Iterators

Iterable supplies an Iterator, enabling enhanced for. An iterator is a cursor; call hasNext before next. Many iterators are fail-fast on unsupported structural changes, but this is bug detection rather than a concurrency guarantee.

Controlled removal

Iterator<String> iterator = names.iterator();
while (iterator.hasNext()) {
    if (iterator.next().isBlank()) {
        iterator.remove();
    }
}

Removing through the iterator keeps its expected modification state synchronized. ListIterator moves both directions and supports add, set, and index queries. forEachRemaining consumes remaining elements. Spliterator reports characteristics and can partition traversal for stream pipelines. Do not reuse exhausted iterators, assume stable order from unordered collections, or modify a collection concurrently without its documented mechanism. Prefer collection bulk methods or streams when manual cursor control adds no value.