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DecimalFormat (Java SE 24 & JDK 24)
  1. java.base
  2. java.text
  3. DecimalFormat
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  1. Description
    1. Getting a DecimalFormat
    2. Using DecimalFormat
    3. Formatting and Parsing
    1. Synchronization
    2. DecimalFormat Pattern
  2. Nested Class Summary
  3. Field Summary
  4. Constructor Summary
  5. Method Summary
  6. Constructor Details
    1. DecimalFormat()
    2. DecimalFormat(String)
    3. DecimalFormat(String, DecimalFormatSymbols)
  7. Method Details
    1. format(Object, StringBuffer, FieldPosition)
    2. format(double, StringBuffer, FieldPosition)
    3. format(long, StringBuffer, FieldPosition)
    4. formatToCharacterIterator(Object)
    5. parse(String, ParsePosition)
    6. getDecimalFormatSymbols()
    7. setDecimalFormatSymbols(DecimalFormatSymbols)
    8. getPositivePrefix()
    9. setPositivePrefix(String)
    10. getNegativePrefix()
    11. setNegativePrefix(String)
    12. getPositiveSuffix()
    13. setPositiveSuffix(String)
    14. getNegativeSuffix()
    15. setNegativeSuffix(String)
    16. getMultiplier()
    17. setMultiplier(int)
    18. getGroupingSize()
    19. setGroupingSize(int)
    20. isDecimalSeparatorAlwaysShown()
    21. setDecimalSeparatorAlwaysShown(boolean)
    22. isStrict()
    23. setStrict(boolean)
    24. isParseBigDecimal()
    25. setParseBigDecimal(boolean)
    26. clone()
    27. equals(Object)
    28. hashCode()
    29. toString()
    30. toPattern()
    31. toLocalizedPattern()
    32. applyPattern(String)
    33. applyLocalizedPattern(String)
    34. setMaximumIntegerDigits(int)
    35. setMinimumIntegerDigits(int)
    36. setMaximumFractionDigits(int)
    37. setMinimumFractionDigits(int)
    38. getMaximumIntegerDigits()
    39. getMinimumIntegerDigits()
    40. getMaximumFractionDigits()
    41. getMinimumFractionDigits()
    42. getCurrency()
    43. setCurrency(Currency)
    44. getRoundingMode()
    45. setRoundingMode(RoundingMode)

Class DecimalFormat

java.lang.Object
java.text.Format
java.text.NumberFormat
java.text.DecimalFormat
All Implemented Interfaces:
Serializable, Cloneable
public class DecimalFormat extends NumberFormat
DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers in a localized manner. 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).

Getting a DecimalFormat

To obtain a standard decimal format for a specific locale, including the default locale, it is recommended to call one of the NumberFormat factory methods, such as NumberFormat.getInstance(). These factory methods may not always return a DecimalFormat depending on the locale-service provider implementation installed. Thus, to use an instance method defined by DecimalFormat, the NumberFormat returned by the factory method should be type checked before converted to DecimalFormat. If the installed locale-sensitive service implementation does not support the given Locale, the parent locale chain will be looked up, and a Locale used that is supported.

If the factory methods are not desired, use one of the constructors such as DecimalFormat(String pattern). See the Pattern section for more information on the pattern parameter.

Using DecimalFormat

The following is an example of formatting and parsing,
CopyCopy snippet [Copy snippet] 
NumberFormat nFmt = NumberFormat.getCurrencyInstance(Locale.US);
if (nFmt instanceof DecimalFormat dFmt) {
    // pattern match to DecimalFormat to use setPositiveSuffix(String)
    dFmt.setPositiveSuffix(" dollars");
    dFmt.format(100000); // returns "$100,000.00 dollars"
    dFmt.parse("$100,000.00 dollars"); // returns 100000
}

Formatting and Parsing

Rounding

When formatting, DecimalFormat can adjust its rounding using setRoundingMode(RoundingMode). By default, it uses RoundingMode.HALF_EVEN.

Digits

When formatting, DecimalFormat uses the ten consecutive characters starting with the localized zero digit defined in the DecimalFormatSymbols object as digits.

When parsing, these digits as well as all Unicode decimal digits, as defined by Character.digit, are recognized.

Integer and Fraction Digit Limits

Implementation Requirements:
When formatting a Number other than BigInteger and BigDecimal, 309 is used as the upper limit for integer digits, and 340 as the upper limit for fraction digits. This occurs, even if one of the DecimalFormat getter methods, for example, getMinimumFractionDigits() returns a numerically greater value.

Special Values

  • Not a Number (NaN) is formatted as a string, which is typically given as "NaN". This string is determined by DecimalFormatSymbols.getNaN(). This is the only value for which the prefixes and suffixes are not attached.

  • Infinity is formatted as a string, which is typically given as "∞" (U+221E), with the positive or negative prefixes and suffixes attached. This string is determined by DecimalFormatSymbols.getInfinity().

  • Negative zero ("-0") parses to

    • BigDecimal(0) if isParseBigDecimal() is true
    • Long(0) if isParseBigDecimal() is false and isParseIntegerOnly() is true
    • Double(-0.0) if both isParseBigDecimal() and isParseIntegerOnly() are false

Synchronization

Decimal formats are generally not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.

