Application: gvSIG desktop

As an alternative to a default mask for everyone, you can try to get the default mask for the current locale with the following code:

 String format = "#,###.000";
 NumberFormat f = NumberFormat.getInstance(loc);
 if (f instanceof DecimalFormat) {
     format = ((DecimalFormat) f).toPattern();
 }

Also, it would be nice to apply the user provided pattern to the locale default DecimalFormat, something like:

 DecimalFormat decimalFormat = null;
 NumberFormat f = NumberFormat.getInstance(loc);
 if (f instanceof DecimalFormat) {
     decimalFormat = (DecimalFormat) f;
 } else {
     decimalFormat = new DecimalFormat();
 }
 decimalFormat.apply(userFormatString);

This is because a DecimalFormat not only provides a formatting mask, but also the symbols to use for decimal, grouping and others. So don't think the format "#,###" will use the "," character in the generated String, it will depend on the locale symbols. This is an example taken from the Java tutorial where the same pattern is applied with different locales:

Value: 123456.789
Pattern: ###,###.###

en_US: 123,456.789
de_DE: 123.456,789
fr_FR: 123 456,789

Finally, it would be nice if some kind of preview could be used for the user to see how the provided mask would apply to a sample number.