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# PluralRules

`public class PluralRules`
`extends Object` `implements Serializable`

java.lang.Object
↳ | android.icu.text.PluralRules

Defines rules for mapping non-negative numeric values onto a small set of keywords.

Rules are constructed from a text description, consisting of a series of keywords and conditions. The `select(double)` method examines each condition in order and returns the keyword for the first condition that matches the number. If none match, `KEYWORD_OTHER` is returned.

A PluralRules object is immutable. It contains caches for sample values, but those are synchronized.

PluralRules is Serializable so that it can be used in formatters, which are serializable.

For more information, details, and tips for writing rules, see the LDML spec, C.11 Language Plural Rules

Examples:

     "one: n is 1; few: n in 2..4"

This defines two rules, for 'one' and 'few'. The condition for 'one' is "n is 1" which means that the number must be equal to 1 for this condition to pass. The condition for 'few' is "n in 2..4" which means that the number must be between 2 and 4 inclusive - and be an integer - for this condition to pass. All other numbers are assigned the keyword "other" by the default rule.

     "zero: n is 0; one: n is 1; zero: n mod 100 in 1..19"

This illustrates that the same keyword can be defined multiple times. Each rule is examined in order, and the first keyword whose condition passes is the one returned. Also notes that a modulus is applied to n in the last rule. Thus its condition holds for 119, 219, 319...

     "one: n is 1; few: n mod 10 in 2..4 and n mod 100 not in 12..14"

This illustrates conjunction and negation. The condition for 'few' has two parts, both of which must be met: "n mod 10 in 2..4" and "n mod 100 not in 12..14". The first part applies a modulus to n before the test as in the previous example. The second part applies a different modulus and also uses negation, thus it matches all numbers _not_ in 12, 13, 14, 112, 113, 114, 212, 213, 214...

Syntax:

     rules         = rule (';' rule)*
     rule          = keyword ':' condition
     keyword       = <identifier>
     condition     = and_condition ('or' and_condition)*
     and_condition = relation ('and' relation)*
     relation      = not? expr not? rel not? range_list
     expr          = ('n' | 'i' | 'f' | 'v' | 't') (mod value)?
     not           = 'not' | '!'
     rel           = 'in' | 'is' | '=' | '≠' | 'within'
     mod           = 'mod' | '%'
     range_list    = (range | value) (',' range_list)*
     value         = digit+
     digit         = 0|1|2|3|4|5|6|7|8|9
     range         = value'..'value

Each not term inverts the meaning; however, there should not be more than one of them.

The i, f, t, and v values are defined as follows:

- i to be the integer digits.
- f to be the visible decimal digits, as an integer.
- t to be the visible decimal digits—without trailing zeros—as an integer.
- v to be the number of visible fraction digits.
- j is defined to only match integers. That is j is 3 fails if v != 0 (eg for 3.1 or 3.0).

Examples are in the following table:

n | i | f | v
--- | --- | --- | ---
1.0 | 1 | 0 | 1
1.00 | 1 | 0 | 2
1.3 | 1 | 3 | 1
1.03 | 1 | 3 | 2
1.23 | 1 | 23 | 2

An "identifier" is a sequence of characters that do not have the Unicode Pattern_Syntax or Pattern_White_Space properties.

The difference between 'in' and 'within' is that 'in' only includes integers in the specified range, while 'within' includes all values. Using 'within' with a range_list consisting entirely of values is the same as using 'in' (it's not an error).

## Summary

### Nested classes
`enum` | `PluralRules.PluralType` Type of plurals and PluralRules.

### Constants
`String` | `KEYWORD_FEW` Common name for the 'paucal' or other special plural form.
`String` | `KEYWORD_MANY` Common name for the arabic (11 to 99) plural form.
`String` | `KEYWORD_ONE` Common name for the 'singular' plural form.
`String` | `KEYWORD_OTHER` Common name for the default plural form.
`String` | `KEYWORD_TWO` Common name for the 'dual' plural form.
`String` | `KEYWORD_ZERO` Common name for the 'zero' plural form.
`double` | `NO_UNIQUE_VALUE` Value returned by `getUniqueKeywordValue(String)` when there is no unique value to return.

### Fields
`public static final PluralRules` | `DEFAULT` The default rules that accept any number and return `KEYWORD_OTHER`.

