Class ChoiceFormat

java.lang.Object
java.text.Format
java.text.NumberFormat
java.text.ChoiceFormat
All Implemented Interfaces:
Serializable, Cloneable
public class ChoiceFormat extends NumberFormat
ChoiceFormat is a concrete subclass of NumberFormat that 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.

Patterns

A ChoiceFormat pattern has the following syntax:
Pattern:
SubPattern *("|" SubPattern)
SubPattern:
Limit Relation Format
Note: Each additional SubPattern must have an ascending Limit-Relation interval
Limit:
Number / "∞" / "-∞"
Number:
["-"] *(Digit) 1*(Decimal / Digit) *(Digit) [Exponent]
Decimal:
1*(Digit ".") / 1*("." Digit)
Digit:
0 - 9
Exponent:
*(Digit) Digit ExponentSymbol Digit *(Digit)
ExponentSymbol:
"e" / "E"
Relation:
"#" / "<" / "≤"
Format:
Any characters except the special pattern character '|'
Note:The relation ≤ is not equivalent to <=

To use a reserved special pattern character within a Format pattern, it must be single quoted. For example, new ChoiceFormat("1#'|'foo'|'").format(1) returns "|foo|". Use two single quotes in a row to produce a literal single quote. For example, new ChoiceFormat("1# ''one'' ").format(1) returns " 'one' ".

Usage Information

A ChoiceFormat can be constructed using either an array of formats and an array of limits or a string pattern. When constructing with format and limit arrays, 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.)

Below is an example of constructing a ChoiceFormat with arrays to format and parse values: 

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));
}

Below is an example of constructing a ChoiceFormat with a String pattern: 

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(fmt.format(Double.NEGATIVE_INFINITY)); // outputs "is negative"
System.out.println(fmt.format(-1.0)); // outputs "is negative"
System.out.println(fmt.format(0)); // outputs "is zero or fraction"
System.out.println(fmt.format(0.9)); // outputs "is zero or fraction"
System.out.println(fmt.format(1)); // outputs "is one"
System.out.println(fmt.format(1.5)); // outputs "is 1+"
System.out.println(fmt.format(2)); // outputs "is two"
System.out.println(fmt.format(2.1)); // outputs "is more than 2."
System.out.println(fmt.format(Double.NaN)); // outputs "is negative"
System.out.println(fmt.format(Double.POSITIVE_INFINITY)); // outputs "is more than 2."

For more sophisticated patterns, ChoiceFormat can be used with MessageFormat to produce accurate forms for singular and plural: 

MessageFormat msgFmt = new MessageFormat("The disk \"{0}\" contains {1}.");
double[] fileLimits = {0,1,2};
String[] filePart = {"no files","one file","{1,number} files"};
ChoiceFormat fileChoices = new ChoiceFormat(fileLimits, filePart);
msgFmt.setFormatByArgumentIndex(1, fileChoices);
Object[] args = {"MyDisk", 1273};
System.out.println(msgFmt.format(args));
The output with different values for fileCount: 
 The disk "MyDisk" contains no files.
 The disk "MyDisk" contains one file.
 The disk "MyDisk" contains 1,273 files.
See MessageFormat for caveats regarding MessageFormat patterns within a ChoiceFormat pattern.

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.

API Note:
A subclass could perform more consistent pattern validation by throwing an IllegalArgumentException for all incorrect cases. See the Implementation Note for this implementation's behavior regarding incorrect patterns.

This class inherits instance methods from NumberFormat it does not utilize; a subclass could override and throw UnsupportedOperationException for such methods.

Implementation Note:
Given an incorrect pattern, this implementation may either throw an exception or succeed and discard the incorrect portion. A NumberFormatException is thrown if a limit can not be parsed as a numeric value and an IllegalArgumentException is thrown if a SubPattern is missing, or the intervals are not ascending. Discarding the incorrect portion may result in a ChoiceFormat with empty limits and formats.
Since:
1.1
See Also:

  • Constructor Details

  • Method Details

    • applyPattern

      public void applyPattern(String newPattern)
      Apply the given pattern to this ChoiceFormat object. The syntax and error related caveats for the ChoiceFormat pattern can be found in the Patterns section. Unlike setChoices(double[], String[]), this method will throw an IllegalArgumentException if the limits are not in ascending order.
      Parameters:
      newPattern - a pattern string
      Throws:
      NullPointerException - if newPattern is null
      IllegalArgumentException - if newPattern violates the pattern syntax
      See Also:

    • toPattern

      public String toPattern()
      Returns a pattern string that represents the limits and formats of this ChoiceFormat object. The string returned is not guaranteed to be the same input string passed to either applyPattern(String) or ChoiceFormat(String).
      Returns:
      a pattern string that represents the limits and formats of this ChoiceFormat object
      See Also:

    • 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.
      Throws:
      NullPointerException - if limits or formats is null
      IllegalArgumentException - if the length of limits and formats are not equal

    • getLimits

      public double[] getLimits()
      Returns the limits of this ChoiceFormat.
      Returns:
      the limits of this ChoiceFormat

    • getFormats

      public Object[] getFormats()
      Returns the formats of this ChoiceFormat.
      Returns:
      the formats of this ChoiceFormat

    • 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
      Parameters:
      number - number to be formatted and substituted.
      toAppendTo - where text is appended.
      status - ignore no useful status is returned.
      Returns:
      the formatted StringBuffer
      Throws:
      ArrayIndexOutOfBoundsException - if either the limits or formats of this ChoiceFormat are empty
      NullPointerException - if toAppendTo is null
      See Also:

    • format

      public StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition status)
      Returns pattern with formatted double.
      Specified by:
      format in class NumberFormat
      Parameters:
      number - number to be formatted and substituted.
      toAppendTo - where text is appended.
      status - ignore no useful status is returned.
      Returns:
      the formatted StringBuffer
      Throws:
      ArrayIndexOutOfBoundsException - if either the limits or formats of this ChoiceFormat are empty
      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
      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 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.
      Returns:
      A Number representing the value of the number parsed.
      Throws:
      NullPointerException - if status is null or if text is null and the list of choice strings is not empty.
      See Also:

    • isStrict

      public boolean isStrict()
      Description copied from class: NumberFormat
      Returns true if this format will parse numbers strictly; false otherwise.
      Overrides:
      isStrict in class NumberFormat
      Returns:
      true if this format will parse numbers strictly; false otherwise
      Since:
      23
      See Also:

    • setStrict

      public void setStrict(boolean strict)
      Description copied from class: NumberFormat
      Change the leniency value for parsing. Parsing can either be strict or lenient, by default it is lenient.
      Overrides:
      setStrict in class NumberFormat
      Parameters:
      strict - true if parsing should be done strictly; false otherwise
      Since:
      23
      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)
      Parameters:
      d - the reference value
      Returns:
      the least double value greater than d
      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)
      Parameters:
      d - the reference value
      positive - true if the least double is desired; false otherwise
      Returns:
      the least or greater double value

    • 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)
      Parameters:
      d - the reference value
      Returns:
      the greatest double value less than d
      See Also:

    • clone

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

    • hashCode

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

    • toString

      public String toString()
      Returns a string identifying this ChoiceFormat, for debugging.
      Overrides:
      toString in class Object
      Returns:
      a string identifying this ChoiceFormat, for debugging

    • equals

      public boolean equals(Object obj)
      Compares the specified object with this ChoiceFormat for equality. Returns true if the object is also a ChoiceFormat and the two formats would format any value the same.
      Overrides:
      equals in class NumberFormat
      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 ChoiceFormat
      See Also: