Re: reverse-iterator for LinkedList

Eric Sosman <>
Wed, 13 Feb 2008 17:33:03 -0500
Andreas Leitgeb wrote:

In some app of mine I've got a LinkedList of items. Now,
I want to check the last couple of items for some condition.

In practice I expect the list to be about 30 elements
long, and only the last three elements to be actually
visited. Oh and the context is somewhat time-critical.

Now, I think that an Iterator (actually ListIterator) would be
appropriate for my task, but the only way to get one seems to be
through method listIterator(int index). I can't help, but passing
in the lists size for the index feels like it would search forward
completely through the list to obtain an iterator that starts
from end.

     "Use the source, Andreas," and you'll find that LinkedList
initializes its ListIterator by searching from the nearer end.

Is there some better way to just scan the "last few elements"
from a LinkedList, or can someone assure me that calling
listIterator with an index at end will be efficient, or
is it best to redesign my app to build up the list in reverse
order in the first place, so I can use a "normal" iterator?

     Keeping the list in the other order seems plausible, but
I can't say whether it would be a good idea without having a
lot more information about your situation. Are you positive
that a LinkedList -- or even any flavor of List -- is the
right data structure for the job at hand?


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