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

From:

Robert Klemme <shortcutter@googlemail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 04 Oct 2012 23:01:48 +0200

Message-ID:

<ad6bpvFcuttU1@mid.individual.net>

On 04.10.2012 14:09, Jan Burse wrote:

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?

I guess they omitted it because the purpose is to provide a Map which
always returns elements in insertion order (and not reverse insertion
order).

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.

There you see why it's not in LinkedHashMap: it's neither a NavigableMap
nor a SortedMap.

But SortedMap map assumes a compartor, whereby the
sorting in LinkedHashMap is implicit.

There is no sorting going on - you just get insertion order.

Cheers

robert

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