Iterator Pattern
Overview
The Iterator Pattern is a design pattern in object-oriented programming that provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. The pattern falls under the category of behavioral patterns because it's used to manage algorithms, relationships, and responsibilities between objects.
Concept
The iterator pattern decouples algorithms from containers. In some cases, algorithms are necessarily container-specific and thus cannot be decoupled. The iterator pattern is used to traverse a container and access the container's elements. The iterator pattern decouples algorithms from containers; in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.
Structure
The iterator pattern involves two key types of actor classes: the 'Iterator' and the 'Aggregate'. The 'Iterator' defines an interface for accessing and traversing elements. The 'ConcreteIterator' implements the Iterator interface and keeps track of the current position in the traversal of the aggregate. The 'Aggregate' defines an interface for creating an Iterator object. The 'ConcreteAggregate' implements the Iterator creation interface to return an instance of the proper ConcreteIterator.
Implementation
The iterator pattern is implemented by creating an iterator interface that all iterators must implement. This iterator declares methods for traversing the container. A concrete iterator is then defined that implements the iterator interface. This concrete iterator keeps track of the current position in the traversal of the aggregate.
The container class then provides a method that returns a concrete iterator that will be used to traverse its contents. Thus, the client doesn't need to know about the concrete iterator, but only the iterator interface.
Advantages
The Iterator Pattern has several advantages. It supports variations in the traversal of a collection, it simplifies the interface of the collection, and it provides a uniform interface for traversing different types of collections.
Disadvantages
However, the Iterator Pattern also has some disadvantages. It can be overkill if a collection is simple and easily accessed. It can also be inefficient, as the iterator may need to keep track of every element in the collection.