DecimalFormat

Class Overview

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, or Indic digits. It also supports different flavors of numbers, including integers ("123"), fixed-point numbers ("123.4"), scientific notation ("1.23E4"), percentages ("12%"), and currency amounts ("$123"). All of these flavors can be easily localized.

This is an enhanced version of DecimalFormat that is based on the standard version in the RI. New or changed functionality is labeled NEW.

To obtain a NumberFormat for a specific locale (including the default locale), call one of NumberFormat's factory methods such as NumberFormat.getInstance. Do not call the DecimalFormat constructors directly, unless you know what you are doing, 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);
 }
 

Patterns

A DecimalFormat consists of a pattern and a set of symbols. The pattern may be set directly using applyPattern(String), 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 DecimalFormatSymbols object. When using the NumberFormat factory methods, the pattern and symbols are read from ICU's locale data.

Special Pattern Characters

Many characters in a pattern are taken literally; they are matched during parsing and are written out unchanged during formatting. On the other hand, special characters 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 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	No	NEW  Significant digit.
#	Number	Yes	Digit, leading zeroes are not shown.
.	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. Does not need to be quoted in prefix or suffix.
+	Exponent	Yes	NEW  Prefix positive exponents with localized plus sign. Does not need to 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".
*	Prefix or suffix boundary	Yes	NEW  Pad escape, precedes pad character.

A DecimalFormat pattern contains a positive 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. This means that "#,##0.0#;(#)" produces 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 parse(String) to be able to 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 is 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 "#,##,###,####", "###,###,####" and "##,#,###,####" produce the same result.

Illegal patterns, such as "#.#.#" or "#.###,###", will cause DecimalFormat to throw an IllegalArgumentException with a message that describes the problem.

Pattern BNF

 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
 

Not indicated in the BNF syntax above:

• The grouping separator ',' can occur inside the integer and sigDigits elements, between any two pattern characters of that element, as long as the integer or sigDigits element is not followed by the exponent element.
• NEW  Two grouping intervals are recognized: The one between the decimal point and the first grouping symbol and the one between the first and second grouping symbols. These intervals are identical in most locales, but in some locales they differ. For example, the pattern "#,##,###" formats the number 123456789 as "12,34,56,789".
• NEW  The pad specifier padSpec may appear before the prefix, after the prefix, before the suffix, after the suffix or not at all.

Parsing

DecimalFormat parses all Unicode characters that represent decimal digits, as defined by digit(int, int). 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 written out.

During parsing, grouping separators are ignored.

If parse(String, ParsePosition) fails to parse a string, it returns null and leaves the parse position unchanged.

Formatting

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.

• If the number of actual integer digits exceeds the maximum integer digits, then only the least significant digits are shown. For example, 1997 is formatted as "97" if maximum integer digits is set to 2.
• If the number of actual integer digits is less than the minimum integer digits, then leading zeros are added. For example, 1997 is formatted as "01997" if minimum integer digits is set to 5.
• If the number of actual fraction digits exceeds the maximum fraction digits, then half-even rounding is performed to the maximum fraction digits. For example, 0.125 is formatted as "0.12" if the maximum fraction digits is 2.
• If the number of actual fraction digits is less than the minimum fraction digits, then trailing zeros are added. For example, 0.125 is formatted as "0.1250" if the minimum fraction digits is set to 4.
• Trailing fractional zeros are not displayed if they occur j positions after the decimal, where j is less than the maximum fraction digits. For example, 0.10004 is formatted as "0.1" if the maximum fraction digits is four or less.

Special Values

NaN is represented 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 represented as a single character, typically \u221E, with the positive or negative prefixes and suffixes applied. The infinity character is determined by the 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 does not need to 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".

