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State Pattern From GoF

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Avatar for Chris Bushell Chris Bushell
July 07, 2010
Programming
1
68

State Pattern From GoF

Prepared for the Melbourne Patterns Group

Avatar for Chris Bushell

Chris Bushell

July 07, 2010
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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