Hi,
The failfast argument is is irrelevant. It only matters if you use
it.remove() which is no different than any other failfast situation.
Obviously the 3rd argument is bogus too, as you say.
The second argument, ok, is not arguable, as it's just a persons
opinion. The bug report is in the genre of subList implementation which
is different than this use, but ok. The problem is that there are no
reasonable concurrent indexable collections, and the thought of copying
large collections into a List everytime you want to do this is crazy.
Unfortunately you can't even have one-off fixes for specific collections
by having an iterator with a 'copy constructor' for instance, as in the
case of collection iterators you _really_ have no business knowing what
the real class is.
On 09/11/2016 05:40 AM, Remi Forax wrote:
Hi,
digging a little bit in the bug database, there is a bug from 1999
https://bugs.openjdk.java.net/browse/JDK-4244952
answers seems to be
- having different iterators on the same collection is error prone because
iterators are failfast,
the proposed workaround to use an array or a List with several indexes
- it's too C++ish, C++ defines clone and equals, Java tries to define a simpler
iteration protocol
(from now, given that this question is raised only once in a while, it's
doesn't seem to be a bad idea)
- iterators are interfaces, so having several iterators means several virtual
dispatch calls
(this one is not true anymore because any JITs routinely devirtualize this
kind of call).
cheers,
Rémi
----- Mail original -----
De: "Dave Brosius" <dbros...@mebigfatguy.com>
À: "Louis Wasserman" <lowas...@google.com>, "Jonathan Bluett-Duncan"
<jbluettdun...@gmail.com>
Cc: core-libs-dev@openjdk.java.net
Envoyé: Dimanche 11 Septembre 2016 02:23:41
Objet: Re: Make iterators cloneable?
Iterators reading from a BufferedReader
yes that's true. altho given the contract of Cloneable, adding the clone
method on Iterator would be safe, as it would only be available if the
real implementing class 'extends Cloneable'... it's actually kind of
funny that Object methods aren't available on interface references, anyway.
But i get the "age of Iterator" answer.. Shame there isn't an answer, tho.
thanks, dave
On 09/10/2016 07:44 PM, Louis Wasserman wrote:
Some iterators might be. Many may not be. Certainly Iterator as an
interface has been out there for long enough there are Iterator
implementations out there that aren't cloneable -- say, Iterators
reading from a BufferedReader, where there really won't be any way to
do what you're hoping for; BufferedReaders certainly aren't cloneable.
On Sat, Sep 10, 2016 at 4:33 PM Dave Brosius <dbros...@mebigfatguy.com
<mailto:dbros...@mebigfatguy.com>> wrote:
Yes Louis is correct.
I want the pair wise associations or all elements of a set.
Fee-Fi
Fee-Fo
Fee-Fum
Fi-Fo
Fi-Fum
Fo-Fum
the independent iterators produce Fee-Fee (etc) as well as the
duplicate Fee-Fi and Fi-Fee (etc), both of which i don't want.
This is obviously simplistic with index based collections, but not
with sets/maps
I don't see why an Iterator isn't by nature easily cloneable.
On 09/10/2016 06:45 PM, Jonathan Bluett-Duncan wrote:
Ah okay Louis, if that's the case then that certainly makes
sense, and I'd agree that there's no good way of doing so, as one
would need to copy the set into a list.
Dave, did Louis hit the mark? If not, would you kindly go into
further detail as to exactly what it is you're trying to do?
Best,
Jonathan
On 10 September 2016 at 23:36, Jonathan Bluett-Duncan
<jbluettdun...@gmail.com <mailto:jbluettdun...@gmail.com>> wrote:
Hi Dave,
Rather than using Iterator.clone(), how about you just call
collection.iterator() 2 times to return 2 unique, non-same
iterators; something like the following:
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
public class Example {public static void main(String[] args) {
Set<String> s =
Collections.newSetFromMap(new ConcurrentHashMap<String,
Boolean>()); s.add("Fee"); s.add("Fi"); s.add("Fo");
s.add("Fum"); Iterator<String> it1 = s.iterator(); for (String v1
=null;
it1.hasNext(); v1 =it1.next()) {
Iterator<String> it2 = s.iterator();// a completely separate
iterator to it1 for
(String v2 =null; it2.hasNext(); v2 = it2.next())
{System.out.println(v1 + "
<-->" + v2); } } } }
Or, even better, if you're using Java 5+, you can skip using
Iterators altogether and use for-loops directly:
import java.util.Collections;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
public class Example {public static void main(String[] args) {
Set<String> s =
Collections.newSetFromMap(new ConcurrentHashMap<String,
Boolean>()); s.add("Fee"); s.add("Fi"); s.add("Fo");
s.add("Fum"); for (String v1 : s) {
for (String v2 : s) {System.out.println(v1 + "<-->" + v2); } }
} }
Kind regards,
Jonathan
On 10 September 2016 at 23:13, Dave Brosius
<dbros...@mebigfatguy.com <mailto:dbros...@mebigfatguy.com>>
wrote:
It would be nice to be able to associate each element in
a collection with another element in the collection,
which is something very easily done with index based
collections, but with sets, etc this isn't so easy...
unless i'm having a brainfart. So i'd like to do this,
but Iterator doesn't implement Cloneable... Any reason
not to? or is there another way that's missing me? public
class ItClone { public static void main(String[]
args) { Set<String> s =
Collections.newSetFromMap(new ConcurrentHashMap<String,
Boolean>()); s.add("Fee"); s.add("Fi");
s.add("Fo"); s.add("Fum");
Iterator<String> it1 = s.iterator(); while
(it1.hasNext()) { String v1 = it1.next();
Iterator<String> it2 = (Iterator<String>)
it1.*clone*(); while (it2.hasNext()) {
String v2 = it2.next();
System.out.println(v1 + " <-->" + v2); }
} } }
