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:
  • Constructor Details

  • Method Details

    • 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:
    • format

      public StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition status)
      Returns pattern with formatted double.
      Specified by:
      format in class NumberFormat
      number - number to be formatted and substituted.
      toAppendTo - where text is appended.
      status - ignore no useful status is returned.
      the formatted StringBuffer
      NullPointerException - if toAppendTo is null
      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:
    • 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.

      Implementation Note:
      This is equivalent to calling Math.nextUp(d)
      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.
      Implementation Note:
      This is equivalent to calling Math.nextDown(d)
      d - the reference value
      the greatest double value less than d
      See Also:
    • clone

      public Object clone()
      Overrides Cloneable
      clone in class NumberFormat
      a clone of this instance.
      See Also:
    • hashCode

      public int hashCode()
      Generates a hash code for the message format object.
      hashCode in class NumberFormat
      a hash code value for this object.
      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:
    • 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.
      Implementation Note:
      This is equivalent to calling positive ? Math.nextUp(d) : Math.nextDown(d)
      d - the reference value
      positive - true if the least double is desired; false otherwise
      the least or greater double value