iterator

Iterator

Intent

Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Also Known As

Cursor

Applicability

Use the Iterator pattern

• to access an aggregate object's contents without exposing its internal representation
• to support multiple traversals of aggregate objects
• to provide a uniform interface for traversing different aggregate structures (that is, to support polymorphic iteration)

Participants

• Iterator
  • defines an interface for accessing and traversing elements
• ConcreteIterator
  • implements the Iterator interface
  • keeps track of the current position in the traversal of the aggregate
• Aggregate
  • defines an interface for creating an Iterator object
• ConcreteAggregate
  • implements the Iterator creation interface to return an instance of the proper ConcreteIterator

Related Patterns

Composite: Iterators are often applied to recursive structures such as Composites. Factory Method: Polymorphic iterators rely on factory methods to instantiate the appropriate Iterator subclass. Memento is often used in conjunction with the Iterator pattern. An iterator can use a memento to capture the state of an iteration. The iterator stores the memento internally.

Disclaimer*

Code not implemented because it is part of the standard java class library