now...
we can start replacing the switch in Movie with PolyMorphism

simple subclassing Movie to allow
each kind of Movie to have its own getCharge will
not work... as a Movie can change its class during
its lifetime...

We will use State pattern to solve this...

requires 3 refactorings
  Replace Type Code with State/Strategy
  Move Method
  Replace Conditional with Polymorphism

First, Replace type code with State
  step one is Self Encapsulate Field
  to make sure all uses of the type code go through accessors methods.

We are working in Movie class...