Make iterators cloneable?

[Peter Levart]

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> }
>