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JavaBeginner#exceptions
JavaIntermediate#design-patterns#spring
What is dependency injection?
Design pattern where dependencies are provided to a class rather than created inside it. Frameworks like Spring use constructor, setter, or field injection. Improves testability and decoupling.
Example
@Service
class OrderService {
private final PaymentService paymentService;
OrderService(PaymentService paymentService) { this.paymentService = paymentService; } // constructor injection
}