[Solved] Why does the following code cause a NullPointerException at runtime?@Component public class OrderService { private PaymentService paymentService; public void process() { paymentService.pay(); } } | Spring Boot

Spring Boot - Inversion of Control and Dependency Injection

Why does the following code cause a NullPointerException at runtime?

@Component
public class OrderService {
  private PaymentService paymentService;

  public void process() {
    paymentService.pay();
  }
}

ApaymentService is not injected because @Autowired is missing

BPaymentService class is not annotated with @Component

Cprocess() method is private

DOrderService is missing a constructor

Step-by-Step Solution

Solution:

Step 1: Check injection of paymentService
Without @Autowired, Spring does not inject PaymentService, so paymentService remains null.
Step 2: Understand NullPointerException cause
Calling pay() on null causes NullPointerException.
Final Answer:
paymentService is not injected because @Autowired is missing -> Option A
Quick Check:
Missing @Autowired = null dependency = NullPointerException [OK]

Quick Trick: Always add @Autowired to inject dependencies [OK]

Common Mistakes:

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Why does the following code cause a NullPointerException at runtime?