java.text

Class RuleBasedCollator

java.lang.Object

java.text.Collator

java.text.RuleBasedCollator

All Implemented Interfaces:

Cloneable, Comparator<Object>

public class RuleBasedCollator
extends Collator

A concrete subclass of Collator. It is based on the ICU RuleBasedCollator which implements the CLDR and Unicode collation algorithms.

Most of the time, you create a Collator instance for a Locale by calling the Collator.getInstance() factory method. You can construct a RuleBasedCollator if you need a custom sort order.

The root collator's sort order is the CLDR root collation order which in turn is the Unicode default sort order with a few modifications. A RuleBasedCollator is built from a rule String which changes the sort order of some characters and strings relative to the default order.

A rule string usually contains one or more rule chains. A rule chain consists of a reset followed by one or more rules. The reset anchors the following rules in the default sort order. The rules change the order of the their characters and strings relative to the reset point.

A reset is an ampersand & followed by one or more characters for the reset position. A rule is a relation operator, which specifies the level of difference, also followed by one or more characters. A multi-character rule creates a "contraction". A multi-character reset position usually creates "expansions".

For example, the following rules make "ä" sort with a diacritic-like (secondary) difference from "ae" (like in German phonebook sorting), and make "å" and "aa" sort as a base letter (primary) after "z" (like in Danish). Uppercase forms sort with a case-like (tertiary) difference after their lowercase forms.

 &AE<<ä <<<Ä
 &z<å<<<Å<<<aa<<<Aa<<<AA
 

For details see

• CLDR Collation Rule Syntax
• ICU User Guide Collation Customization

Note: earlier versions of RuleBasedCollator up to and including Android 4.4 (KitKat) allowed the omission of the reset from the first rule chain. This was interpreted as an implied reset after the last non-Han script in the default order. However, this is not a useful reset position, except for large tailorings of Han characters themselves. Starting with the CLDR 24 collation specification and the ICU 53 implementation, the initial reset is required.

If the rule string does not follow the syntax, then RuleBasedCollator throws a ParseException.

Field Summary

Fields inherited from class java.text.Collator

CANONICAL_DECOMPOSITION, FULL_DECOMPOSITION, IDENTICAL, NO_DECOMPOSITION, PRIMARY, SECONDARY, TERTIARY

Constructor Summary

Constructors

Constructor and Description
RuleBasedCollator(String rules) Constructs a new instance of RuleBasedCollator using the specified rules.

Method Summary

Modifier and Type	Method and Description
Object	clone() Returns a new collator with the same collation rules, decomposition mode and strength value as this collator.
int	compare(String source, String target) Compares the source text to the target text according to the collation rules, strength and decomposition mode for this RuleBasedCollator.
boolean	equals(Object obj) Compares the specified object with this RuleBasedCollator and indicates if they are equal.
CollationElementIterator	getCollationElementIterator(CharacterIterator source) Obtains a CollationElementIterator for the given CharacterIterator.
CollationElementIterator	getCollationElementIterator(String source) Obtains a CollationElementIterator for the given string.
CollationKey	getCollationKey(String source) Returns the CollationKey for the given source text.
String	getRules() Returns the collation rules of this collator.
int	hashCode() Returns an integer hash code for this object.

Methods inherited from class java.text.Collator

compare, equals, getAvailableLocales, getDecomposition, getInstance, getInstance, getStrength, setDecomposition, setStrength

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Comparator

comparing, comparing, comparingDouble, comparingInt, comparingLong, naturalOrder, nullsFirst, nullsLast, reversed, reverseOrder, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

Constructor Detail

RuleBasedCollator

public RuleBasedCollator(String rules)
                  throws ParseException

Constructs a new instance of RuleBasedCollator using the specified rules. (See the class description.)

Note that the rules are interpreted as a delta to the default sort order. This differs from other implementations which work with full rules specifications and may result in different behavior.

Parameters:

rules - the collation rules.

Throws:

NullPointerException - if rules == null.

ParseException - if rules contains rules with invalid collation rule syntax.

Method Detail

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(CharacterIterator source)

Obtains a CollationElementIterator for the given CharacterIterator. The source iterator's integrity will be preserved since a new copy will be created for use.

Parameters:

source - the source character iterator.

Returns:

a CollationElementIterator for source.

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(String source)

Obtains a CollationElementIterator for the given string.

Parameters:

source - the source string.

Returns:

the CollationElementIterator for source.

getRules

public String getRules()

Returns the collation rules of this collator. These rules can be fed into the RuleBasedCollator(String) constructor.

The returned string will be empty unless you constructed the instance yourself. The string forms of the collation rules are omitted to save space on the device.

clone

public Object clone()

Returns a new collator with the same collation rules, decomposition mode and strength value as this collator.

Overrides:

clone in class Collator

Returns:

a shallow copy of this collator.

See Also:

Cloneable

compare

public int compare(String source,
                   String target)

Compares the source text to the target text according to the collation rules, strength and decomposition mode for this RuleBasedCollator. See the Collator class description for an example of use.

Specified by:

compare in class Collator

Parameters:

source - the source text.

target - the target text.

Returns:

an integer which may be a negative value, zero, or else a positive value depending on whether source is less than, equivalent to, or greater than target.

getCollationKey

public CollationKey getCollationKey(String source)

Returns the CollationKey for the given source text.

Specified by:

getCollationKey in class Collator

Parameters:

source - the specified source text.

Returns:

the CollationKey for the given source text.

hashCode

public int hashCode()

Description copied from class: Object

Returns an integer hash code for this object. By contract, any two objects for which Object.equals(java.lang.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.

Specified by:

hashCode in class Collator

Returns:

this object's hash code.

See Also:

Object.equals(java.lang.Object)

equals

public boolean equals(Object obj)

Compares the specified object with this RuleBasedCollator and indicates if they are equal. In order to be equal, object must be an instance of Collator with the same collation rules and the same attributes.

Specified by:

equals in interface Comparator<Object>

Overrides:

equals in class Collator

Parameters:

obj - the object to compare with this object.

Returns:

true if the specified object is equal to this RuleBasedCollator; false otherwise.

See Also:

hashCode()