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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: hashCode
Date: Fri, 10 Aug 2012 12:45:07 -0700 (PDT)
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Cc: Roedy Green <see_website@mindprod.com.invalid>
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Roedy Green wrote:
> bob smith wrote, quoted or indirectly quoted someone
> who said :
>=20
>>	@Override
> >	public int hashCode() {
> >		return 1;
> >	}
>=20
> that's about the worst possible hashCode function.

Normally that's correct, but it's conceivable that one might do it for=20
some hackish reason. In most situations where one might do such=20
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=20
using the Knuth constants is usually good enough.

h(object) =3D Sum(i =E2=88=88 0.. n-1) of ( attribute[i] * pow(31, n - 1 - =
i) );

or=20

public static int calculateHash(Foo arg) {
   int h =3D 0;

   for ( each attribute of Foo that contributes to 'equals()' )
   {
        h =3D 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

--=20
Lew