Java With Us

Iterator

Updated on 2026-04-21 Reviewed by the Java With Us editorial team

An Iterator is an object that traverses a collection one element at a time. Every Collection provides one via the iterator() method. The enhanced for loop (for (var x : coll)) uses an iterator under the hood.

Example

List<String> names = List.of("Ada", "Grace", "Linus");
Iterator<String> it = names.iterator();
while (it.hasNext()) {
    String name = it.next();
    System.out.println(name);
}

Remove during iteration

You cannot call list.remove(x) during iteration — it throws ConcurrentModificationException. Use iterator.remove() instead:

Iterator<Integer> it = numbers.iterator();
while (it.hasNext()) {
    if (it.next() < 0) it.remove();  // safe
}
// Since Java 8, simpler:
numbers.removeIf(n -> n < 0);

ListIterator

ListIterator extends Iterator with bidirectional traversal and in-place mutation (previous(), set(e), add(e)). Only List provides it.

Iterable vs Iterator

Iterable is what a collection is; Iterator is what you get from calling iterator(). Any class implementing Iterable works with the enhanced for loop.

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