The bridge pattern is a design pattern used in software engineering which is meant to "decouple an abstraction from its implementation so that
- a) decoupling and
- b) abstraction can vary independently.
The bridge uses encapsulation, aggregation, and can use inheritance to separate responsibilities into different classes.
When a class varies often, the features of object-oriented programming become very useful because changes to a program's code can be made easily with minimal prior knowledge about the program.
The bridge pattern is useful when both the class as well as what it does vary often.
The 1) class itself can be thought of as the implementation and 2) what the class can do as the abstraction.
The bridge pattern can also be thought of as two layers of abstraction.