After iterating over data with an iterator, is the order of data retrieval guaranteed?

The order of data retrieval using an iterator is not guaranteed automatically.

The guarantee of order depends on the type of collection being iterated over.

• Collections with guaranteed order:

  • ArrayList
  • LinkedList
  • LinkedHashSet
  • TreeMap (sorted by key)
  • LinkedHashMap (sorted by insertion or access order)

  Iterators of these collections will return elements in a predefined order for that collection.

• Collections without guaranteed order:

  • HashSet
  • HashMap

  The iteration order over these collections can be unpredictable and may change when adding/removing elements or even between program runs.

// Example of iterating over ArrayList (order guaranteed)
List<String> list = new ArrayList<>();
list.add("Apple");
list.add("Banana");
list.add("Cherry");

Iterator<String> listIterator = list.iterator();
while (listIterator.hasNext()) {
    System.out.println(listIterator.next()); // Will output Apple, Banana, Cherry
}

// Example of iterating over HashSet (order not guaranteed)
Set<String> set = new HashSet<>();
set.add("Apple");
set.add("Banana");
set.add("Cherry");

Iterator<String> setIterator = set.iterator();
while (setIterator.hasNext()) {
    System.out.println(setIterator.next()); // Output order may vary
}