Dagger
Fast dependency injector for Android and Java
...Declare dependencies, specify how to satisfy them, and ship your app. Dependency injection frameworks have existed for years with a whole variety of APIs for configuring and injecting. So, why reinvent the wheel? Dagger 2 is the first to implement the full stack with generated code. The guiding principle is to generate code that mimics the code that a user might have hand-written to ensure that dependency injection is simple.