Decouple an abstraction from its implementation so that the two can vary independently. Bridge pattern has structural purpose and applies to objects, so it deals with the composition of objects.

• you want to avoid a permanent binding between an abstraction and its implementation
• both the abstractions and their implementations should be extensible by subclassing
• changes in the implementation of an abstraction should have no impact on clients
• you want to hide the implementation of an abstraction completely from clients