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

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Class java.text.NumberFormat

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

public abstract class NumberFormat
extends Format
implements Cloneable

NumberFormat is the abstract base class for all number formats. This class provides the interface for formatting and parsing numbers. NumberFormat also provides methods for determining which locales have number formats, and what their names are.

NumberFormat helps you to format and parse numbers for any locale. Your code can be completely independent of the locale conventions for decimal points, thousands-separators, or even the particular decimal digits used, or whether the number format is even decimal.

To format a number for the current Locale, use one of the factory class methods:

  myString = NumberFormat.getInstance().format(myNumber);

If you are formatting multiple numbers, it is more efficient to get the format and use it multiple times so that the system doesn't have to fetch the information about the local language and country conventions multiple times.

 NumberFormat nf = NumberFormat.getInstance();
 for (int i = 0; i < a.length; ++i) {
     output.println(nf.format(myNumber[i]) + "; ");
 }

To format a number for a different Locale, specify it in the call to getInstance.

 NumberFormat nf = NumberFormat.getInstance(Locale.FRENCH);

You can also use a NumberFormat to parse numbers:

 myNumber = nf.parse(myString);

Use getInstance or getNumberInstance to get the normal number format. Use getCurrencyInstance to get the currency number format. And use getPercentInstance to get a format for displaying percentages. With this format, a fraction like 0.53 is displayed as 53%.

You can also control the display of numbers with such methods as setMinimumFractionDigits. If you want even more control over the format or parsing, or want to give your users more control, you can try casting the NumberFormat you get from the factory methods to a DecimalNumberFormat. This will work for the vast majority of locales; just remember to put it in a try block in case you encounter an unusual one.

NumberFormat and DecimalFormat are designed such that some controls work for formatting and others work for parsing. The following is the detailed description for each these control methods,

setParseIntegerOnly : only affects parsing, e.g. if true, "3456.78" -> 3456 (and leaves the parse position just after index 6) if false, "3456.78" -> 3456.78 (and leaves the parse position just after index 8) This is independent of formatting. If you want to not show a decimal point where there might be no digits after the decimal point, use setDecimalSeparatorAlwaysShown.

setDecimalSeparatorAlwaysShown : only affects formatting, and only where there might be no digits after the decimal point, such as with a pattern like "#,##0.##", e.g., if true, 3456.00 -> "3,456." if false, 3456.00 -> "3456" This is independent of parsing. If you want parsing to stop at the decimal point, use setParseIntegerOnly.

You can also use forms of the parse and format methods with ParsePosition and FieldPosition to allow you to:

progressively parse through pieces of a string
align the decimal point and other areas

For example, you can align numbers in two ways:

If you are using a monospaced font with spacing for alignment, you can pass the FieldPosition in your format call, with field = INTEGER_FIELD. On output, getEndIndex will be set to the offset between the last character of the integer and the decimal. Add (desiredSpaceCount - getEndIndex) spaces at the front of the string.
If you are using proportional fonts, instead of padding with spaces, measure the width of the string in pixels from the start to getEndIndex. Then move the pen by (desiredPixelWidth - widthToAlignmentPoint) before drawing the text. It also works where there is no decimal, but possibly additional characters at the end, e.g. with parentheses in negative numbers: "(12)" for -12.

See Also:: DecimalFormat, ChoiceFormat

FRACTION_FIELD: Field constant used to construct a FieldPosition object.
INTEGER_FIELD: Field constant used to construct a FieldPosition object.

NumberFormat()

