In the next workbook, one of your instructions is to copy this method:

 protected double round(double amount) {
     DecimalFormat formatter = new DecimalFormat("#.##");
     return Double.parseDouble(formatter.format(amount));
 }

If you live in Europe or Asia, your Locale probably uses , for decimals. You will need to set your DecimalFormat's Locale to English.

 protected double round(double amount) {
     DecimalFormat formatter = new DecimalFormat("#.##", new DecimalFormatSymbols(Locale.ENGLISH));
     return Double.parseDouble(formatter.format(amount));
 }