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 in a localized manner. This enables code that can be completely independent of the locale conventions for decimal points, thousands-separators, the particular decimal digits used, or whether the number format is even decimal. For example, this class could be used within an application to produce a number in a currency format according to the conventions of the desired locale.

Getting a NumberFormat

To get a NumberFormat for the default Locale, use one of the static factory methods that return a concrete subclass of NumberFormat. The following formats all provide an example of formatting the Number "2000.50" with the US locale as the default locale. Alternatively, if a NumberFormat for a different locale is required, use one of the overloaded factory methods that take Locale as a parameter, for example, getIntegerInstance(Locale). If the installed locale-sensitive service implementation does not support the given Locale, the parent locale chain will be looked up, and a Locale used that is supported.

Locale Extensions

Formatting behavior can be changed when using a locale that contains any of the following Unicode extensions,

If both "nu" and "rg" are specified, the decimal digits from the "nu" extension supersedes the implicit one from the "rg" extension. Although Unicode extensions defines various keys and values, actual locale-sensitive service implementations in a Java Runtime Environment might not support any particular Unicode locale attributes or key/type pairs.

Below is an example of a "US" locale currency format with accounting style,

NumberFormat.getCurrencyInstance(Locale.forLanguageTag("en-US-u-cf-account"));
With this style, a negative value is formatted enclosed in parentheses, instead of being prepended with a minus sign.

Using NumberFormat

The following is an example of formatting and parsing in a localized fashion, 
NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(Locale.US);
currencyFormat.format(100000); // returns "$100,000.00"
currencyFormat.parse("$100,000.00"); // returns 100000

Customizing NumberFormat

NumberFormat provides API to customize formatting and parsing behavior,
  • setParseIntegerOnly(boolean); when true, will only return the integer portion of the number parsed from the String.
  • setMinimumFractionDigits(int); Use to adjust the expected digits when formatting. Use any of the other minimum/maximum or fraction/integer setter methods in the same manner.
  • setGroupingUsed(boolean); when true, formatted numbers will be displayed with grouping separators. Additionally, when false, parsing will not expect grouping separators in the parsed String.
  • setStrict(boolean); when true, parsing will be done strictly. The behavior of strict parsing should be referred to in the implementing NumberFormat subclass.

To provide more control over formatting or parsing behavior, type checking can be done to safely convert to an implementing subclass of NumberFormat; this provides additional methods defined by the subclass. For example, 

NumberFormat nFmt = NumberFormat.getInstance(Locale.US);
if (nFmt instanceof DecimalFormat dFmt) {
    dFmt.setDecimalSeparatorAlwaysShown(true);
    dFmt.format(100); // returns "100."
}
The NumberFormat subclass returned by the factory methods is dependent on the locale-service provider implementation installed, and may not always be DecimalFormat or CompactNumberFormat.

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.

Leniency

NumberFormat by default, parses leniently. Subclasses may consider implementing strict parsing and as such, overriding and providing implementations for the optional isStrict() and setStrict(boolean) methods.

Lenient parsing should be used when attempting to parse a number out of a String that contains non-numerical or non-format related values. For example, using a Locale.US currency format to parse the number 1000 out of the String "$1,000.00 was paid".

Strict parsing should be used when attempting to ensure a String adheres exactly to a locale's conventions, and can thus serve to validate input. For example, successfully parsing the number 1000.55 out of the String "1.000,55" confirms the String exactly adhered to the Locale.GERMANY numerical conventions.

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:
Null Parameter Handling Default RoundingMode
Since:
1.1
External Specifications
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 the given string to produce an object.

      This 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 object 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.

      Specified by:
      parseObject in class Format
      Implementation Requirements:
      This implementation is equivalent to calling parse(source, pos).
      Parameters:
      source - the String to parse
      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)
      Parses text from the beginning of the given string to produce a Number.

      This method attempts to parse text starting at the index given by the ParsePosition. If parsing succeeds, then the index of the ParsePosition 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 ParsePosition can be used to indicate the starting point for the next call to this method. If an error occurs, then the index of the ParsePosition is not changed, the error index of the ParsePosition is set to the index of the character where the error occurred, and null is returned.

