What is the best way to inject dependency? Also, state the reason.
The best way to inject dependencies in software design is typically through Constructor Injection. This approach involves providing the dependencies of a class through its constructor, ensuring that the class receives all the necessary dependencies at the time of its creation.
Immutability: Dependencies can be made immutable, as they are set at construction time and cannot be changed afterward. This leads to more predictable and easier-to-understand code.
Explicit Dependencies: Constructor injection makes the dependencies of a class explicit. When you look at the constructor, you can immediately see what dependencies are required, which improves code readability and maintainability.
Easier Testing: It simplifies unit testing because you can easily pass mock or stub implementations of the dependencies when creating an instance of the class. This allows for isolated testing of the class without relying on the actual implementations of its dependencies.
Encourages Single Responsibility Principle: By requiring dependencies to be provided at construction, it encourages classes to focus on a single responsibility and not manage their own dependencies, which can lead to better separation of concerns.
Avoids Service Locator Anti-pattern: Constructor injection avoids the pitfalls of the Service Locator pattern, which can lead to hidden dependencies and make the code harder to understand and maintain.
While constructor injection is often preferred, there are other methods such as Setter Injection and Interface Injection. Each has its use cases, but they may introduce issues like mutable dependencies or hidden dependencies, which can complicate testing and maintenance.
In summary, constructor injection is generally considered the best practice for dependency injection due to its benefits in immutability, clarity, testability, and adherence to design principles.