NumberFormat (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

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java.text
Class NumberFormat

java.lang.Object
  java.text.Format
      java.text.NumberFormat

All Implemented Interfaces:: Serializable, Cloneable

Direct Known Subclasses:: ChoiceFormat, DecimalFormat

public abstract class NumberFormat
extends Format
extends Format

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 getIntegerInstance to get an integer 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 DecimalFormat. 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.

Synchronization

Number 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.

See Also:: DecimalFormat, ChoiceFormat, Serialized Form

Nested Class Summary

static class NumberFormat.Field
          Defines constants that are used as attribute keys in the AttributedCharacterIterator returned from NumberFormat.formatToCharacterIterator and as field identifiers in FieldPosition.

Field Summary

static int FRACTION_FIELD
          Field constant used to construct a FieldPosition object.

static int INTEGER_FIELD
          Field constant used to construct a FieldPosition object.

Constructor Summary

NumberFormat()


Method Summary

Object clone()
          Overrides Cloneable

boolean equals(Object obj)
          Overrides equals

String format(double number)
          Specialization of format.

abstract StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition pos)
          Specialization of format.

String format(long number)
          Specialization of format.

abstract StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition pos)
          Specialization of format.

StringBuffer format(Object number, StringBuffer toAppendTo, FieldPosition pos)
          Formats a number and appends the resulting text to the given string buffer.

static Locale[] getAvailableLocales()
          Returns an array of all locales for which the get*Instance methods of this class can return localized instances.

Currency getCurrency()
          Gets the currency used by this number format when formatting currency values.

static NumberFormat getCurrencyInstance()
          Returns a currency format for the current default locale.

static NumberFormat getCurrencyInstance(Locale inLocale)
          Returns a currency format for the specified locale.

static NumberFormat getInstance()
          Returns a general-purpose number format for the current default locale.

static NumberFormat getInstance(Locale inLocale)
          Returns a general-purpose number format for the specified locale.

static NumberFormat getIntegerInstance()
          Returns an integer number format for the current default locale.

static NumberFormat getIntegerInstance(Locale inLocale)
          Returns an integer number format for the specified locale.

int getMaximumFractionDigits()
          Returns the maximum number of digits allowed in the fraction portion of a number.

int getMaximumIntegerDigits()
          Returns the maximum number of digits allowed in the integer portion of a number.

int getMinimumFractionDigits()
          Returns the minimum number of digits allowed in the fraction portion of a number.

int getMinimumIntegerDigits()
          Returns the minimum number of digits allowed in the integer portion of a number.

static NumberFormat getNumberInstance()
          Returns a general-purpose number format for the current default locale.

static NumberFormat getNumberInstance(Locale inLocale)
          Returns a general-purpose number format for the specified locale.

static NumberFormat getPercentInstance()
          Returns a percentage format for the current default locale.

static NumberFormat getPercentInstance(Locale inLocale)
          Returns a percentage format for the specified locale.

int hashCode()
          Overrides hashCode

boolean isGroupingUsed()
          Returns true if grouping is used in this format.

boolean isParseIntegerOnly()
          Returns true if this format will parse numbers as integers only.

Number parse(String source)
          Parses text from the beginning of the given string to produce a number.

abstract Number parse(String source, ParsePosition parsePosition)
          Returns a Long if possible (e.g., within the range [Long.MIN_VALUE, Long.MAX_VALUE] and with no decimals), otherwise a Double.

Object parseObject(String source, ParsePosition pos)
          Parses text from a string to produce a Number.

void setCurrency(Currency currency)
          Sets the currency used by this number format when formatting currency values.

void setGroupingUsed(boolean newValue)
          Set whether or not grouping will be used in this format.

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 setParseIntegerOnly(boolean value)
          Sets whether or not numbers should be parsed as integers only.

Methods inherited from class java.text.Format

format, formatToCharacterIterator, parseObject

Methods inherited from class java.lang.Object

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

Nested Class Summary
`static class`	`NumberFormat.Field` Defines constants that are used as attribute keys in the `AttributedCharacterIterator` returned from `NumberFormat.formatToCharacterIterator` and as field identifiers in `FieldPosition`.

Field Summary
`static int`	`FRACTION_FIELD` Field constant used to construct a FieldPosition object.
`static int`	`INTEGER_FIELD` Field constant used to construct a FieldPosition object.

