| Formats and parses numbers using locale-sensitive patterns.
This class provides comprehensive and flexible support for a wide variety of
localized formats, including
- Locale-specific symbols such as decimal point, group separator,
digit representation, currency symbol, percent, and permill
- Numeric variations including integers ("123"), fixed-point
numbers ("123.4"), scientific notation ("1.23E4"), percentages ("12%"), and
currency amounts ("$123")
- Predefined standard patterns that can be used both for parsing
and formatting, including
NumberFormat.getDecimalFormat() decimal ,
NumberFormat.getCurrencyFormat() currency ,
NumberFormat.getPercentFormat() percentages , and
NumberFormat.getScientificFormat() scientific
- Custom patterns and supporting features designed to make it
possible to parse and format numbers in any locale, including support for
Western, Arabic, and Indic digits
Patterns
Formatting and parsing are based on customizable patterns that can include a
combination of literal characters and special characters that act as
placeholders and are replaced by their localized counterparts. 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, for example, the ',' grouping character is
replaced by the same character ','. However, the replacement
is still actually happening, and in a different locale, the grouping
character may change to a different character, such as '.'.
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.
The characters listed below are used in patterns. Localized symbols use the
corresponding characters taken from corresponding locale symbol collection,
which can be found in the properties files residing in the
com.google.gwt.i18n.client.constants. 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.
| 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 |
E |
Subpattern boundary |
Yes |
Separates positive and negative subpatterns |
% |
Prefix or suffix |
Yes |
Multiply by 100 and show as percentage |
\u2030 (\u005Cu2030) |
Prefix or suffix |
Yes |
Multiply by 1000 and show as per mille |
\u00A4 (\u005Cu00A4) |
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 succession, such as
"# o''clock" |
A NumberFormat pattern contains a postive and negative
subpattern separated by a semicolon, such as
"#,##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, 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".
Pattern Grammar (BNF)
The pattern itself uses the following grammar:
| pattern |
:= |
subpattern (';'
subpattern)? |
| subpattern |
:= |
prefix? number exponent? suffix? |
| number |
:= |
(integer ('.' fraction)?) |
sigDigits |
| prefix |
:= |
'\u005Cu0000'..'\u005CuFFFD' -
specialCharacters |
| suffix |
:= |
'\u005Cu0000'..'\u005CuFFFD' -
specialCharacters |
| integer |
:= |
'#'* '0'*'0' |
| fraction |
:= |
'0'* '#'* |
| sigDigits |
:= |
'#'* '@''@'* '#'* |
| exponent |
:= |
'E' '+'? '0'* '0' |
| padSpec |
:= |
'*' padChar |
| padChar |
:= |
'\u005Cu0000'..'\u005CuFFFD' - 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.
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