Idiom for pairwise iteration through a sorted collection

Question

Is there a Java idiom for pairwise iteration through the elements of a sorted Collection? By that I mean that each iteration has access to one element of the co

Answer 1

For Sets (and other non-indexable collections) you will need to use their Iterators as returned by the iterator() method of Collection:

Iterator iter = set.iterator();
Thing thing1 = iter.next();  // might want to check if this exists
while (iter.hasNext()) {
    Thing thing2 = iter.next();
    operateOnAdjacentPair(thing1, thing2);
    thing1 = thing2;
}

You can do the same for Maps, using the Iterator of their entrySet()s.

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Now that I understand your question better, you could also try this:

Iterator iter1 = set.iterator(), iter2 = set.iterator();

if (iter2.hasNext())
    iter2.next();  // burn first element

while (iter2.hasNext()) {
    final Thing thing1 = iter1.next();
    final Thing thing2 = iter2.next();
    operateOnAdjacentPair(thing1, thing2);
}