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Groups > comp.lang.java.programmer > #39121
| From | Eric Sosman <esosman@comcast-dot-net.invalid> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: Best way to make a hashcode? |
| Date | 2019-08-26 17:41 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <qk1jmg$8ck$1@dont-email.me> (permalink) |
| References | <89cadee9-0108-4c76-9e94-c8f716290582@googlegroups.com> |
On 8/26/2019 4:51 PM, Eric Douglas wrote:
> I want a custom class that works like the java.awt.Point class but a bit more complicated.
> They use this hashcode:
> public int hashCode() {
> long bits = java.lang.Double.doubleToLongBits(getX());
> bits ^= java.lang.Double.doubleToLongBits(getY()) * 31;
> return (((int) bits) ^ ((int) (bits >> 32)));
> }
> I want a custom class that has say 6 String type properties to be able to generate a common hashcode if they all match so I can use the class instances as keys to a hashmap.
>
Just stir the String's hashes into what you've already got:
public int hashCode() {
long bits = java.lang.Double.doubleToLongBits(getX());
bits ^= java.lang.Double.doubleToLongBits(getY()) * 31;
bits ^= Objects.hashCode(getStringThing()) * 29;
bits ^= Objects.hashCode(getStrungOut()) * 37;
bits ^= Objects.hashCode(getStringBikini()) * 59;
...
return ...
}
Choice of multipliers is up to you; perhaps you'd want a few large long
values to stir some string bits into the high order half (might not make
much difference post-fold, though).
Note that all the String values must also be tested in equals().
--
esosman@comcast-dot-net.invalid
Five hundred thirteen days to go.
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Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-26 13:51 -0700
Re: Best way to make a hashcode? Eric Sosman <esosman@comcast-dot-net.invalid> - 2019-08-26 17:41 -0400
Re: Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-27 06:24 -0700
Re: Best way to make a hashcode? Eric Sosman <esosman@comcast-dot-net.invalid> - 2019-08-27 09:39 -0400
Re: Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-27 07:29 -0700
Re: Best way to make a hashcode? Eric Sosman <esosman@comcast-dot-net.invalid> - 2019-08-27 11:49 -0400
Re: Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-27 11:05 -0700
Re: Best way to make a hashcode? Eric Sosman <esosman@comcast-dot-net.invalid> - 2019-08-27 15:16 -0400
Re: Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-27 13:04 -0700
Re: Best way to make a hashcode? Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2019-08-27 23:51 +0200
Re: Best way to make a hashcode? Silvio <silvio@internet.com> - 2019-08-28 01:27 +0200
Re: Best way to make a hashcode? Marcel Mueller <news.5.maazl@spamgourmet.org> - 2019-09-06 19:42 +0200
Re: Best way to make a hashcode? Arne Vajhøj <arne@vajhoej.dk> - 2019-08-26 19:03 -0400
Re: Best way to make a hashcode? Eric Douglas <e.d.programmer@gmail.com> - 2019-08-27 04:59 -0700
Re: Best way to make a hashcode? Arne Vajhøj <arne@vajhoej.dk> - 2019-08-27 21:08 -0400
Re: Best way to make a hashcode? ross.finlayson@gmail.com - 2019-09-05 20:27 -0700
Re: Best way to make a hashcode? trisha guillot <guillottrisha347@gmail.com> - 2020-01-18 07:25 -0800
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