Class DecimalFormat
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)
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 ResourceBundle s.
Patterns
Pattern: PositivePattern PositivePattern ; NegativePattern PositivePattern: Prefixopt Number Suffixopt NegativePattern: Prefixopt Number Suffixopt Prefix: any Unicode characters exceptU+FFFE,U+FFFF, and special characters Suffix: any Unicode characters exceptU+FFFE,U+FFFF, 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 minus sign ( ‘-‘ U+002D HYPHEN-MINUS ) 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, grouping 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 grouping 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.
Chart showing symbol, location, localized, and meaning.
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 or monetary 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 U+2030 Prefix or suffix Yes Multiply by 1000 and show as per mille value ¤ ( U+00A4 ) 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/grouping separators are used instead of the decimal/grouping separators. ‘ 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
- 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» .
Rounding
DecimalFormat provides rounding modes defined in RoundingMode for formatting. By default, it uses RoundingMode.HALF_EVEN .
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 string, which typically has a single character U+FFFD . This string 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 string, which typically has a single character U+221E , with the positive or negative prefixes and suffixes applied. The infinity string is determined by the DecimalFormatSymbols object.
- BigDecimal(0) if isParseBigDecimal() is true,
- Long(0) if isParseBigDecimal() is false and isParseIntegerOnly() is true,
- Double(-0.0) if both isParseBigDecimal() and isParseIntegerOnly() are false.
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 localeLocale[] 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) <> > >