Dependency injection is a programming technique in which an object or function receives other objects or functions that it requires, as opposed to creating them internally. This aims to separate the concerns of constructing objects and using them, leading to loosely coupled programs. The pattern ensures that an object or function is provided with its dependencies by external code, making implicit dependencies explicit and helping to solve various problems in software engineering. Dependency injection is a useful technique for testing, as it allows dependencies to be mocked or stubbed out
. In more general terms, dependency injection is a process of supplying a resource that a given piece of code requires in object-oriented programming. The required resource, often a component of the application itself, is called a dependency. This process helps to decouple objects that are dependent on each other and can be useful in relieving various code modules from the task of instantiating references to dependencies
. The main goal of dependency injection is to make a class independent of its dependencies by decoupling the usage of an object from its creation. This helps to follow SOLID's dependency inversion and single responsibility principles, improving the reusability of code and reducing the frequency of changes to a class. By separating the creation of an object from its usage, dependency injection enables the replacement of a dependency without changing any code and reduces the amount of required boilerplate code, thus improving flexibility
. In summary, dependency injection is a powerful technique that promotes code reusability, flexibility, and testability by decoupling the construction and use of objects, making implicit dependencies explicit, and providing a way to supply required resources to code components
