Editing Bridge pattern (section)

{{Short description|Design pattern used in software engineering}}
The '''bridge pattern''' is a [[software design pattern|design pattern]] used in [[software engineering]] that is meant to ''"decouple an [[Abstraction (computer science)|abstraction]] from its [[implementation]] so that the two can vary independently"'', introduced by the [[Design Patterns|Gang of Four]].{{r|GoFp151}} The ''bridge'' uses [[encapsulation (computer science)|encapsulation]], [[Object composition#Aggregation|aggregation]], and can use [[inheritance (object-oriented programming)|inheritance]] to separate responsibilities into different [[Class (computer science)|classes]].

When a class varies often, the features of [[object-oriented programming]] become very useful because changes to a [[Computer program|program]]'s [[Source code|code]] can be made easily with minimal prior knowledge about the program. The bridge pattern is useful when both the class and what it does vary often. The class itself can be thought of as the ''abstraction'' and what the class can do as the ''implementation''. The bridge pattern can also be thought of as two layers of abstraction.

When there is only one fixed implementation, this pattern is known as the [[Pimpl]] idiom in the [[C++]] world.

The bridge pattern is often confused with the [[adapter pattern]], and is often implemented using the [[Adapter_pattern#Object_adapter_pattern|object adapter pattern]]; e.g., in the Java code below.

Variant: The implementation can be decoupled even more by deferring the presence of the implementation to the point where the abstraction is utilized<!-- (as illustrated by the [[Visual Prolog]] example below)-->.