PluralFormat

Kotlin |Java

open class PluralFormat : UFormat

kotlin.Any
↳	java.text.Format
	↳	android.icu.text.UFormat
		↳	android.icu.text.PluralFormat

PluralFormat supports the creation of internationalized messages with plural inflection. It is based on plural selection, i.e. the caller specifies messages for each plural case that can appear in the user's language and the PluralFormat selects the appropriate message based on the number.

The Problem of Plural Forms in Internationalized Messages

Different languages have different ways to inflect plurals. Creating internationalized messages that include plural forms is only feasible when the framework is able to handle plural forms of all languages correctly. ChoiceFormat doesn't handle this well, because it attaches a number interval to each message and selects the message whose interval contains a given number. This can only handle a finite number of intervals. But in some languages, like Polish, one plural case applies to infinitely many intervals (e.g., the paucal case applies to numbers ending with 2, 3, or 4 except those ending with 12, 13, or 14). Thus ChoiceFormat is not adequate.

PluralFormat deals with this by breaking the problem into two parts:

It uses PluralRules that can define more complex conditions for a plural case than just a single interval. These plural rules define both what plural cases exist in a language, and to which numbers these cases apply.
It provides predefined plural rules for many languages. Thus, the programmer need not worry about the plural cases of a language and does not have to define the plural cases; they can simply use the predefined keywords. The whole plural formatting of messages can be done using localized patterns from resource bundles. For predefined plural rules, see the CLDR Language Plural Rules page at https://unicode-org.github.io/cldr-staging/charts/latest/supplemental/language_plural_rules.html

Usage of `PluralFormat`

Note: Typically, plural formatting is done via MessageFormat with a plural argument type, rather than using a stand-alone PluralFormat.

This discussion assumes that you use PluralFormat with a predefined set of plural rules. You can create one using one of the constructors that takes a ULocale object. To specify the message pattern, you can either pass it to the constructor or set it explicitly using the applyPattern() method. The format() method takes a number object and selects the message of the matching plural case. This message will be returned.

Patterns and Their Interpretation

The pattern text defines the message output for each plural case of the specified locale. Syntax:

pluralStyle = [offsetValue] (selector '{' message '}')+
  offsetValue = "offset:" number
  selector = explicitValue | keyword
  explicitValue = '=' number  // adjacent, no white space in between
  keyword = [^[[:Pattern_Syntax:][:Pattern_White_Space:]]]+
  message: see <code><a docref="android.icu.text.MessageFormat">MessageFormat</a></code>

Pattern_White_Space between syntax elements is ignored, except between the {curly braces} and their sub-message, and between the '=' and the number of an explicitValue.

There are 6 predefined case keywords in CLDR/ICU - 'zero', 'one', 'two', 'few', 'many' and 'other'. You always have to define a message text for the default plural case "other" which is contained in every rule set. If you do not specify a message text for a particular plural case, the message text of the plural case "other" gets assigned to this plural case.

When formatting, the input number is first matched against the explicitValue clauses. If there is no exact-number match, then a keyword is selected by calling the PluralRules with the input number minus the offset. (The offset defaults to 0 if it is omitted from the pattern string.) If there is no clause with that keyword, then the "other" clauses is returned.

An unquoted pound sign () in the selected sub-message itself (i.e., outside of arguments nested in the sub-message) is replaced by the input number minus the offset. The number-minus-offset value is formatted using a NumberFormat for the PluralFormat's locale. If you need special number formatting, you have to use a MessageFormat and explicitly specify a NumberFormat argument. Note: That argument is formatting without subtracting the offset! If you need a custom format and have a non-zero offset, then you need to pass the number-minus-offset value as a separate parameter.

For a usage example, see the MessageFormat class documentation.

Defining Custom Plural Rules

If you need to use PluralFormat with custom rules, you can create a PluralRules object and pass it to PluralFormat's constructor. If you also specify a locale in this constructor, this locale will be used to format the number in the message texts.

For more information about PluralRules, see PluralRules.

