NumberFormat

public abstract class NumberFormat extends Format
Known Direct Subclasses

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 < myNumber.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:
  1. 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.
  2. 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.

Nested Class Summary

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

Constant Summary

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

Protected Constructor Summary

NumberFormat()
Sole constructor.

Public Method Summary

Object
clone()
Overrides Cloneable
boolean
equals(Object obj)
Overrides equals
StringBuffer
format(Object number, StringBuffer toAppendTo, FieldPosition pos)
Formats a number and appends the resulting text to the given string buffer.
final String
format(double number)
Specialization of format.
abstract StringBuffer
format(double number, StringBuffer toAppendTo, FieldPosition pos)
Specialization of format.
final String
format(long number)
Specialization of format.
abstract StringBuffer
format(long number, StringBuffer toAppendTo, FieldPosition pos)
Specialization of format.
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(Locale inLocale)
Returns a currency format for the specified locale.
final static NumberFormat
getCurrencyInstance()
Returns a currency format for the current default locale.
final 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.
final 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.
final 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(Locale inLocale)
Returns a percentage format for the specified locale.
final static NumberFormat
getPercentInstance()
Returns a percentage format for the current default locale.
RoundingMode
getRoundingMode()
Gets the RoundingMode used in this NumberFormat.
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.
final 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.
void
setRoundingMode(RoundingMode roundingMode)
Sets the RoundingMode used in this NumberFormat.

Inherited Method Summary

Constants

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
Constant Value: 1

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
Constant Value: 0

Protected Constructors

protected NumberFormat ()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Public Methods

public Object clone ()

Overrides Cloneable

Returns
  • a clone of this instance.

public boolean equals (Object obj)

Overrides equals

Parameters
obj the object to compare this instance with.
Returns
  • true if the specified object is equal to this Object; false otherwise.

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 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 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.

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
ArithmeticException if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
See Also

public final String format (double number)

Specialization of format.

Parameters
number
Throws
ArithmeticException if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
See Also

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

Specialization of format.

Parameters
number
toAppendTo
pos
Throws
ArithmeticException if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
See Also

public final String format (long number)

Specialization of format.

Parameters
number
Throws
ArithmeticException if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
See Also

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

Specialization of format.

Parameters
number
toAppendTo
pos
Throws
ArithmeticException if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
See Also

public static Locale[] getAvailableLocales ()

Returns an array of all locales for which the get*Instance methods of this class can return localized instances. The returned array represents the union of locales supported by the Java runtime and by installed NumberFormatProvider implementations. It must contain at least a Locale instance equal to Locale.US.

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

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

public static NumberFormat getCurrencyInstance (Locale inLocale)

Returns a currency format for the specified locale.

Parameters
inLocale

public static final NumberFormat getCurrencyInstance ()

Returns a currency format for the current default locale.

public static final NumberFormat getInstance ()

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

public static NumberFormat getInstance (Locale inLocale)

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

Parameters
inLocale

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 half-even rounding (see RoundingMode.HALF_EVEN) for formatting, and to parse only the integer part of an input string (see isParseIntegerOnly).

Returns
  • a number format for integer values

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 half-even rounding (see RoundingMode.HALF_EVEN) for formatting, and to parse only the integer part of an input string (see isParseIntegerOnly).

Parameters
inLocale
Returns
  • a number format for integer values

public int getMaximumFractionDigits ()

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

public int getMaximumIntegerDigits ()

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

public int getMinimumFractionDigits ()

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

public int getMinimumIntegerDigits ()

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

public static final NumberFormat getNumberInstance ()

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

public static NumberFormat getNumberInstance (Locale inLocale)

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

Parameters
inLocale

public static NumberFormat getPercentInstance (Locale inLocale)

Returns a percentage format for the specified locale.

Parameters
inLocale

public static final NumberFormat getPercentInstance ()

Returns a percentage format for the current default locale.

public RoundingMode getRoundingMode ()

Gets the RoundingMode used in this NumberFormat. The default implementation of this method in NumberFormat always throws UnsupportedOperationException. Subclasses which handle different rounding modes should override this method.

Returns
  • The RoundingMode used for this NumberFormat.
Throws
UnsupportedOperationException The default implementation always throws this exception

public int hashCode ()

Overrides hashCode

Returns
  • this object's hash code.

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.

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.

public Number parse (String source)

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.

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!

Parameters
source
parsePosition

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.

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.

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

public void setGroupingUsed (boolean newValue)

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

Parameters
newValue
See Also

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.

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.

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.

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.

public void setParseIntegerOnly (boolean value)

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

Parameters
value

public void setRoundingMode (RoundingMode roundingMode)

Sets the RoundingMode used in this NumberFormat. The default implementation of this method in NumberFormat always throws UnsupportedOperationException. Subclasses which handle different rounding modes should override this method.

Parameters
roundingMode The RoundingMode to be used
Throws
UnsupportedOperationException The default implementation always throws this exception
NullPointerException if roundingMode is null