• 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". To prefix positive exponents with a localized plus sign, specify '+' between the exponent and the digits: "0.###E+0" will produce formats "1E+1", "1E+0", "1E-1", etc. (In localized patterns, use the localized plus sign rather than '+'.)
• The minimum number of integer digits is achieved by adjusting the exponent. Example: 0.00123 formatted with "00.###E0" yields "12.3E-4". This only happens if there is no maximum number of integer digits. If there is a maximum, then the minimum number of integer digits is fixed at one.
• The maximum number of integer digits, if present, specifies the exponent grouping. The most common use of this is to generate engineering notation, in which the exponent is a multiple of three, e.g., "##0.###E0". The number 12345 is formatted using "##0.###E0" as "12.345E3".
• When using scientific notation, the formatter controls the digit counts using significant digits logic. The maximum number of significant digits limits the total number of integer and fraction digits that will be shown in the mantissa; it does not affect parsing. For example, 12345 formatted with "##0.##E0" is "12.3E3". See the section on significant digits for more details.
• The number of significant digits shown is determined as follows: If no significant digits are used in the pattern then the minimum number of significant digits shown is one, the maximum number of significant digits shown is the sum of the minimum integer and maximum fraction digits, and it is unaffected by the maximum integer digits. If this sum is zero, then all significant digits are shown. If significant digits are used in the pattern then the number of integer digits is fixed at one and there is no exponent grouping.
• Exponential patterns may not contain grouping separators.

DecimalFormat has two ways of controlling how many digits are shown: (a) significant digit counts or (b) integer and fraction digit counts. Integer and fraction digit counts are described above. When a formatter uses 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 as many integer and fraction digits as 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

• Significant digit counts may be expressed using patterns that specify a minimum and maximum number of significant digits. These are indicated by the '@' 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".
• If a pattern uses significant digits, it may not contain a decimal separator, nor the '0' pattern character. Patterns such as "@00" or "@.###" are disallowed.
• Any number of '#' characters may be prepended to the left of the leftmost '@' character. These have no effect on the minimum and maximum significant digit counts, but may be used to position grouping separators. For example, "#,#@#" indicates a minimum of one significant digit, a maximum of two significant digits, and a grouping size of three.
• In order to enable significant digits formatting, use a pattern containing the '@' pattern character.
• In order to disable significant digits formatting, use a pattern that does not contain the '@' pattern character.
• The number of significant digits has no effect on parsing.
• Significant digits may be used together with exponential notation. Such patterns are equivalent to a normal exponential pattern with a minimum and maximum integer digit count of one, a minimum fraction digit count of the number of '@' characters in the pattern - 1, and a maximum fraction digit count of the number of '@' and '#' characters in the pattern - 1. For example, the pattern "@@###E0" is equivalent to "0.0###E0".
• If significant digits are in use then the integer and fraction digit counts, as set via the API, are ignored.

NEW  Padding

DecimalFormat supports padding the result of format to a specific width. Padding may be specified either through 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. For example, "$*x#,##0.00" formats 123 to "$xx123.00", and 1234 to "$1,234.00".

• When padding is in effect, the width of the positive subpattern, including prefix and suffix, determines the format width. For example, in the pattern "* #0 o''clock", the format width is 10.
• The width is counted in 16-bit code units (Java chars).
• Some parameters which usually do not matter have meaning when padding is used, because the pattern width is significant with padding. In the pattern "* ##,##,#,##0.##", the format width is 14. The initial characters "##,##," do not affect the grouping size or maximum integer digits, but they do affect the format width.
• Padding may be inserted at one of four locations: before the prefix, after the prefix, before the suffix or after the suffix. If padding is specified in any other location, applyPattern(String) throws an IllegalArgumentException. If there is no prefix, before the prefix and after the prefix are equivalent, likewise for the suffix.
• When specified in a pattern, the 16-bit 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.

Synchronization

DecimalFormat objects are not synchronized. Multiple threads should not access one formatter concurrently.

Summary

[Expand] Inherited Constants
From class java.text.NumberFormat int FRACTION_FIELD Field constant identifying the fractional part of a number. int INTEGER_FIELD Field constant identifying the integer part of a number.

