String.format() to format double in Java

java

formatting

decimal-format

locale-specific-formatting

byAnton Shumikhin·Sep 2, 2024

Use String.format("%.2f", number) to format a double to a String in Java. This rounds the number to two decimal places.

String formatted = String.format("%.2f", 123.456); //Captain, we've rounded off the decimals!

This gives you "123.46", a neat String representation of your double.

Want to include a thousands separator? Use String.format("%1$,.2f", number):

String formatted = String.format("%1$,.2f", 123456.789); //Those commas really weigh a thousand., right?

You get "123,456.79"— with a , as the thousands separator.

Code breakdown and custom separators

Demystifying the format pattern

Let's dissect our pattern "%1$,.2f":

%1$ points to the first argument.
, inserts a thousands separator.
.2 limits output to two decimal places.
f ensures a floating-point representation.

Custom decimal and grouping separators

Encountered a scenario asking for a custom decimal or grouping separator? Time to invoke DecimalFormat and DecimalFormatSymbols:

DecimalFormatSymbols symbols = new DecimalFormatSymbols();
symbols.setDecimalSeparator('.'); //Making a point. 🎯
symbols.setGroupingSeparator(' '); //Space: The final frontier. 🚀
DecimalFormat decimalFormat = new DecimalFormat("#,##0.00", symbols);

String formatted = decimalFormat.format(123456.789); // We've got some separation anxiety here.

Voilà! We're using a space as the grouping separator and a dot for decimals, giving you "123 456.79".

Locale-specific formatting

Your project may demand locale-specific formatting. Trust NumberFormat:

Locale currentLocale = Locale.FRANCE; //Vive la France! 🇫🇷
NumberFormat numberFormat = NumberFormat.getNumberInstance(currentLocale);
String formatted = numberFormat.format(123456.789); //Maintenant, nous parlons français! Now, we're speaking French!

Above, we format following French locale conventions. That's locale handling à la Java!