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 in the package
java.text.resource.
Example
// Print out a number using the localized number, currency,
// and percent format for each locale
Locale[] locales = NumberFormat.getAvailableLocales();
double myNumber = -1234.56;
NumberFormat form;
for (int j=0; j<3; ++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.getCurrencyInstance(locales[i]); break;
default:
form = NumberFormat.getPercentInstance(locales[i]); break;
}
try {
// Assume form is a DecimalFormat
System.out.print(": " + ((DecimalFormat) form).toPattern()
+ " -> " + form.format(myNumber));
} catch (IllegalArgumentException e) {}
try {
System.out.println(" -> " + form.parse(form.format(myNumber)));
} catch (ParseException e) {}
}
}
Patterns
A DecimalFormat pattern contains a postive 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
('-' 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 "#,##,###,####" == "######,####" == "##,####,####".
Illegal patterns, such as "#.#.#" or "#.###,###", will cause
DecimalFormat to throw an IllegalArgumentException
with a message that describes the problem.
Parsing
DecimalFormat parses all Unicode characters that represent
decimal digits, as defined by Character.digit(). In addition,
DecimalFormat also recognizes as digits the ten consecutive
characters starting with the localized zero digit defined in the
DecimalFormatSymbols object. During formatting, the
DecimalFormatSymbols-based digits are output.
DecimalFormat.parse returns a subclass of
java.lang.Number representing the parsed numeric string.
DecimalFormat chooses the most economical subclass that can
represent the numeric string. This means most integer values are returned as
Long objects, no matter how they are written: "17" and "17.000"
both parse to Long(17). Values that cannot fit into a
Long are returned as Doubles. This includes values
with a fractional part, infinite values, NaN, and the value
-0.0. DecimalFormat does not decide whether to return
a Double or a Long based on the presence of a
decimal separator in the source string. Doing so would prevent integers that
overflow the mantissa of a double, such as "10,000,000,000,000,000.00", from
being parsed accurately. Currently, the only classes that
DecimalFormat returns are Long and
Double, but callers should not rely on this. Callers may use
the Number methods doubleValue,
longValue, etc., to obtain the type they want.
If DecimalFormat.parse(String, ParsePosition) fails to parse
a string, it returns null, leaves the ParsePosition
index unchanged, and sets the ParsePosition error index. The
convenience method DecimalFormat.parse(String) indicates parse
failure by throwing a ParseException.
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).
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.
Pattern Syntax
pattern := pos_pattern{';' neg_pattern}
pos_pattern := {prefix}number{suffix}
neg_pattern := {prefix}number{suffix}
number := integer{'.' fraction}{exponent}
prefix := '\u0000'..'\uFFFD' - special_characters
suffix := '\u0000'..'\uFFFD' - special_characters
integer := min_int | '#' | '#' integer | '#' ',' integer
min_int := '0' | '0' min_int | '0' ',' min_int
fraction := '0'* '#'*
exponent := 'E' '0' '0'*
Notation:
X* 0 or more instances of X
{ X } 0 or 1 instances of X
X | Y either X or Y
X..Y any character from X up to Y, inclusive
S - T characters in S, except those in T
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
Y
Digit
#
Number
Y
Digit, zero shows as absent
.
Number
Y
Decimal separator or monetary decimal separator
-
Number
Y
Minus sign
,
Number
Y
Grouping separator
E
Number
Y
Separates mantissa and exponent in scientific notation.
Need not be quoted in prefix or suffix.
;
Subpattern boundary
Y
Separates positive and negative subpatterns
%
Prefix or suffix
Y
Multiply by 100 and show as percentage
\u2030
Prefix or suffix
Y
Multiply by 1000 and show as per mille
¤ (\u00A4)
Prefix or suffix
N
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
N
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".
Create a DecimalFormat using the default pattern and symbols
for the default locale. This is a convenient way to obtain a
DecimalFormat when internationalization is not the main concern.
