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Dependency Injection for Loose Coupling

In designing an object-oriented application, a major tenet of design is "loose coupling". Loosely, not meant for the pun, "loose coupling" means that objects should only have as many dependencies as is needed to do their job - and the dependencies should be few. Furthermore, an object's dependencies should be on interfaces and not on "concrete" objects, when possible. (A concrete object is any object created with the keyword new.) Loose coupling promotes greater reusability, easier maintainability, and allows you to easily provide "mock" objects in place of expensive services, such as a socket-communicator. "Dependency Injection" (DI), also more cryptically known as "Inversion of Control" (IoC), can be used as a technique for encouraging this loose coupling. There are two primary approaches to implementing DI: constructor injection and setter injection. Obviously, at some point, something must be responsible for creati…