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Understanding the Iterator Design Pattern Using the Dev.to and Medium Social Networks
Dive deep and iterate
There are 23 classic design patterns described in the original book, Design Patterns: Elements of Reusable Object-Oriented Software. These patterns provide solutions to particular problems, often repeated in software development.
In this article, I am going to describe what the Iterator Pattern is and how and when it should be applied.
Iterator Pattern: Basic Idea
In object-oriented programming, the iterator pattern is a design pattern in which an iterator 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. — Wikipedia
Provide a way to access the elements of an aggregate object sequentially
without exposing its underlying representation. — Design Patterns: Elements of Reusable Object-Oriented Software
The main feature of this pattern is that it lets you traverse elements of a collection without exposing its underlying representation (array, map, tree, etc.). Therefore, these are two problems that this pattern resolves:
- It allows us to change the internal implementation of a collection with no change in the algorithm’s implementation.
- It allows us to add new algorithms that work all existing collection types.
To sum up, the iterator pattern hides the internal implementation of a collection from the client. The UML diagram of this pattern is the following one:
The Iterator class is an interface which defines the different operations to navigate through to the collection ( next or hasNext) while that Aggregate class will create the Iterator. Finally, the system will use the ConcreteAggregate and ConcreteIterator.
- Your collection has a complex data structure under the hood, but you want to hide its complexity from clients.
