@Entity
public abstract class Payment implements Serializable {

    @Id private String id;

    public Payment() {}

    public Payment(String id) {
        this.id = id;
    }
}

@Entity
public class CreditcardPayment extends Payment implements Serializable {

    private String ccnumber;

    private String company;

    @OneToMany(fetch=FetchType.EAGER, cascade=CascadeType.PERSIST)
    public List<CreditcardPrice> prices = new ArrayList<>();

    protected CreditcardPayment() {}

    public CreditcardPayment(String id, String ccno, String company) {
        super(id);
        this.ccnumber = ccno;
        this.company = company;
    }
}

@Entity
public class MobilePayment extends Payment implements Serializable {

   private String mobileAddress;

   @OneToMany(fetch = FetchType.EAGER, cascade=CascadeType.PERSIST)
   public List<MobilePrice> prices = new ArrayList<>();

   
   protected MobilePayment() {}

   public MobilePayment(String id, String mobileAdr) {
       super(id);
       this.mobileAddress = mobileAdr;
   }
}

@Entity
public abstract class BasePrice implements Serializable {

       @Id private String id;

   protected int amount;
   
   protected BasePrice() {}   

   protected BasePrice(String id, int amount) {
       this.id = id;
       this.amount = amount;
   }   
}

@Entity
public class CreditcardPrice extends BasePrice implements Serializable {

   private String company;
   
   protected CreditcardPrice() {}   

   public CreditcardPrice(String id, int amount, String company) {
       super(id, amount);
       this.company = company;
   }   
}

@Entity
public class MobilePrice extends BasePrice implements Serializable {

   private String operator;
   
   protected MobilePrice() {}   

   public MobilePrice(String id, int amount, String operator) {
       super(id, amount);
       this.operator = operator;
   }   
}

public class JpaMain {

    private EntityManagerFactory emf;
   
    private EntityManager em;

    private EntityTransaction tx;
   
   
    public JpaMain() {
        emf = Persistence.createEntityManagerFactory("JpaTest");
        em = emf.createEntityManager();
        tx = em.getTransaction();
    }
   
    public void close() {
        if (em != null) {
            em.close();
        }
        emf.close();
    }
   
    private void create() {
        tx.begin();

        CreditcardPayment cc_pm;
        CreditcardPrice cc_pr;
        MobilePrice m_pr;
        MobilePayment m_pm;
       
        cc_pm = new CreditcardPayment("CC1", "54893423", "Machocard");
        cc_pr = new CreditcardPrice("CC$1", 12, "Wiesacart");
        cc_pm.prices.add(cc_pr);
        cc_pr = new CreditcardPrice("CC$2", 12, "Döners Club");
        cc_pm.prices.add(cc_pr);
        em.persist(cc_pm);
       
        m_pm = new MobilePayment("MP2", "+49171723737");
        m_pr = new MobilePrice("MP$2", 81, "Vodafone");
        m_pm.prices.add(m_pr);
        em.persist(m_pm);
       
        tx.commit();
    }

    private void query() {
        em.clear();     // clear cache
       
        Payment pm = em.find(Payment.class, "CC1"); // may result in WrongClassException
        System.out.println(pm);
       
        pm = em.find(Payment.class, "MP2");  // may result in WrongClassException
        System.out.println(pm);
    }
   
    public static void main(String[] args) {
        JpaMain main = new JpaMain();
        try {
            main.create();
            main.query();
        }
        finally {
            main.close();
        }
    }
}