What's the difference IoC and Dependency Injection?

Inversion of Control (IoC) and Dependency Injection (DI) are related concepts, but they are not the same thing.

Question. Is Dependency Injection the same as Inversion of Control?

Answer: No. IoC is a principle, while DI is one way to implement that principle.

1. What is Inversion of Control (IoC)?

Normally, an object creates and manages its own dependencies.

Without IoC

public class OrderService {



    private PaymentService paymentService;



    public OrderService() {

        paymentService = new PaymentService();

    }

    public void placeOrder() {

        paymentService.processPayment();

    }

}

What happens here?

paymentService = new PaymentService();

OrderService is responsible for:

• Creating the dependency


• Managing the dependency


• Using the dependency

The control is inside OrderService

Problem

Suppose tomorrow you want:

CreditCardPaymentService instead of PaymentService

You must modify: OrderService

This creates tight coupling.

IoC Concept

With IoC: Object creation responsibility is moved outside the class.

Instead of: OrderService creates PaymentService

we do:

• Someone else creates PaymentService


• Someone else gives it to OrderService

Control is inverted.

That's why it is called: Inversion of Control

Real-Life Example

Imagine a restaurant.

Without IoC - You go into the kitchen and cook your own food.

Customer --> Kitchen --> Cooks food

Customer controls everything.

With IoC - You sit at the table.

Waiter brings food.

Customer <-- Waiter <-- Kitchen

Customer doesn't control food preparation.

Control has been inverted.