Module java.base
Package java.text

Class NumberFormat

java.lang.Object
java.text.Format
java.text.NumberFormat
All Implemented Interfaces:
Serializable, Cloneable
Direct Known Subclasses:
ChoiceFormat, CompactNumberFormat, 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 < 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);

If the locale contains "nu" (numbers) and/or "rg" (region override) Unicode extensions, the decimal digits, and/or the country used for formatting are overridden. If both "nu" and "rg" are specified, the decimal digits from the "nu" extension supersedes the implicit one from the "rg" extension.

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. Use getCompactNumberInstance to get the compact number format to format a number in shorter form. For example, 2000 can be formatted as "2K" in US locale. 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 or CompactNumberFormat depending on the factory method used. 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.

Implementation Requirements:
The format(double, StringBuffer, FieldPosition), format(long, StringBuffer, FieldPosition) and parse(String, ParsePosition) methods may throw NullPointerException, if any of their parameter is null. The subclass may provide its own implementation and specification about NullPointerException.

The default implementation provides rounding modes defined in RoundingMode for formatting numbers. It uses the round half-even algorithm. To change the rounding mode use setRoundingMode. The NumberFormat returned by the static factory methods is configured to round floating point numbers using half-even rounding (see RoundingMode.HALF_EVEN) for formatting.

Since:
1.1
See Also:

  • Field Details

    • 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:

    • 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:

  • Constructor Details

    • NumberFormat

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

  • Method Details

    • 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 - keeps track on the position of the field within the returned string. For example, for formatting a number 1234567.89 in Locale.US locale, if the given fieldPosition is INTEGER_FIELD, the begin index and end index of fieldPosition will be set to 0 and 9, respectively for the output string 1,234,567.89.
      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:

    • 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 source or pos is null.

    • format

      public final String format(double number)
      Specialization of format.
      Parameters:
      number - the double number to format
      Returns:
      the formatted String
      Throws:
      ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
      See Also:

    • format

      public final String format(long number)
      Specialization of format.
      Parameters:
      number - the long number to format
      Returns:
      the formatted String
      Throws:
      ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
      See Also:

    • format

      public abstract StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition pos)
      Specialization of format.
      Parameters:
      number - the double number to format
      toAppendTo - the StringBuffer to which the formatted text is to be appended
      pos - keeps track on the position of the field within the returned string. For example, for formatting a number 1234567.89 in Locale.US locale, if the given fieldPosition is INTEGER_FIELD, the begin index and end index of fieldPosition will be set to 0 and 9, respectively for the output string 1,234,567.89.
      Returns:
      the formatted StringBuffer
      Throws:
      ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
      See Also:

    • format

      public abstract StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition pos)
      Specialization of format.
      Parameters:
      number - the long number to format
      toAppendTo - the StringBuffer to which the formatted text is to be appended
      pos - keeps track on the position of the field within the returned string. For example, for formatting a number 123456789 in Locale.US locale, if the given fieldPosition is INTEGER_FIELD, the begin index and end index of fieldPosition will be set to 0 and 11, respectively for the output string 123,456,789.
      Returns:
      the formatted StringBuffer
      Throws:
      ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
      See Also:

    • 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!
      Parameters:
      source - the String to parse
      parsePosition - the parse position
      Returns:
      the parsed value
      See Also:

    • 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 dependent and determined by sub-classes of NumberFormat.
      Returns:
      true if numbers should be parsed as integers only; false otherwise

    • setParseIntegerOnly

      public void setParseIntegerOnly(boolean value)
      Sets whether or not numbers should be parsed as integers only.
      Parameters:
      value - true if numbers should be parsed as integers only; false otherwise
      See Also:

    • getInstance

      public static final NumberFormat getInstance()
      Returns a general-purpose number format for the current default FORMAT locale. This is the same as calling getNumberInstance().
      Returns:
      the NumberFormat instance for general-purpose number formatting

    • 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).
      Parameters:
      inLocale - the desired locale
      Returns:
      the NumberFormat instance for general-purpose number formatting

    • getNumberInstance

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

      This is equivalent to calling getNumberInstance(Locale.getDefault(Locale.Category.FORMAT)).

