A DecimalFormat consists of a pattern and a set of symbols. The pattern may be set directly using {@link #applyPattern}, or indirectly using other API methods which manipulate aspects of the pattern, such as the minimum number of integer digits. The symbols are stored in a {@link DecimalFormatSymbols}object. When using the {@link NumberFormat} factory methods, thepattern and symbols are read from ICU's locale data.
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. For example, the '#' character is replaced by a localized digit. Often the replacement character is the same as the pattern character; in the U.S. locale, the ',' grouping character is replaced by ','. However, the replacement is still happening, and if the symbols are modified, the grouping character changes. Some special characters affect the behavior of the formatter by their presence; for example, if the percent character is seen, then the value is multiplied by 100 before being displayed.
To insert a special character in a pattern as a literal, that is, without any special meaning, the character must be quoted. There are some exceptions to this which are noted below.
The characters listed here are used in non-localized patterns. Localized patterns use the corresponding characters taken from this formatter's {@link DecimalFormatSymbols} object instead, and these characters losetheir special status. Two exceptions are the currency sign and quote, which are not localized.
Symbol Location Localized? Meaning 0Number Yes Digit 1-9Number Yes NEW '1' through '9' indicate rounding. @Number No NEW Significant digit #Number Yes Digit, zero shows as absent .Number Yes Decimal separator or monetary decimal separator -Number Yes Minus sign ,Number Yes Grouping separator ENumber Yes Separates mantissa and exponent in scientific notation. Need not be quoted in prefix or suffix. +Exponent Yes NEW Prefix positive exponents with localized plus sign. 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 \u2030Prefix 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".*Prefix or suffix boundary Yes NEW Pad escape, precedes pad character
A DecimalFormat pattern contains a postive and negative subpattern, for example, "#,##0.00;(#,##0.00)". Each subpattern has a prefix, a numeric part, and a suffix. If there is no explicit negative subpattern, the negative subpattern is the localized minus sign prefixed to the positive 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 ignored in the negative subpattern. That means that "#,##0.0#;(#)" has precisely the same result 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 {@link #parse} to be ableto distinguish positive from negative values. Another example is that the decimal separator and thousands separator should be distinct characters, or parsing will be impossible.
The grouping separator is a character that separates clusters of integer digits to make large numbers more legible. It commonly used for thousands, but in some locales it separates ten-thousands. The grouping size is the number of digits between the grouping separators, such as 3 for "100,000,000" or 4 for "1 0000 0000". There are actually two different grouping sizes: One used for the least significant integer digits, the primary grouping size, and one used for all others, the secondary grouping size. In most locales these are the same, but sometimes they are different. For example, if the primary grouping interval is 3, and the secondary is 2, then this corresponds to the pattern "#,##,##0", and the number 123456789 is formatted as "12,34,56,789". If a pattern contains multiple grouping separators, the interval between the last one and the end of the integer defines the primary grouping size, and the interval between the last two defines the secondary grouping size. All others are ignored, so "#,##,###,####" == "###,###,####" == "##,#,###,####".
Illegal patterns, such as "#.#.#" or "#.###,###", will cause DecimalFormat to throw an {@link IllegalArgumentException}with a message that describes the problem.
pattern := subpattern (';' subpattern)? subpattern := prefix? number exponent? suffix? number := (integer ('.' fraction)?) | sigDigits prefix := '\u0000'..'\uFFFD' - specialCharacters suffix := '\u0000'..'\uFFFD' - specialCharacters integer := '#'* '0'* '0' fraction := '0'* '#' sigDigits := '#'* '@' '@'* '#' exponent := 'E' '+'? '0'* '0' padSpec := '*' padChar padChar := '\u0000'..'\uFFFD' - quote Notation: X* 0 or more instances of X X? 0 or 1 instances of X X|Y either X or Y C..D any character from C up to D, inclusive S-T characters in S, except those in T The first subpattern is for positive numbers. The second (optional) subpattern is for negative numbers. Not indicated in the BNF syntax above:
padSpec may appear before the prefix, after the prefix, before the suffix, after the suffix, or not at all. DecimalFormat parses all Unicode characters that represent decimal digits, as defined by {@link UCharacter#digit}. In addition, DecimalFormat also recognizes as digits the ten consecutive characters starting with the localized zero digit defined in the {@link DecimalFormatSymbols} object. During formatting, the{@link DecimalFormatSymbols}-based digits are output.
