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
"#,##,###,####"
== "######,####"
==
"##,####,####"
.
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"
.
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"
.
"0.###E0 m/s"
.
"##0.#####E0"
. Using this pattern, the number 12345
formats to "12.345E3"
, and 123456 formats to
"123.456E3"
.
"00.###E0"
yields
"12.3E-4"
. "##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.
DecimalFormat
uses half-even rounding (see ROUND_HALF_EVEN
)
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.
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)
.