### Public methods
`static PluralRules` | `createRules(String description)` Creates a PluralRules from a description if it is parsable, otherwise returns null.
`boolean` | `equals(PluralRules rhs)` Returns true if rhs is equal to this.
`boolean` | `equals(Object rhs)` Indicates whether some other object is "equal to" this one.
`static PluralRules` | `forLocale(ULocale locale, PluralRules.PluralType type)` Provides access to the predefined `PluralRules` for a given locale and the plural type.
`static PluralRules` | `forLocale(Locale locale, PluralRules.PluralType type)` Provides access to the predefined `PluralRules` for a given `Locale` and the plural type.
`static PluralRules` | `forLocale(ULocale locale)` Provides access to the predefined cardinal-number `PluralRules` for a given locale.
`static PluralRules` | `forLocale(Locale locale)` Provides access to the predefined cardinal-number `PluralRules` for a given `Locale`.
`Collection<Double>` | `getAllKeywordValues(String keyword)` Returns all the values that trigger this keyword, or null if the number of such values is unlimited.
`Set<String>` | `getKeywords()` Returns a set of all rule keywords used in this `PluralRules` object.
`Collection<Double>` | `getSamples(String keyword)` Returns a list of integer values for which select() would return that keyword, or null if the keyword is not defined.
`double` | `getUniqueKeywordValue(String keyword)` Returns the unique value that this keyword matches, or `NO_UNIQUE_VALUE` if the keyword matches multiple values or is not defined for this PluralRules.
`static PluralRules` | `parseDescription(String description)` Parses a plural rules description and returns a PluralRules.
`String` | `select(double number)` Given a floating-point number, returns the keyword of the first rule that applies to the number.
`String` | `toString()` Returns a string representation of the object.

### Inherited methods
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Constants

### KEYWORD_FEW

    public static final String KEYWORD_FEW

Common name for the 'paucal' or other special plural form.

Constant Value: "few"

### KEYWORD_MANY

    public static final String KEYWORD_MANY

Common name for the arabic (11 to 99) plural form.

Constant Value: "many"

### KEYWORD_ONE

    public static final String KEYWORD_ONE

Common name for the 'singular' plural form.

Constant Value: "one"

### KEYWORD_OTHER

    public static final String KEYWORD_OTHER

Common name for the default plural form. This name is returned for values to which no other form in the rule applies. It can additionally be assigned rules of its own.

Constant Value: "other"

### KEYWORD_TWO

    public static final String KEYWORD_TWO

Common name for the 'dual' plural form.

Constant Value: "two"

### KEYWORD_ZERO

    public static final String KEYWORD_ZERO

Common name for the 'zero' plural form.

Constant Value: "zero"

### NO_UNIQUE_VALUE

    public static final double NO_UNIQUE_VALUE

Value returned by `getUniqueKeywordValue(String)` when there is no unique value to return.

Constant Value: -0.00123456777

## Fields

### DEFAULT

    public static final PluralRules DEFAULT

The default rules that accept any number and return `KEYWORD_OTHER`.

## Public methods

### createRules

    public static PluralRules createRules (String description)

Creates a PluralRules from a description if it is parsable, otherwise returns null.

Parameters
`description` | `String`: the rule description.

Returns
`PluralRules` | the PluralRules

### equals

    public boolean equals (PluralRules rhs)

Returns true if rhs is equal to this.

Parameters
`rhs` | `PluralRules`: the PluralRules to compare to.

Returns
`boolean` | true if this and rhs are equal.

### 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 return `true`.
- It is symmetric: for any non-null reference values `x` and `y`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
- It is transitive: for any non-null reference values `x`, `y`, and `z`, if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.
- It is consistent: for any non-null reference values `x` and `y`, multiple invocations of `x.equals(y)` consistently return `true` or consistently return `false`, provided no information used in `equals` comparisons on the objects is modified.
- For any non-null reference value `x`, `x.equals(null)` should return `false`.

The `equals` method for class `Object` implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values `x` and `y`, this method returns `true` if and only if `x` and `y` refer to the same object (`x == y` has the value `true`).

Note that it is generally necessary to override the `hashCode` method whenever this method is overridden, so as to maintain the general contract for the `hashCode` method, which states that equal objects must have equal hash codes.

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.

### forLocale

    public static PluralRules forLocale (ULocale locale,
                    PluralRules.PluralType type)

Provides access to the predefined `PluralRules` for a given locale and the plural type.

