Name:
  Iterator

Intent:
  - sequentially access the element of a collection
    without revealing/exposing the collection structure (and interface)

Structure:
  - define/use an Enumeration interface (already provided, 2 methods)
      - hasMoreElements
      - nextElement
  - iterator class is encapsulated
  - iterator object is returned by a method of the collection
    conventionally called elements()

Notes:
  - beware of changing the collection while iterating over its elements
  - the version in this directory is based on java Enumeration interface