Why Dependency injection is loosely coupled?

Question

Interviewer asked if either parameter or method newly added in interface then the whole method or parameter handled in controller. Then how we told Dependency injection as loosely coupled....

Sachin Singh · Answer

No, when you will change the interface (add/remove methods) then only the related classes which implements the interface will be impacted not the controller. example public Interface IEmployee { public IEnumerable GetAll(); } public Class Employee:IEmployee { public IEnumerable GetAll() { // implementation } } public Class HomeController : Controller { private IEmployee _emps; public HomeController(IEmployee emps) { _emps=emps; } public List GetEmployeesData() { return _emps.GetAll(); } } Now if you will do anything to interface then how will it impact controller? It won't. Meaning UI layer is decoupled from Business Layer, so is called Loosely coupled. Changing In BLL Interfaces will just impact BLL classes and the other Layers.

Rajanikant Hawaldar · Answer

Interfaces allow multiple concrete classes to implement them, not just one. The dependency a class has when implementing an interface is only to the 'contract' which interface provides. The implementing class is coupled to the contract and not to the functionality. This allows two or more classes implementing the same interface to have different functionality defined to the implemented contract. This way classes are not dependent on each other, and thus are loosely coupled.

Raja · Answer

Actually if we include new method in interface.then we want to write a definition in controller also for that method right ? that's what they are asking is this tightly coupling or loosely coupling?

Rajanikant Hawaldar · Answer

can you try to be clearer