DecimalFormat Pattern

A DecimalFormat comprises a pattern and a set of symbols. The pattern may be set directly using applyPattern(), or indirectly using the various API methods. The symbols are stored in a DecimalFormatSymbols object. When using the NumberFormat factory methods, the pattern and symbols are created from the locale-sensitive service implementation installed.

DecimalFormat patterns have the following syntax: 

 Pattern:
         PositivePattern
         PositivePattern ; NegativePattern
 PositivePattern:
         Prefixopt Number Suffixopt
 NegativePattern:
         Prefixopt Number Suffixopt
 Prefix:
         Any characters except the special pattern characters
 Suffix:
         Any characters except the special pattern 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

Special Pattern Characters

The special characters in the table below are interpreted syntactically when used in the DecimalFormat pattern. They must be quoted, unless noted otherwise, if they are to appear in the prefix or suffix as literals.

The characters in the Symbol column are used in non-localized patterns. The corresponding characters in the Localized Symbol column are used in localized patterns, with the characters in Symbol losing their syntactical meaning. Two exceptions are the currency sign (U+00A4) and quote (U+0027), which are not localized.

Non-localized patterns should be used when calling applyPattern(String). Localized patterns should be used when calling applyLocalizedPattern(String).

Chart showing symbol, location, localized, and meaning.
Symbol Localized Symbol Location Meaning
0 DecimalFormatSymbols.getZeroDigit() Number Digit
# DecimalFormatSymbols.getDigit() Number Digit, zero shows as absent
. DecimalFormatSymbols.getDecimalSeparator() Number Decimal separator or monetary decimal separator
- (U+002D) DecimalFormatSymbols.getMinusSign() Number Minus sign
, DecimalFormatSymbols.getGroupingSeparator() Number Grouping separator or monetary grouping separator
E DecimalFormatSymbols.getExponentSeparator() Number Separates mantissa and exponent in scientific notation. This value is case sensistive. Need not be quoted in prefix or suffix.
; DecimalFormatSymbols.getPatternSeparator() Subpattern boundary Separates positive and negative subpatterns
% DecimalFormatSymbols.getPercent() Prefix or suffix Multiply by 100 and show as percentage
‰ (U+2030) DecimalFormatSymbols.getPerMill() Prefix or suffix Multiply by 1000 and show as per mille value
¤ (U+00A4) n/a (not localized) Prefix or suffix Currency sign, replaced by currency symbol. If doubled, replaced by international currency symbol. If present in a pattern, the monetary decimal/grouping separators are used instead of the decimal/grouping separators.
' (U+0027) n/a (not localized) Prefix or suffix 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".

Maximum Digits Derivation

For any given DecimalFormat pattern, if the pattern is not in scientific notation, the maximum number of integer digits will not be derived from the pattern, and instead set to Integer.MAX_VALUE. Otherwise, if the pattern is in scientific notation, the maximum number of integer digits will be derived from the pattern. This derivation is detailed in the Scientific Notation section. setMaximumIntegerDigits(int) can be used to manually adjust the maximum integer digits.

Negative Subpatterns

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 minus sign '-' (U+002D HYPHEN-MINUS) 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, grouping 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 grouping separator should be distinct characters, or parsing will be impossible.

Grouping Separator

The grouping separator is commonly used for thousands, but in some locales 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. For example, "#,##,###,####" == "######,####" == "##,####,####".

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 maximum integer digits is the sum of '0's and '#'s prior to the decimal point. The minimum integer digits is the sum of the '0's prior to the decimal point. The maximum fraction and minimum fraction digits follow the same rules, but apply to the digits after the decimal point but before the exponent. For example, the following pattern: "#00.0####E0" would have a minimum number of integer digits = 2("00") and a maximum number of integer digits = 3("#00"). It would have a minimum number of fraction digits = 1("0") and a maximum number of fraction digits= 5("0####").
  • 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".
  • For a given number, the amount of significant digits in the mantissa can be calculated as such 
     Mantissa Digits:
         min(max(Minimum Pattern Digits, Original Number Digits), Maximum Pattern Digits)
 Minimum pattern Digits:
         Minimum Integer Digits + Minimum Fraction Digits
 Maximum pattern Digits:
         Maximum Integer Digits + Maximum Fraction Digits
 Original Number Digits:
         The amount of significant digits in the number to be formatted
    This means that generally, a mantissa will have up to the combined maximum integer and fraction digits, if the original number itself has enough significant digits. However, if there are more minimum pattern digits than significant digits in the original number, the mantissa will have significant digits that equals the combined minimum integer and fraction digits. The number of significant digits does not affect parsing.

    It should be noted, that the integer portion of the mantissa will give any excess digits to the fraction portion, whether it be for precision or for satisfying the total amount of combined minimum digits.

    This behavior can be observed in the following example,

    CopyCopy snippet [Copy snippet] 
        DecimalFormat df = new DecimalFormat("#000.000##E0");
    df.format(12); // returns "12.0000E0"
    df.format(123456789) // returns "1.23456789E8"
  • Exponential patterns may not contain grouping separators.

Since:
1.1
External Specifications
See Also:

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