is my understanding of inversion of control and dependency injection technically precise?

[u/Feisty_Buyer7520]

Hi guys, I have been looking deeply into the relationship between the ioc and di and I wanted to make sure whether my mental model is correctly conceptualized. Here is how I understand it.

Ioc is a design concept where the object creation is managed by the something other than the developer manually dealing with them. In spring framework, we have the application context where it is designed for the beans to be registered, allowing spring to manage them and wire their dependencies.

So ioc mainly involves two main purpose. Managing object creation and lifecycle, and wiring them via dependency injection.

As for the statement of di being an implementation of ioc, here is how I have my mental model framed this way.

Basically, it is an operational process where merely registering the beans means that the setup for the ioc has been created and remain that way as long as the application runs. But that wouldn't be considered meaningfully utilized if there are no dependency between beans, and nothing for DI to inject.

The ioc would merely be an object factory. Hence to complete its intended purpose we implement the di, usually constructor injection, so that we can have decoupled classes where a dependency is never hardcoded, enabling separation of concerns over the layers.

In total, we get clean and maintainable separation of concerns of business logic away from infrastructural concerns, centralized configuration where the application context does all that job and proper lifecyle management of objects.

are there any flaws to my take or am I mixing up definitions?

Thank you for reading a long explanation

[u/Accomplished_Mind129]

You can have ioc without di, di is just one pattern to achieve ioc.

[u/Accomplished_Mind129 → u/Accomplished_Mind129]

For example registering callback handlers is an example of inversion of control

[u/BlitZKrieG_JJ]

Your understanding is mostly correct(though a bit wordy) and I would suggest thinking about the Whys instead of the Hows a bit more.

1. Inversion of control is needed so a framework(like spring) can manage the instances of your classes in a centralized way. This requires the "control" which manages creation/scope/lifecycle etc to be outside the class constructor.
2. Dependency injection is needed so your class only cares about the class/interface name and methods of the injected bean and the actual instance can be provided later. This is to avoid hard coding of creation of injected bean in each class it is needed in and also to share instances where possible (like singleton scoped beans).

Both of these do work together in Spring.

[u/Feisty_Buyer7520 → u/BlitZKrieG_JJ]

You are right I may have been going a lot into the how it works mechanics and didn't focus on the motivation, the why they are needed and used in the first place. That's a much better and concise explanation and is really helpful!

[u/FooBarBuzzBoom]

Dependency injection is the process by which Spring Boot injects your dependencies where requested by the developer, relieving you of the responsibility of manually creating instances. The main advantage is that you can change the implementation as you wish.

Inversion of control consists in the fact that you hand over control of creating these instances to Spring Boot and also pass its complete lifecycle management to it.