java.text
Class DecimalFormat

java.lang.Object
  |
  +--java.text.Format
        |
        +--java.text.NumberFormat
              |
              +--java.text.DecimalFormat

All Implemented Interfaces:

Cloneable, Serializable

public class DecimalFormat

extends NumberFormat

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 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, forces the exponent to be a multiple of that number. 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".
• 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".

See Also:

Format, NumberFormat, ChoiceFormat, ParsePosition, Serialized Form

Fields inherited from class java.text.NumberFormat

FRACTION_FIELD, INTEGER_FIELD

Constructor Summary

DecimalFormat()
Create a DecimalFormat using the default pattern and symbols for the default locale.

DecimalFormat(String pattern)
Create a DecimalFormat from the given pattern and the symbols for the default locale.

DecimalFormat(String pattern, DecimalFormatSymbols symbols)
Create a DecimalFormat from the given pattern and symbols.

Method Summary

void	applyLocalizedPattern(String pattern) Apply the given pattern to this Format object.
void	applyPattern(String pattern) Apply the given pattern to this Format object.
Object	clone() Standard override; no change in semantics.
boolean	equals(Object obj) Overrides equals
StringBuffer	format(double number, StringBuffer result, FieldPosition fieldPosition) Formats a double to produce a string.
StringBuffer	format(long number, StringBuffer result, FieldPosition fieldPosition) Format a long to produce a string.
DecimalFormatSymbols	getDecimalFormatSymbols() Returns the decimal format symbols, which is generally not changed by the programmer or user.
int	getGroupingSize() Return the grouping size.
int	getMultiplier() Get the multiplier for use in percent, permill, etc.
String	getNegativePrefix() Get the negative prefix.
String	getNegativeSuffix() Get the negative suffix.
String	getPositivePrefix() Get the positive prefix.
String	getPositiveSuffix() Get the positive suffix.
int	hashCode() Overrides hashCode
boolean	isDecimalSeparatorAlwaysShown() Allows you to get the behavior of the decimal separator with integers.
Number	parse(String text, ParsePosition parsePosition) Returns an instance of Number with a value matching the given string.
void	setDecimalFormatSymbols(DecimalFormatSymbols newSymbols) Sets the decimal format symbols, which is generally not changed by the programmer or user.
void	setDecimalSeparatorAlwaysShown(boolean newValue) Allows you to set the behavior of the decimal separator with integers.
void	setGroupingSize(int newValue) Set the grouping size.
void	setMaximumFractionDigits(int newValue) Sets the maximum number of digits allowed in the fraction portion of a number.
void	setMaximumIntegerDigits(int newValue) Sets the maximum number of digits allowed in the integer portion of a number.
void	setMinimumFractionDigits(int newValue) Sets the minimum number of digits allowed in the fraction portion of a number.
void	setMinimumIntegerDigits(int newValue) Sets the minimum number of digits allowed in the integer portion of a number.
void	setMultiplier(int newValue) Set the multiplier for use in percent, permill, etc.
void	setNegativePrefix(String newValue) Set the negative prefix.
void	setNegativeSuffix(String newValue) Set the positive suffix.
void	setPositivePrefix(String newValue) Set the positive prefix.
void	setPositiveSuffix(String newValue) Set the positive suffix.
String	toLocalizedPattern() Synthesizes a localized pattern string that represents the current state of this Format object.
String	toPattern() Synthesizes a pattern string that represents the current state of this Format object.

Methods inherited from class java.text.NumberFormat

format, format, format, getAvailableLocales, getCurrencyInstance, getCurrencyInstance, getInstance, getInstance, getMaximumFractionDigits, getMaximumIntegerDigits, getMinimumFractionDigits, getMinimumIntegerDigits, getNumberInstance, getNumberInstance, getPercentInstance, getPercentInstance, isGroupingUsed, isParseIntegerOnly, parse, parseObject, setGroupingUsed, setParseIntegerOnly

Methods inherited from class java.text.Format

format, parseObject

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DecimalFormat

public DecimalFormat()

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.

See Also:

NumberFormat.getInstance(), NumberFormat.getNumberInstance(), NumberFormat.getCurrencyInstance(), NumberFormat.getPercentInstance()

DecimalFormat

public DecimalFormat(String pattern)

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.

Parameters:

pattern - A non-localized pattern string.

Throws:

IllegalArgumentException - if the given pattern is invalid.

See Also:

NumberFormat.getInstance(), NumberFormat.getNumberInstance(), NumberFormat.getCurrencyInstance(), NumberFormat.getPercentInstance()

DecimalFormat

public DecimalFormat(String pattern,
                     DecimalFormatSymbols symbols)

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.

Parameters:

pattern - a non-localized pattern string

symbols - the set of symbols to be used

Throws:

IllegalArgumentException - if the given pattern is invalid

See Also:

NumberFormat.getInstance(), NumberFormat.getNumberInstance(), NumberFormat.getCurrencyInstance(), NumberFormat.getPercentInstance(), DecimalFormatSymbols

Method Detail

format

public StringBuffer format(double number,
                           StringBuffer result,
                           FieldPosition fieldPosition)

Formats a double to produce a string.

Overrides:

format in class NumberFormat

Parameters:

number - The double to format

toAppendTo - where the text is to be appended

fieldPosition - On input: an alignment field, if desired. On output: the offsets of the alignment field.