ICU defines plural rules for many locales based on CLDR Language Plural Rules. For these predefined rules, see CLDR page at http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html

Parameters
`locale` | `ULocale`: The locale for which a `PluralRules` object is returned.
`type` | `PluralRules.PluralType`: The plural type (e.g., cardinal or ordinal).

Returns
`PluralRules` | The predefined `PluralRules` object for this locale. If there's no predefined rules for this locale, the rules for the closest parent in the locale hierarchy that has one will be returned. The final fallback always returns the default rules.

### forLocale

    public static PluralRules forLocale (Locale locale,
                    PluralRules.PluralType type)

Provides access to the predefined `PluralRules` for a given `Locale` and the plural type.

ICU defines plural rules for many locales based on CLDR Language Plural Rules. For these predefined rules, see CLDR page at http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html

Parameters
`locale` | `Locale`: The locale for which a `PluralRules` object is returned.
`type` | `PluralRules.PluralType`: The plural type (e.g., cardinal or ordinal).

Returns
`PluralRules` | The predefined `PluralRules` object for this locale. If there's no predefined rules for this locale, the rules for the closest parent in the locale hierarchy that has one will be returned. The final fallback always returns the default rules.

### forLocale

    public static PluralRules forLocale (ULocale locale)

Provides access to the predefined cardinal-number `PluralRules` for a given locale. Same as forLocale(locale, PluralType.CARDINAL).

ICU defines plural rules for many locales based on CLDR Language Plural Rules. For these predefined rules, see CLDR page at http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html

Parameters
`locale` | `ULocale`: The locale for which a `PluralRules` object is returned.

Returns
`PluralRules` | The predefined `PluralRules` object for this locale. If there's no predefined rules for this locale, the rules for the closest parent in the locale hierarchy that has one will be returned. The final fallback always returns the default rules.

### forLocale

    public static PluralRules forLocale (Locale locale)

Provides access to the predefined cardinal-number `PluralRules` for a given `Locale`. Same as forLocale(locale, PluralType.CARDINAL).

ICU defines plural rules for many locales based on CLDR Language Plural Rules. For these predefined rules, see CLDR page at http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html

Parameters
`locale` | `Locale`: The locale for which a `PluralRules` object is returned.

Returns
`PluralRules` | The predefined `PluralRules` object for this locale. If there's no predefined rules for this locale, the rules for the closest parent in the locale hierarchy that has one will be returned. The final fallback always returns the default rules.

### getAllKeywordValues

    public Collection<Double> getAllKeywordValues (String keyword)

Returns all the values that trigger this keyword, or null if the number of such values is unlimited.

Parameters
`keyword` | `String`: the keyword

Returns
`Collection<Double>` | the values that trigger this keyword, or null. The returned collection is immutable. It will be empty if the keyword is not defined.

### getKeywords

    public Set<String> getKeywords ()

Returns a set of all rule keywords used in this `PluralRules` object. The rule "other" is always present by default.

Returns
`Set<String>` | The set of keywords.

### getSamples

    public Collection<Double> getSamples (String keyword)

Returns a list of integer values for which select() would return that keyword, or null if the keyword is not defined. The returned collection is unmodifiable. The returned list is not complete, and there might be additional values that would return the keyword.

Parameters
`keyword` | `String`: the keyword to test

Returns
`Collection<Double>` | a list of values matching the keyword.

### getUniqueKeywordValue

    public double getUniqueKeywordValue (String keyword)

Returns the unique value that this keyword matches, or `NO_UNIQUE_VALUE` if the keyword matches multiple values or is not defined for this PluralRules.

Parameters
`keyword` | `String`: the keyword to check for a unique value

Returns
`double` | The unique value for the keyword, or NO_UNIQUE_VALUE.

### parseDescription

    public static PluralRules parseDescription (String description)

Parses a plural rules description and returns a PluralRules.

Parameters
`description` | `String`: the rule description.

Returns
`PluralRules` |

Throws
`ParseException` | if the description cannot be parsed. The exception index is typically not set, it will be -1.

### select

    public String select (double number)

Given a floating-point number, returns the keyword of the first rule that applies to the number.

Parameters
`number` | `double`: The number for which the rule has to be determined.

Returns
`String` | The keyword of the selected rule.

### toString

    public String toString ()

Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

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

Returns
`String` | a string representation of the object.

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