Design Pattern – Bridge (Structural) References Yih-shoung Chen, Department of Information Engineering, Feng Chia University,Taiwan, R.O.C. The Bridge Pattern, SENG Design Patterns, University of Calgary The Bridge Pattern, CpSc 872 Software Engineering Gamma, E., R. Helm, R. Johnson, J. Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software.

By Tulika Rathi 2 Intent Decouple an abstraction from its implementation so that the two can vary independently Allows different implementations of an interface to be decided upon dynamically. Also known as Handle/Body pattern

By Tulika Rathi 3 Motivation & Applicability Avoid a permanent binding between an abstraction and its implementation Both the abstractions and their implementation should be extensible by subclassing Changes in the implementation of an abstraction do not impact the clients Share an implementation among multi objects and this facts should be hidden from the client E.g.: Windows

By Tulika Rathi 4 Participants Abstraction Refined abstraction Concrete implementor Implementor

By Tulika Rathi 5 Structure

By Tulika Rathi 6 Example of problem suitable for bridge

By Tulika Rathi 7 A more complex situation

By Tulika Rathi 8 Solution using Bridge

By Tulika Rathi 9 Pros & Cons Pros decoupling of the implementation from the interface improved extensibility of classes additional capability for hiding implementation details from clients best leveraged as a pure design-time pattern Cons (Implementation Issues) abstractions that have only one implementation creating the right Implementor sharing implementors use of multiple inheritance

By Tulika Rathi 10 Adapter vs Bridge Similarities: Both used to hide the details of the underlying implementation. Difference: The adapter pattern is geared towards making unrelated components work together Applied to systems after they’re designed (reengineering, interface engineering). A bridge, on the other hand, is used up-front in a design to let abstractions and implementations vary independently. Green field engineering of an “extensible system” New “beasts” can be added to the “object zoo”, even if these are not known at analysis or system design time. Structural difference: Bridge can abstract a complex entity from its implementation; Adapter only abstracts a single interface

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