public class BankAccount
{
    private class Money
    {
        private long dollars;
        private int cents;

        public Money(String stringAmount)
        {
            abortOnNull(stringAmount);
            int length = stringAmount.length( );
            dollars = Long.parseLong(
                         stringAmount.substring(0, length - 3));
            cents = Integer.parseInt(
                         stringAmount.substring(length - 2, length));
        }

        public String getAmount( )
        {
            if (cents > 9)
               return (dollars + "." + cents);
            else
               return (dollars + ".0" + cents);
        }

        public void addIn(Money secondAmount)
        {
            abortOnNull(secondAmount);
            int newCents = (cents + secondAmount.cents)%100;
            long carry = (cents + secondAmount.cents)/100;
            cents = newCents;
            dollars = dollars + secondAmount.dollars + carry;
        }

       private void abortOnNull(Object o)
       {
           if (o == null)
           {
                System.out.println("Unexpected null argument.");
                System.exit(0);
           }
        }
    }

    private Money balance;

    public BankAccount( )
    {
        balance = new Money("0.00");
    }

    public String getBalance( )
    {
        return balance.getAmount( );
    }

    public void makeDeposit(String depositAmount)
    {
        balance.addIn(new Money(depositAmount));
    }

    public void closeAccount( )
    {
        balance.dollars = 0;
        balance.cents = 0;
    }
}