If you want to iterate through a List that has an unspecified
implementation (at the point of iteration) always use an iterator; this
is the only way to implement performant code without making assumptions
about the implementation of the list.
Phil :n.
On Mon, 2005-02-28 at 11:30, Jose Alberto Fernandez wrote:
> I do not think so, from LinkedList implementation:
>
> /**
> * Return the indexed entry.
> */
> private Entry entry(int index) {
> if (index < 0 || index >= size)
> throw new IndexOutOfBoundsException("Index: "+index+
> ", Size: "+size);
> Entry e = header;
> if (index < size/2) {
> for (int i = 0; i <= index; i++)
> e = e.next;
> } else {
> for (int i = size; i > index; i--)
> e = e.previous;
> }
> return e;
> }
>
> It will iterate on every call.
>
> Enough of this, as I think it is becoming a little out of subject for
> the ANT list :-)
>
> Jose Alberto
>
> > -----Original Message-----
> > From: Kev Jackson [mailto:[EMAIL PROTECTED]
> > Sent: 28 February 2005 11:19
> > To: Ant Developers List
> > Subject: Re: Massively OT, 'Closures in Java' [was Re: AW:
> > [Patch] modifiedselector, style, remove unused code, slightly
> > more lazy DigestAlgorithm.getValue (now with added source code -doh!)]
> >
> >
> > Jose Alberto Fernandez wrote:
> >
> > >AFAIU, LinkedList.get(N) requires traversing the list to
> > position N on
> > >every call [O(n^2)], so usage of an iteratoe is much cheaper on this
> > >case as there is no array behind the scenes.
> > >
> > >Jose Alberto
> > >
> > >
> > I've just worked out why it's ok to do it this way (with
> > respect to my
> > particular use-case). Basically I *want* to traverse the
> > entire list,
> > I'm not trying to pick out any particular position in the list (yes
> > truly expensive using LinkedList.get(i)). In my method I simply call
> > get(i) from 0..List.size():
> >
> > from docs
> > <quote>Operations that index into the list will traverse the
> > list from
> > the begining or the end, whichever is closer to the specified
> > index.</quote>
> >
> > So as I'm asking for position 0, the traversal starts at the
> > head of the
> > list, then I simply walk the list with the loop calling get(i), which
> > also happens to be the next element in the list from where the list
> > cursor currently is (ListIterator interface docs). Serendipity I
> > suppose, but my usage is the most efficient for LinkedLists and also
> > happens to be performant with ArrayLists, to do the
> > particular traversal
> > that I'm doing.
> >
> > Kev
> >
> > ---------------------------------------------------------------------
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> > For additional commands, e-mail: [EMAIL PROTECTED]
> >
> >
>
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--
Phil Weighill-Smith <[EMAIL PROTECTED]>
Volantis Systems
