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Dependency Injection in Programming

dependency injection in programming

Dependency Injection in Programming

Dependency Injection simplifies codes, and this has increased its popularity among programmers.

As I explained in my previous article on the importance of dependency management, the rising complexity of software dependencies creates the need for dependencies and classes to function independently.

When your classes can function independently, plugging into the dependencies they need, it improves the usability of your code. The method for achieving this is called Dependency Injection.

Dependency Injection may sound complex if you’re new to programming, so in this article, I’ll discuss what a Dependency injection is, its benefits, and its disadvantages.

What is Dependency Injection?

Dependency injection is a software engineering technique that makes a class independent of its dependencies rather than creating dependencies – the class requests dependencies from external sources.

Dependency injection aims to improve how your code functions and reduce the frequency of class replacement.

Instead of a class or object reaching for the dependencies they need, they are directly injected into them to improve their functionality, enabling you to replace dependencies without altering the class or object.

Here’s a simple analogy to understand how dependency injection works;

If a child wants to get a mug from the top shelf and goes there alone, he may break something while trying to reach it or get hurt. But if he states his needs, “I need a cup,” instead of going himself, the child gets a cup, stays safe, and nothing gets broken.

The Four Roles of Dependency Injection

If you want to use the dependency injection techniques, your classes must fulfill the following four primary roles:

  • The Service: A service is any class that contains functionality. This class provides a service to the client class.
  • The Client: A client class is any class that is dependent on the service class.
  • An Interface: Clients don’t need to know how their dependencies function. So, interfaces are services that retrieve dependencies behind the scenes without the client knowing how they are implemented.
  • The injector: The role of the injector is to inject the service class into the client class.

Types of Dependency Injection

As we see above, the service class (dependency) is injected into the client class by the injector class.

The injector class injects dependencies in the following three major ways:

  • Constructor Injection: This injection occurs when the injector provides dependency through the client class constructor.
  • Interface Injection: In this type of injection, the dependency interface provides an injector method for the clients you pass to it.
  • Property/Setter Injection: In this injection method, the client reveals a setter method that accepts the dependency.

Here, you need to understand that Dependency Injection’s role is to create objects. You also need to identify the classes that require those objects and how to provide those classes with the objects.

Benefits of Dependency Injection

The advantages of using dependency injection make the technique highly effective. However, it also has limitations, making some developers underrate its effectiveness.

Like every other tool, there are certain conditions where dependency injections are beneficial and others where you need caution.

So, what are the advantages of Dependency Injections?

  • It decouples component logic.
  • It eases the unit testing of applications through mock databases injected dependencies.
  • It enhances the configuration of applications
  • It improves code reusability
  • It makes it easier to extend the application classes
  • It reduces boilerplate code because dependencies are initialized by their injector component

Disadvantages of Dependency Injection

As I mentioned earlier, despite the growth in popularity, dependency injection has some limitations that hinder its acceptability.

Some of these limitations include the following:

  • Learning it can be slightly tricky.
  • It can lead to management issues if you misuse it.
  • It can make troubleshooting difficult.
  • Finally, it increases complexity since it increases the number of classes.


Dependency injection can be advantageous when you use it correctly. It makes codebases easier to manage and makes working with several developers more effective.

More so, with dependency injection, your dependencies can be maintained separately, which makes the project more maintainable, readable, and extensible, saving you costs and time.

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