Name:
  Prototype

Intent:
  As the Abstract Factory (even with variation of Factory Method)
  Create families of related products without concern of their concrete types.

Structure:
  for each product:
     - there is an abstract class
     - for each family:
         -there is a concrete class
  there is a single factory class, the prototype
     - class holds each product of a family
     - class has device to change families of products
     - class has method to clone and returns held products

Notes:
  - about cloning
      - products implement Cloneable
      - products must override method clone to make it accessible
      - products clone by calling clone in the superclass
      - products either handle or propagate the exception
      - optional covariance