[Expand] Inherited Methods
From class java.text.NumberFormat Object clone() Returns a new NumberFormat with the same properties. boolean equals( Object object) Compares the specified object to this number format and indicates if they are equal. abstract StringBuffer format(long value, StringBuffer buffer, FieldPosition field) Formats the specified long value as a string using the pattern of this number format and appends the string to the specified string buffer. final String format(long value) Formats the specified long using the rules of this number format. abstract StringBuffer format(double value, StringBuffer buffer, FieldPosition field) Formats the specified double value as a string using the pattern of this number format and appends the string to the specified string buffer. StringBuffer format( Object object, StringBuffer buffer, FieldPosition field) Formats a number into a supplied buffer. final String format(double value) Formats the specified double using the rules of this number format. static Locale[] getAvailableLocales() Returns an array of locales for which custom NumberFormat instances are available. Currency getCurrency() Returns the currency used by this number format. final static NumberFormat getCurrencyInstance() Returns a NumberFormat for formatting and parsing currency values for the user's default locale. static NumberFormat getCurrencyInstance( Locale locale) Returns a NumberFormat for formatting and parsing currency values for the specified locale. static NumberFormat getInstance( Locale locale) Returns a NumberFormat for formatting and parsing numbers for the specified locale. final static NumberFormat getInstance() Returns a NumberFormat for formatting and parsing numbers for the default locale. static NumberFormat getIntegerInstance( Locale locale) Returns a NumberFormat for formatting and parsing integers for the specified locale. final static NumberFormat getIntegerInstance() Returns a NumberFormat for formatting and parsing integers for the user's default locale. int getMaximumFractionDigits() Returns the maximum number of fraction digits that are printed when formatting. int getMaximumIntegerDigits() Returns the maximum number of integer digits that are printed when formatting. int getMinimumFractionDigits() Returns the minimum number of fraction digits that are printed when formatting. int getMinimumIntegerDigits() Returns the minimum number of integer digits that are printed when formatting. final static NumberFormat getNumberInstance() Returns a NumberFormat for formatting and parsing numbers for the user's default locale. static NumberFormat getNumberInstance( Locale locale) Returns a NumberFormat for formatting and parsing numbers for the specified locale. final static NumberFormat getPercentInstance() Returns a NumberFormat for formatting and parsing percentage values for the user's default locale. static NumberFormat getPercentInstance( Locale locale) Returns a NumberFormat for formatting and parsing percentage values for the given locale. RoundingMode getRoundingMode() Returns the RoundingMode used by this NumberFormat. int hashCode() Returns an integer hash code for this object. boolean isGroupingUsed() Indicates whether this number format formats and parses numbers using a grouping separator. boolean isParseIntegerOnly() Indicates whether this number format only parses integer numbers. Number parse( String string) Parses a Number from the specified string using the rules of this number format. abstract Number parse( String string, ParsePosition position) Parses a Number from the specified string starting at the index specified by position. final Object parseObject( String string, ParsePosition position) Parses the specified string starting at the index specified by position. void setCurrency( Currency currency) Sets the currency used by this number format when formatting currency values. void setGroupingUsed(boolean value) Sets whether this number format formats and parses numbers using a grouping separator. void setMaximumFractionDigits(int value) Sets the maximum number of fraction digits that are printed when formatting. void setMaximumIntegerDigits(int value) Sets the new maximum count of integer digits that are printed when formatting. void setMinimumFractionDigits(int value) Sets the minimum number of fraction digits that are printed when formatting. void setMinimumIntegerDigits(int value) Sets the minimum number of integer digits that are printed when formatting. void setParseIntegerOnly(boolean value) Specifies if this number format should parse numbers only as integers or else as any kind of number. void setRoundingMode( RoundingMode roundingMode) Sets the RoundingMode used by this NumberFormat.
From class java.text.Format Object clone() Returns a copy of this Format instance. final String format( Object object) Formats the specified object using the rules of this format. abstract StringBuffer format( Object object, StringBuffer buffer, FieldPosition field) Appends the specified object to the specified string buffer using the rules of this format. AttributedCharacterIterator formatToCharacterIterator( Object object) Formats the specified object using the rules of this format and returns an AttributedCharacterIterator with the formatted string and no attributes. Object parseObject( String string) Parses the specified string using the rules of this format. abstract Object parseObject( String string, ParsePosition position) Parses the specified string starting at the index specified by position.
From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals( Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.