In Constructors

In Fields

Returned by

As method parameter

Library: | Java SE, Sun OpenJDK7.b12 |

Package: | java.text |

Class

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`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:A

`DecimalFormat`

comprises apatternand a set ofsymbols. 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`ResourceBundle`

s.## Patterns

`DecimalFormat`

patterns have the following syntax: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 (`'-'`

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

`"#,##,###,####"`

==`"######,####"`

==`"##,####,####"`

.## 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.## 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 notationonly 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"`

.notthe prefix and suffix from the pattern. This allows patterns such as`"0.###E0 m/s"`

.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"`

.`"00.###E0"`

yields`"12.3E-4"`

.minimum integerandmaximum fractiondigits, 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.## Rounding

`DecimalFormat`

provides rounding modes defined in RoundingMode for formatting. By default, it uses RoundingMode.HALF_EVEN .## Digits

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.## Special Values

`NaN`

is formatted as a string, which typically has a single character`\uFFFD`

. This string 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 string, which typically has a single character

`\u221E`

, with the positive or negative prefixes and suffixes applied. The infinity string is determined by the`DecimalFormatSymbols`

object.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.

## Example