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 (); } }

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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…