Do it Yourself – Dependency Injection
A friend of mine has put together a set of documents which talk about do-it-yourself dependency-inject. Being that I am a fan of DI and how it helps with testability I wanted to share it with you. It is a good read for anyone interested in getting better at DI.
I want to evangelize this technique so that people know a lightweight way they can adopt DI. I think we need to refine the definition of dependency injection. It shouldn’t mean the use of a framework like Guice, because that’s just one possible implementation. It should mean the separation of glue code from business logic. The glue code, (which is represented by annotations in Guice, but could just as well be static helpers), is neither easy nor important to test. On the other hand, the business logic should be made easy to test. The secret to testability does not lie in removing untestable code as much as in segregating the untestable code.
The “dependency injection” (DI) technique is a way to improve testability and maintainability of object-oriented code. Typically adoption of dependency injection is coupled with adoption of a dependency injection framework, such as Guice  or Spring . These materials show how dependency injection can be accomplished without any framework. The same benefits provided by frameworks can be realized using “do-it-yourself” (DIY) handcrafted code. This model is named DIY-DI, pronounced die-die.