java.text
Class DecimalFormat

java.lang.Object
  |
  +--java.text.Format
        |
        +--java.text.NumberFormat
              |
              +--java.text.DecimalFormat

All Implemented Interfaces:

Cloneable, Serializable

public class DecimalFormat

extends NumberFormat

DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers. It has a variety of features designed to make it possible to parse and format numbers in any locale, including support for Western, Arabic, and Indic digits. It also supports different kinds of numbers, including integers (123), fixed-point numbers (123.4), scientific notation (1.23E4), percentages (12%), and currency amounts ($123). All of these can be localized.

To obtain a NumberFormat for a specific locale, including the default locale, call one of NumberFormat's factory methods, such as getInstance(). In general, do not call the DecimalFormat constructors directly, since the NumberFormat factory methods may return subclasses other than DecimalFormat. If you need to customize the format object, do something like this:

 NumberFormat f = NumberFormat.getInstance(loc);
 if (f instanceof DecimalFormat) {
     ((DecimalFormat) f).setDecimalSeparatorAlwaysShown(true);
 }
 

A DecimalFormat comprises a pattern and a set of symbols. The pattern may be set directly using applyPattern(), or indirectly using the API methods. The symbols are stored in a DecimalFormatSymbols object. When using the NumberFormat factory methods, the pattern and symbols are read from localized ResourceBundles.

Patterns

DecimalFormat patterns have the following syntax:

 Pattern:
         PositivePattern
         PositivePattern ; NegativePattern
 PositivePattern:
         Prefixopt Number Suffixopt
 NegativePattern:
         Prefixopt Number Suffixopt
 Prefix:
         any Unicode characters except \uFFFE, \uFFFF, and special characters
 Suffix:
         any Unicode characters except \uFFFE, \uFFFF, and special characters
 Number:
         Integer Exponentopt
         Integer . Fraction Exponentopt
 Integer:
         MinimumInteger
         #
         # Integer
         # , Integer
 MinimumInteger:
         0
         0 MinimumInteger
         0 , MinimumInteger
 Fraction:
         MinimumFractionopt OptionalFractionopt
 MinimumFraction:
         0 MinimumFractionopt
 OptionalFraction:
         # OptionalFractionopt
 Exponent:
         E MinimumExponent
 MinimumExponent:
         0 MinimumExponentopt
 

A DecimalFormat pattern contains a positive and negative subpattern, for example, "#,##0.00;(#,##0.00)". Each subpattern has a prefix, numeric part, and suffix. The negative subpattern is optional; if absent, then the positive subpattern prefixed with the localized minus sign (code>'-' in most locales) is used as the negative subpattern. That is, "0.00" alone is equivalent to "0.00;-0.00". If there is an explicit negative subpattern, it serves only to specify the negative prefix and suffix; the number of digits, minimal digits, and other characteristics are all the same as the positive pattern. That means that "#,##0.0#;(#)" produces precisely the same behavior as "#,##0.0#;(#,##0.0#)".

The prefixes, suffixes, and various symbols used for infinity, digits, thousands separators, decimal separators, etc. may be set to arbitrary values, and they will appear properly during formatting. However, care must be taken that the symbols and strings do not conflict, or parsing will be unreliable. For example, either the positive and negative prefixes or the suffixes must be distinct for DecimalFormat.parse() to be able to distinguish positive from negative values. (If they are identical, then DecimalFormat will behave as if no negative subpattern was specified.) Another example is that the decimal separator and thousands separator should be distinct characters, or parsing will be impossible.

The grouping separator is commonly used for thousands, but in some countries it separates ten-thousands. The grouping size is a constant number of digits between the grouping characters, such as 3 for 100,000,000 or 4 for 1,0000,0000. If you supply a pattern with multiple grouping characters, the interval between the last one and the end of the integer is the one that is used. So "#,##,###,####" == "######,####" == "##,####,####".

Special Pattern Characters

Many characters in a pattern are taken literally; they are matched during parsing and output unchanged during formatting. Special characters, on the other hand, stand for other characters, strings, or classes of characters. They must be quoted, unless noted otherwise, if they are to appear in the prefix or suffix as literals.

The characters listed here are used in non-localized patterns. Localized patterns use the corresponding characters taken from this formatter's DecimalFormatSymbols object instead, and these characters lose their special status. Two exceptions are the currency sign and quote, which are not localized.

