PluralFormat
public
class
PluralFormat
extends UFormat
java.lang.Object | |||
↳ | 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:
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
.
Summary
Public constructors | |
---|---|
PluralFormat()
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale)
Creates a new cardinal-number |
|
PluralFormat(Locale locale)
Creates a new cardinal-number |
|
PluralFormat(PluralRules rules)
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale, PluralRules rules)
Creates a new cardinal-number |
|
PluralFormat(Locale locale, PluralRules rules)
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale, PluralRules.PluralType type)
Creates a new |
|
PluralFormat(Locale locale, PluralRules.PluralType type)
Creates a new |
|
PluralFormat(String pattern)
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale, String pattern)
Creates a new cardinal-number |
|
PluralFormat(PluralRules rules, String pattern)
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale, PluralRules rules, String pattern)
Creates a new cardinal-number |
|
PluralFormat(ULocale ulocale, PluralRules.PluralType type, String pattern)
Creates a new |
Public methods | |
---|---|
void
|
applyPattern(String pattern)
Sets the pattern used by this plural format. |
boolean
|
equals(Object rhs)
Indicates whether some other object is "equal to" this one. |
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 |
int
|
hashCode()
Returns a hash code value for the object. |
Number
|
parse(String text, ParsePosition parsePosition)
This method is not yet supported by |
Object
|
parseObject(String source, ParsePosition pos)
This method is not yet supported by |
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 representation of the object. |
Inherited methods | |
---|---|
Public constructors
PluralFormat
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:
PluralFormat
public PluralFormat (ULocale ulocale)
Creates a new cardinal-number PluralFormat
for a given locale.
Parameters | |
---|---|
ulocale |
ULocale : the PluralFormat will be configured with
rules for this locale. This locale will also be used for standard
number formatting. |
PluralFormat
public PluralFormat (Locale locale)
Creates a new cardinal-number PluralFormat
for a given
Locale
.
Parameters | |
---|---|
locale |
Locale : the PluralFormat will be configured with
rules for this locale. This locale will also be used for standard
number formatting. |
PluralFormat
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 |
PluralRules : defines the behavior of the PluralFormat
object. |
See also:
PluralFormat
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 |
ULocale : the default number formatting will be done using this
locale. |
rules |
PluralRules : defines the behavior of the PluralFormat
object. |
PluralFormat
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 |
Locale : the default number formatting will be done using this
locale. |
rules |
PluralRules : defines the behavior of the PluralFormat
object. |
PluralFormat
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 |
ULocale : the default number formatting will be done using this
locale. |
type |
PluralRules.PluralType : The plural type (e.g., cardinal or ordinal). |
PluralFormat
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 |
Locale : the default number formatting will be done using this
locale. |
type |
PluralRules.PluralType : The plural type (e.g., cardinal or ordinal). |
PluralFormat
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 |
String : the pattern for this PluralFormat . |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
See also:
PluralFormat
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:
ULocale locEn = new ULocale("en"); ULocale locSl = new ULocale("sl"); String patEn = "one{dog} other{dogs}"; // English 'dog' String patSl = "one{pes} two{psa} few{psi} other{psov}"; // Slovenian translation of dog in Plural Form // Create a new PluralFormat for a given locale locale and pattern string PluralFormat plfmtEn = new PluralFormat(locEn, patEn); PluralFormat plfmtSl = new PluralFormat(locSl, patSl); // Constructs a MessageFormat for the specified locale and pattern. MessageFormat msgfmtEn = new MessageFormat("{0,number} {1}", locEn); MessageFormat msgfmtSl = new MessageFormat("{0,number} {1}", locSl); final int[] numbers = {0, 1, 2, 3, 4, 5, 10, 100, 101, 102}; System.out.println("Output by using PluralFormat and MessageFormat API\n"); System.out.printf("%-16s%-16s%-16s\n", "Number", "English", "Slovenian"); // Use MessageFormat.format () to format the objects and appends to the given StringBuffer for (int num : numbers) { StringBuffer msgEn = new StringBuffer(); StringBuffer msgSl = new StringBuffer(); msgfmtEn.format(new Object[] {num, plfmtEn.format(num)}, msgEn, new FieldPosition(0)); msgfmtSl.format(new Object[] {num, plfmtSl.format(num)}, msgSl, new FieldPosition(0)); System.out.printf("%-16s%-16s%-16s\n", num, msgEn, msgSl); } System.out.println(); // Equivalent code with message format pattern String msgPatEn = "{0,plural, one{# dog} other{# dogs}}"; String msgPatSl = "{0,plural, one{# pes} two{# psa} few{# psi} other{# psov}}"; MessageFormat altMsgfmtEn = new MessageFormat(msgPatEn, locEn); MessageFormat altMsgfmtSl = new MessageFormat(msgPatSl, locSl); System.out.println("Same Output by using MessageFormat API only\n"); System.out.printf("%-16s%-16s%-16s\n", "Number", "English", "Slovenian"); for (int num : numbers) { StringBuffer msgEn = new StringBuffer(); StringBuffer msgSl = new StringBuffer(); altMsgfmtEn.format(new Object[] {num}, msgEn, new FieldPosition(0)); altMsgfmtSl.format(new Object[] {num}, msgSl, new FieldPosition(0)); System.out.printf("%-16s%-16s%-16s\n", num, msgEn, msgSl); } /** output of the sample code: ******************************************************************** Number English Slovenian 0 0 dogs 0 psov 1 1 dog 1 pes 2 2 dogs 2 psa 3 3 dogs 3 psi 4 4 dogs 4 psi 5 5 dogs 5 psov 10 10 dogs 10 psov 100 100 dogs 100 psov 101 101 dogs 101 pes 102 102 dogs 102 psa *******************************************************************/
