Locale-Sensitive Java Constructor

java.lang.Double

Double(double value)
Double(String s)

Internationalization (I18n) Method Overview

The Double class wraps a double primitive type in an object. To construct a Double object, you pass in either a double value or a floating point string.

I18n Issues

The problem with calling the Double constructor with a string parameter is that it is not locale aware. For example, if a string is set to "2,3" where a comma is used as the decimal separator, the Double constructor will not create the correct Double object. This is because it is designed to assume that a period will be used as the decimal separator.

Suggested Replacement

To ensure that locale is applied when converting between double values and double strings, use the DecimalFormat class.

For example, instead of:

Double myDouble = new Double(myDecimalString);


Use:

Double myDouble = null;

//Retrieve the runtime user's locale
Locale locale = getUserLocale();

//Now call the NumberFormat factory method
//and pass the locale object
NumberFormat f = NumberFormat.getInstance(locale);

//If it is in fact an instance of DecimalFormat,
//cast it as such and use it as needed
if (f instanceof DecimalFormat) {
    try {
        myDouble = new Double(((DecimalFormat) f).parse(myDecimalString).doubleValue());
    } catch (ParseException e) {}
}


Please see Number Formatting for more information.