Symbol	Location	Localized?	Meaning
0	Number	Yes	Digit
#	Number	Yes	Digit, zero shows as absent
.	Number	Yes	Decimal separator or monetary decimal separator
-	Number	Yes	Minus sign
,	Number	Yes	Grouping separator
E	Number	Yes	Separates mantissa and exponent in scientific notation. Need not be quoted in prefix or suffix.
;	Subpattern boundary	Yes	Separates positive and negative subpatterns
%	Prefix or suffix	Yes	Multiply by 100 and show as percentage
\u2030	Prefix or suffix	Yes	Multiply by 1000 and show as per mille
¤ (\u00A4)	Prefix or suffix	No	Currency sign, replaced by currency symbol. If doubled, replaced by international currency symbol. If present in a pattern, the monetary decimal separator is used instead of the decimal separator.
'	Prefix or suffix	No	Used to quote special characters in a prefix or suffix, for example, "'#'#" formats 123 to "#123". To create a single quote itself, use two in a row: "# o''clock".

Scientific Notation

Numbers in scientific notation are expressed as the product of a mantissa and a power of ten, for example, 1234 can be expressed as 1.234 x 10^3. The mantissa is often in the range 1.0 <= x < 10.0, but it need not be. DecimalFormat can be instructed to format and parse scientific notation only via a pattern; there is currently no factory method that creates a scientific notation format. In a pattern, the exponent character immediately followed by one or more digit characters indicates scientific notation. Example: "0.###E0" formats the number 1234 as "1.234E3".

• The number of digit characters after the exponent character gives the minimum exponent digit count. There is no maximum. Negative exponents are formatted using the localized minus sign, not the prefix and suffix from the pattern. This allows patterns such as "0.###E0 m/s".
• The minimum and maximum number of integer digits are interpreted together:
  • If the maximum number of integer digits is greater than their minimum number and greater than 1, it forces the exponent to be a multiple of the maximum number of integer digits, and the minimum number of integer digits to be interpreted as 1. The most common use of this is to generate engineering notation, in which the exponent is a multiple of three, e.g., "##0.#####E0". Using this pattern, the number 12345 formats to "12.345E3", and 123456 formats to "123.456E3".
  • Otherwise, the minimum number of integer digits is achieved by adjusting the exponent. Example: 0.00123 formatted with "00.###E0" yields "12.3E-4".
• The number of significant digits in the mantissa is the sum of the minimum integer and maximum fraction digits, and is unaffected by the maximum integer digits. For example, 12345 formatted with "##0.##E0" is "12.3E3". To show all digits, set the significant digits count to zero. The number of significant digits does not affect parsing.
• Exponential patterns may not contain grouping separators.

Rounding

DecimalFormat uses half-even rounding (see ROUND_HALF_EVEN) for formatting.

Digits

For formatting, DecimalFormat uses the ten consecutive characters starting with the localized zero digit defined in the DecimalFormatSymbols object as digits. For parsing, these digits as well as all Unicode decimal digits, as defined by Character.digit, are recognized.

Special Values

NaN is formatted as a single character, typically \uFFFD. This character is determined by the DecimalFormatSymbols object. This is the only value for which the prefixes and suffixes are not used.

Infinity is formatted as a single character, typically \u221E, with the positive or negative prefixes and suffixes applied. The infinity character is determined by the DecimalFormatSymbols object.

Negative zero ("-0") parses to Double(-0.0), unless isParseIntegerOnly() is true, in which case it parses to Long(0).

Synchronization

Decimal formats are generally not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.

Example

 // Print out a number using the localized number, integer, currency,
 // and percent format for each locale
 Locale[] locales = NumberFormat.getAvailableLocales();
 double myNumber = -1234.56;
 NumberFormat form;
 for (int j=0; j<4; ++j) {
     System.out.println("FORMAT");
     for (int i = 0; i < locales.length; ++i) {
         if (locales[i].getCountry().length() == 0) {
            continue; // Skip language-only locales
         }
         System.out.print(locales[i].getDisplayName());
         switch (j) {
         case 0:
             form = NumberFormat.getInstance(locales[i]); break;
         case 1:
             form = NumberFormat.getIntegerInstance(locales[i]); break;
         case 2:
             form = NumberFormat.getCurrencyInstance(locales[i]); break;
         default:
             form = NumberFormat.getPercentInstance(locales[i]); break;
         }
         if (form instanceof DecimalFormat) {
             System.out.print(": " + ((DecimalFormat) form).toPattern());
         }
         System.out.print(" -> " + form.format(myNumber));
         try {
             System.out.println(" -> " + form.parse(form.format(myNumber)));
         } catch (ParseException e) {}
     }
 }
 

