Make iterators cloneable?

[Dave Brosius]

Sure, but both of those algorithms are n^2, which is a bit painful, 
especially given all the pointer chasing that occurs with iterators.


On 09/11/2016 08:20 AM, Peter Levart wrote:
> Hi,
>
> Even if the elements are not comparable, you could rely on the fact 
> that Collection(s) usually create iterators with stable iteration 
> order, so you could do the following:
>
>
>         Set<Integer> set = Set.of(1, 2, 3, 4);
>
>         Iterator<Integer> it1 = set.iterator();
>         for (int n1 = 0; it1.hasNext(); n1++) {
>             Integer e1 = it1.next();
>             Iterator<Integer> it2 = set.iterator();
>             for (int n2 = 0; n2 < n1; n2++) {
>                 Integer e2 = it2.next();
>                 System.out.println(e1 + " <-> " + e2);
>             }
>         }
>
>
> Regards, Peter
>
> On 09/11/2016 02:02 PM, Tagir F. Valeev wrote:
>> Hello!
>>
>> As your keys are comparable, you can create normal iterators and
>> filter the results like this:
>>
>> for(String v1 : s) {
>>    for(String v2 : s) {
>>      if(v1.compareTo(v2) < 0) {
>>        System.out.println(v1 + " <-->" + v2);
>>      }
>>    }
>> }
>>
>> Or using Stream API:
>>
>> s.stream().flatMap(v1 -> s.stream()
>>      .filter(v2 -> v1.compareTo(v2) < 0).map(v2 -> v1 + " <-->" + v2))
>>   .forEach(System.out::println);
>>
>> With best regards,
>> Tagir Valeev.
>>
>>
>> DB> It would be nice to be able to associate each element in a collection
>> DB> with another element in the collection, which is something very easily
>> DB> done with index based collections, but with sets, etc this isn't so
>> DB> easy... unless i'm having a brainfart.
>>
>> DB> So i'd like to do this, but Iterator doesn't implement Cloneable... Any
>> DB> reason not to? or is there another way that's missing me?
>>
>> DB> public class ItClone {
>>
>> DB>      public static void main(String[] args) {
>> DB>          Set<String> s = Collections.newSetFromMap(new
>> DB> ConcurrentHashMap<String, Boolean>());
>>
>> DB>          s.add("Fee");
>> DB>          s.add("Fi");
>> DB>          s.add("Fo");
>> DB>          s.add("Fum");
>>
>> DB>          Iterator<String> it1 = s.iterator();
>> DB>          while (it1.hasNext()) {
>> DB>              String v1 = it1.next();
>>
>> DB>              Iterator<String> it2 = (Iterator<String>) it1.*clone*();
>> DB>              while (it2.hasNext()) {
>> DB>                  String v2 = it2.next();
>>
>> DB>                  System.out.println(v1 + " <-->" + v2);
>> DB>              }
>> DB>          }
>> DB>      }
>> DB> }
>>
>