Dependency Injection

What is Dependency Injection?

A software design pattern that implements inversion of control for resolving dependencies is known as Dependency Injection. In dependency injection a ‘dependency’ is an object that can be used (service) and ‘injection’ is the passing of a dependency to a dependent object or a client that would use it. Dependency Injection is a subset of Inversion of Control (IOC) that supports the dependency inversion principle and is a way of injecting properties to an object. Additionally, it explains how to inject the concrete implementation into an object that is using abstraction. The main idea of Dependency Injection is to reduce the coupling between objects and to move the binding of abstraction and concrete implementation out of the dependent object. Dependency injection is how one object gets information about the other dependent object, which is abstracted. Moreover, dependency injection provides objects what they require and ensure that this process is hassle free.

Types of Dependency Injection:

In today’s day and age, Dependency Injection is one of the most popular design paradigms used by software programmers all over the world. It is a process of removing dependency of object, which further creates independent business objects. Moreover, this framework is extremely useful for Test Driven Development. However, the process of dependency injection is usually carried out through three types of injections, each of which plays a very crucial role in the development of test cases. These types of dependency injection used by developers around the world are:

  1. Constructor Injection: is used to interface parameter that are exposed through the parameterized contractor. It injects the dependencies through a contractor method during instance instantiation.
  2. Setter Injection: This is the most favoured method of dependency injection in Spring. Dependencies are “set” in the objects through setter methods, which are then defined in a Spring configuration file. Also, it injects the dependency by using default public properties procedure.
  3. Interface-based Injection: This involves mapping items to inject to specific interfaces. Clients must implement an interface that exposes a setter method that accepts the dependency.

Advantages of Dependency Injection:

The process of injecting and converting coupled or dependent objects into decoupled or independent objects is called Dependency Injection. It is a process that allows concurrent and or independent development. Through dependency injection, two developers can independently develop classes that use each other, while only needing to know the interface the classes will communicate through. Moreover, dependency injection decreases coupling between classes and its dependency. Other advantages of dependency injection are mentioned below:

  • Dependency injection allows a client the flexibility of being configurable.
  • Can be used to externalize a system's configuration details into configuration files, allowing the system to be reconfigured without recompilation.
  • Separate configurations can be written for different situations that require different implementations of components. This includes, but is not limited to, testing.
  • Due to decoupling, the reusability of the code is increased.
  • Improved code maintainability and testing.
  • It can be applied to legacy code as a code refactoring.
  • The ease of testing is often the first benefit noticed when using dependency injection.
  • It allows reduction of boilerplate code in the application objects, since all work to initialize or set up dependencies is handled by a provider component.

Disadvantages of Dependency Injection:

Even though there are uncountable benefits of using Dependency Injection, it is of utmost importance to check the drawbacks and disadvantages provided by it. From encouraging dependence on a dependency injection framework to forcing complexity to move out of classes and into the linkages between classes, which might not always be desirable or easily managed, there are several disadvantages of dependency injection. Therefore, to help you get complete information about this framework, here are some other disadvantages of using dependency injection.

  • Dependency injection creates clients that demand configuration details to be supplied by construction code. This can be difficult when obvious defaults are available.
  • Dependency injection can make code difficult to trace (read) because it separates behaviour from construction. This means developers must refer to more files to follow how a system performs.
  • It requires more upfront development effort.

Why is Dependency Injection Useful?

Dependency injection plays an important role in test driven development of a software and it is a design paradigms that is used by software programmers all over the world. Moreover, this framework takes care of creating complicated and advanced objects for developers without allowing them to worry about providing right elements or ingredients. However, the importance of dependency injection is extremely high for unit testing, validation and exception management, as it is tremendously helpful to them in various ways. Hence, elaborated here is the use of dependency injection in unit testing and validation or exception management.

  1. Unit Testing: In unit testing, dependency injection enables one to replace complex dependencies, such as databases, with mocked implementations of those dependencies. This further allows them to completely isolate the code that is being tested by the team of expert testers.
  2. Validation or Exception Management: With the assistance of dependency injection, an individual can inject additional code between the available dependencies. Also, it is possible to inject exception management logic or validation logic, which means that the developer no longer needs to write similar logic for every phase of development.


A subset of Inversion of Control (IOC), Dependency Injection is a very famous design paradigms used by developers and programmers for code related issues. It explains how to inject the concrete implementation into an object that is using abstraction. Moreover, through dependency injection a developer can reduce the coupling between two objects and ensure that they get what they require without any hassle or difficulty. Another reason that makes dependency injection popular among software developers is that, it allows a client the flexibility of being configurable. It can additionally be used to externalize a system's configuration details into configuration files, which allows the system to be reconfigured without recompilation. However, relying on dependency framework to perform construction can lead to forbidding the use of the new keywords, or allowing direct construction of value objects. Therefore, it is best to get a proper understanding of this framework before using it in test driven development.

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