Book.java

package modern.challenge;

import java.util.Optional;

public class Book {

    public static final String BOOK_STATUS = "UNKNOWN";

    // Avoid
    public String findStatusAvoid() {

        // fetch an Optional prone to be empty
        Optional<String> status = Optional.empty();

        if (status.isPresent()) {
            return status.get();
        } else {
            return BOOK_STATUS;
        }
    }

    // Prefer
    public String findStatusPrefer() {

        // fetch an Optional prone to be empty
        Optional<String> status = Optional.empty(); 

        return status.orElse(BOOK_STATUS);
    }
}