Difference between Bridge pattern and Adapter pattern

Question

What is the difference between the Bridge and Adapter patterns?

Answer 1

This post has been around for quite a while. However, it is important to understand that a facade is somewhat similar to an adapter but it's not quite the same thing. An adapter "adapts" an existing class to a usually non-compatible client class. Let's say that you have an old workflow system that your application is using as a client. Your company could possibly replace the workflow system with a new "incompatible" one (in terms of interfaces). In most cases, you could use the adapter pattern and write code that actually calls the new workflow engine's interfaces. A bridge is generally used in a different way. If you actually have a system that needs to work with different file systems (i.e. local disk, NFS, etc.) you could use the bridge pattern and create one abstraction layer to work with all your file systems. This would basically be a simple use case for the bridge pattern. The Facade and the adapter do share some properties but facades are usually used to simplify an existing interface/class. In the early days of EJBs there were no local calls for EJBs. Developers always obtained the stub, narrowed it down and called it "pseudo-remotely". This often times caused performance problems (esp. when really called over the wire). Experienced developers would use the facade pattern to provide a very coarse-grained interface to the client. This facade would then in turn do multiple calls to different more fine-grained methods. All in all, this greatly reduced the number of method calls required and increased performance.