Parameters | |
---|---|
ulocale |
ULocale : the PluralFormat will be configured with
rules for this locale. This locale will also be used for standard
number formatting. |
pattern |
String : the pattern for this PluralFormat . |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
PluralFormat
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 |
PluralRules : defines the behavior of the PluralFormat
object. |
pattern |
String : the pattern for this PluralFormat . |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
See also:
PluralFormat
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 |
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 . |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
PluralFormat
public PluralFormat (ULocale ulocale, PluralRules.PluralType type, String pattern)
Creates a new PluralFormat
for a plural type, a
pattern and a locale.
Parameters | |
---|---|
ulocale |
ULocale : the PluralFormat will be configured with
rules for this locale. This locale will also be used for standard
number formatting. |
type |
PluralRules.PluralType : The plural type (e.g., cardinal or ordinal). |
pattern |
String : the pattern for this PluralFormat . |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
Public methods
applyPattern
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 |
String : the pattern for this plural format. |
Throws | |
---|---|
IllegalArgumentException |
if the pattern is invalid. |
equals
public boolean equals (Object rhs)
Indicates whether some other object is "equal to" this one.
The equals
method implements an equivalence relation
on non-null object references:
- It is reflexive: for any non-null reference value
x
,x.equals(x)
should returntrue
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified. - For any non-null reference value
x
,x.equals(null)
should returnfalse
.
An equivalence relation partitions the elements it operates on into equivalence classes; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.
Parameters | |
---|---|
rhs |
Object : the reference object with which to compare. |
Returns | |
---|---|
boolean |
true if this object is the same as the obj
argument; false otherwise. |
equals
public boolean equals (PluralFormat rhs)
Returns true if this equals the provided PluralFormat.
Parameters | |
---|---|
rhs |
PluralFormat : the PluralFormat to compare against |
Returns | |
---|---|
boolean |
true if this equals rhs |
format
public final String format (double number)
Formats a plural message for a given number.
Parameters | |
---|---|
number |
double : 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 | |
---|---|
String |
the string containing the formatted plural message. |
format
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 |
Object : 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 |
StringBuffer : the formatted message will be appended to this
StringBuffer . |
pos |
FieldPosition : will be ignored by this method. |
Returns | |
---|---|
StringBuffer |
the string buffer passed in as toAppendTo, with formatted text appended. |
Throws | |
---|---|
IllegalArgumentException |
if number is not an instance of Number |
hashCode
public int hashCode ()
Returns a hash code value for the object. This method is
supported for the benefit of hash tables such as those provided by
HashMap
.
The general contract of hashCode
is:
- Whenever it is invoked on the same object more than once during
an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. - If two objects are equal according to the
equals
method, then calling thehashCode
method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal
according to the
equals
method, then calling thehashCode
method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
Returns | |
---|---|
int |
a hash code value for this object. |
parse
public Number parse (String text, ParsePosition parsePosition)
This method is not yet supported by PluralFormat
.
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. |
Returns | |
---|---|
Number |
nothing because this method is not yet implemented. |
Throws | |
---|---|
UnsupportedOperationException |
will always be thrown by this method. |
parseObject
public Object parseObject (String source, ParsePosition pos)
This method is not yet supported by PluralFormat
.
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. |
Returns | |
---|---|
Object |
nothing because this method is not yet implemented. |
Throws | |
---|---|
UnsupportedOperationException |
will always be thrown by this method. |
setNumberFormat
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 |
NumberFormat : the number format to use. |
toPattern
public String toPattern ()
Returns the pattern for this PluralFormat.
Returns | |
---|---|
String |
the pattern string |
toString
public String toString ()
Returns a string representation of the object.
Returns | |
---|---|
String |
a string representation of the object. |