How to change the decimal separator of DecimalFormat from comma to dot/point?

java

number-formatting

decimal-separator

locale-conventions

byAnton Shumikhin·Feb 15, 2025

Switch the decimal separator from comma to dot in DecimalFormat by creating DecimalFormatSymbols and setting .setDecimalSeparator('.'). Here's the core idea distilled into Java:

DecimalFormatSymbols symbols = new DecimalFormatSymbols();
symbols.setDecimalSeparator('.');
DecimalFormat df = new DecimalFormat("0.00", symbols);

String formatted = df.format(1234.56); // Outputs "1234.56", no more comma drama

Configure formatting per Locale

DecimalFormatSymbols allows for manual configuration of decimal separators. But you can also use Locale conventions for automatic number formatting. For instance, in the UK, where the decimal separator is traditionally a dot:

NumberFormat nf = NumberFormat.getInstance(Locale.UK);
String formatted = nf.format(1234.56); // Outputs "1,234.56", cheers mate!

Beware of the grouping separator (used for thousands) as it might change with the Locale (e.g., becomes comma in many European countries).

Un-group those separators

To get numbers appearing slick and simple, you may want to remove the grouping separators (like commas in "1,000"):

DecimalFormat df = new DecimalFormat("0.00");
DecimalFormatSymbols symbols = df.getDecimalFormatSymbols();

symbols.setDecimalSeparator('.');
symbols.setGroupingSeparator('\u0000');  // The null character jettisons the grouping

df.setDecimalFormatSymbols(symbols);
df.setGroupingUsed(false);

String formatted = df.format(1234.56); // Outputs "1234.56", as clean as a whistle

BigDecimal for the win in precision

When it comes to high precision operations such as financial calculations, BigDecimal takes the gold:

BigDecimal number = new BigDecimal("1234.56");
DecimalFormat df = new DecimalFormat("0.00");
df.setRoundingMode(RoundingMode.HALF_UP); // To tackle any sneaky rounding errors

String formatted = df.format(number); // Outputs "1234.56"

Do note, the BigDecimal format may not abide by the Locale settings. You'll need to manually set the format if locale-specific formatting becomes a necessity.

Accommodating diverse formats

By using a custom format, we can ensure unique string representations, minimizing the chances of those pesky human errors!

DecimalFormat customFormat = new DecimalFormat("0.00");
customFormat.setDecimalFormatSymbols(new DecimalFormatSymbols(Locale.US));

String precise = customFormat.format(1234.5678); // "1234.57", nice and clean!

This way we are all set with precise and locale-aware formats, all ready to go for international applications or data exchange!

Serialization and debugging implications

Changing the number format can have significant implications for serialization and debugging. Make sure that the serialized data maintains its format across systems! And remember, debuggers might not show numbers as you expected them to, making error hunting a little tricky!

Reviewing and testing: the final frontiers

Nothing beats thorough review and testing! Make sure to read through the DecimalFormat and NumberFormat documentation, and test your number formatting with various inputs:

// Test scenario - What happens when the number turns negative?
DecimalFormat df = new DecimalFormat("0.00", new DecimalFormatSymbols(Locale.UK));
String formatted = df.format(-1234.56); // Outputs "-1234.56"