public class CoffeeCard
{
    #region Private Fields

    private decimal _balance;

    #endregion

    #region Constructors

    public CoffeeCard(decimal initialBalance = 0)
    {
        _balance = initialBalance;
    }

    #endregion

    #region Public Methods

    public void ChargeCard(decimal value)
    {
        ChargeCardInternal(value);
    }

    public decimal GetBalance()
    {
        return _balance;
    }

    public void AddBalance(decimal value)
    {
        AddBalanceInternal(value);
    }

    #endregion

    #region Private Methods

    private void AddBalanceInternal(decimal value)
    {
        _balance += value;

        //update in database
    }

    private void ChargeCardInternal(decimal value)
    {
        _balance -= value;

        // update in database
    }
    #endregion
}