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/OpenJDK 25

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 <&equals;

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:

Nested Class Summary

Nested classes/interfaces declared in class NumberFormat

NumberFormat.Field, NumberFormat.Style

Field Summary

Fields declared in class NumberFormat

FRACTION_FIELD, INTEGER_FIELD

Constructor Summary

Constructor Description
ChoiceFormat(double[] limits, String[] formats)
Constructs with the limits and the corresponding formats.
ChoiceFormat(String newPattern)
Constructs a ChoiceFormat with limits and corresponding formats based on the pattern.

Method Summary

Modifier and Type Method Description
void applyPattern(String newPattern)
Apply the given pattern to this ChoiceFormat object.
Object clone()
Overrides Cloneable
boolean equals(Object obj)
Compares the specified object with this ChoiceFormat for equality.
StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition status)
Returns pattern with formatted double.
StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition status)
Specialization of format.
Object[] getFormats()
Returns the formats of this ChoiceFormat.
double[] getLimits()
Returns the limits of this ChoiceFormat.
int hashCode()
Returns the hash code for this ChoiceFormat.
boolean isStrict()
Returns true if this format will parse numbers strictly; false otherwise.
static final double nextDouble(double d)
Finds the least double greater than d.
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).
Number parse(String text, ParsePosition status)
Parses the input text starting at the index given by the ParsePosition as a Double.
static final double previousDouble(double d)
Finds the greatest double less than d.
void setChoices(double[] limits, String[] formats)
Set the choices to be used in formatting.
void setStrict(boolean strict)
Change the leniency value for parsing.
String toPattern()
Returns a pattern string that represents the limits and formats of this ChoiceFormat object.
String toString()
Returns a string identifying this ChoiceFormat, for debugging.

Methods declared in class NumberFormat

format, format, format, getAvailableLocales, getCompactNumberInstance, getCompactNumberInstance, getCurrency, getCurrencyInstance, getCurrencyInstance, getInstance, getInstance, getIntegerInstance, getIntegerInstance, getMaximumFractionDigits, getMaximumIntegerDigits, getMinimumFractionDigits, getMinimumIntegerDigits, getNumberInstance, getNumberInstance, getPercentInstance, getPercentInstance, getRoundingMode, isGroupingUsed, isParseIntegerOnly, parse, parseObject, setCurrency, setGroupingUsed, setMaximumFractionDigits, setMaximumIntegerDigits, setMinimumFractionDigits, setMinimumIntegerDigits, setParseIntegerOnly, setRoundingMode

Methods declared in class Format

format, formatToCharacterIterator, parseObject

Methods declared in class Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Details

ChoiceFormat

public ChoiceFormat(String newPattern)
Constructs a ChoiceFormat with limits and corresponding formats based on the pattern. The syntax and error related caveats for the ChoiceFormat pattern can be found in the Patterns section. Unlike ChoiceFormat(double[], String[]), this constructor will throw an IllegalArgumentException if the limits are not in ascending order.
Parameters:
newPattern - the new pattern string
Throws:
NullPointerException - if newPattern is null
IllegalArgumentException - if newPattern violates the pattern syntax
See Also:

ChoiceFormat

public ChoiceFormat(double[] limits, String[] formats)
Constructs with the limits and the corresponding formats.
Parameters:
limits - limits in ascending order
formats - corresponding format strings
Throws:
NullPointerException - if limits or formats is null
IllegalArgumentException - if the length of limits and formats are not equal
See Also:

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 the input text starting at the index given by the ParsePosition as a Double. The value returned is the limit corresponding to the format that is the longest substring of the input text. Matching is done in ascending order, when multiple formats match the text equivalently in strength, the first matching limit is returned. If there is no match, Double.NaN is returned.

For example, 

var fmt = new ChoiceFormat("0#foo|1#bar|2#baz");
fmt.parse("baz", new ParsePosition(0)); // returns 2.0
fmt.parse("quux", new ParsePosition(0)); // returns NaN
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 which represents the limit corresponding to the format parsed, or Double.NaN if the parse fails.
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:

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/text/ChoiceFormat.html