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From: Jim Janney <jjanney@shell.xmission.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Glitch in Java Collections (No descendingMap in LinkedHashMap)
Date: Tue, 09 Oct 2012 14:16:47 -0600
Organization: Terminate and Stay Resident
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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.

-- 
Jim Janney