Constructor Summary
`NumberFormat()`

Method Summary
`Object`	`clone()` Overrides Cloneable
`boolean`	`equals(Object obj)` Overrides equals
`String`	`format(double number)` Specialization of format.
`abstract StringBuffer`	`format(double number, StringBuffer toAppendTo, FieldPosition pos)` Specialization of format.
`String`	`format(long number)` Specialization of format.
`abstract StringBuffer`	`format(long number, StringBuffer toAppendTo, FieldPosition pos)` Specialization of format.
`StringBuffer`	`format(Object number, StringBuffer toAppendTo, FieldPosition pos)` Formats a number and appends the resulting text to the given string buffer.
`static Locale[]`	`getAvailableLocales()` Returns an array of all locales for which the `get*Instance` methods of this class can return localized instances.
`Currency`	`getCurrency()` Gets the currency used by this number format when formatting currency values.
`static NumberFormat`	`getCurrencyInstance()` Returns a currency format for the current default locale.
`static NumberFormat`	`getCurrencyInstance(Locale inLocale)` Returns a currency format for the specified locale.
`static NumberFormat`	`getInstance()` Returns a general-purpose number format for the current default locale.
`static NumberFormat`	`getInstance(Locale inLocale)` Returns a general-purpose number format for the specified locale.
`static NumberFormat`	`getIntegerInstance()` Returns an integer number format for the current default locale.
`static NumberFormat`	`getIntegerInstance(Locale inLocale)` Returns an integer number format for the specified locale.
`int`	`getMaximumFractionDigits()` Returns the maximum number of digits allowed in the fraction portion of a number.
`int`	`getMaximumIntegerDigits()` Returns the maximum number of digits allowed in the integer portion of a number.
`int`	`getMinimumFractionDigits()` Returns the minimum number of digits allowed in the fraction portion of a number.
`int`	`getMinimumIntegerDigits()` Returns the minimum number of digits allowed in the integer portion of a number.
`static NumberFormat`	`getNumberInstance()` Returns a general-purpose number format for the current default locale.
`static NumberFormat`	`getNumberInstance(Locale inLocale)` Returns a general-purpose number format for the specified locale.
`static NumberFormat`	`getPercentInstance()` Returns a percentage format for the current default locale.
`static NumberFormat`	`getPercentInstance(Locale inLocale)` Returns a percentage format for the specified locale.
`int`	`hashCode()` Overrides hashCode
`boolean`	`isGroupingUsed()` Returns true if grouping is used in this format.
`boolean`	`isParseIntegerOnly()` Returns true if this format will parse numbers as integers only.
`Number`	`parse(String source)` Parses text from the beginning of the given string to produce a number.
`abstract Number`	`parse(String source, ParsePosition parsePosition)` Returns a Long if possible (e.g., within the range [Long.MIN_VALUE, Long.MAX_VALUE] and with no decimals), otherwise a Double.
`Object`	`parseObject(String source, ParsePosition pos)` Parses text from a string to produce a `Number`.
`void`	`setCurrency(Currency currency)` Sets the currency used by this number format when formatting currency values.
`void`	`setGroupingUsed(boolean newValue)` Set whether or not grouping will be used in this format.
`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`	`setParseIntegerOnly(boolean value)` Sets whether or not numbers should be parsed as integers only.

Methods inherited from class java.text.Format
`format, formatToCharacterIterator, parseObject`

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

Field Detail

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, Constant Field Values

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, Constant Field Values

Constructor Detail

NumberFormat

public NumberFormat()

Method Detail

format

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

Formats a number and appends the resulting text to the given string buffer. The number can be of any subclass of Number.

This implementation extracts the number's value using Number.longValue() for all integral type values that can be converted to long without loss of information, including BigInteger values with a bit length of less than 64, and Number.doubleValue() for all other types. It then calls format(long,java.lang.StringBuffer,java.text.FieldPosition) or format(double,java.lang.StringBuffer,java.text.FieldPosition). This may result in loss of magnitude information and precision for BigInteger and BigDecimal values.

Specified by:: format in class Format

Parameters:: number - the number to format; toAppendTo - the StringBuffer to which the formatted text is to be appended; pos - On input: an alignment field, if desired. On output: the offsets of the alignment field.
Returns:: the value passed in as toAppendTo
Throws:: IllegalArgumentException - if number is null or not an instance of Number.; NullPointerException - if toAppendTo or pos is null
See Also:: FieldPosition

parseObject

public final Object parseObject(String source,
                                ParsePosition pos)

Parses text from a string to produce a Number.

The method attempts to parse text starting at the index given by pos. If parsing succeeds, then the index of pos is updated to the index after the last character used (parsing does not necessarily use all characters up to the end of the string), and the parsed number is returned. The updated pos can be used to indicate the starting point for the next call to this method. If an error occurs, then the index of pos is not changed, the error index of pos is set to the index of the character where the error occurred, and null is returned.

See the parse(String, ParsePosition) method for more information on number parsing.

Specified by:: parseObject in class Format

Parameters:: source - A String, part of which should be parsed.; pos - A ParsePosition object with index and error index information as described above.
Returns:: A Number parsed from the string. In case of error, returns null.
Throws:: NullPointerException - if pos is null.

format

public final String format(double number)

Specialization of format.

See Also:: Format.format(java.lang.Object)

format

public final String format(long number)

Specialization of format.

See Also:: Format.format(java.lang.Object)

format

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

Specialization of format.

See Also:: Format.format(java.lang.Object)

format

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

Specialization of format.

See Also:: Format.format(java.lang.Object)

parse

public abstract Number parse(String source,
                             ParsePosition parsePosition)

Returns a Long if possible (e.g., within the 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(), Format.parseObject(java.lang.String, java.text.ParsePosition)

parse

public Number parse(String source)
             throws ParseException

Parses text from the beginning of the given string to produce a number. The method may not use the entire text of the given string.