During parsing, grouping separators are ignored.
If {@link #parse(String,ParsePosition)} fails to parsea string, it returns null and leaves the parse position unchanged. The convenience method {@link #parse(String)}indicates parse failure by throwing a {@link java.text.ParseException}.
Formatting is guided by several parameters, all of which can be specified either using a pattern or using the API. The following description applies to formats that do not use scientific notation or significant digits.
Special Values
NaN is represented as a single character, typically \uFFFD. This character is determined by the {@link DecimalFormatSymbols} object. This is the only value for whichthe prefixes and suffixes are not used.
Infinity is represented as a single character, typically \u221E, with the positive or negative prefixes and suffixes applied. The infinity character is determined by the {@link DecimalFormatSymbols} object.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 103. The mantissa is typically in the half-open interval [1.0, 10.0) or sometimes [0.0, 1.0), but it need not be. DecimalFormat supports arbitrary mantissas. DecimalFormat can be instructed to use scientific notation through the API or through the pattern. 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".
DecimalFormat has two ways of controlling how many digits are shows: (a) significant digits counts, or (b) integer and fraction digit counts. Integer and fraction digit counts are described above. When a formatter is using significant digits counts, the number of integer and fraction digits is not specified directly, and the formatter settings for these counts are ignored. Instead, the formatter uses however many integer and fraction digits are required to display the specified number of significant digits. Examples:
Pattern Minimum significant digits Maximum significant digits Number Output of format() @@@3 3 12345 12300@@@3 3 0.12345 0.123@@##2 4 3.14159 3.142@@##2 4 1.23004 1.23
'@' and '#' characters. The minimum number of significant digits is the number of '@' characters. The maximum number of significant digits is the number of '@' characters plus the number of '#' characters following on the right. For example, the pattern "@@@" indicates exactly 3 significant digits. The pattern "@##" indicates from 1 to 3 significant digits. Trailing zero digits to the right of the decimal separator are suppressed after the minimum number of significant digits have been shown. For example, the pattern "@##" formats the number 0.1203 as "0.12". '0' pattern character. Patterns such as "@00" or "@.###" are disallowed. '#' characters may be prepended to the left of the leftmost '@' character. These have no effect on the minimum and maximum significant digits counts, but may be used to position grouping separators. For example, "#,#@#" indicates a minimum of one significant digits, a maximum of two significant digits, and a grouping size of three. '@' pattern character. Alternatively, call {@link #setSignificantDigitsUsed setSignificantDigitsUsed(true)}. '@' pattern character. Alternatively, call {@link #setSignificantDigitsUsed setSignificantDigitsUsed(false)}. getMinimumSignificantDigits() - 1, and a maximum fraction digit count of getMaximumSignificantDigits() - 1. For example, the pattern "@@###E0" is equivalent to "0.0###E0". DecimalFormat supports padding the result of {@link #format} to a specific width. Padding may be specified eitherthrough the API or through the pattern syntax. In a pattern the pad escape character, followed by a single pad character, causes padding to be parsed and formatted. The pad escape character is '*' in unlocalized patterns, and can be localized using {@link DecimalFormatSymbols#setPadEscape}. For example, "$*x#,##0.00" formats 123 to "$xx123.00", and 1234 to "$1,234.00".
"* #0 o''clock", the format width is 10. chars). char immediately following the pad escape is the pad character. This may be any character, including a special pattern character. That is, the pad escape escapes the following character. If there is no character after the pad escape, then the pattern is illegal. NEW Rounding
DecimalFormat supports rounding to a specific increment. For example, 1230 rounded to the nearest 50 is 1250. 1.234 rounded to the nearest 0.65 is 1.3. The rounding increment may be specified through the API or in a pattern. To specify a rounding increment in a pattern, include the increment in the pattern itself. "#,#50" specifies a rounding increment of 50. "#,##0.05" specifies a rounding increment of 0.05.
DecimalFormat objects are not synchronized. Multiple threads should not access one formatter concurrently.
@see java.text.Format
@see NumberFormat
@author Mark Davis
@author Alan Liu
@stable ICU 2.0
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