clone(): Overrides Cloneable
equals(Object): Overrides equals
format(double): Specialization of format.
format(double, StringBuffer, FieldPosition): Specialization of format.
format(long): Specialization of format.
format(long, StringBuffer, FieldPosition): Specialization of format.
format(Object, StringBuffer, FieldPosition): Formats an object to produce a string.
getAvailableLocales(): Get the set of Locales for which NumberFormats are installed
getCurrencyInstance(): Returns a currency format for the current default locale.
getCurrencyInstance(Locale): Returns a currency format for the specified locale.
getInstance(): Returns the default number format for the current default locale.
getInstance(Locale): Returns the default number format for the specified locale.
getMaximumFractionDigits(): Returns the maximum number of digits allowed in the fraction portion of a number.
getMaximumIntegerDigits(): Returns the maximum number of digits allowed in the integer portion of a number.
getMinimumFractionDigits(): Returns the minimum number of digits allowed in the fraction portion of a number.
getMinimumIntegerDigits(): Returns the minimum number of digits allowed in the integer portion of a number.
getNumberInstance(): Returns a general-purpose number format for the current default locale.
getNumberInstance(Locale): Returns a general-purpose number format for the specified locale.
getPercentInstance(): Returns a percentage format for the current default locale.
getPercentInstance(Locale): Returns a percentage format for the specified locale.
hashCode(): Overrides hashCode
isGroupingUsed(): Returns true if grouping is used in this format.
isParseIntegerOnly(): Returns true if this format will parse numbers as integers only.
parse(String): Convenience method.
parse(String, ParsePosition): Returns a Long if possible (e.g.
parseObject(String, ParsePosition): Parses a string to produce an object.
setGroupingUsed(boolean): Set whether or not grouping will be used in this format.
setMaximumFractionDigits(int): Sets the maximum number of digits allowed in the fraction portion of a number.
setMaximumIntegerDigits(int): Sets the maximum number of digits allowed in the integer portion of a number.
setMinimumFractionDigits(int): Sets the minimum number of digits allowed in the fraction portion of a number.
setMinimumIntegerDigits(int): Sets the minimum number of digits allowed in the integer portion of a number.
setParseIntegerOnly(boolean): Sets whether or not numbers should be parsed as integers only.

INTEGER_FIELD

 public static final int INTEGER_FIELD

Field constant used to construct a FieldPosition object. Signifies that the position of the integer part of a formatted number should be returned.

See Also:: FieldPosition

FRACTION_FIELD

 public static final int FRACTION_FIELD

Field constant used to construct a FieldPosition object. Signifies that the position of the fraction part of a formatted number should be returned.

See Also:: FieldPosition

NumberFormat

 public NumberFormat()

format

 public final StringBuffer format(Object number,
                                  StringBuffer toAppendTo,
                                  FieldPosition pos)

Formats an object to produce a string.

Overrides:: format in class Format

parseObject

 public final Object parseObject(String source,
                                 ParsePosition parsePosition)

Parses a string to produce an object.

Overrides:: parseObject in class Format

format

 public final String format(double number)

Specialization of format.

See Also:: format

format

 public final String format(long number)

Specialization of format.

See Also:: format

format

 public abstract StringBuffer format(double number,
                                     StringBuffer toAppendTo,
                                     FieldPosition pos)

Specialization of format.

See Also:: format

format

 public abstract StringBuffer format(long number,
                                     StringBuffer toAppendTo,
                                     FieldPosition pos)

Specialization of format.

See Also:: format

parse

 public abstract Number parse(String text,
                              ParsePosition parsePosition)

Returns a Long if possible (e.g. within range [Long.MIN_VALUE, Long.MAX_VALUE], and with no decimals), otherwise a Double. If IntegerOnly is set, will stop at a decimal point (or equivalent; e.g. for rational numbers "1 2/3", will stop after the 1). Does not throw an exception; if no object can be parsed, index is unchanged!

See Also:: isParseIntegerOnly, parseObject

parse

 public Number parse(String text) throws ParseException

Convenience method.

Throws: ParseException: if the specified string is invalid.
See Also:: format

isParseIntegerOnly

 public boolean isParseIntegerOnly()

Returns true if this format will parse numbers as integers only. For example in the English locale, with ParseIntegerOnly true, the string "1234." would be parsed as the integer value 1234 and parsing would stop at the "." character. Of course, the exact format accepted by the parse operation is locale dependant and determined by sub-classes of NumberFormat.

setParseIntegerOnly

 public void setParseIntegerOnly(boolean value)

Sets whether or not numbers should be parsed as integers only.

