@Autowired enables automatic dependency injection. Spring automatically injects matching beans by type. It can be used on:

• Constructors
• Setter methods
• Fields
• Method parameters

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository; // Field injection
    
    @Autowired
    public UserService(UserRepository userRepository) { // Constructor injection
        this.userRepository = userRepository;
    }
}