Apa iku dependency injection lan container IoC ing Spring?

Question

IT Interview Practice · Accepted Answer

**Dependency injection (DI)** tegese sawijining kelas ora nggawe kolaborator-e dhewe — iku ndeklarasi apa sing dibutuhake lan framework sing nyediakake. **Container IoC (Inversion of Control)** iku bagean Spring sing mbangun object (*bean*), ngkabel dependensi-e, lan ngatur siklus uripe. "Inversion of control" = kowe nyerahake kendhali panggawean object menyang container tinimbang nganggo `new`.

## Ndeklarasi lan nyuntik bean

```java
@Service // registers this class as a bean the container manages
public class OrderService {

private final PaymentGateway gateway;

// Constructor injection: the container passes the PaymentGateway bean here.
    // No @Autowired needed when there is a single constructor.
    public OrderService(PaymentGateway gateway) {
        this.gateway = gateway;
    }
}

@Component // any Spring-managed bean; @Service/@Repository are specializations
public class StripeGateway implements PaymentGateway { /* ... */ }
```

Nalika wiwitan, `@ComponentScan` nemokake kelas-kelas iki, container nginstansiasi `StripeGateway`, banjur nyusun `OrderService` kanthi nyuntikake instansi kuwi.

## Luwih becik constructor injection

```java
@Autowired private PaymentGateway gateway; // field injection — avoid
```

Constructor injection ngidini kowe menehi tandha field `final` (ora bisa owah), gawe dependensi cetha, gagal cepet yen ana bean sing ilang, lan ora mbutuhake Spring kanggo unit-test — kowe mung nyeluk `new OrderService(mock)`.

## Kenapa iki penting

DI iku dhasar sing didhasari sakabehe liyane ing Spring. Pewawancara pengin krungu *kenapa* iki mbiyantu: iki misahake kelas saka kolaborator konkret-e, mula kowe bisa ngganti `StripeGateway` karo `PayPalGateway` utawa mock tanpa ndemek `OrderService`. Nyaranake constructor tinimbang field injection nuduhake yen kowe wis ngrasakake lara testing sing disebabake field injection.

Ndeklarasi lan nyuntik bean

Luwih becik constructor injection

Kenapa iki penting

Pitakon sing gegandhengan