PluralFormat

public class PluralFormat extends UFormat

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 http://unicode.org/repos/cldr-tmp/trunk/diff/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 MessageFormat
 
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.

Public Constructor Summary

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

Public Method Summary

void
applyPattern(String pattern)
Sets the pattern used by this plural format.
boolean
equals(Object rhs)
Compares this instance with the specified object and indicates if they are equal.
boolean
equals(PluralFormat rhs)
Returns true if this equals the provided PluralFormat.
final String
format(double number)
Formats a plural message for a given number.
StringBuffer
format(Object number, StringBuffer toAppendTo, FieldPosition pos)
Formats a plural message for a given number and appends the formatted message to the given StringBuffer.
int
hashCode()
Returns an integer hash code for this object.
Number
parse(String text, ParsePosition parsePosition)
This method is not yet supported by PluralFormat.
Object
parseObject(String source, ParsePosition pos)
This method is not yet supported by PluralFormat.
void
setNumberFormat(NumberFormat format)
Sets the number format used by this formatter.
String
toPattern()
Returns the pattern for this PluralFormat.
String
toString()
Returns a string containing a concise, human-readable description of this object.

Inherited Method Summary

Public Constructors

public PluralFormat ()

Creates a new cardinal-number PluralFormat for the default FORMAT locale. This locale will be used to get the set of plural rules and for standard number formatting.

See Also

public PluralFormat (ULocale ulocale)

Creates a new cardinal-number PluralFormat for a given locale.

Parameters
ulocale the PluralFormat will be configured with rules for this locale. This locale will also be used for standard number formatting.

public PluralFormat (Locale locale)

Creates a new cardinal-number PluralFormat for a given Locale.

Parameters
locale the PluralFormat will be configured with rules for this locale. This locale will also be used for standard number formatting.

public PluralFormat (PluralRules rules)

Creates a new cardinal-number PluralFormat for a given set of rules. The standard number formatting will be done using the default FORMAT locale.

Parameters
rules defines the behavior of the PluralFormat object.
See Also

public PluralFormat (ULocale ulocale, PluralRules rules)

Creates a new cardinal-number PluralFormat for a given set of rules. The standard number formatting will be done using the given locale.

Parameters
ulocale the default number formatting will be done using this locale.
rules defines the behavior of the PluralFormat object.

public PluralFormat (Locale locale, PluralRules rules)

Creates a new cardinal-number PluralFormat for a given set of rules. The standard number formatting will be done using the given locale.

Parameters
locale the default number formatting will be done using this locale.
rules defines the behavior of the PluralFormat object.

public PluralFormat (ULocale ulocale, PluralRules.PluralType type)

Creates a new PluralFormat for the plural type. The standard number formatting will be done using the given locale.

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

public PluralFormat (Locale locale, PluralRules.PluralType type)

Creates a new PluralFormat for the plural type. The standard number formatting will be done using the given Locale.

Parameters
locale the default number formatting will be done using this locale.
type The plural type (e.g., cardinal or ordinal).

public PluralFormat (String pattern)

Creates a new cardinal-number PluralFormat for a given pattern string. The default FORMAT locale will be used to get the set of plural rules and for standard number formatting.

Parameters
pattern the pattern for this PluralFormat.
Throws
IllegalArgumentException if the pattern is invalid.
See Also

public PluralFormat (ULocale ulocale, String pattern)

Creates a new cardinal-number PluralFormat for a given pattern string and locale. The locale will be used to get the set of plural rules and for standard number formatting.

Example code:

INCLUDE_ERROR

Parameters
ulocale the PluralFormat will be configured with rules for this locale. This locale will also be used for standard number formatting.
pattern the pattern for this PluralFormat.
Throws
IllegalArgumentException if the pattern is invalid.

public PluralFormat (PluralRules rules, String pattern)

Creates a new cardinal-number PluralFormat for a given set of rules and a pattern. The standard number formatting will be done using the default FORMAT locale.

Parameters
rules defines the behavior of the PluralFormat object.
pattern the pattern for this PluralFormat.
Throws
IllegalArgumentException if the pattern is invalid.
See Also

public PluralFormat (ULocale ulocale, PluralRules rules, String pattern)

Creates a new cardinal-number PluralFormat for a given set of rules, a pattern and a locale.

Parameters
ulocale the PluralFormat will be configured with rules for this locale. This locale will also be used for standard number formatting.
rules defines the behavior of the PluralFormat object.
pattern the pattern for this PluralFormat.
Throws
IllegalArgumentException if the pattern is invalid.

public PluralFormat (ULocale ulocale, PluralRules.PluralType type, String pattern)

Creates a new PluralFormat for a plural type, a pattern and a locale.

Parameters
ulocale the PluralFormat will be configured with rules for this locale. This locale will also be used for standard number formatting.
type The plural type (e.g., cardinal or ordinal).
pattern the pattern for this PluralFormat.
Throws
IllegalArgumentException if the pattern is invalid.

Public Methods

public void applyPattern (String pattern)

Sets the pattern used by this plural format. The method parses the pattern and creates a map of format strings for the plural rules. Patterns and their interpretation are specified in the class description.

Parameters
pattern the pattern for this plural format.
Throws
IllegalArgumentException if the pattern is invalid.

public boolean equals (Object rhs)

Compares this instance with the specified object and indicates if they are equal. In order to be equal, o must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be reflexive, symmetric, and transitive. Also, no object reference other than null is equal to null.

The default implementation returns true only if this == o. See Writing a correct equals method if you intend implementing your own equals method.

The general contract for the equals and hashCode() methods is that if equals returns true for any two objects, then hashCode() must return the same value for these objects. This means that subclasses of Object usually override either both methods or neither of them.

Parameters
rhs the object to compare this instance with.
Returns
  • true if the specified object is equal to this Object; false otherwise.

public boolean equals (PluralFormat rhs)

Returns true if this equals the provided PluralFormat.

Parameters
rhs the PluralFormat to compare against
Returns
  • true if this equals rhs

public final String format (double number)

Formats a plural message for a given number.

Parameters
number a 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.
Returns
  • the string containing the formatted plural message.

public StringBuffer format (Object number, StringBuffer toAppendTo, FieldPosition pos)

Formats a plural message for a given number and appends the formatted message to the given StringBuffer.

Parameters
number 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.
toAppendTo the formatted message will be appended to this StringBuffer.
pos will be ignored by this method.
Returns
  • the string buffer passed in as toAppendTo, with formatted text appended.
Throws
IllegalArgumentException if number is not an instance of Number

public int hashCode ()

Returns an integer hash code for this object. By contract, any two objects for which equals(Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

Note that hash values must not change over time unless information used in equals comparisons also changes.

See Writing a correct hashCode method if you intend implementing your own hashCode method.

Returns
  • this object's hash code.

public Number parse (String text, ParsePosition parsePosition)

This method is not yet supported by PluralFormat.

Parameters
text the string to be parsed.
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.
Returns
  • nothing because this method is not yet implemented.
Throws
UnsupportedOperationException will always be thrown by this method.

public Object parseObject (String source, ParsePosition pos)

This method is not yet supported by PluralFormat.

Parameters
source the string to be parsed.
pos 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.
Returns
  • nothing because this method is not yet implemented.
Throws
UnsupportedOperationException will always be thrown by this method.

public void setNumberFormat (NumberFormat format)

Sets the number format used by this formatter. You only need to call this if you want a different number format than the default formatter for the locale.

Parameters
format the number format to use.

public String toPattern ()

Returns the pattern for this PluralFormat.

Returns
  • the pattern string

public String toString ()

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns
  • a printable representation of this object.