Module java.base
Package java.text

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.

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));
}
For more sophisticated patterns, ChoiceFormat can be used with MessageFormat to produce accurate forms for singular and plural: 
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] = Integer.valueOf(i);
    testArgs[2] = testArgs[0];
    System.out.println(pattform.format(testArgs));
}
Would output the following: 

 There are no files on ADisk
 There is one file on ADisk
 There are 2 files on ADisk
 There are 3 files on ADisk

Patterns

A ChoiceFormat pattern has the following syntax:
Pattern:
SubPattern *("|" SubPattern)
Note: Each additional SubPattern must have a Limit greater than the previous SubPattern's Limit
SubPattern:
Limit Relation Format
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 Relation symbols
Note:The relation ≤ is not equivalent to <=

If a Relation symbol is to be used within a Format pattern, it must be single quoted. For example, new ChoiceFormat("1# '#'1 ").format(1) returns " #1 ". Use two single quotes in a row to produce a literal single quote. For example, new ChoiceFormat("1# ''one'' ").format(1) returns " 'one' ".

Below is an example of constructing a ChoiceFormat with a 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."

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.

Since:
1.1
See Also: