19 19:42 -0400
Re: hashCode Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-21 10:30 +0000
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-19 19:47 -0400
Re: hashCode Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-21 10:43 +0000
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-27 19:04 -0400
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-27 16:55 -0700
Re: hashCode markspace <-@.> - 2012-08-27 17:03 -0700
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-27 17:49 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-27 21:37 -0400
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-27 18:58 -0700
Re: hashCode markspace <-@.> - 2012-08-27 21:19 -0700
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-28 01:06 -0700
Re: hashCode markspace <-@.> - 2012-08-28 09:19 -0700
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-28 16:33 -0700
Re: hashCode markspace <-@.> - 2012-08-28 17:02 -0700
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-29 11:06 -0700
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-29 14:49 -0400
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-29 13:40 -0700
Re: hashCode Gene Wirchenko <genew@ocis.net> - 2012-08-29 18:02 -0700
Re: hashCode Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-08-31 00:52 +0200
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-30 21:43 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-30 21:52 -0400
Re: hashCode Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-08-31 04:18 +0200
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-31 09:08 -0600
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-31 11:38 -0400
Re: hashCode Robert Klemme <shortcutter@googlemail.com> - 2012-08-31 17:55 +0200
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-31 09:56 -0600
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-31 14:32 -0400
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-31 14:38 -0600
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-31 15:33 -0700
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-31 16:41 -0600
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-31 16:26 -0700
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-09-02 11:54 -0600
Re: hashCode Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-09-03 00:47 +0200
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-09-03 21:44 -0600
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-31 09:08 -0600
Re: hashCode Robert Klemme <shortcutter@googlemail.com> - 2012-08-31 17:58 +0200
Re: hashCode markspace <-@.> - 2012-08-29 11:51 -0700
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-29 13:28 -0700
Re: hashCode markspace <-@.> - 2012-08-29 16:05 -0700
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-29 16:23 -0700
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-29 20:56 -0400
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-30 11:19 +0200
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-30 10:03 -0700
Re: hashCode Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 18:34 +0000
Re: hashCode Jim Janney <jjanney@shell.xmission.com> - 2012-08-30 08:11 -0600
Re: hashCode Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-30 10:06 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-30 19:16 -0400
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-28 13:58 -0700
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-28 13:56 -0700
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-28 14:07 -0700
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-28 14:38 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-27 21:12 -0400
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-11 07:58 -0400
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 16:29 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:16 -0400
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-12 03:46 -0700
Re: hashCode Joshua Cranmer <Pidgeot18@verizon.invalid> - 2012-08-12 12:23 -0400
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-12 09:40 -0700
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-12 13:59 -0400
Re: hashCode Patricia Shanahan <pats@acm.org> - 2012-08-12 11:17 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-12 17:02 -0400
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-12 19:03 +0200
Re: hashCode Roedy Green <see_website@mindprod.com.invalid> - 2012-08-10 12:17 -0700
Re: hashCode Lew <lewbloch@gmail.com> - 2012-08-10 12:45 -0700
Re: hashCode Roedy Green <see_website@mindprod.com.invalid> - 2012-08-11 04:54 -0700
Re: hashCode Joerg Meier <joergmmeier@arcor.de> - 2012-08-11 18:25 +0200
Re: hashCode Mike Winter <usenet@michael-winter.me.invalid> - 2012-08-11 18:53 +0100
Re: hashCode Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-08-11 09:56 -0700
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-11 18:58 +0200
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:40 -0400
Re: hashCode rossum <rossum48@coldmail.com> - 2012-08-11 18:47 +0100
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-10 19:25 -0400
Re: hashCode Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-11 08:00 -0400
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 09:49 -0400
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-11 15:33 +0200
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-11 15:34 +0200
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 16:34 -0700
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 16:37 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-11 22:19 -0400
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-11 21:48 -0700
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-12 12:08 +0200
Re: hashCode Jan Burse <janburse@fastmail.fm> - 2012-08-12 12:18 +0200
Re: hashCode Lew <noone@lewscanon.com> - 2012-08-12 11:27 -0700
Re: hashCode Arne Vajhøj <arne@vajhoej.dk> - 2012-08-12 17:11 -0400
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