Wednesday, March 11, 2009

How do the Proxy, Decorator, Adaptor, and Bridge Patterns differ?

A user recently asked:
I was looking at the Proxy Pattern, and to me it seems an awful lot like the Decorator, Adaptor, and Bridge Patterns. Am I misunderstanding something? What's the difference? Why would I use the proxy pattern veses the others? How have you used them in the past in real world projects?
Proxy, Decorator, Adapter, and Bridge are all variations on "wrapping" a class. But their uses are different.
  • Proxy could be used when you want to lazy-instantiate an object, or hide the fact that you're calling a remote service, or control access to the object.
  • Decorator is also called "Smart Proxy." This is used when you want to add functionality to an object, but not by extending that object's type. This allows you to do so at runtime.
  • Adapter is used when you have an abstract interface, and you want to map that interface to another object which has similar functional role, but a different interface.
  • Bridge is very similar to Adapter, but we call it Bridge when you define both the abstract interface and the underlying implementation. I.e. you're not adapting to some legacy or third-party code, you're the designer of all the code but you need to be able to swap out different implementations.


I'm posting to my blog the questions I've answered on StackOverflow, which earned the "Good Answer" badge. This was my answer to "How do the Proxy, Decorator, Adaptor, and Bridge Patterns differ?"

1 comment:

dharmendra said...

Great Explanation. Another great article i would recommend is this one