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Java Standard Edition (SE)

NumberFormat


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Class NumberFormat

  • All Implemented Interfaces:
    Serializable, Cloneable
    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 < 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.

    See Also:
    DecimalFormat, ChoiceFormat, Serialized Form
    • 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, Constant Field Values
      • 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, Constant Field Values
    • Constructor Detail

      • NumberFormat

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

      • 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 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.format(java.lang.Object)
      • 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.format(java.lang.Object)
      • 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 - the field position
        Returns:
        the formatted StringBuffer
        Throws:
        ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
        See Also:
        Format.format(java.lang.Object)
      • 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 - the field position
        Returns:
        the formatted StringBuffer
        Throws:
        ArithmeticException - if rounding is needed with rounding mode being set to RoundingMode.UNNECESSARY
        See Also:
        Format.format(java.lang.Object)
      • 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:
        isParseIntegerOnly(), Format.parseObject(java.lang.String, java.text.ParsePosition)
      • 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 dependant 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:
        isParseIntegerOnly()
      • 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 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 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:
        getRoundingMode()
      • getCurrencyInstance

        public static NumberFormat getCurrencyInstance(Locale inLocale)
        Returns a currency format for the specified locale.
        Parameters:
        inLocale - the desired locale
        Returns:
        the NumberFormat instance for currency formatting
      • 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
      • 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.
      • 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:
        Object.hashCode(), HashMap
      • clone

        public Object clone()
        Overrides Cloneable.
        Overrides:
        clone in class Format
        Returns:
        a clone of this instance.
        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.
        Returns:
        true if grouping is used; false otherwise
        See Also:
        setGroupingUsed(boolean)
      • 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:
        isGroupingUsed()
      • 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(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.
        Returns:
        the minimum number of digits
        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.
        Returns:
        the maximum number of digits.
        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.
        Returns:
        the minimum number of digits
        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()
      • 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


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