Definition
The facade pattern (or façade pattern) is a software design pattern commonly used with object-oriented programming. The name is by analogy to an architectural facade.
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 which 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.[1] Alternatively, an adapter can be used when the wrapper must respect a particular interface and must support polymorphicbehavior. A decorator makes it possible to add or alter behavior of an interface at run-time.
|
Pattern |
Intent |
|
Adapter |
Converts one interface to another so that it matches what the client is expecting |
|
Decorator |
Dynamically adds responsibility to the interface by wrapping the original code |
|
Facade |
Provides a simplified interface |
The facade pattern is typically used when:
Structure
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
Systems