This is my second presentation about design patterns. It covers proxy and bridge patterns.

1. 02 Proxy and Bridge Pattern Design Patterns © Prafulla Paraskar 2010

2. Proxy Structural Design Pattern

3. Definition A proxy, in its most general form, is a class functioning as an interface to something else. The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. (wikipedia) © Prafulla Paraskar 2010

4. Proxy Pattern – Explained (1/2) Resources Proxy Client © Prafulla Paraskar 2010

5. Proxy Pattern – Explained (2/2) Provides a surrogate or placeholder for another object to control access to it. A mechanism to enforce authentication and authorization. Creates expensive objects only when required. Allows optimization techniques such as caching to be implemented. Release expensive resources soon as they are no longer required (smart pointers). © Prafulla Paraskar 2010

6. Proxy Pattern – UML Diagram © Prafulla Paraskar 2010

7. Proxy Pattern – Real World Samples Image/document editors. Reference counting pointer (smart pointer). Friend lists on social networking sites. COM Components at the lower level. CORBA proxy/stub objects. .NET web services proxy classes. © Prafulla Paraskar 2010

8. Proxy Pattern – Guidelines (1/2) You have objects that: Are expensive to create. Need access control. Access remote sites. Need to perform some action whenever they are accessed. © Prafulla Paraskar 2010

9. Proxy Pattern – Guidelines (2/2) You want to: Create objects only when their operations are requested. Perform checks or housekeeping on objects whenever accessed. Have a local object that will refer to a remote object. Implement access rights on objects as their operations are requested. © Prafulla Paraskar 2010

10. Bridge Structural Design Pattern

11. Definition The bridge pattern is a design pattern used in software engineering which is meant to "decouple an abstraction from its implementation so that the two can vary independently“.(wikipedia) © Prafulla Paraskar 2010

12. Bridge Pattern – Explained (1/2) © Prafulla Paraskar 2010

13. Bridge Pattern – Explained (2/2) Decouples an abstraction from implementation. Specially useful in the situations where a new version of component library needs to replace older one with backward compatibility. Client specifies which implementation to use (sometimes implicitly). Unlike Adapter pattern, client knows about the implementation in use all the time. © Prafulla Paraskar 2010

14. Bridge Pattern – UML Diagram © Prafulla Paraskar 2010

15. BridgePattern – Real World Samples Electric switch (abstraction) / Appliances (implementations). Different types of displays (implementation) providing one essential set of capabilities defined in the a bridge interface (abstraction). Client calls the abstraction to display something and the abstraction deciding the display based on the capabilities. © Prafulla Paraskar 2010

16. Bridge Pattern– Guidelines (1/2) You can: Identify that there are operations that do not always need to be implemented in the same way. © Prafulla Paraskar 2010

17. Bridge Pattern– Guidelines (2/2) You want to: Completely hide implementations from client. Avoid binding an implementation to an abstraction directly. Change an implementation without even recompiling an abstraction. Combine different parts of a system at runtime. © Prafulla Paraskar 2010

18. Thank you! http://geekswithblogs.net/technomad Presentation by Prafulla Paraskar eprafulla@gmail.com © 2010 Prafulla Paraskar