      This method will return a Long if possible (e.g., within the range [Long.MIN_VALUE, Long.MAX_VALUE] and with no decimals), otherwise a Double.

      Parameters:
      source - the String to parse
      parsePosition - A ParsePosition object with index and error index information as described above.
      Returns:
      A Number parsed from the string. In case of failure, returns null.
      Throws:
      NullPointerException - if source or ParsePosition is null.
      See Also:

    • parse

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

      This method will return a Long if possible (e.g., within the range [Long.MIN_VALUE, Long.MAX_VALUE] and with no decimals), otherwise a Double.

      Parameters:
      source - A String, to be parsed from the beginning.
      Returns:
      A Number parsed from the string.
      Throws:
      ParseException - if parsing fails
      NullPointerException - if source is null.
      See Also:

    • isParseIntegerOnly

      public boolean isParseIntegerOnly()
      Returns true if this format will parse numbers as integers only. The ParsePosition index will be set to the position of the decimal symbol. The exact format accepted by the parse operation is locale dependent. For example in the English locale, with ParseIntegerOnly true, the string "123.45" would be parsed as the integer value 123.
      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:

    • isStrict

      public boolean isStrict()
      Returns true if this format will parse numbers strictly; false otherwise.
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses should override this method when implementing strict parsing.
      Returns:
      true if this format will parse numbers strictly; false otherwise
      Throws:
      UnsupportedOperationException - if the implementation of this method does not support this operation
      Since:
      23
      See Also:

    • setStrict

      public void setStrict(boolean strict)
      Change the leniency value for parsing. Parsing can either be strict or lenient, by default it is lenient.
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses should override this method when implementing strict parsing.
      Parameters:
      strict - true if parsing should be done strictly; false otherwise
      Throws:
      UnsupportedOperationException - if the implementation of this method does not support this operation
      Since:
      23
      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
      External Specifications

    • 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. At a minimum, the returned array must contain a Locale instance equal to Locale.ROOT and a Locale instance equal to Locale.US.
      Returns:
      An array of locales for which localized NumberFormat instances are available.

    • hashCode

      public int hashCode()
      Returns the hash code for this NumberFormat.
      Overrides:
      hashCode in class Object
      Implementation Requirements:
      This method calculates the hash code value using the values returned by getMaximumIntegerDigits() and getMaximumFractionDigits().
      Returns:
      the hash code for this NumberFormat
      See Also:

    • equals

      public boolean equals(Object obj)
      Compares the specified object with this NumberFormat for equality. Returns true if the object is also a NumberFormat and the two formats would format any value the same.
      Overrides:
      equals in class Object
      Implementation Requirements:
      This method performs an equality check with a notion of class identity based on getClass(), rather than instanceof. Therefore, in the equals methods in subclasses, no instance of this class should compare as equal to an instance of a subclass.
      Parameters:
      obj - object to be compared for equality
      Returns:
      true if the specified object is equal to this NumberFormat
      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(Currency).
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses should override this method if currency formatting is desired.
      Returns:
      the currency used by this number format, or null
      Throws:
      UnsupportedOperationException - if the implementation of this method does not support this operation
      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.
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses should override this method if currency formatting is desired.
      Parameters:
      currency - the new currency to be used by this number format
      Throws:
      NullPointerException - if currency is null
      UnsupportedOperationException - if the implementation of this method does not support this operation
      Since:
      1.4

    • getRoundingMode

      public RoundingMode getRoundingMode()
      Gets the RoundingMode used in this NumberFormat.
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses which handle different rounding modes should override this method.
      Returns:
      The RoundingMode used for this NumberFormat.
      Throws:
      UnsupportedOperationException - if the implementation of this method does not support this operation
      Since:
      1.6
      See Also:

    • setRoundingMode

      public void setRoundingMode(RoundingMode roundingMode)
      Sets the RoundingMode used in this NumberFormat.
      Implementation Requirements:
      The default implementation always throws UnsupportedOperationException. Subclasses which handle different rounding modes should override this method.
      Parameters:
      roundingMode - The RoundingMode to be used
      Throws:
      NullPointerException - if roundingMode is null
      UnsupportedOperationException - if the implementation of this method does not support this operation
      Since:
      1.6
      See Also: