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Class java.text.DecimalFormat - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.text.DecimalFormat 

java.lang.Object
   |
   +----java.text.Format
           |
           +----java.text.NumberFormat
                   |
                   +----java.text.DecimalFormat
public class DecimalFormat
extends NumberFormat
DecimalFormat is a concrete subclass of NumberFormat for formatting decimal numbers. This class allows for a variety of parameters, and localization to Western, Arabic, or Indic numbers.

Normally, you get the proper NumberFormat for a specific locale (including the default locale) using one of NumberFormat's factory methods such as getInstance. You may then modify it from there (after testing to make sure it is a DecimalFormat, of course!)

Either the prefixes or the suffixes must be different for the parse to distinguish positive from negative. Parsing will be unreliable if the digits, thousands or decimal separators are the same, or if any of them occur in the prefixes or suffixes.

Special cases:

NaN is formatted as a single character, typically \\uFFFD.

+/-Infinity is formatted as a single character, typically \\u221E, plus the positive and negative pre/suffixes.

Note: this class is designed for common users; for very large or small numbers, use a format that can express exponential values.

Example: 

 // normally we would have a GUI with a menu for this
 Locale[] locales = NumberFormat.getAvailableLocales();
 double myNumber = -1234.56;
 NumberFormat form;
 // just for fun, we print out a number with the locale number, currency
 // and percent format for each locale we can.
 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) {
            // skip language-only
            continue;
         }
         System.out.print(locales[i].getDisplayName());
         switch (j) {
         default:
             form = NumberFormat.getInstance(locales[i]); break;
         case 1:
             form = NumberFormat.getCurrencyInstance(locales[i]); break;
         case 0:
             form = NumberFormat.getPercentInstance(locales[i]); break;
         }
         try {
             System.out.print(": " + ((DecimalFormat)form).toPattern()
                          + " -> " + form.format(myNumber));
         } catch (IllegalArgumentException iae) { }
         try {
             System.out.println(" -> " + form.parse(form.format(myNumber)));
         } catch (ParseException pe) { }
     }
 }
The following shows the structure of the pattern. 
 pattern    := subpattern{;subpattern}
 subpattern := {prefix}integer{.fraction}{suffix}
 prefix     := '\\u0000'..'\\uFFFD' - specialCharacters
 suffix     := '\\u0000'..'\\uFFFD' - specialCharacters
 integer    := '#'* '0'* '0'
 fraction   := '0'* '#'*
 Notation:
  X*       0 or more 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
The first subpattern is for positive numbers. The second (optional) subpattern is for negative numbers. (In both cases, ',' can occur inside the integer portion--it is just too messy to indicate in BNF.)

Here are the special characters used in the parts of the subpattern, with notes on their usage. 

 Symbol Meaning
 0      a digit
 #      a digit, zero shows as absent
 .      placeholder for decimal separator
 ,      placeholder for grouping separator.
 ;      separates formats.
 -      default negative prefix.
 %      multiply by 100 and show as percentage
 ? multiply by 1000 and show as per mille
 � 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.
 X      any other characters can be used in the prefix or suffix
 '      used to quote special characters in a prefix or suffix.

Notes

If there is no explicit negative subpattern, - is prefixed to the positive form. That is, "0.00" alone is equivalent to "0.00;-0.00".

Illegal patterns, such as "#.#.#" or mixing '_' and '*' in the same pattern, will cause an IllegalArgumentException to be thrown. From the message of IllegalArgumentException, you can find the place in the string where the error occurred.

The grouping separator is commonly used for thousands, but in some countries for ten-thousands. The interval is a constant number of digits between the grouping characters, such as 100,000,000 or 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 "#,##,###,####" == "######,####" == "##,####,####".

When calling DecimalFormat.parse(String, ParsePosition) and parsing fails, a null object will be returned. The unchanged parse position also reflects that an error has occurred during parsing. When calling the convenient method DecimalFormat.parse(String) and parsing fails, a ParseException will be thrown.

This class only handles localized digits where the 10 digits are contiguous in Unicode, from 0 to 9. Other digits sets (such as superscripts) would need a different subclass.

See Also:
Format, NumberFormat, ChoiceFormat

Constructor Index

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

Method Index

o applyLocalizedPattern(String)
Apply the given pattern to this Format object.
o applyPattern(String)
Apply the given pattern to this Format object.
o clone()
Standard override; no change in semantics.
o equals(Object)
Overrides equals
o format(double, StringBuffer, FieldPosition)
Specialization of format.
o format(long, StringBuffer, FieldPosition)
Specialization of format.
o getDecimalFormatSymbols()
Returns the decimal format symbols, which is generally not changed by the programmer or user.
o getGroupingSize()
Return the grouping size.
o getMultiplier()
Get the multiplier for use in percent, permill, etc.
o getNegativePrefix()
Get the negative prefix.
o getNegativeSuffix()
Get the negative suffix.
o getPositivePrefix()
Get the positive prefix.
o getPositiveSuffix()
Get the positive suffix.
o hashCode()
Overrides hashCode
o isDecimalSeparatorAlwaysShown()
Allows you to get the behavior of the decimal separator with integers.
o parse(String, ParsePosition)
Returns a Long if possible (e.g.
o setDecimalFormatSymbols(DecimalFormatSymbols)
Sets the decimal format symbols, which is generally not changed by the programmer or user.
o setDecimalSeparatorAlwaysShown(boolean)
Allows you to set the behavior of the decimal separator with integers.
o setGroupingSize(int)
Set the grouping size.
o setMultiplier(int)
Set the multiplier for use in percent, permill, etc.
o setNegativePrefix(String)
Set the negative prefix.
o setNegativeSuffix(String)
Set the positive suffix.
o setPositivePrefix(String)
Set the positive prefix.
o setPositiveSuffix(String)
Set the positive suffix.
o toLocalizedPattern()
Synthesizes a localized pattern string that represents the current state of this Format object.
o toPattern()
Synthesizes a pattern string that represents the current state of this Format object.

Constructors

o 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:
getInstance, getNumberInstance, getCurrencyInstance, getPercentInstance
o 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:
getInstance, getNumberInstance, getCurrencyInstance, getPercentInstance
o 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:
getInstance, getNumberInstance, getCurrencyInstance, getPercentInstance, DecimalFormatSymbols

Methods

o format 
 public StringBuffer format(double number,
                            StringBuffer result,
                            FieldPosition fieldPosition)
Specialization of format.

Overrides:
format in class NumberFormat
o format 
 public StringBuffer format(long number,
                            StringBuffer result,
                            FieldPosition fieldPosition)
Specialization of format.

Overrides:
format in class NumberFormat
o parse 
 public Number parse(String text,
                     ParsePosition parsePosition)
Returns a Long if possible (e.g.

Overrides:
parse in class NumberFormat
o 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
o 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
o getPositivePrefix 
 public String getPositivePrefix()
Get the positive prefix.

Examples: +123, $123, sFr123

o setPositivePrefix 
 public void setPositivePrefix(String newValue)
Set the positive prefix.

Examples: +123, $123, sFr123

o getNegativePrefix 
 public String getNegativePrefix()
Get the negative prefix.

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

o setNegativePrefix 
 public void setNegativePrefix(String newValue)
Set the negative prefix.

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

o getPositiveSuffix 
 public String getPositiveSuffix()
Get the positive suffix.

Example: 123%

o setPositiveSuffix 
 public void setPositiveSuffix(String newValue)
Set the positive suffix.

Example: 123%

o getNegativeSuffix 
 public String getNegativeSuffix()
Get the negative suffix.

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

o setNegativeSuffix 
 public void setNegativeSuffix(String newValue)
Set the positive suffix.

Examples: 123%

o 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

o 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

o 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, isGroupingUsed, getGroupingSeparator
o 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, setGroupingUsed, setGroupingSeparator
o 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

o 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

o clone 
 public Object clone()
Standard override; no change in semantics.

Overrides:
clone in class NumberFormat
o equals 
 public boolean equals(Object obj)
Overrides equals

Overrides:
equals in class NumberFormat
o hashCode 
 public int hashCode()
Overrides hashCode

Overrides:
hashCode in class NumberFormat
o toPattern 
 public String toPattern()
Synthesizes a pattern string that represents the current state of this Format object.

See Also:
applyPattern
o toLocalizedPattern 
 public String toLocalizedPattern()
Synthesizes a localized pattern string that represents the current state of this Format object.

See Also:
applyPattern
o 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.

o 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. 

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