Returns:

The value passed in as the result parameter

See Also:

FieldPosition

format

public StringBuffer format(long number,
                           StringBuffer result,
                           FieldPosition fieldPosition)

Format a long to produce a string.

Overrides:

format in class NumberFormat

Parameters:

number - The long to format

toAppendTo - where the text is to be appended

fieldPosition - On input: an alignment field, if desired. On output: the offsets of the alignment field.

Returns:

The value passed in as the result parameter

See Also:

FieldPosition

parse

public Number parse(String text,
                    ParsePosition parsePosition)

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.

Overrides:

parse in class NumberFormat

Parameters:

text - the string to be parsed

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.

Returns:

the parsed value, or null if the parse fails

getDecimalFormatSymbols

public DecimalFormatSymbols getDecimalFormatSymbols()

Returns the decimal format symbols, which is generally not changed by the programmer or user.

Returns:

desired DecimalFormatSymbols

See Also:

DecimalFormatSymbols

setDecimalFormatSymbols

public void setDecimalFormatSymbols(DecimalFormatSymbols newSymbols)

Sets the decimal format symbols, which is generally not changed by the programmer or user.

Parameters:

newSymbols - desired DecimalFormatSymbols

See Also:

DecimalFormatSymbols

getPositivePrefix

public String getPositivePrefix()

Get the positive prefix.

Examples: +123, $123, sFr123

setPositivePrefix

public void setPositivePrefix(String newValue)

Set the positive prefix.

Examples: +123, $123, sFr123

getNegativePrefix

public String getNegativePrefix()

Get the negative prefix.

Examples: -123, ($123) (with negative suffix), sFr-123

setNegativePrefix

public void setNegativePrefix(String newValue)

Set the negative prefix.

Examples: -123, ($123) (with negative suffix), sFr-123

getPositiveSuffix

public String getPositiveSuffix()

Get the positive suffix.

Example: 123%

setPositiveSuffix

public void setPositiveSuffix(String newValue)

Set the positive suffix.

Example: 123%

getNegativeSuffix

public String getNegativeSuffix()

Get the negative suffix.

Examples: -123%, ($123) (with positive suffixes)

setNegativeSuffix

public void setNegativeSuffix(String newValue)

Set the positive suffix.

Examples: 123%

getMultiplier

public int getMultiplier()

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.

See Also:

setGroupingSize(int), NumberFormat.isGroupingUsed(), DecimalFormatSymbols.getGroupingSeparator()

setGroupingSize

public void setGroupingSize(int newValue)

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.

See Also:

getGroupingSize(), NumberFormat.setGroupingUsed(boolean), DecimalFormatSymbols.setGroupingSeparator(char)

isDecimalSeparatorAlwaysShown

public boolean isDecimalSeparatorAlwaysShown()

Allows you to get the behavior of the decimal separator with integers. (The decimal separator will always appear with decimals.)

Example: Decimal ON: 12345 -> 12345.; OFF: 12345 -> 12345

setDecimalSeparatorAlwaysShown

public void setDecimalSeparatorAlwaysShown(boolean newValue)

Allows you to set the behavior of the decimal separator with integers. (The decimal separator will always appear with decimals.)

Example: Decimal ON: 12345 -> 12345.; OFF: 12345 -> 12345

clone

public Object clone()

Standard override; no change in semantics.

Overrides:

clone in class NumberFormat

Following copied from class: java.lang.Object

Returns:

a clone of this instance.

Throws:

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.

OutOfMemoryError - if there is not enough memory.

See Also:

Cloneable

equals

public boolean equals(Object obj)

Overrides equals

Overrides:

equals in class NumberFormat

Following copied from class: java.lang.Object

Parameters:

obj - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Boolean.hashCode(), Hashtable

hashCode

public int hashCode()

Overrides hashCode

Overrides:

hashCode in class NumberFormat

Following copied from class: java.lang.Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), Hashtable

toPattern

public String toPattern()

Synthesizes a pattern string that represents the current state of this Format object.

See Also:

applyPattern(java.lang.String)

toLocalizedPattern

public String toLocalizedPattern()

Synthesizes a localized pattern string that represents the current state of this Format object.

See Also:

applyPattern(java.lang.String)

applyPattern

public void applyPattern(String pattern)

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.

applyLocalizedPattern

public void applyLocalizedPattern(String 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.

Overrides:

setMaximumIntegerDigits in class NumberFormat

See Also:

NumberFormat.setMaximumIntegerDigits(int)

setMinimumIntegerDigits

public void setMinimumIntegerDigits(int newValue)

Sets the minimum number of digits allowed in the integer portion of a number. This override limits the integer digit count to 309.

Overrides:

setMinimumIntegerDigits in class NumberFormat

See Also:

NumberFormat.setMinimumIntegerDigits(int)

setMaximumFractionDigits

public void setMaximumFractionDigits(int newValue)

Sets the maximum number of digits allowed in the fraction portion of a number. This override limits the fraction digit count to 340.

Overrides:

setMaximumFractionDigits in class NumberFormat

See Also:

NumberFormat.setMaximumFractionDigits(int)

setMinimumFractionDigits

public void setMinimumFractionDigits(int newValue)

Sets the minimum number of digits allowed in the fraction portion of a number. This override limits the fraction digit count to 340.

Overrides:

setMinimumFractionDigits in class NumberFormat

See Also:

NumberFormat.setMinimumFractionDigits(int)