Summary

Public constructors
`PluralFormat()` Creates a new cardinal-number `PluralFormat` for the default `FORMAT` locale.
`PluralFormat(rules: PluralRules!)` Creates a new cardinal-number `PluralFormat` for a given set of rules.
`PluralFormat(rules: PluralRules!, pattern: String!)` Creates a new cardinal-number `PluralFormat` for a given set of rules and a pattern.
`PluralFormat(ulocale: ULocale!)` Creates a new cardinal-number `PluralFormat` for a given locale.
`PluralFormat(ulocale: ULocale!, rules: PluralRules!)` Creates a new cardinal-number `PluralFormat` for a given set of rules.
`PluralFormat(ulocale: ULocale!, rules: PluralRules!, pattern: String!)` Creates a new cardinal-number `PluralFormat` for a given set of rules, a pattern and a locale.
`PluralFormat(ulocale: ULocale!, type: PluralRules.PluralType!)` Creates a new `PluralFormat` for the plural type.
`PluralFormat(ulocale: ULocale!, type: PluralRules.PluralType!, pattern: String!)` Creates a new `PluralFormat` for a plural type, a pattern and a locale.
`PluralFormat(ulocale: ULocale!, pattern: String!)` Creates a new cardinal-number `PluralFormat` for a given pattern string and locale.
`PluralFormat(pattern: String!)` Creates a new cardinal-number `PluralFormat` for a given pattern string.
`PluralFormat(locale: Locale!)` Creates a new cardinal-number `PluralFormat` for a given `java.util.Locale`.
`PluralFormat(locale: Locale!, rules: PluralRules!)` Creates a new cardinal-number `PluralFormat` for a given set of rules.
`PluralFormat(locale: Locale!, type: PluralRules.PluralType!)` Creates a new `PluralFormat` for the plural type.

Public methods
open Unit	`applyPattern(pattern: String!)` Sets the pattern used by this plural format.
open Boolean	`equals(rhs: PluralFormat!)` Returns true if this equals the provided PluralFormat.
open Boolean	`equals(other: Any?)` Indicates whether some other object is "equal to" this one.
String!	`format(number: Double)` Formats a plural message for a given number.
open StringBuffer!	`format(number: Any!, toAppendTo: StringBuffer!, pos: FieldPosition!)` Formats a plural message for a given number and appends the formatted message to the given `StringBuffer`.
open Int	`hashCode()` Returns a hash code value for the object.
open Number!	`parse(text: String!, parsePosition: ParsePosition!)` This method is not yet supported by `PluralFormat`.
open Any!	`parseObject(source: String!, pos: ParsePosition!)` This method is not yet supported by `PluralFormat`.
open Unit	`setNumberFormat(format: NumberFormat!)` Sets the number format used by this formatter.
open String!	`toPattern()` Returns the pattern for this PluralFormat.
open String	`toString()` Returns a string representation of the object.

Parameters
`rules`	PluralRules!: defines the behavior of the `PluralFormat` object.
`pattern`	String!: the pattern for this `PluralFormat`.

Parameters
`ulocale`	ULocale!: the default number formatting will be done using this locale.
`rules`	PluralRules!: defines the behavior of the `PluralFormat` object.

Parameters
`ulocale`	ULocale!: the `PluralFormat` will be configured with rules for this locale. This locale will also be used for standard number formatting.
`rules`	PluralRules!: defines the behavior of the `PluralFormat` object.
`pattern`	String!: the pattern for this `PluralFormat`.

Parameters
`ulocale`	ULocale!: the default number formatting will be done using this locale.
`type`	PluralRules.PluralType!: The plural type (e.g., cardinal or ordinal).

Parameters
`locale`	Locale!: the default number formatting will be done using this locale.
`rules`	PluralRules!: defines the behavior of the `PluralFormat` object.

Parameters
`obj`	The object to format
`toAppendTo`	StringBuffer!: the formatted message will be appended to this `StringBuffer`.
`pos`	FieldPosition!: will be ignored by this method.
`number`	Any!: a number object (instance of `Number` for which the plural message should be formatted. If no pattern has been applied to this `PluralFormat` object yet, the formatted number will be returned. Note: If this object is not an instance of `Number`, the `toAppendTo` will not be modified.

Exceptions
`java.lang.NullPointerException`	if `toAppendTo` or `pos` is null
`java.lang.IllegalArgumentException`	if number is not an instance of Number

Parameters
`text`	String!: the string to be parsed.
`parsePosition`	ParsePosition!: defines the position where parsing is to begin, and upon return, the position where parsing left off. If the position has not changed upon return, then parsing failed.

Parameters
`source`	String!: the string to be parsed.
`pos`	ParsePosition!: defines the position where parsing is to begin, and upon return, the position where parsing left off. If the position has not changed upon return, then parsing failed.

Exceptions
`java.lang.NullPointerException`	if `source` or `pos` is null.
`java.lang.UnsupportedOperationException`	will always be thrown by this method.

PluralFormat

The Problem of Plural Forms in Internationalized Messages

Usage of PluralFormat

Patterns and Their Interpretation

Defining Custom Plural Rules

Summary

Public constructors

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

PluralFormat

Public methods

applyPattern

equals

equals

format

format

hashCode

parse

parseObject

setNumberFormat

toPattern

toString

Usage of `PluralFormat`