What is Dependency Injection? - Intro to dependency injection with example.

Dependency injection is a popular term in the programming world. It might be easy to get confused about what it means. It's actually a simple term and you probably already use it. Popular dependency injection libraries exist such as Dagger, which is popular in Android development.

Dependency Injection is useful for separation of concerns, for making refactoring easier and also to make classes easy to test.

According to Wikipedia: In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies. In the typical "using" relationship the receiving object is called a client and the passed (that is, "injected") object is called a service.

The common types of dependency injections are constructor injection, setter injection and injection by reflection.