Design Patterns in Java™, Second Edition

6 Bridge

THE BRIDGE, OR Driver, pattern focuses on the design of an abstraction. The word abstraction refers to a class that relies on a set of abstract operations, where several implementations of the set of abstract operations are possible.

The ordinary way to implement an abstraction is to create a class hierarchy, with an abstract class that defines the abstract operations at the top; each subclass in the hierarchy provides a different implementation of the set of abstract operations. This approach becomes insufficient when you need to subclass the hierarchy for some other reason.

You can create a BRIDGE by moving the set of abstract operations to an interface, so that an abstraction will depend on an implementation of the interface.