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Facade pattern

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Facade pattern

The facade pattern (also spelled façade) is a software design pattern commonly used with object-oriented programming. The name is by analogy to an architectural façade.

Contents

A facade is an object that provides a simplified interface to a larger body of code, such as a class library. A facade can

  • make a software library easier to use, understand and test, since the facade has convenient methods for common tasks,
  • make the library more readable, for the same reason,
  • reduce dependencies of outside code on the inner workings of a library, since most code uses the facade, thus allowing more flexibility in developing the system,
  • wrap a poorly designed collection of APIs with a single well-designed API.

    • The Facade design pattern is often used when a system is very complex or difficult to understand because the system has a large number of interdependent classes or its source code is unavailable. This pattern hides the complexities of the larger system and provides a simpler interface to the client. It typically involves a single wrapper class that contains a set of members required by client. These members access the system on behalf of the facade client and hide the implementation details.

    Usage

    A Facade is used when an easier or simpler interface to an underlying object is desired. Alternatively, an adapter can be used when the wrapper must respect a particular interface and must support polymorphic behavior. A decorator makes it possible to add or alter behavior of an interface at run-time.

    The facade pattern is typically used when

  • a simple interface is required to access a complex system,
  • a system is very complex or difficult to understand,
  • an entry point is needed to each level of layered software, or
  • the abstractions and implementations of a subsystem are tightly coupled.
    • Facade
    The facade class abstracts Packages 1, 2, and 3 from the rest of the application.
    Clients
    The objects are using the Facade Pattern to access resources from the Packages.

    Example

    This is an abstract example of how a client ("you") interacts with a facade (the "computer") to a complex system (internal computer parts, like CPU and HardDrive).

    References

    Facade pattern Wikipedia
    (Text) CC BY-SA