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Façade Design Pattern

Façade Design Pattern. Source: Design Patterns – Elements of Reusable Object-Oriented Software; Gamma, et. al. Problem. A subsystem contains lots of classes, all of which are necessary to perform its function Most of the subsystem's internal complexity is not directly relevant to its clients

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Façade Design Pattern

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  1. Façade Design Pattern Source: Design Patterns – Elements of Reusable Object-Oriented Software; Gamma, et. al.

  2. Problem • A subsystem contains lots of classes, all of which are necessary to perform its function • Most of the subsystem's internal complexity is not directly relevant to its clients • We want to simplify the client's interface to the subsystem to make it easier to use • We want to minimize client dependencies on the subsystem's internal details

  3. Solution • Introduce a Façade object that provides a simplified interface to the subsystem • The Façade's interface provides exactly those operations needed by most clients, and no more • The Façade translates high-level client requests into lower-level requests on subsystem objects • Internal subsystem objects have no knowledge of the Façade

  4. Solution • Most clients interact with the subsystem strictly through the Façade • Advanced clients may still be allowed to access the full scope of subsystem functionality, but most clients don't need or want to • Similar to keeping a class' implementation details private, and making public only those operations directly needed by clients (i.e., information hiding)

  5. Consequences • Makes using the subsystem easier • Reduces coupling between clients and the subsystem • Reduces compilation dependencies, thus minimizing recompilation time • Useful for defining the interfaces between layers in a layered system

  6. Known Uses: Compilers

  7. Known Uses: Web Applications

  8. Known Uses: CS240 Chess Program

  9. Known Uses: CS240 Chess Program

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