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The Iterator design pattern introduces an external object that allows to go through the items of collections without knowing the internal structure of the collections. This is one of the most popular pattern, and you can find it implemented in standard libraries of almost all programming languages. Sometimes, it's called Enumerator instead of Iterator.


Today's programming languages often provide rich variety of collections, i.e., arrays, lists, dictionaries (hashmap), but also e.g. trees. Sometimes, it's useful to implement our own collection, especially if it's supposed to provide some special operations over its elements. At some point, we need to iterate through every collection, i.e. to go through all its elements from the first to the last one and print them, for example. If each collection implemented its own interface to iterate over its elements, first, we'd have to examine them, and collections are sometimes really complicated. And second, the language itself won't be able to support syntactic sugar such as the foreach loop. If you think of introducing some general interface the


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The Iterator design pattern introduces an external object that allows to go through a collection linearly without having to know its internal structure.

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Article has been written for you by David Capka
The author is a programmer, who likes web technologies and being the lead/chief article writer at He shares his knowledge with the community and is always looking to improve. He believes that anyone can do what they set their mind to.
Unicorn university The author learned IT at the Unicorn University - a prestigious college providing education on IT and economics.
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