What is an Iterator

Question

Hi... Ques : What is an Iterator ? What is the difference between java.util.Iterator and java.util.ListIterator ?

Satyapriya Nayak · Answer

Hi Manish, The List and Set collections provide iterators , which are objects that allow going over all the elements of a collection in sequence. The java.util.Iterator interface provides for one-way traversal and java.util.ListIterator provides two-way traversal. Iterator is a replacement for the older Enumeration class which was used before collections were added to Java. Creating an Iterator Iterators are created by calling the iterator() or listIterator() method of a List, Set, or other data collection with iterators. Iterator Methods Iterator defines three methods, one of which is optional. Result Method Description b = it . hasNext () true if there are more elements for the iterator. obj = it . next () Returns the next object. If a generic list is being accessed, the iterator will return something of the list's type. Pre-generic Java iterators always returned type Object , so a downcast was usually required. it .remove() Removes the most recent element that was returned by next . Not all collections support delete . An UnsupportedOperationException will be thrown if the collection does not support remove() . Iterator : Enables you to traverse through a collection in the forward direction only, for obtaining or removing elements ListIterator : extends Iterator, and allows bidirectional traversal of list and also allows the modification of elements. Thanks