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.

Answer 2

Use the same number format to parse data

percentage = df.parse(df.format(percentage), new ParsePosition(0))

Other solution is to set your own format symbols

DecimalFormat df = new DecimalFormat('#.0', new DecimalFormatSymbols())

I recommend first solution. I tested it on locale that uses comma as decimal separator.

Answer 3

    NumberFormat numberFormat = NumberFormat.getNumberInstance(context.getResources().getConfiguration().locale); // Locale.getDefaultLocale()
    DecimalFormat  decimalFormat = (DecimalFormat)numberFormat;
    char separator =decimalFormat.getDecimalFormatSymbols().getDecimalSeparator();
    decimalFormat.applyPattern("#".concat(Character.toString(separator)).concat("0"));"

You need to get the decimal separator based on the Locale

Answer 4

You can set the currency for a test value, then format and find whether there is a comma or . and handle appropriately if ,

DecimalFormat test = new DecimalFormat("0.00"); test.setCurrency(c);

String testsample = test.format(1.23); char ch = sample.indexOf(".") > 0 ? "." : ",";

Answer 5

convert the decimal to a string and apply this to it

str = str.replaceAll(",","."); // or "\\.", it doesn't matter...

it will turn all , to .