Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class NumberFormat - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.text
Class NumberFormat

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

Direct Known Subclasses:: ChoiceFormat, DecimalFormat

public abstract class NumberFormat
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 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, Serialized Form

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 an object to produce a string.

static Locale[] getAvailableLocales()
          Get the set of Locales for which NumberFormats are installed

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 the default number format for the current default locale.

static NumberFormat getInstance(Locale inLocale)
          Returns the default 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 text)
          Convenience method.

abstract Number parse(String text, 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 parsePosition)
          Parses a string to produce an object.

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, 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

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

Constructor Detail

NumberFormat

public NumberFormat()

Method Detail

format

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

Description copied from class: Format

Formats an object to produce a string. Subclasses will implement for particular object, such as:

 StringBuffer format (Number obj, StringBuffer toAppendTo)
 Number parse (String str)

These general routines allow polymorphic parsing and formatting for objects such as the MessageFormat.

Overrides:: format in class Format

Tags copied from class: Format

Parameters:: obj - The object to format; toAppendTo - where the 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 (this allows chaining, as with StringBuffer.append())
Throws:: IllegalArgumentException - when the Format cannot format the given object.
See Also:: MessageFormat, FieldPosition

parseObject

public final Object parseObject(String source,
                                ParsePosition parsePosition)

Description copied from class: Format

Parses a string to produce an object. Subclasses will typically implement for particular object, such as:

       String format (Number obj);
       String format (long obj);
       String format (double obj);
       Number parse (String str);

Overrides:: parseObject in class Format

Tags copied from class: Format

Parameters:

status - Input-Output parameter.

Before calling, set status.index to the offset you want to start parsing at in the source. After calling, status.index is the end of the text you parsed. If error occurs, index is unchanged.

When parsing, leading whitespace is discarded (with successful parse), while trailing whitespace is left as is.

Example: Parsing "_12_xy" (where _ represents a space) for a number, with index == 0 will result in the number 12, with status.index updated to 3 (just before the second space). Parsing a second time will result in a ParseException since "xy" is not a number, and leave index at 3.

Subclasses will typically supply specific parse methods that return different types of values. Since methods can't overload on return types, these will typically be named "parse", while this polymorphic method will always be called parseObject. Any parse method that does not take a status should throw ParseException when no text in the required format is at the start position.

Returns:

Object parsed from string. In case of error, returns null.

See Also:

ParsePosition

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 text,
                             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 text)
             throws ParseException

Convenience method.

Throws:: ParseException - if the specified string is invalid.
See Also:: format(java.lang.Object, java.lang.StringBuffer, java.text.FieldPosition)

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

Tags copied from 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

Tags copied from 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:: Boolean.hashCode(), Hashtable

clone

public Object clone()

Overrides Cloneable

Overrides:: clone in class Format

Tags copied from class: 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

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()

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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.

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 an object to produce a string.
`static Locale[]`	`getAvailableLocales()` Get the set of Locales for which NumberFormats are installed
`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 the default number format for the current default locale.
`static NumberFormat`	`getInstance(Locale inLocale)` Returns the default 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 text)` Convenience method.
`abstract Number`	`parse(String text, 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 parsePosition)` Parses a string to produce an object.
`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.

Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class NumberFormat - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

java.text Class NumberFormat

INTEGER_FIELD

FRACTION_FIELD

NumberFormat

format

parseObject

format

format

format

format

parse

parse

isParseIntegerOnly

setParseIntegerOnly

getInstance

getInstance

getNumberInstance

getNumberInstance

getCurrencyInstance

getCurrencyInstance

getPercentInstance

getPercentInstance

getAvailableLocales

hashCode

equals

clone

isGroupingUsed

setGroupingUsed

getMaximumIntegerDigits

setMaximumIntegerDigits

getMinimumIntegerDigits

setMinimumIntegerDigits

getMaximumFractionDigits

setMaximumFractionDigits

getMinimumFractionDigits

setMinimumFractionDigits

java.text
Class NumberFormat