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Re: Glitch in Java Collections (No descendingMap in LinkedHashMap)

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Jim Janney <jjanney@shell.xmission.com> writes:

> Jan Burse <janburse@fastmail.fm> writes:
>
>> Dear All,
>>
>> I just wonder whether I have overlooked something.
>> But could it be that LinkedHashMap is lacking the
>> following API:
>>
>>    Map<K,V> descendingMap();
>>
>> So I can only iterate from oldest to youngest, and
>> not the other direction?
>>
>> Although under the hood it uses a double linked list,
>> and a reverse iterator would be simple.
>>
>> Also the whole matter seems to be complicated, since
>> the other collections have descendingMap() in an
>> Interface NavigableMap, which extends SortedMap.
>>
>> But SortedMap map assumes a compartor, whereby the
>> sorting in LinkedHashMap is implicit.
>>
>> Is there some shortcut to arrive at a reverse iterator
>> of LinkedHashMap?
>>
>> (Troll disclaimer: No I have no SSCCE (Short, Self
>> Contained, Correct (Compilable), Example). This is
>> a conceptual question.)
>>
>> Bye
>
> You haven't overlooked anything.  The ability is not there and I don't
> see any simple way to add it without package access to java.util.
> LinkedHashMap is a bit of an oddity in the collections framework, but
> it's useful enough that I don't mind.
>
> If I really needed that functionality I'd probably try maintaining my
> own access-order list in parallel to the map.

Oops, stupid me.  The other way is to define a comparator based on
insertion order, and then use a SortedMap.

-- 
Jim Janney

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Thread

Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-04 14:09 +0200
  Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Robert Klemme <shortcutter@googlemail.com> - 2012-10-04 23:01 +0200
    Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Lew <lewbloch@gmail.com> - 2012-10-04 14:43 -0700
      Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-05 00:17 +0200
      Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Robert Klemme <shortcutter@googlemail.com> - 2012-10-05 19:11 +0200
        Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Lew <lewbloch@gmail.com> - 2012-10-05 11:05 -0700
          Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-05 20:18 +0200
          Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-10-05 12:06 -0700
            Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Lew <lewbloch@gmail.com> - 2012-10-05 13:04 -0700
              Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-05 23:44 +0200
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-05 23:50 +0200
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-06 00:00 +0200
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-10-05 23:39 +0000
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-06 12:18 +0200
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-06 12:22 +0200
              Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-10-05 15:51 -0700
          Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Robert Klemme <shortcutter@googlemail.com> - 2012-10-06 13:53 +0200
  Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-09 14:16 -0600
    Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-10 09:00 -0600
      Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-10 11:34 -0400
        Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-10 10:28 -0600
          Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-10 11:45 -0600
            Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Lew <lewbloch@gmail.com> - 2012-10-10 10:52 -0700
              Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-10 12:47 -0600
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-11 14:17 -0600
            Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-10 18:20 -0400
              Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-10 16:51 -0600
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-12 14:34 +0200
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jim Janney <jjanney@shell.xmission.com> - 2012-10-12 09:12 -0600
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-12 11:42 -0400
                Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Jan Burse <janburse@fastmail.fm> - 2012-10-12 21:02 +0200

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