Dependency Injection is a software design pattern that is used to manage the dependencies between objects in a program. The main idea behind dependency injection is to decouple the objects in a system so that they are not tightly bound to one another. This makes the objects more reusable and easier to maintain, as changes to one object will not affect the others.
In dependency injection, the dependencies between objects are injected into the dependent object by an external source, usually a framework or container. This external source is responsible for creating and managing the objects, and for providing the dependencies to the dependent object when it is constructed or when it needs them.
There are three main types of dependency injection: constructor injection, setter injection, and interface injection. Constructor injection involves providing the dependencies to an object through its constructor, while setter injection involves providing the dependencies through setter methods. Interface injection involves defining an interface that specifies the dependencies that an object requires, and then providing those dependencies through an implementing class.
One of the benefits of dependency injection is that it makes the objects in a system more testable, as you can easily replace the dependencies with mock objects during testing. It also makes it easier to change the implementation of a component, as the dependencies are separated from the component itself.
In summary, Dependency Injection is a design pattern that is used to manage the dependencies between objects in a program. It allows the dependencies to be injected into the dependent object by an external source, making the objects more reusable and easier to maintain, and helping to improve the testability and adaptability of the system.