      Returns:
      the NumberFormat instance for general-purpose number formatting
      See Also:

    • getNumberInstance

      public static NumberFormat getNumberInstance(Locale inLocale)
      Returns a general-purpose number format for the specified locale.
      Parameters:
      inLocale - the desired locale
      Returns:
      the NumberFormat instance for general-purpose number formatting

    • getIntegerInstance

      public static final NumberFormat getIntegerInstance()
      Returns an integer number format for the current default FORMAT 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).

      This is equivalent to calling getIntegerInstance(Locale.getDefault(Locale.Category.FORMAT)).

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

    • 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 half-even rounding (see RoundingMode.HALF_EVEN) for formatting, and to parse only the integer part of an input string (see isParseIntegerOnly).
      Parameters:
      inLocale - the desired locale
      Returns:
      a number format for integer values
      Since:
      1.4
      See Also:

    • getCurrencyInstance

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

      This is equivalent to calling getCurrencyInstance(Locale.getDefault(Locale.Category.FORMAT)).

      Returns:
      the NumberFormat instance for currency formatting
      See Also:

    • getCurrencyInstance

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

      If the specified locale contains the "cf" ( currency format style) Unicode extension, the returned currency format uses the style if it is available. Otherwise, the style uses the default "standard" currency format. For example, if the style designates "account", negative currency amounts use a pair of parentheses in some locales.

      Parameters:
      inLocale - the desired locale
      Returns:
      the NumberFormat instance for currency formatting

    • getPercentInstance

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

      This is equivalent to calling getPercentInstance(Locale.getDefault(Locale.Category.FORMAT)).

      Returns:
      the NumberFormat instance for percentage formatting
      See Also:

    • getPercentInstance

      public static NumberFormat getPercentInstance(Locale inLocale)
      Returns a percentage format for the specified locale.
      Parameters:
      inLocale - the desired locale
      Returns:
      the NumberFormat instance for percentage formatting

    • getCompactNumberInstance

      public static NumberFormat getCompactNumberInstance()
      Returns a compact number format for the default FORMAT locale with "SHORT" format style.
      Returns:
      A NumberFormat instance for compact number formatting
      Since:
      12
      See Also:

    • getCompactNumberInstance

      public static NumberFormat getCompactNumberInstance(Locale locale, NumberFormat.Style formatStyle)
      Returns a compact number format for the specified locale and formatStyle.
      Parameters:
      locale - the desired locale
      formatStyle - the style for formatting a number
      Returns:
      A NumberFormat instance for compact number formatting
      Throws:
      NullPointerException - if locale or formatStyle is null
      Since:
      12
      See Also:

    • 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 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.

    • hashCode

      public int hashCode()
      Overrides hashCode.
      Overrides:
      hashCode in class Object
      Returns:
      a hash code value for this object.
      See Also:

    • 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:

    • clone

      public Object clone()
      Overrides Cloneable.
      Overrides:
      clone in class Format
      Returns:
      a clone of this instance.
      See Also:

    • 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 dependent and is determined by sub-classes of NumberFormat.
      Returns:
      true if grouping is used; false otherwise
      See Also:

    • setGroupingUsed

      public void setGroupingUsed(boolean newValue)
      Set whether or not grouping will be used in this format.
      Parameters:
      newValue - true if grouping is used; false otherwise
      See Also:

    • getMaximumIntegerDigits

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

    • 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:

    • getMinimumIntegerDigits

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

    • 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:

    • getMaximumFractionDigits

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

    • 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:

    • getMinimumFractionDigits

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

    • 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 maximumFractionDigits 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:

    • 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

    • getRoundingMode

      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
      Since:
      1.6
      See Also:

    • setRoundingMode

      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
      Since:
      1.6
      See Also: