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.