Iterator design pattern is used to access and traverse an aggregate object without exposing its internal structure.
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
The intent of iterator design pattern is to provide the access of aggregate object without exposing its internal structure.
Need to access the elements of an aggregate object without exposing the internal details of object.
Accessing elements of object is required with traversal, and at the same time it should not expose the internal structure of
aggregate object. Also this may be applicable to different data structures, which provide different algorithms for accessing
Provide a way to access and traverse an aggregate object by giving responsibility of access and traversal to another
So there can be common interface, which can be applicable for different data structures to provide interface for accessing and
traversing. There will be separate objects having this interface and will have responsibility to access the elements and
traversal of aggregate objects.
Where iterator design pattern is applicable?
Access and traversal of aggregate object is required without exposing its internal structure.
Common interface is required to access and traverse different data structures.
Iterator Design Pattern UML Structure
Participant classes of iterator design pattern
Iterator class provides the interface for accessing the elements and traversal of the aggregate object.
ConcreteIterator class implements the interface of Iterator class and keeps track of current item of aggregate
Aggregate class provides the interface for creating Iterator object.
ConcreteAggregate class implements the method CreateIterator().
How they work together?
The client creates the ConcreteAggregate object. It uses the CreateIterator interface to create the ConcreteIterator
object. This will have the current item information to track the aggregate object. Now it uses the Iterator interface to
access the elements and traversal of aggregate object.
So we can have different data structures, and their concrete iterators can implement interface according to their
traversal algorithm. This makes the access and traversal simple for different data structures.
Suresh Kumar Srivastava is founder of online learning site coursegalaxy.com and author of popular books C In Depth,
Data Structures Through C In Depth. He has 18+ years experience in industry and worked on architecture and design of
multiple products. This article Iterator Design Pattern is from his Design Patterns course.
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