Why Spring Exists

The idea Spring is built on: a class should be handed the objects it depends on instead of creating them itself. A class that creates its own dependencies works until you need to swap one, for a test, a different provider or a stand-in that does not touch the network. It covers the cost of a hard-coded new, Inversion of Control and Dependency Injection, and two examples written by hand with no framework. It leaves Spring itself for the topics that follow it in this subject.