Use Java 8 Optional in existing Java 7 code

Question

I have an assignment in which I need to convert the following pre-Java 8 code to Java 8 code. Below is just one method which is giving me hard time to finish up:

Answer 1

If you really want to convert flow control to Optional, the code keep consistent with yours should be like this(I break the code in 2 lines for printing):

public static Optional> loadMatchingJava8(Region region, 
                                                            String nameStartsWith,
                                                            VehicleLoader loader) {
    if ((nameStartsWith == null) || (region == null) || (loader == null)) {
        throw new IllegalArgumentException("The VehicleLoader and both region and " +
                "nameStartsWith are required when loading VehicleMake matches");
    }


    return Optional.ofNullable(loader.getVehicleMakesByRegion(region.name()))
            .map(makers -> makers.stream()
                    .filter((it) -> it.getName() != null
                            && it.getName().startsWith(nameStartsWith))
                    .collect(Collectors.toList()));
}

NOTE: you can see more about why do not abuse Optional in this question.