User.java

    public void changeEmail(String newEmail)
    {
        Object[] data = Database.getUserById(userId);
        email = (String)data[1];
        userType = (UserType)data[2];

        if (Objects.equals(email, newEmail))
            return;

        Object[] companyData = Database.getCompany(userId);
        int companyId = (int)companyData[0];
        String companyDomainName = (String)companyData[1];
        int numberOfEmployees = (int)companyData[2];

        String emailDomain = newEmail.split("@")[1];
        boolean isEmailCorporate = Objects.equals(emailDomain, companyDomainName);
        UserType newType = isEmailCorporate
                ? UserType.Employee
                : UserType.Customer;

        if (userType != newType)
        {
            int delta = newType == UserType.Employee ? 1 : -1;
            int newNumber = numberOfEmployees + delta;
            Database.saveCompany(companyId, companyDomainName, newNumber);
        }

        email = newEmail;
        userType = newType;

        Database.saveUser(this);
        MessageBus.sendEmailChangedMessage(this.userId, newEmail);
    }