See the parse(String, ParsePosition) method for more information on number parsing.

Parameters:: source - A String whose beginning should be parsed.
Returns:: A Number parsed from the string.
Throws:: ParseException - if the beginning of the specified string cannot be parsed.

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 a general-purpose number format for the current default locale. This is the same as calling getNumberInstance().

getInstance

public static NumberFormat getInstance(Locale inLocale)

Returns a general-purpose number format for the specified locale. This is the same as calling getNumberInstance(inLocale).

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.

getIntegerInstance

public static final NumberFormat getIntegerInstance()

Returns an integer number format for the current default locale. The returned number format is configured to round floating point numbers to the nearest integer using IEEE half-even rounding (see ROUND_HALF_EVEN) for formatting, and to parse only the integer part of an input string (see isParseIntegerOnly).

Returns:: a number format for integer values
Since:: 1.4

getIntegerInstance

public static NumberFormat getIntegerInstance(Locale inLocale)

Returns an integer number format for the specified locale. The returned number format is configured to round floating point numbers to the nearest integer using IEEE half-even rounding (see ROUND_HALF_EVEN) for formatting, and to parse only the integer part of an input string (see isParseIntegerOnly).

Parameters:: inLocale - the locale for which a number format is needed
Returns:: a number format for integer values
Since:: 1.4

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()

Returns an array of all locales for which the get*Instance methods of this class can return localized instances. The array returned must contain at least a Locale instance equal to Locale.US.

Returns:: An array of locales for which localized NumberFormat instances are available.

hashCode

public int hashCode()

Overrides hashCode

Overrides:: hashCode in class Object

Returns:: a hash code value for this object.
See Also:: Object.equals(java.lang.Object), Hashtable

equals

public boolean equals(Object obj)

Overrides equals

Overrides:: equals in class 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:: Object.hashCode(), Hashtable

clone

public Object clone()

Overrides Cloneable

Overrides:: clone in class Format

Returns:: a clone of this instance.
See Also:: Cloneable

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(boolean)

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(int)

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.

Parameters:: newValue - the maximum number of integer digits to be shown; if less than zero, then zero is used. The concrete subclass may enforce an upper limit to this value appropriate to the numeric type being formatted.
See Also:: getMaximumIntegerDigits()

getMinimumIntegerDigits

public int getMinimumIntegerDigits()

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

See Also:: setMinimumIntegerDigits(int)

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

Parameters:: newValue - the minimum number of integer digits to be shown; if less than zero, then zero is used. The concrete subclass may enforce an upper limit to this value appropriate to the numeric type being formatted.
See Also:: getMinimumIntegerDigits()

getMaximumFractionDigits

public int getMaximumFractionDigits()

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

See Also:: setMaximumFractionDigits(int)

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.

Parameters:: newValue - the maximum number of fraction digits to be shown; if less than zero, then zero is used. The concrete subclass may enforce an upper limit to this value appropriate to the numeric type being formatted.
See Also:: getMaximumFractionDigits()

getMinimumFractionDigits

public int getMinimumFractionDigits()

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

See Also:: setMinimumFractionDigits(int)

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

Parameters:: newValue - the minimum number of fraction digits to be shown; if less than zero, then zero is used. The concrete subclass may enforce an upper limit to this value appropriate to the numeric type being formatted.
See Also:: getMinimumFractionDigits()

getCurrency

public Currency getCurrency()

Gets the currency used by this number format when formatting currency values. The initial value is derived in a locale dependent way. The returned value may be null if no valid currency could be determined and no currency has been set using setCurrency.

The default implementation throws UnsupportedOperationException.

Returns:: the currency used by this number format, or null
Throws:: UnsupportedOperationException - if the number format class doesn't implement currency formatting
Since:: 1.4

setCurrency

public void setCurrency(Currency currency)

Sets the currency used by this number format when formatting currency values. This does not update the minimum or maximum number of fraction digits used by the number format.

The default implementation throws UnsupportedOperationException.

Parameters:: currency - the new currency to be used by this number format
Throws:: UnsupportedOperationException - if the number format class doesn't implement currency formatting; NullPointerException - if currency is null
Since:: 1.4

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

NumberFormat (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

java.text Class NumberFormat

Synchronization

INTEGER_FIELD

FRACTION_FIELD

NumberFormat

format

parseObject

format

format

format

format

parse

parse

isParseIntegerOnly

setParseIntegerOnly

getInstance

getInstance

getNumberInstance

getNumberInstance

getIntegerInstance

getIntegerInstance

getCurrencyInstance

getCurrencyInstance

getPercentInstance

getPercentInstance

getAvailableLocales

hashCode

equals

clone

isGroupingUsed

setGroupingUsed

getMaximumIntegerDigits

setMaximumIntegerDigits

getMinimumIntegerDigits

setMinimumIntegerDigits

getMaximumFractionDigits

setMaximumFractionDigits

getMinimumFractionDigits

setMinimumFractionDigits

getCurrency

setCurrency

java.text
Class NumberFormat