Re: Glitch in Java Collections (No descendingMap in LinkedHashMap)
On 04.10.2012 23:43, Lew wrote:
Robert Klemme wrote:
Jan Burse wrote:
But SortedMap map assumes a compartor, whereby the
sorting in LinkedHashMap is implicit.
There is no sorting going on - you just get insertion order.
You get insertion order how?
First paragraph of JavaDoc:
Hash table and linked list implementation of the Map interface, with
predictable iteration order. This implementation differs from HashMap in
that it maintains a doubly-linked list running through all of its
entries. This linked list defines the iteration ordering, which is
normally the order in which keys were inserted into the map
(insertion-order). Note that insertion order is not affected if a key is
re-inserted into the map.
The interesting thing about this class is that it has no public methods that reveal
the order.
Why would they need to?
So what difference does the order make?
There are some use cases described in the class JavaDoc.
I can guess, but the docs don't confirm, that iterators off the keyset or entryset would
respect the order, but the documentation for the 'keySet()' and 'entrySet()' methods doesn't
promise this.
You do not have to guess - logical reasoning is enough. The only way to
iterate through a Map is via entrySet(), keySet() and values(). What
other methods could make use of the order if not these?
It's useful for subclasses, from what the documentation hints, but to the public?
It seems you could create a LRU Map with this, right. Other uses are
described in the class doc as mentioned above.
Kind regards
robert
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