State Pattern From GoF

Prepared for the Melbourne Patterns Group

Transcript

1. State  Pa'ern  From  GoF   Chris  Bushell  7th  July  2010    
2. Mo<va<on   “Allow  an  object  to  alter  its  behavior  when  its   internal  state  changes”  
3. Code  
4. Applicability   •  Behavior  depends  on  state   •  Opera<ons  have  large  condi<onal  statements   which  depend  on  state  
5. Par<cipants  
6. Collabora<ons   •  Context  and  Concrete  State   •  Context  is  primary  interface  for  clients  
7. Consequences   •  Localizes  state  specific  behavior.  Avoids  code   duplica<on   •  State  changes  are  well  defined,  atomic   opera<ons   •  State  objects  can  be  shared  
8. Implementa<on   •  Context  or  Concrete  State  defines  transi<ons?   •  Table  based  approach  to  defining  transi<ons   •  Singleton,  Flyweight