To obtain standard formats for a given locale, use the factory methods
on NumberFormat such as getNumberInstance. These factories will
return the most appropriate sub-class of NumberFormat for a given
locale.
Create a DecimalFormat from the given pattern and the symbols
for the default locale. This is a convenient way to obtain a
DecimalFormat when internationalization is not the main concern.
To obtain standard formats for a given locale, use the factory methods
on NumberFormat such as getNumberInstance. These factories will
return the most appropriate sub-class of NumberFormat for a given
locale.
Create a DecimalFormat from the given pattern and symbols.
Use this constructor when you need to completely customize the
behavior of the format.
To obtain standard formats for a given
locale, use the factory methods on NumberFormat such as
getInstance or getCurrencyInstance. If you need only minor adjustments
to a standard format, you can modify the format returned by
a NumberFormat factory method.
Returns an instance of Number with a value matching the
given string. The most economical subclass that can represent all the
bits of the source string is chosen.
parsePosition - on entry, where to begin parsing; on exit, just past
the last parsed character. If parsing fails, the index will not move and
the error index will be set.
Get the multiplier for use in percent, permill, etc.
For a percentage, set the suffixes to have "%" and the multiplier to be 100.
(For Arabic, use arabic percent symbol).
For a permill, set the suffixes to have "?" and the multiplier to be 1000.
Examples: with 100, 1.23 -> "123", and "123" -> 1.23
setMultiplier
public void setMultiplier(int newValue)
Set the multiplier for use in percent, permill, etc.
For a percentage, set the suffixes to have "%" and the multiplier to be 100.
(For Arabic, use arabic percent symbol).
For a permill, set the suffixes to have "?" and the multiplier to be 1000.
Examples: with 100, 1.23 -> "123", and "123" -> 1.23
getGroupingSize
public int getGroupingSize()
Return the grouping size. Grouping size is the number of digits between
grouping separators in the integer portion of a number. For example,
in the number "123,456.78", the grouping size is 3.
Set the grouping size. Grouping size is the number of digits between
grouping separators in the integer portion of a number. For example,
in the number "123,456.78", the grouping size is 3.
CloneNotSupportedException - if the object's class does not
support the Cloneable interface. Subclasses
that override the clone method can also
throw this exception to indicate that an instance cannot
be cloned.
Apply the given pattern to this Format object. A pattern is a
short-hand specification for the various formatting properties.
These properties can also be changed individually through the
various setter methods.
There is no limit to integer digits are set
by this routine, since that is the typical end-user desire;
use setMaximumInteger if you want to set a real value.
For negative numbers, use a second pattern, separated by a semicolon
Example "#,#00.0#" -> 1,234.56
This means a minimum of 2 integer digits, 1 fraction digit, and
a maximum of 2 fraction digits.
Example: "#,#00.0#;(#,#00.0#)" for negatives in parantheses.
In negative patterns, the minimum and maximum counts are ignored;
these are presumed to be set in the positive pattern.
Apply the given pattern to this Format object. The pattern
is assumed to be in a localized notation. A pattern is a
short-hand specification for the various formatting properties.
These properties can also be changed individually through the
various setter methods.
There is no limit to integer digits are set
by this routine, since that is the typical end-user desire;
use setMaximumInteger if you want to set a real value.
For negative numbers, use a second pattern, separated by a semicolon
Example "#,#00.0#" -> 1,234.56
This means a minimum of 2 integer digits, 1 fraction digit, and
a maximum of 2 fraction digits.
Example: "#,#00.0#;(#,#00.0#)" for negatives in parantheses.
In negative patterns, the minimum and maximum counts are ignored;
these are presumed to be set in the positive pattern.
setMaximumIntegerDigits
public void setMaximumIntegerDigits(int newValue)
Sets the maximum number of digits allowed in the integer portion of a
number. This override limits the integer digit count to 309.
Submit a bug or feature For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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