What is an Iterator

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