Iterator Pattern 迭代器模式

Definition

Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
提供一种方法访问一个容器对象中各个元素，而又不需暴露该对象的内部细节。

Participants

The classes and objects participating in this pattern are:

Iterator (AbstractIterator)

• defines an interface for accessing and traversing elements.

ConcreteIterator (Iterator)

• implements the Iterator interface.
• keeps track of the current position in the traversal of the aggregate.

Aggregate (AbstractCollection)

• defines an interface for creating an Iterator object

ConcreteAggregate (Collection)

• implements the Iterator creation interface to return an instance of the proper ConcreteIterator