Class PluralFormat
- All Implemented Interfaces:
Serializable
,Cloneable
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:
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.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: seeMessageFormat
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
.
- Author:
- tschumann (Tim Schumann)
- See Also:
-
Nested Class Summary
Nested classes/interfaces inherited from class com.ibm.icu.text.UFormat
UFormat.SpanField
Nested classes/interfaces inherited from class java.text.Format
Format.Field
-
Constructor Summary
ConstructorsConstructorDescriptionCreates a new cardinal-numberPluralFormat
for the defaultFORMAT
locale.PluralFormat
(PluralRules rules) Creates a new cardinal-numberPluralFormat
for a given set of rules.PluralFormat
(PluralRules rules, String pattern) Creates a new cardinal-numberPluralFormat
for a given set of rules and a pattern.PluralFormat
(ULocale ulocale) Creates a new cardinal-numberPluralFormat
for a given locale.PluralFormat
(ULocale ulocale, PluralRules rules) Creates a new cardinal-numberPluralFormat
for a given set of rules.PluralFormat
(ULocale ulocale, PluralRules.PluralType type) Creates a newPluralFormat
for the plural type.PluralFormat
(ULocale ulocale, PluralRules.PluralType type, String pattern) Creates a newPluralFormat
for a plural type, a pattern and a locale.PluralFormat
(ULocale ulocale, PluralRules rules, String pattern) Creates a new cardinal-numberPluralFormat
for a given set of rules, a pattern and a locale.PluralFormat
(ULocale ulocale, String pattern) Creates a new cardinal-numberPluralFormat
for a given pattern string and locale.PluralFormat
(String pattern) Creates a new cardinal-numberPluralFormat
for a given pattern string.PluralFormat
(Locale locale) Creates a new cardinal-numberPluralFormat
for a givenLocale
.PluralFormat
(Locale locale, PluralRules rules) Creates a new cardinal-numberPluralFormat
for a given set of rules.PluralFormat
(Locale locale, PluralRules.PluralType type) Creates a newPluralFormat
for the plural type. -
Method Summary
Modifier and TypeMethodDescriptionvoid
applyPattern
(String pattern) Sets the pattern used by this plural format.boolean
equals
(PluralFormat rhs) Returns true if this equals the provided PluralFormat.boolean
final String
format
(double number) Formats a plural message for a given number.format
(Object number, StringBuffer toAppendTo, FieldPosition pos) Formats a plural message for a given number and appends the formatted message to the givenStringBuffer
.int
hashCode()
parse
(String text, ParsePosition parsePosition) This method is not yet supported byPluralFormat
.parseObject
(String source, ParsePosition pos) This method is not yet supported byPluralFormat
.void
Deprecated.ICU 50 This method clears the pattern and might create a different kind of PluralRules instance; use one of the constructors to create a new instance instead.void
setNumberFormat
(NumberFormat format) Sets the number format used by this formatter.Returns the pattern for this PluralFormat.toString()
Methods inherited from class java.text.Format
clone, format, formatToCharacterIterator, parseObject
-
Constructor Details
-
PluralFormat
public PluralFormat()Creates a new cardinal-numberPluralFormat
for the defaultFORMAT
locale. This locale will be used to get the set of plural rules and for standard number formatting.- See Also:
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a given locale.- Parameters:
ulocale
- thePluralFormat
will be configured with rules for this locale. This locale will also be used for standard number formatting.
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a givenLocale
.- Parameters:
locale
- thePluralFormat
will be configured with rules for this locale. This locale will also be used for standard number formatting.
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a given set of rules. The standard number formatting will be done using the defaultFORMAT
locale.- Parameters:
rules
- defines the behavior of thePluralFormat
object.- See Also:
-
PluralFormat
Creates a new cardinal-numberPluralFormat
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 thePluralFormat
object.
-
PluralFormat
Creates a new cardinal-numberPluralFormat
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 thePluralFormat
object.
-
PluralFormat
Creates a newPluralFormat
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).
-
PluralFormat
Creates a newPluralFormat
for the plural type. The standard number formatting will be done using the givenLocale
.- Parameters:
locale
- the default number formatting will be done using this locale.type
- The plural type (e.g., cardinal or ordinal).
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a given pattern string. The defaultFORMAT
locale will be used to get the set of plural rules and for standard number formatting.- Parameters:
pattern
- the pattern for thisPluralFormat
.- Throws:
IllegalArgumentException
- if the pattern is invalid.- See Also:
-
PluralFormat
Creates a new cardinal-numberPluralFormat
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:invalid input: '{@'.jcite com.ibm.icu.samples.text.pluralformat.PluralFormatSample:---PluralFormatExample}
- Parameters:
ulocale
- thePluralFormat
will be configured with rules for this locale. This locale will also be used for standard number formatting.pattern
- the pattern for thisPluralFormat
.- Throws:
IllegalArgumentException
- if the pattern is invalid.
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a given set of rules and a pattern. The standard number formatting will be done using the defaultFORMAT
locale.- Parameters:
rules
- defines the behavior of thePluralFormat
object.pattern
- the pattern for thisPluralFormat
.- Throws:
IllegalArgumentException
- if the pattern is invalid.- See Also:
-
PluralFormat
Creates a new cardinal-numberPluralFormat
for a given set of rules, a pattern and a locale.- Parameters:
ulocale
- thePluralFormat
will be configured with rules for this locale. This locale will also be used for standard number formatting.rules
- defines the behavior of thePluralFormat
object.pattern
- the pattern for thisPluralFormat
.- Throws:
IllegalArgumentException
- if the pattern is invalid.
-
PluralFormat
Creates a newPluralFormat
for a plural type, a pattern and a locale.- Parameters:
ulocale
- thePluralFormat
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 thisPluralFormat
.- Throws:
IllegalArgumentException
- if the pattern is invalid.
-
-
Method Details
-
applyPattern
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.
-
toPattern
Returns the pattern for this PluralFormat.- Returns:
- the pattern string
-
format
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 thisPluralFormat
object yet, the formatted number will be returned.- Returns:
- the string containing the formatted plural message.
-
format
Formats a plural message for a given number and appends the formatted message to the givenStringBuffer
.- Specified by:
format
in classFormat
- Parameters:
number
- a number object (instance ofNumber
for which the plural message should be formatted. If no pattern has been applied to thisPluralFormat
object yet, the formatted number will be returned. Note: If this object is not an instance ofNumber
, thetoAppendTo
will not be modified.toAppendTo
- the formatted message will be appended to thisStringBuffer
.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
-
parse
This method is not yet supported byPluralFormat
.- 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.
-
parseObject
This method is not yet supported byPluralFormat
.- Specified by:
parseObject
in classFormat
- 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.
-
setLocale
Deprecated.ICU 50 This method clears the pattern and might create a different kind of PluralRules instance; use one of the constructors to create a new instance instead.Sets the locale used by thisPluraFormat
object. Note: Calling this method resets thisPluraFormat
object, i.e., a pattern that was applied previously will be removed, and the NumberFormat is set to the default number format for the locale. The resulting format behaves the same as one constructed fromPluralFormat(ULocale, PluralRules.PluralType)
with PluralType.CARDINAL.- Parameters:
ulocale
- theULocale
used to configure the formatter. Ifulocale
isnull
, the defaultFORMAT
locale will be used.- See Also:
-
setNumberFormat
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.
-
equals
-
equals
Returns true if this equals the provided PluralFormat.- Parameters:
rhs
- the PluralFormat to compare against- Returns:
- true if this equals rhs
-
hashCode
public int hashCode() -
toString
-