java.text

Class ChoiceFormat

Contents
  • 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) {
     status.setIndex(0);
     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}");
 pattform.setFormats(testFormats);
 Object[] testArgs = {null, "ADisk", null};
 for (int i = 0; i < 4; ++i) {
     testArgs[0] = new Integer(i);
     testArgs[2] = testArgs[0];
     System.out.println(pattform.format(testArgs));
 }

    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.

    Synchronization

    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.
        Parameters:
        newPattern - See the class description.

      • toPattern

        public String toPattern()
        Gets the pattern.

      • setChoices

        public void setChoices(double[] limits,
              String[] formats)
        Set the choices to be used in formatting.
        Parameters:
        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.

      • getLimits

        public double[] getLimits()
        Get the limits passed in the constructor.
        Returns:
        the limits.

      • getFormats

        public Object[] getFormats()
        Get the formats passed in the constructor.
        Returns:
        the formats.

      • parse

        public Number parse(String text,
           ParsePosition status)
        Parses a Number from the input text.
        Specified by:
        parse in class NumberFormat
        Parameters:
        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 occured, 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.
        Returns:
        A Number representing the value of the number parsed.
        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.

        See Also:
        previousDouble(double)

      • previousDouble

        public static final double previousDouble(double d)
        Finds the greatest double less than d. If NaN, returns same value.
        See Also:
        nextDouble(double)

      • equals

        public boolean equals(Object obj)
        Equality comparision between two
        Overrides:
        equals in class NumberFormat
        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

      • nextDouble

        public static double nextDouble(double d,
                boolean positive)
        Finds the least double greater than d (if positive == true), or the greatest double less than d (if positive == 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)

Document created the 11/06/2005, last modified the 04/03/2020
Source of the printed document:https://www.gaudry.be/en/java-api-rf-java/text/choiceformat.html

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