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Groups > comp.lang.java.programmer > #6927
| From | Tom Anderson <twic@urchin.earth.li> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: setSize ArrayList, when will it come? |
| Date | 2011-08-09 22:38 +0100 |
| Organization | Stack Usenet News Service |
| Message-ID | <alpine.DEB.2.00.1108092230010.20857@urchin.earth.li> (permalink) |
| References | <j1pp1j$3rf$1@news.albasani.net> <ojp247dlgld0hso4hkamufus1jr0hd6m7t@4ax.com> <1eadnROad6gX8NzTnZ2dnUVZ_tydnZ2d@earthlink.com> |
On Tue, 9 Aug 2011, Patricia Shanahan wrote:
> On 8/9/2011 9:58 AM, Roedy Green wrote:
> ...
>> Further, I would hope ArrayList.addAll would be smart enough to grow
>> the array only once, if needed.
> ...
>
> It does the following:
>
> 1. Grow to the needed size.
>
> 2. Call the other collection's toArray method.
>
> 3. System.arraycopy the toArray result into the ArrayList's elementData.
>
> This double copy is going to be faster than the one at a time approach
> only if large numbers of nulls are being added. If that is the case, the
> structure is probably too sparse for ArrayList to be a good choice.
It would be nice if ArrayList used a loop to do the copy for small added
collections; it could cut over to the array method for larger addends.
Anyway, with List.addAll and Collections.nCopies, we can write:
<T> void setSize(List<T> list, int size) {
int change = size - list.size();
if (change > 0) {
list.addAll(Collections.nCopies(change, null));
}
else if (change < 0) {
list.subList(size, list.size()).clear();
if (list instanceof ArrayList) ((ArrayList)list).trimToSize();
}
// else do nothing
}
I haven't tried that, but it should work.
So, Jan, less whining, more coding, please.
tom
--
As Emiliano Zapata supposedly said, "Better to die on your feet than
live on your knees." And years after he died, Marlon Brando played him
in a movie. So just think, if you unionize, Marlon Brando might play
YOU in a movie. Even though he's dead. -- ChrisV82
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setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 00:47 +0200
Re: setSize ArrayList, when will it come? Knute Johnson <september@knutejohnson.com> - 2011-08-08 16:53 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 02:30 +0200
Re: setSize ArrayList, when will it come? Arne Vajhøj <arne@vajhoej.dk> - 2011-08-08 20:50 -0400
Re: setSize ArrayList, when will it come? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-08 21:09 -0400
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 04:16 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-08 21:39 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 09:33 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 09:42 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-09 07:56 +0000
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 11:18 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-09 10:36 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 18:30 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-09 16:30 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 00:31 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-09 20:36 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 09:04 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-10 08:50 +0000
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-10 18:16 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 01:55 +0200
Re: setSize ArrayList, when will it come? Patricia Shanahan <pats@acm.org> - 2011-08-09 01:33 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 11:16 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 11:32 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-09 11:35 +0200
Re: setSize ArrayList, when will it come? Patricia Shanahan <pats@acm.org> - 2011-08-09 04:00 -0700
Re: setSize ArrayList, when will it come? Arne Vajhøj <arne@vajhoej.dk> - 2011-08-09 20:11 -0400
Re: setSize ArrayList, when will it come? Robert Klemme <shortcutter@googlemail.com> - 2011-08-10 10:21 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-10 09:14 +0000
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 12:29 +0200
Re: setSize ArrayList, when will it come? Robert Klemme <shortcutter@googlemail.com> - 2011-08-10 19:27 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 20:22 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 20:37 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-10 18:22 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 01:52 +0200
Re: setSize ArrayList, when will it come? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-08-10 21:43 -0500
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 14:19 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-10 22:23 +0000
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 01:47 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-11 00:23 +0000
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 09:19 +0200
Re: setSize ArrayList, when will it come? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-12 15:06 +0000
Re: setSize ArrayList, when will it come? Roedy Green <see_website@mindprod.com.invalid> - 2011-08-09 09:58 -0700
Re: setSize ArrayList, when will it come? Patricia Shanahan <pats@acm.org> - 2011-08-09 10:25 -0700
Re: setSize ArrayList, when will it come? Tom Anderson <twic@urchin.earth.li> - 2011-08-09 22:38 +0100
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 00:36 +0200
Re: setSize ArrayList, when will it come? Roedy Green <see_website@mindprod.com.invalid> - 2011-08-09 15:55 -0700
Re: setSize ArrayList, when will it come? Knute Johnson <september@knutejohnson.com> - 2011-08-09 16:03 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 09:18 +0200
Re: setSize ArrayList, when will it come? Mayeul <mayeul.marguet@free.fr> - 2011-08-10 11:26 +0200
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 12:35 +0200
Re: setSize ArrayList, when will it come? Lew <lewbloch@gmail.com> - 2011-08-10 09:33 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-10 20:22 +0200
Re: setSize ArrayList, when will it come? Patricia Shanahan <pats@acm.org> - 2011-08-09 22:13 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 02:01 +0200
Re: setSize ArrayList, when will it come? Patricia Shanahan <pats@acm.org> - 2011-08-10 18:42 -0700
Re: setSize ArrayList, when will it come? Jan Burse <janburse@fastmail.fm> - 2011-08-11 14:21 +0200
Re: setSize ArrayList, when will it come? Arne Vajhøj <arne@vajhoej.dk> - 2011-08-09 20:09 -0400
Re: setSize ArrayList, when will it come? Roedy Green <see_website@mindprod.com.invalid> - 2011-08-09 16:02 -0700
Re: setSize ArrayList, when will it come? Arne Vajhøj <arne@vajhoej.dk> - 2011-08-09 20:13 -0400
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