Hibernate - SortedSet Mapping

import java.util.SortedSet;

public class Freelancer {
    // data members
    private int freelancerId;
    private String freelancerName;
    private int freelancerAge;
    private int pricePerHour;
    // As one freelancer works for multiple companies, let
    // us have that as SortedSet here for companies
    private SortedSet companies;

    public int getFreelancerId() { return freelancerId; }
    public void setFreelancerId(int freelancerId)
    {
        this.freelancerId = freelancerId;
    }
    public String getFreelancerName()
    {
        return freelancerName;
    }
    public void setFreelancerName(String freelancerName)
    {
        this.freelancerName = freelancerName;
    }
    public int getFreelancerAge() { return freelancerAge; }
    public void setFreelancerAge(int freelancerAge)
    {
        this.freelancerAge = freelancerAge;
    }
    public int getPricePerHour() { return pricePerHour; }
    public void setPricePerHour(int pricePerHour)
    {
        this.pricePerHour = pricePerHour;
    }
    public SortedSet getCompanies() { return companies; }
    public void setCompanies(SortedSet companies)
    {
        this.companies = companies;
    }
    // no argument constructor
    public Freelancer() {}
    // argument constructor
    public Freelancer(String freelancerName,
                      int freelancerAge, int pricePerHour)
    {
        this.freelancerName = freelancerName;
        this.freelancerAge = freelancerAge;
        this.pricePerHour = pricePerHour;
    }
}

public class Company implements Comparable<Company> {
    private int companyId;
    private String companyName;
    public int getCompanyId() { return companyId; }

    public void setCompanyId(int companyId)
    {
        this.companyId = companyId;
    }

    public String getCompanyName() { return companyName; }

    public void setCompanyName(String companyName)
    {
        this.companyName = companyName;
    }

    public Company(String companyName)
    {
        this.companyName = companyName;
    }

    public Company() {}

    @Override
    // This method has to be implemented as we are following
    // SortedSet
    public int compareTo(Company company)
    {
        if (company == null) {
            return -1;
        }
        Comparable company1 = this.getCompanyName();
        Comparable company2 = company.getCompanyName();
        if (company1 == null) {
            return 1;
        }
        else if (company2 == null) {
            return -1;
        }
        else {
            return company1.compareTo(company2);
        }
    }
}

import com.gfg.sortedsetmapping.pojo.Company;
import com.gfg.sortedsetmapping.pojo.Freelancer;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class SortedSetMappingPatternOfStoringData {
    private static SessionFactory factory;

    public static void main(String[] args)
    {

        try {
            factory = new Configuration()
                          .configure()
                          .buildSessionFactory();
        }
        catch (Throwable ex) {
            System.err.println(
                "Failed to create sessionFactory object."
                + ex);
            throw new ExceptionInInitializerError(ex);
        }

        // As one freelancer works for multiple companies,
        // via TreeSet we can represent that
        TreeSet companySet1 = new TreeSet();
        companySet1.add(new Company("Company A"));
        companySet1.add(new Company("Company B"));

        TreeSet companySet2 = new TreeSet();
        companySet2.add(new Company("Company A"));
        companySet2.add(new Company("Company C"));
        companySet2.add(new Company("Company E"));

        // Create the Freelancer object.
        Freelancer freelancer1
            = new Freelancer("Freelancer A", 20, 1000);
        freelancer1.setCompanies(
            companySet1); // Freelancer A associated to 2
        // companies

        Freelancer freelancer2
            = new Freelancer("Freelancer B", 20, 2000);
        freelancer2.setCompanies(
            companySet2); // Freelancer B associated to 2
        // companies

        SortedSetMappingPatternOfStoringData
            sortedMapMappingPatternOfStoringData
            = new SortedSetMappingPatternOfStoringData();
        // insert freelancer object.
        Integer freelancerId1
            = sortedMapMappingPatternOfStoringData
                  .addFreelancer(freelancer1);

        Integer freelancerId2
            = sortedMapMappingPatternOfStoringData
                  .addFreelancer(freelancer2);

        // show all Language and book details object.
        sortedMapMappingPatternOfStoringData
            .listFreelancerAndCompanyDetails();
    }

    public Integer addFreelancer(Freelancer freelancer)
    {
        Session session = factory.openSession();
        Transaction tx = null;
        Integer languageId = null;
        try {
            tx = session.beginTransaction();
            languageId = (Integer)session.save(freelancer);
            tx.commit();
        }
        catch (HibernateException e) {
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        }
        finally {
            session.close();
        }
        return languageId;
    }

    // Method to list all the freelancers and company detail
    public void listFreelancerAndCompanyDetails()
    {
        Session session = factory.openSession();
        Transaction tx = null;

        try {
            tx = session.beginTransaction();
            List<Freelancer> freelancers
                = session.createQuery("FROM Freelancer")
                      .list();
            for (Freelancer freelancer : freelancers) {
                System.out.println(
                    "Freelancer Name: "
                    + freelancer.getFreelancerName());
                System.out.println(
                    "Freelancer Age: "
                    + freelancer.getFreelancerAge());
                System.out.println(
                    "Price Per Hour: "
                    + freelancer.getPricePerHour());
                Set<Company> companies
                    = freelancer.getCompanies();
                for (Company company : companies) {
                    System.out.println(
                        "Company Name:"
                        + company.getCompanyName());
                }
            }
            tx.commit();
        }
        catch (HibernateException e) {
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        }
        finally {
            session.close();
        }
    }
}