44.2 DecimalFormat Patterns

DecimalFormat extends NumberFormat with custom pattern strings for fine-grained control.

44.2.1 Pattern Syntax

0     Digit (shows zero if absent)
#     Digit (omits if absent)
.     Decimal separator
,     Grouping separator
-     Minus sign
E     Exponent separator (scientific notation)
%     Multiply by 100 and show percent
‰     Multiply by 1000 and show per mille

44.2.2 Basic Patterns

import java.text.DecimalFormat;

DecimalFormat df = new DecimalFormat("#,##0.00");
String s1 = df.format(1234.5);    // "1,234.50"
String s2 = df.format(0.5);       // "0.50"

DecimalFormat df2 = new DecimalFormat("#,###.##");
String s3 = df2.format(1234.5);   // "1,234.5"
String s4 = df2.format(0.5);      // "0.5"

44.2.3 Scientific Notation

DecimalFormat sci = new DecimalFormat("0.00E0");
String s = sci.format(12345);    // "1.23E4"

DecimalFormat sci2 = new DecimalFormat("##0.0E0");
String s2 = sci2.format(12345);  // "12.3E3"

44.2.4 Percent and Per Mille

DecimalFormat pct = new DecimalFormat("#,##0.00%");
String s1 = pct.format(0.1234);  // "12.34%"

DecimalFormat pmille = new DecimalFormat("#,##0.0‰");
String s2 = pmille.format(0.1234); // "123.4‰"

44.2.5 Custom Decimal Symbols

import java.text.DecimalFormatSymbols;

DecimalFormatSymbols symbols = new DecimalFormatSymbols(Locale.US);
symbols.setGroupingSeparator('_');
symbols.setDecimalSeparator('·');

DecimalFormat df = new DecimalFormat("#,##0.00", symbols);
String s = df.format(1234.56); // "1_234·56"