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Groups > comp.lang.java.programmer > #19999

Re: optimsed HashMap

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On 11/26/12 5:28 PM, Eric Sosman wrote:
> On 11/26/2012 6:44 PM, Daniel Pitts wrote:
>> On 11/23/12 5:12 PM, Roedy Green wrote:
>>> 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.
>>>
>>
>> I don't think your use-case needs this kind of (read "micro")
>> optimization.  However, I have often wished for a way to get a Map.Entry
>> for a key, which could then be used to insert a new value efficiently.
>>
>> Map.Entry<K,V> getOrAddEntry(K key);
>>
>>
>> Map.Entry<K,V> e = map.getOrAddEntry(myKey);
>>
>> if (e.getValue() == null) {
>>     e.setValue(newValue(myKey));
>> }
>>
>> useValue(e.getValue());
>>
>> Alas, not exactly possible to add it now.
>
>      java.util.concurrent.ConcurrentMap has putIfAbsent().
>
putIfAbsent isn't exactly what I want. First, I might not want to go to 
the expense of creating a new value *unless* there isn't already one. 
Second, this is an operation that may not need the overhead of a 
concurrency-safe map.

The first problem *can* be overcome by using a wrapper object, but that 
adds additional overhead, and the point of this is to reduce overhead.

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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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