Question

As per my knowledge the main difference between Iterator and ListIterator is

Iterator : Enables you to cycle through a collection in the forward direction only, for obtaining or removing elements

ListIterator : It extends Iterator, allow bidirectional traversal of list and the modification of elements

If ListIterator is more powerful than Iterator then sun java developer should have provide implementation for ListIterator only and deprecate iterator. Why Iterator is still exists in java? Is there any advantage of using Iterator than ListIterator?

Answer 1

It’s because not all collections support both forward and backward iteration. ListIterators are specifically for collections that have list semantics, i.e. they define an ordering over the elements. Some collection types (Sets, for example) do not define the ordering of their elements, so a ListIterator does not make sense for them.

There is also an extra overhead incurred when the iterator implementation needs to maintain enough state to support forward and backward iteration and in-place modification. By supporting both Iterator and ListIterator it is possible to have a light-weight implementation of Iterator when it is needed, and a heavier ListIterator for those cases where the extra functionality is required.