What is the difference between the @Nullable/@NonNull annotations (from libraries like JetBrains or JSR-305) and Java's built-in Optional type for expressing nullability?

@Nullable/@NonNull are purely advisory annotations (not enforced by the JVM at runtime by default) primarily consumed by static analysis tools and IDEs to warn about potential null dereferences at compile/edit time, with zero runtime cost since they carry no actual null-check logic themselves -- Optional, by contrast, is an actual runtime container type that forces callers to explicitly handle the possibly-absent case through its API (isPresent(), orElse(), map()), providing genuine runtime behavior rather than just static hinting, making the two complementary rather than interchangeable tools.

public class UserService {
    @Nullable
    public User findById(String id) {  // IDE/static analysis warns callers to null-check
        return repository.get(id);
    }

    public Optional<User> findByIdSafely(String id) {  // forces explicit handling at compile time
        return Optional.ofNullable(repository.get(id));
    }
}