Bad classification

Static diagram :

Strong points :

1. 1. Extensibility
   1. 1.1 States' protocol factorization
   2. 1.2 Addition or removal of a state does not need code modification
2. 2. Simplified management
   1. 2.1 Possibility of state modification at execution time without deletion
   2. 2.2 State behavior decoupling

Spoiled pattern instantiations on different problems

Problem 1 :

Name :

Dynamic state changing

Problem wording :

Design a VOD platform. The platform provides its customers with movies in three categories: Child, Normal and New. A movie is in the "New" category for a few weeks, then moves on to one of the other categories. The price of the movies depends on the category. The system may evolve so that the Horror category will be added.

Optimal solution :

Static diagram :

Thanks to the inheritance links, we are able to distinct the movies to its states. In these case, the addition of a new state does not imply code modification.

Alternative solution :

Static diagram :

The category is a subclass of VOD imposing instances destruction to change of category. The question of the validity of this solution is open in regard of the proposed exercise. However, we have considered this solution valid in using a prototype creational pattern with a category as parameter.