See Also:

Java Tutorial, NumberFormat, DecimalFormatSymbols, ParsePosition, Serialized Form

Nested Class Summary

 

Nested classes inherited from class java.text.NumberFormat

NumberFormat.Field

 

Nested classes inherited from class java.text.Format

Format.Field

 

Field Summary

 

Fields inherited from class java.text.NumberFormat

FRACTION_FIELD, INTEGER_FIELD

 

Constructor Summary
DecimalFormat()     Creates a DecimalFormat using the default pattern and symbols for the default locale.
DecimalFormat(String pattern)     Creates a DecimalFormat using the given pattern and the symbols for the default locale.
DecimalFormat(String pattern, DecimalFormatSymbols symbols)     Creates a DecimalFormat using the given pattern and symbols.

 

Method Summary
void	applyLocalizedPattern(String pattern)     Apply the given pattern to this Format object.
void	applyPattern(String pattern)     Apply the given pattern to this Format object.
Object	clone()     Standard override; no change in semantics.
boolean	equals(Object obj)     Overrides equals
StringBuffer	format(double number, StringBuffer result, FieldPosition fieldPosition)     Formats a double to produce a string.
StringBuffer	format(long number, StringBuffer result, FieldPosition fieldPosition)     Format a long to produce a string.
AttributedCharacterIterator	formatToCharacterIterator(Object obj)     Formats an Object producing an AttributedCharacterIterator.
Currency	getCurrency()     Gets the currency used by this decimal format when formatting currency values.
DecimalFormatSymbols	getDecimalFormatSymbols()     Returns the decimal format symbols, which is generally not changed by the programmer or user.
int	getGroupingSize()     Return the grouping size.
int	getMultiplier()     Get the multiplier for use in percent, permill, etc.
String	getNegativePrefix()     Get the negative prefix.
String	getNegativeSuffix()     Get the negative suffix.
String	getPositivePrefix()     Get the positive prefix.
String	getPositiveSuffix()     Get the positive suffix.
int	hashCode()     Overrides hashCode
boolean	isDecimalSeparatorAlwaysShown()     Allows you to get the behavior of the decimal separator with integers.
Number	parse(String text, ParsePosition pos)     Parses text from a string to produce a Number.
void	setCurrency(Currency currency)     Sets the currency used by this number format when formatting currency values.
void	setDecimalFormatSymbols(DecimalFormatSymbols newSymbols)     Sets the decimal format symbols, which is generally not changed by the programmer or user.
void	setDecimalSeparatorAlwaysShown(boolean newValue)     Allows you to set the behavior of the decimal separator with integers.
void	setGroupingSize(int newValue)     Set the grouping size.
void	setMaximumFractionDigits(int newValue)     Sets the maximum number of digits allowed in the fraction portion of a number.
void	setMaximumIntegerDigits(int newValue)     Sets the maximum number of digits allowed in the integer portion of a number.
void	setMinimumFractionDigits(int newValue)     Sets the minimum number of digits allowed in the fraction portion of a number.
void	setMinimumIntegerDigits(int newValue)     Sets the minimum number of digits allowed in the integer portion of a number.
void	setMultiplier(int newValue)     Set the multiplier for use in percent, permill, etc.
void	setNegativePrefix(String newValue)     Set the negative prefix.
void	setNegativeSuffix(String newValue)     Set the positive suffix.
void	setPositivePrefix(String newValue)     Set the positive prefix.
void	setPositiveSuffix(String newValue)     Set the positive suffix.
String	toLocalizedPattern()     Synthesizes a localized pattern string that represents the current state of this Format object.
String	toPattern()     Synthesizes a pattern string that represents the current state of this Format object.

 

Methods inherited from class java.text.NumberFormat

format, format, format, getAvailableLocales, getCurrencyInstance, getCurrencyInstance, getInstance, getInstance, getIntegerInstance, getIntegerInstance, getMaximumFractionDigits, getMaximumIntegerDigits, getMinimumFractionDigits,