Iterator Pattern

The Iterator Pattern provides a way to access the elements of an aggregates object sequentially without exposing its underlying representation.

Bates and Sierra — Head First Design Patterns

Class Diagram

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Key Points

• Encapsulate what varies. Iterator
  • knows how to iterate over a collection of item;
  • hides the collection implementation details;
  • depends on the collection and how to iterate over it.
• Single Responsibility Principle.
  • A class should have only one reason to change.
  • Every responsibility of a class is an area of potential change.
• Cohesion.
  • General concept related to Single Responsibility Principle.
  • Measure how closely a class or a module supports a single responsibility.
  • High cohesion: the class is designed around a set of related functions and is more maintainable.
  • Low cohesion: the class is design around a set of unrelated functions and is less maintainable.
• Standard Interface. The Iterator is a well known interface and interact
  • in the same way with all the collections;
  • without knowing collection implementation details, decouples the client from the implementation details.
• Other Interfaces. There are also
  • ListIterator allows to get also the previous item
  • Enumarate old interface
• Polymorphic Iteration. The Iterator code iterate over any collection as long as it supports the interface.
• for/in Statement to iterate over a collection without explicitly creating an iterator.