Dependency Injection

One benefit of using the dependency injection approach is the reduction of boilerplate code in the application objects since all work to initialize or set up dependencies is handled by a provider component.[1]

Another benefit is that it offers configuration flexibility because alternative implementations of a given service can be used without recompiling code. This is useful in unit testing, as it is easy to inject a fake implementation of a service into the object being tested by changing the configuration file, or overriding component registrations at run-time.

http://en.wikipedia.org/wiki/Dependency_Injection