How to get the current loop index when using Iterator?

Question

I had the same question and found using a ListIterator worked. Similar to the test above:

List<String> list = Arrays.asList("zero", "one", "two");

ListIterator<String> iter = list.listIterator();
    
while (iter.hasNext()) {
    System.out.println("index: " + iter.nextIndex() + " value: " + iter.next());
}

Make sure you call the nextIndex() before you actually get the next().

Use your own variable and increment it in the loop.

Here's a way to do it using your own variable and keeping it concise:

List<String> list = Arrays.asList("zero", "one", "two");

int i = 0;
for (Iterator<String> it = list.iterator(); it.hasNext(); i++) {
    String s = it.next();
    System.out.println(i + ": " + s);
}

Output (you guessed it):

0: zero
1: one
2: two

The advantage is that you don't increment your index within the loop (although you need to be careful to only call Iterator#next once per loop - just do it at the top).

You can use ListIterator to do the counting:

final List<String> list = Arrays.asList("zero", "one", "two", "three");

for (final ListIterator<String> it = list.listIterator(); it.hasNext();) {
    final String s = it.next();
    System.out.println(it.previousIndex() + ": " + s);
}