iterator design pattern, which allo

iterator design pattern, which allows to traverse a collection without exposing its internals. we all know about the Java Iterator. But it is not all about iterator, lets dive deeper and do a comprehensive study of iterator pattern.


By the end of this tutorial we will know about internal iterator, external iterator, polymorphic iterator, robust iterator, null iterator and etc.

Intent of an iterator is to provide a way to traverse through a collection (otherwise called an aggregate) in a sequential way without exposing the underlying collection. Initially Java had Enumeration to iterate through the collections and from Java version 1.2 Iterator took its place. Java Iterator is a nice implementation of iterator design pattern allowing us to traverse through a collection in a sequential way. On call, the collection will create an iterator instance and return it, which we can use to iterate.