Module java.base
Package java.text

Class ChoiceFormat

  • All Implemented Interfaces:
    Serializable, Cloneable

    public class ChoiceFormat
    extends NumberFormat
    A ChoiceFormat allows you to attach a format to a range of numbers. It is generally used in a MessageFormat for handling plurals. The choice is specified with an ascending list of doubles, where each item specifies a half-open interval up to the next item:
     X matches j if and only if limit[j] ≤ X < limit[j+1]
    If there is no match, then either the first or last index is used, depending on whether the number (X) is too low or too high. If the limit array is not in ascending order, the results of formatting will be incorrect. ChoiceFormat also accepts \u221E as equivalent to infinity(INF).

    Note: ChoiceFormat differs from the other Format classes in that you create a ChoiceFormat object with a constructor (not with a getInstance style factory method). The factory methods aren't necessary because ChoiceFormat doesn't require any complex setup for a given locale. In fact, ChoiceFormat doesn't implement any locale specific behavior.

    When creating a ChoiceFormat, you must specify an array of formats and an array of limits. The length of these arrays must be the same. For example,

    • limits = {1,2,3,4,5,6,7}
      formats = {"Sun","Mon","Tue","Wed","Thur","Fri","Sat"}
    • limits = {0, 1, ChoiceFormat.nextDouble(1)}
      formats = {"no files", "one file", "many files"}
      (nextDouble can be used to get the next higher double, to make the half-open interval.)

    Here is a simple example that shows formatting and parsing:

     double[] limits = {1,2,3,4,5,6,7};
     String[] dayOfWeekNames = {"Sun","Mon","Tue","Wed","Thur","Fri","Sat"};
     ChoiceFormat form = new ChoiceFormat(limits, dayOfWeekNames);
     ParsePosition status = new ParsePosition(0);
     for (double i = 0.0; i <= 8.0; ++i) {
         System.out.println(i + " -> " + form.format(i) + " -> "
                                  + form.parse(form.format(i),status));
    Here is a more complex example, with a pattern format:
     double[] filelimits = {0,1,2};
     String[] filepart = {"are no files","is one file","are {2} files"};
     ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart);
     Format[] testFormats = {fileform, null, NumberFormat.getInstance()};
     MessageFormat pattform = new MessageFormat("There {0} on {1}");
     Object[] testArgs = {null, "ADisk", null};
     for (int i = 0; i < 4; ++i) {
         testArgs[0] = new Integer(i);
         testArgs[2] = testArgs[0];

    Specifying a pattern for ChoiceFormat objects is fairly straightforward. For example:

     ChoiceFormat fmt = new ChoiceFormat(
          "-1#is negative| 0#is zero or fraction | 1#is one |1.0<is 1+ |2#is two |2<is more than 2.");
     System.out.println("Formatter Pattern : " + fmt.toPattern());
     System.out.println("Format with -INF : " + fmt.format(Double.NEGATIVE_INFINITY));
     System.out.println("Format with -1.0 : " + fmt.format(-1.0));
     System.out.println("Format with 0 : " + fmt.format(0));
     System.out.println("Format with 0.9 : " + fmt.format(0.9));
     System.out.println("Format with 1.0 : " + fmt.format(1));
     System.out.println("Format with 1.5 : " + fmt.format(1.5));
     System.out.println("Format with 2 : " + fmt.format(2));
     System.out.println("Format with 2.1 : " + fmt.format(2.1));
     System.out.println("Format with NaN : " + fmt.format(Double.NaN));
     System.out.println("Format with +INF : " + fmt.format(Double.POSITIVE_INFINITY));
    And the output result would be like the following:
     Format with -INF : is negative
     Format with -1.0 : is negative
     Format with 0 : is zero or fraction
     Format with 0.9 : is zero or fraction
     Format with 1.0 : is one
     Format with 1.5 : is 1+
     Format with 2 : is two
     Format with 2.1 : is more than 2.
     Format with NaN : is negative
     Format with +INF : is more than 2.


    Choice formats are 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, MessageFormat, Serialized Form
    • Method Detail

      • applyPattern

        public void applyPattern​(String newPattern)
        Sets the pattern.
        newPattern - See the class description.
        NullPointerException - if newPattern is null
      • toPattern

        public String toPattern()
        Gets the pattern.
        the pattern string
      • setChoices

        public void setChoices​(double[] limits,
                               String[] formats)
        Set the choices to be used in formatting.
        limits - contains the top value that you want parsed with that format, and should be in ascending sorted order. When formatting X, the choice will be the i, where limit[i] ≤ X < limit[i+1]. If the limit array is not in ascending order, the results of formatting will be incorrect.
        formats - are the formats you want to use for each limit. They can be either Format objects or Strings. When formatting with object Y, if the object is a NumberFormat, then ((NumberFormat) Y).format(X) is called. Otherwise Y.toString() is called.
        NullPointerException - if limits or formats is null
      • getLimits

        public double[] getLimits()
        Get the limits passed in the constructor.
        the limits.
      • getFormats

        public Object[] getFormats()
        Get the formats passed in the constructor.
        the formats.
      • format

        public StringBuffer format​(long number,
                                   StringBuffer toAppendTo,
                                   FieldPosition status)
        Specialization of format. This method really calls format(double, StringBuffer, FieldPosition) thus the range of longs that are supported is only equal to the range that can be stored by double. This will never be a practical limitation.
        Specified by:
        format in class NumberFormat
        number - the long number to format
        toAppendTo - the StringBuffer to which the formatted text is to be appended
        status - 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 NumberFormat.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.
        the formatted StringBuffer
        See Also:
      • parse

        public Number parse​(String text,
                            ParsePosition status)
        Parses a Number from the input text.
        Specified by:
        parse in class NumberFormat
        text - the source text.
        status - an input-output parameter. On input, the status.index field indicates the first character of the source text that should be parsed. On exit, if no error occurred, status.index is set to the first unparsed character in the source text. On exit, if an error did occur, status.index is unchanged and status.errorIndex is set to the first index of the character that caused the parse to fail.
        A Number representing the value of the number parsed.
        NullPointerException - if status is null or if text is null and the list of choice strings is not empty.
        See Also:
        NumberFormat.isParseIntegerOnly(), Format.parseObject(java.lang.String, java.text.ParsePosition)
      • nextDouble

        public static final double nextDouble​(double d)
        Finds the least double greater than d. If NaN, returns same value.

        Used to make half-open intervals.

        d - the reference value
        the least double value greather than d
        See Also:
      • previousDouble

        public static final double previousDouble​(double d)
        Finds the greatest double less than d. If NaN, returns same value.
        d - the reference value
        the greatest double value less than d
        See Also:
      • equals

        public boolean equals​(Object obj)
        Equality comparison between two
        equals in class NumberFormat
        obj - the reference object with which to compare.
        true if this object is the same as the obj argument; false otherwise.
        See Also:
        Object.hashCode(), HashMap
      • nextDouble

        public static double nextDouble​(double d,
                                        boolean positive)
        Finds the least double greater than d (if positive is true), or the greatest double less than d (if positive is false). If NaN, returns same value. Does not affect floating-point flags, provided these member functions do not: Double.longBitsToDouble(long) Double.doubleToLongBits(double) Double.isNaN(double)
        d - the reference value
        positive - true if the least double is desired; false otherwise
        the least or greater double value