When to use Dependency Injection

Question

I\'ve had a certain feeling these last couple of days that dependency-injection should really be called \"I can\'t make up my mind\"-pattern. I know this might sound silly,

Answer 1

Even if you don't change the structure of your program during development phases you will find out you need to access several subsystems from different parts of your program. With DI each of your classes just needs to ask for services and you're free of having to provide all the wiring manually.

This really helps me on concentrating on the interaction of things in the software design and not on "who needs to carry what around because someone else needs it later".

Additionally it also just saves a LOT of work writing boilerplate code. Do I need a singleton? I just configure a class to be one. Can I test with such a "singleton"? Yes, I still can (since I just CONFIGURED it to exist only once, but the test can instantiate an alternative implementation).

But, by the way before I was using DI I didn't really understand its worth, but trying it was a real eye-opener to me: My designs are a lot more object-oriented as they have been before. By the way, with the current application I DON'T unit-test (bad, bad me) but I STILL couldn't live with DI anymore. It is so much easier moving things around and keeping classes small and simple.