See Also:: isParseIntegerOnly

getInstance

 public static final NumberFormat getInstance()

Returns the default number format for the current default locale. The default format is one of the styles provided by the other factory methods: getNumberInstance, getCurrencyInstance or getPercentInstance. Exactly which one is locale dependant.

getInstance

 public static NumberFormat getInstance(Locale inLocale)

Returns the default number format for the specified locale. The default format is one of the styles provided by the other factory methods: getNumberInstance, getCurrencyInstance or getPercentInstance. Exactly which one is locale dependant.

getNumberInstance

 public static final NumberFormat getNumberInstance()

Returns a general-purpose number format for the current default locale.

getNumberInstance

 public static NumberFormat getNumberInstance(Locale inLocale)

Returns a general-purpose number format for the specified locale.

getCurrencyInstance

 public static final NumberFormat getCurrencyInstance()

Returns a currency format for the current default locale.

getCurrencyInstance

 public static NumberFormat getCurrencyInstance(Locale inLocale)

Returns a currency format for the specified locale.

getPercentInstance

 public static final NumberFormat getPercentInstance()

Returns a percentage format for the current default locale.

getPercentInstance

 public static NumberFormat getPercentInstance(Locale inLocale)

Returns a percentage format for the specified locale.

getAvailableLocales

 public static Locale[] getAvailableLocales()

Get the set of Locales for which NumberFormats are installed

Returns:: available locales

hashCode

 public int hashCode()

Overrides hashCode

Overrides:: hashCode in class Object

equals

 public boolean equals(Object obj)

Overrides equals

Overrides:: equals in class Object

clone

 public Object clone()

Overrides Cloneable

Overrides:: clone in class Format

isGroupingUsed

 public boolean isGroupingUsed()

Returns true if grouping is used in this format. For example, in the English locale, with grouping on, the number 1234567 might be formatted as "1,234,567". The grouping separator as well as the size of each group is locale dependant and is determined by sub-classes of NumberFormat.

See Also:: setGroupingUsed

setGroupingUsed

 public void setGroupingUsed(boolean newValue)

Set whether or not grouping will be used in this format.

See Also:: isGroupingUsed

getMaximumIntegerDigits

 public int getMaximumIntegerDigits()

Returns the maximum number of digits allowed in the integer portion of a number.

See Also:: setMaximumIntegerDigits

setMaximumIntegerDigits

 public void setMaximumIntegerDigits(int newValue)

Sets the maximum number of digits allowed in the integer portion of a number. maximumIntegerDigits must be >= minimumIntegerDigits. If the new value for maximumIntegerDigits is less than the current value of minimumIntegerDigits, then minimumIntegerDigits will also be set to the new value.

See Also:: getMaximumIntegerDigits

getMinimumIntegerDigits

 public int getMinimumIntegerDigits()

Returns the minimum number of digits allowed in the integer portion of a number.

See Also:: setMinimumIntegerDigits

setMinimumIntegerDigits

 public void setMinimumIntegerDigits(int newValue)

Sets the minimum number of digits allowed in the integer portion of a number. minimumIntegerDigits must be <= maximumIntegerDigits. If the new value for minimumIntegerDigits exceeds the current value of maximumIntegerDigits, then maximumIntegerDigits will also be set to the new value

See Also:: getMinimumIntegerDigits

getMaximumFractionDigits

 public int getMaximumFractionDigits()

Returns the maximum number of digits allowed in the fraction portion of a number.

See Also:: setMaximumFractionDigits

setMaximumFractionDigits

 public void setMaximumFractionDigits(int newValue)

Sets the maximum number of digits allowed in the fraction portion of a number. maximumFractionDigits must be >= minimumFractionDigits. If the new value for maximumFractionDigits is less than the current value of minimumFractionDigits, then minimumFractionDigits will also be set to the new value.

See Also:: getMaximumFractionDigits

getMinimumFractionDigits

 public int getMinimumFractionDigits()

Returns the minimum number of digits allowed in the fraction portion of a number.

See Also:: setMinimumFractionDigits

setMinimumFractionDigits

 public void setMinimumFractionDigits(int newValue)

Sets the minimum number of digits allowed in the fraction portion of a number. minimumFractionDigits must be <= maximumFractionDigits. If the new value for minimumFractionDigits exceeds the current value of maximumFractionDigits, then maximumIntegerDigits will also be set to the new value

See Also:: getMinimumFractionDigits

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