Facade
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The facade pattern is used to provide a simple interface to a complex set of interfaces. Often facades are produced to further simplify common APIs or adapt them to a more specific use. | The facade pattern is used to provide a simple interface to a complex set of interfaces. Often facades are produced to further simplify common APIs or adapt them to a more specific use. | ||
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| + | ==Structure== | ||
| + | |||
| + | TODO: add UML diagram | ||
| + | |||
| + | ===Participants=== | ||
| + | * Facade: The Facade knows the internal workings of the subsystem and which classes have which responsibilities. It delegates client request to the correct part of the subsystem. | ||
| + | * Subsystem classes: These classes implement the functionality of the subsystem and handle work assigned to them by the facade. However, they are unaware of the existence of the facade. | ||
| + | |||
| + | ===Collaborations=== | ||
| + | * Clients communicate with the subsystem through the facade and don't have access to the subsystem objects directly. | ||
| + | |||
| + | |||
| + | ==Use When== | ||
| + | * You want to provide a simple interface to a complex subsystem. | ||
| + | * Clients are closely coupled with the implementation of an abstraction. Use Facade to decouple clients from the implementation. | ||
| + | * You want to layer subsystems. Create a Facade for each subsystem level as an access point and get the subsystems to communicate with each other through their facades. | ||
The design pattern | The design pattern | ||
Revision as of 07:47, 24 July 2009
The facade pattern is used to provide a simple interface to a complex set of interfaces. Often facades are produced to further simplify common APIs or adapt them to a more specific use.
Contents |
Structure
TODO: add UML diagram
Participants
- Facade: The Facade knows the internal workings of the subsystem and which classes have which responsibilities. It delegates client request to the correct part of the subsystem.
- Subsystem classes: These classes implement the functionality of the subsystem and handle work assigned to them by the facade. However, they are unaware of the existence of the facade.
Collaborations
- Clients communicate with the subsystem through the facade and don't have access to the subsystem objects directly.
Use When
- You want to provide a simple interface to a complex subsystem.
- Clients are closely coupled with the implementation of an abstraction. Use Facade to decouple clients from the implementation.
- You want to layer subsystems. Create a Facade for each subsystem level as an access point and get the subsystems to communicate with each other through their facades.
The design pattern
- provides convenient methods
- makes the inner system more flexible since less methods are called from the outside
- can turn a badly designed API into a very well usable one
Example
The boot process of a computer can be modeled as a Facade. The system's boot() method is called. This method now starts and configures all the services and programs needed to use the computer.
| Design patterns | |
|---|---|
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Creational: Abstract Factory | Builder | Factory Method | Prototype | Singleton | |
