• reference

Dependency in here means there is relation between classes. So, if there is dependency between classes, change of a certain class affects other class.

Injection is to create an object outside the classes and inject the object inside the class.

And Dependency Injection is used for alleviating dependency between classes.

Fig 1. Abstraction about dependency injection

In Fig 1, ‘monitor’ instance which is injected to other classes is stored in another class. we call this class ‘Container’. And now, control handling are no longer in the ‘Computer’ classes, but in the ‘Container’. And we call this situation IOC(Inversion of Control), also ‘Container’ is called ‘IOC Container’.

Pros

• Lossely Coupled & Highly Cohesive between classes.
• Increased Testability & Maintainability.
• Flexibility of run time configuration.

Cons

• Increased code complexity.
• Can complicate debugging during the learning curve
• Code flow becomes not trivial.