DecimalFormat country problems

Question

I have the following lines of code in my app to round my percentage to a reasonable length;

double percentage = ((double)correct*100)/((double)total);
DecimalFormat df = new DecimalFormat("#.0");
percentage = Double.valueOf(df.format(percentage));

This code works well 99% of the time, but when people from some European countries use this is crashes, giving me a NumberFormatException.

This is because when the DecimalFormat rounds the double 56.7777, it rounds it to 56,8(with a comma), which means that when I try to convert it to a double, a NumberFormatException is thrown.

Is there any way to set a locality to DecimalFormat so that I know it will always round to 56.8 and not 56,8?

Answer 1

The problem is that you specify a custom format with your DecimalFormat and then parse the resulting String using the format specified by the default Locale.

You have several options to solve the problem:

1. Use the same DecimalFormat object to both format and parse the number.

2. Use a different rounding algorithm. For example:

   double roundToHundredths(double d) {
       return (int)(d * 100) / 100.0;
   }
   

3. Store the number as an int in "hundredths". Do your calculations with this int and display it as a decimal.

4. Use BigDecimal for greater precision.

Note that using a "rounded" number in any further calculations is still tricky since floating point numbers are imprecise. This means that the "rounded" result is not necessarily exact.