Questions tagged [dependency-injection]

Dependency Injection is a set of software design principles and patterns that enables you to reduce coupling between components

Dependency injection (DI) is a set of software and for object-oriented programming () involving dynamically injecting (inserting) into a software component dependencies (service components) that it needs to function, without needing the dependent component to hard-code a dependency on the service. This reduces coupling between the dependent consumer and the service.

Benefits of Dependency Injection

  • Separation of concerns.
  • Boilerplate-code reduction in application classes because all work to initialize dependencies is handled by the composer.
  • Configurable components makes application easily extendable.
  • Unit testing is easy with mock objects.

Disadvantages of Dependency Injection

  • If overused, it can lead to maintenance issues because effect of changes are known at runtime.
  • Dependency injection hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.

Background questions

Resources / books

The following list of books (in print) focus specifically on Dependency Injection.

Books are presented in opposite order of publication

Related Patterns

26300 questions
39 answers

What is dependency injection?

There have been several questions already posted with specific questions about dependency injection, such as when to use it and what frameworks are there for it. However, What is dependency injection and when/why should or shouldn't it be used?
  • 39,615
  • 9
  • 44
  • 52
30 answers

AngularJS: Service vs provider vs factory

What are the differences between a Service, Provider and Factory in AngularJS?
23 answers

What is a JavaBean exactly?

I understood, I think, that a "Bean" is a Java-class with properties and getters/setters. As much as I understand, it is the equivalent of a C struct. Is that true? Also, is there a real syntactic difference between a JavaBean and a regular class?…
11 answers

What is the difference between @Inject and @Autowired in Spring Framework? Which one to use under what condition?

I am going through some blogs on SpringSource and in one of the blogs, author is using @Inject and I suppose he can also use @Autowired. Here is the piece of code: @Inject private CustomerOrderService customerOrderService; I am not sure about the…
  • 100,387
  • 116
  • 269
  • 365
24 answers

Inversion of Control vs Dependency Injection

According to the paper written by Martin Fowler, inversion of control is the principle where the control flow of a program is inverted: instead of the programmer controlling the flow of a program, the external sources (framework, services, other…
  • 17,924
  • 31
  • 84
  • 131
6 answers

Why does one use dependency injection?

I'm trying to understand dependency injections (DI), and once again I failed. It just seems silly. My code is never a mess; I hardly write virtual functions and interfaces (although I do once in a blue moon) and all my configuration is magically…
30 answers

Why do I need an IoC container as opposed to straightforward DI code?

I've been using Dependency Injection (DI) for a while, injecting either in a constructor, property, or method. I've never felt a need to use an Inversion of Control (IoC) container. However, the more I read, the more pressure I feel from the…
  • 21,044
  • 18
  • 65
  • 101
9 answers

Resolving instances with ASP.NET Core DI from within ConfigureServices

How do I manually resolve a type using the ASP.NET Core MVC built-in dependency injection framework? Setting up the container is easy enough: public void ConfigureServices(IServiceCollection services) { // ... …
Dave New
  • 38,496
  • 59
  • 215
  • 394
30 answers

Dependency Injection vs Factory Pattern

Most of the examples quoted for usage of Dependency Injection, we can solve using the factory pattern as well. Looks like when it comes to usage/design the difference between dependency injection and factory is blurred or thin. Once someone told me…
Binoj Antony
  • 15,886
  • 25
  • 88
  • 96
49 answers

Error when trying to inject a service into an angular component "EXCEPTION: Can't resolve all parameters for component", why?

I've built a basic app in Angular, but I have encountered a strange issue where I cannot inject a service into one of my components. It injects fine into any of the three other components I have created, however. For starters, this is the…
Keith Otto
  • 5,118
  • 2
  • 11
  • 7
30 answers

Dependency Injection error: Unable to resolve service for type while attempting to activate, while class is registered

I created an .NET Core MVC application and use Dependency Injection and Repository Pattern to inject a repository to my controller. However, I am getting an error: InvalidOperationException: Unable to resolve service for type…
  • 13,655
  • 9
  • 62
  • 74
9 answers

One DbContext per web request... why?

I have been reading a lot of articles explaining how to set up Entity Framework's DbContext so that only one is created and used per HTTP web request using various DI frameworks. Why is this a good idea in the first place? What advantages do you…
  • 11,068
  • 17
  • 52
  • 62
11 answers

@Resource vs @Autowired

Which annotation, @Resource (jsr250) or @Autowired (Spring-specific) should I use in DI? I have successfully used both in the past, @Resource(name="blah") and @Autowired @Qualifier("blah") My instinct is to stick with the @Resource tag since it's…
  • 6,663
  • 6
  • 33
  • 26
18 answers

Why is IoC / DI not common in Python?

In Java IoC / DI is a very common practice which is extensively used in web applications, nearly all available frameworks and Java EE. On the other hand, there are also lots of big Python web applications, but beside of Zope (which I've heard should…
4 answers

Why use @PostConstruct?

In a managed bean, @PostConstruct is called after the regular Java object constructor. Why would I use @PostConstruct to initialize by bean, instead of the regular constructor itself?
  • 9,397
  • 13
  • 47
  • 52
2 3
99 100