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Re: optimsed HashMap

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From Jim Janney <jjanney@shell.xmission.com>
Newsgroups comp.lang.java.programmer
Subject Re: optimsed HashMap
Date Mon, 26 Nov 2012 11:13:16 -0700
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Roedy Green <see_website@mindprod.com.invalid> writes:

> Is there something like HashMap but that optimised when nearly always
> the thing you are looking up is not in the list, and when you can add
> the list of words to look up and then freeze it.
>
> I have to scan an entire website looking up every word.

In this case, where you are always looking up a newly created string,
it's likely that computing the hash code takes more time than the actual
lookup: java.lang.String.hashCode() looks at every character in the
string.  You could experiment with a weaker hash code that is cheaper to
compute but generates more collisions, for example only hash the first n
characters for some small value of n.

Or take the length of the string (very cheap to compute) and check it
against a BitSet.  Or do the same with the first (or last) character.
How well these strategies work will depend very much on the actual data.

-- 
Jim Janney

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optimsed HashMap Roedy Green <see_website@mindprod.com.invalid> - 2012-11-23 17:12 -0800
  Re: optimsed HashMap Arne Vajhøj <arne@vajhoej.dk> - 2012-11-23 20:19 -0500
  Re: optimsed HashMap markspace <-@.> - 2012-11-23 17:33 -0800
    Re: optimsed HashMap Roedy Green <see_website@mindprod.com.invalid> - 2012-11-23 22:42 -0800
      Re: optimsed HashMap Roedy Green <see_website@mindprod.com.invalid> - 2012-11-24 03:34 -0800
        Re: optimsed HashMap Knute Johnson <nospam@knutejohnson.com> - 2012-11-24 08:39 -0800
          Re: optimsed HashMap Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2012-11-24 15:14 -0800
      Re: optimsed HashMap Arne Vajhøj <arne@vajhoej.dk> - 2012-11-24 13:24 -0500
      Re: optimsed HashMap markspace <-@.> - 2012-11-24 10:44 -0800
        Re: optimsed HashMap "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-11-25 13:40 +0000
      Re: optimsed HashMap Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-11-26 22:03 +0100
        Re: optimsed HashMap Robert Klemme <shortcutter@googlemail.com> - 2012-11-26 23:32 +0100
          Re: optimsed HashMap Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-11-27 03:24 +0100
            Re: optimsed HashMap Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-11-27 03:35 +0100
              Re: optimsed HashMap Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-11-27 08:44 -0500
                Re: optimsed HashMap Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-11-27 14:20 -0800
                Re: optimsed HashMap Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-11-30 03:35 +0100
  Re: optimsed HashMap Patricia Shanahan <pats@acm.org> - 2012-11-23 19:51 -0800
    Re: optimsed HashMap "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-11-24 10:21 +0000
      Re: optimsed HashMap Roedy Green <see_website@mindprod.com.invalid> - 2012-11-24 03:39 -0800
        Re: optimsed HashMap Robert Klemme <shortcutter@googlemail.com> - 2012-11-24 16:24 +0100
          Re: optimsed HashMap "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-11-25 13:50 +0000
            Re: optimsed HashMap Robert Klemme <shortcutter@googlemail.com> - 2012-11-25 15:30 +0100
      Re: optimsed HashMap "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-11-26 21:13 +0000
    Re: optimsed HashMap Arne Vajhøj <arne@vajhoej.dk> - 2012-11-24 13:16 -0500
  Re: optimsed HashMap v_borchert@despammed.com (Volker Borchert) - 2012-11-24 08:05 +0000
  Re: optimsed HashMap Silvio <silvio@internet.com> - 2012-11-26 11:57 +0100
  Re: optimsed HashMap Jim Janney <jjanney@shell.xmission.com> - 2012-11-26 11:13 -0700
  Re: optimsed HashMap Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-11-26 15:44 -0800
    Re: optimsed HashMap Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-11-26 20:28 -0500
      Re: optimsed HashMap Arved Sandstrom <asandstrom2@eastlink.ca> - 2012-11-27 06:01 -0400
        Re: optimsed HashMap Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-11-27 08:56 -0500
      Re: optimsed HashMap Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-11-27 14:16 -0800

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