wkdalsgh192

class Day {
    public final static Day MONDAY = new Day();
    public final static Day TUESDAY = new Day();
    public final static Day WEDNESDAY = new Day();
}

class Month {
    public final static Month JANUARY = new Month();
    public final static Month FEBRUARY = new Month();
    public final static Month MARCH = new Month();

wkdalsgh192

interface Day {
    int MONDAY = 1;
    int TUESDAY = 2;
    int WEDNESDAY = 3;
    int THURSDAY = 4;
    int FRIDAY = 5;
    int SATURDAY = 6;
    int SUNDAY = 7;
}

wkdalsgh192

public class EnumExample2 {
    
    private final static int MONDAY = 1;
    private final static int TUESDAY = 2;
    private final static int WEDNESDAY = 3;
    private final static int THURSDAY = 4;
    private final static int FRIDAY = 5;
    private final static int SATURDAY = 6;
    private final static int SUNDAY = 7;

wkdalsgh192

public class EnumExample1 {
    public static void main(String[] args) {
        /*
        * Monday == 1
        * Tuesday == 2
        * Wednesday == 3
        * Thursday == 4
        * ...
        * Sunday == 7
        * */

wkdalsgh192

public class PayGroups {
  private List<Pay> pays;
  
  public PayGroups(List<Pay> pays) {
    this.pays = pays;
  }
  
  public Long getPayPalSum() return getTotalSum(pay -> PayType.isPayPal(pay.getPayType()));
  
  public Long getVisaSum() return getTatalSum(pay -> PayType.isVisa(pay.getPayType()));

wkdalsgh192

public void managingStateAndAction() {
  List<Pay> pays = Arrays.asList(
                    new Pay(PAYPAL, 1000),
                    new Pay(VISA, 2000),
                    new Pay(MASTER_CARD, 3000),
                    new Pay(UNION_CARD, 5000)
                  );
  
  Long totalSum = pays.stream().filter(pay -> pay.getPayType().equals(VISA)).mapToLong(Pay::getAmount).sum();

wkdalsgh192

public class Orders {
  private final List<Order> orders;
  
  public Orders(List<Order> orders) {
    this.orders = orders;
  }
  
  public long getAmountSum() {
    return orders.stream()
                  .mapToLong(Order::getAmount)

wkdalsgh192

public class LottoTicket {
  private static final int LOTTO_NUMBERS_SIZE = 6;
  
  public LottoTicket(List<Long> lottoNumbers) {
    List<Long> lottoNumbers = createNonDuplicateNumbers();
    validateSize(lottoNumbers);
    validateDuplicate(lottoNumbers);
  }
  
  public void validateSize(List<Long> lottoNumbers) {

wkdalsgh192

public class LottoService {
  private static final int LOTTO_NUMBERS_SIZE = 6;
  
  public void createLottoNumber() {
    List<Long> lottoNumbers = createNonDuplicateNumbers();
    validateSize(lottoNumbers);
    validateDuplicate(lottoNumbers);
  }
  
  public void validateSize(List<Long> lottoNumbers) {

wkdalsgh192

public class LottoService {
  private static final int LOTTO_NUMBERS_SIZE = 6;
  
  public void createLottoNumber() {
    List<Long> lottoNumbers = createNonDuplicateNumbers();
    validateSize(lottoNumbers);
    validateDuplicate(lottoNumbers);
  }
  
  public void validateSize(List<Long> lottoNumbers) {