com.ibm.icu.text

Class RuleBasedCollator

Implemented Interfaces:
Cloneable, Comparator

public final class RuleBasedCollator
extends Collator

RuleBasedCollator is a concrete subclass of Collator. It allows customization of the Collator via user-specified rule sets. RuleBasedCollator is designed to be fully compliant to the Unicode Collation Algorithm (UCA) and conforms to ISO 14651.

Users are strongly encouraged to read the users guide for more information about the collation service before using this class.

Create a RuleBasedCollator from a locale by calling the getInstance(Locale) factory method in the base class Collator. Collator.getInstance(Locale) creates a RuleBasedCollator object based on the collation rules defined by the argument locale. If a customized collation ordering ar attributes is required, use the RuleBasedCollator(String) constructor with the appropriate rules. The customized RuleBasedCollator will base its ordering on UCA, while re-adjusting the attributes and orders of the characters in the specified rule accordingly.

RuleBasedCollator provides correct collation orders for most locales supported in ICU. If specific data for a locale is not available, the orders eventually falls back to the UCA collation order .

For information about the collation rule syntax and details about customization, please refer to the Collation customization section of the user's guide.

Note that there are some differences between the Collation rule syntax used in Java and ICU4J:

Examples

Creating Customized RuleBasedCollators:

 String simple = "& a < b < c < d";
 RuleBasedCollator simpleCollator = new RuleBasedCollator(simple);

 String norwegian = "& a , A < b , B < c , C < d , D < e , E "
                    + "< f , F < g , G < h , H < i , I < j , "
                    + "J < k , K < l , L < m , M < n , N < "
                    + "o , O < p , P < q , Q < r , R < s , S < "
                    + "t , T < u , U < v , V < w , W < x , X "
                    + "< y , Y < z , Z < \u00E5 = a\u030A "
                    + ", \u00C5 = A\u030A ; aa , AA < \u00E6 "
                    + ", \u00C6 < \u00F8 , \u00D8";
 RuleBasedCollator norwegianCollator = new RuleBasedCollator(norwegian);
 
Concatenating rules to combine Collators:
 // Create an en_US Collator object
 RuleBasedCollator en_USCollator = (RuleBasedCollator)
     Collator.getInstance(new Locale("en", "US", ""));
 // Create a da_DK Collator object
 RuleBasedCollator da_DKCollator = (RuleBasedCollator)
     Collator.getInstance(new Locale("da", "DK", ""));
 // Combine the two
 // First, get the collation rules from en_USCollator
 String en_USRules = en_USCollator.getRules();
 // Second, get the collation rules from da_DKCollator
 String da_DKRules = da_DKCollator.getRules();
 RuleBasedCollator newCollator =
                             new RuleBasedCollator(en_USRules + da_DKRules);
 // newCollator has the combined rules
 
Making changes to an existing RuleBasedCollator to create a new Collator object, by appending changes to the existing rule:
 // Create a new Collator object with additional rules
 String addRules = "& C < ch, cH, Ch, CH";
 RuleBasedCollator myCollator =
     new RuleBasedCollator(en_USCollator + addRules);
 // myCollator contains the new rules
 
How to change the order of non-spacing accents:
 // old rule with main accents
 String oldRules = "= \u0301 ; \u0300 ; \u0302 ; \u0308 "
                 + "; \u0327 ; \u0303 ; \u0304 ; \u0305 "
                 + "; \u0306 ; \u0307 ; \u0309 ; \u030A "
                 + "; \u030B ; \u030C ; \u030D ; \u030E "
                 + "; \u030F ; \u0310 ; \u0311 ; \u0312 "
                 + "< a , A ; ae, AE ; \u00e6 , \u00c6 "
                 + "< b , B < c, C < e, E & C < d , D";
 // change the order of accent characters
 String addOn = "& \u0300 ; \u0308 ; \u0302";
 RuleBasedCollator myCollator = new RuleBasedCollator(oldRules + addOn);
 
Putting in a new primary ordering before the default setting, e.g. sort English characters before or after Japanese characters in the Japanese Collator:
 // get en_US Collator rules
 RuleBasedCollator en_USCollator
                        = (RuleBasedCollator)Collator.getInstance(Locale.US);
 // add a few Japanese characters to sort before English characters
 // suppose the last character before the first base letter 'a' in
 // the English collation rule is \u2212
 String jaString = "& \u2212 < \u3041, \u3042 < \u3043, "
                   + "\u3044";
 RuleBasedCollator myJapaneseCollator
              = new RuleBasedCollator(en_USCollator.getRules() + jaString);
 

This class is not subclassable

Author:
Syn Wee Quek

Nested Class Summary

Nested classes/interfaces inherited from class com.ibm.icu.text.Collator

Collator.CollatorFactory

Field Summary

Fields inherited from class com.ibm.icu.text.Collator

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

Constructor Summary

RuleBasedCollator(String rules)
Constructor that takes the argument rules for customization.

Method Summary

Object
clone()
Clones the RuleBasedCollator
int
compare(String source, String target)
Compares the source text String to the target text String according to the collation rules, strength and decomposition mode for this RuleBasedCollator.
boolean
equals(Object obj)
Compares the equality of two RuleBasedCollator objects.
CollationElementIterator
getCollationElementIterator(CharacterIterator source)
Return a CollationElementIterator for the given CharacterIterator.
CollationElementIterator
getCollationElementIterator(String source)
Return a CollationElementIterator for the given String.
CollationElementIterator
getCollationElementIterator(UCharacterIterator source)
Return a CollationElementIterator for the given UCharacterIterator.
CollationKey
getCollationKey(String source)
Get a Collation key for the argument String source from this RuleBasedCollator.
void
getContractionsAndExpansions(UnicodeSet contractions, UnicodeSet expansions, boolean addPrefixes)
Gets unicode sets containing contractions and/or expansions of a collator
boolean
getNumericCollation()
Method to retrieve the numeric collation value.
RawCollationKey
getRawCollationKey(String source, RawCollationKey key)
Gets the simpler form of a CollationKey for the String source following the rules of this Collator and stores the result into the user provided argument key.
String
getRules()
Gets the collation rules for this RuleBasedCollator.
String
getRules(boolean fullrules)
Returns current rules.
UnicodeSet
getTailoredSet()
Get an UnicodeSet that contains all the characters and sequences tailored in this collator.
VersionInfo
getUCAVersion()
Get the UCA version of this collator object.
int
getVariableTop()
Gets the variable top value of a Collator.
VersionInfo
getVersion()
Get the version of this collator object.
int
hashCode()
Generates a unique hash code for this RuleBasedCollator.
boolean
isAlternateHandlingShifted()
Checks if the alternate handling behaviour is the UCA defined SHIFTED or NON_IGNORABLE.
boolean
isCaseLevel()
Checks if case level is set to true.
boolean
isFrenchCollation()
Checks if French Collation is set to true.
boolean
isHiraganaQuaternary()
Checks if the Hiragana Quaternary mode is set on.
boolean
isLowerCaseFirst()
Return true if a lowercase character is sorted before the corresponding uppercase character.
boolean
isUpperCaseFirst()
Return true if an uppercase character is sorted before the corresponding lowercase character.
void
setAlternateHandlingDefault()
Sets the alternate handling mode to the initial mode set during construction of the RuleBasedCollator.
void
setAlternateHandlingShifted(boolean shifted)
Sets the alternate handling for QUATERNARY strength to be either shifted or non-ignorable.
void
setCaseFirstDefault()
Sets the case first mode to the initial mode set during construction of the RuleBasedCollator.
void
setCaseLevel(boolean flag)
When case level is set to true, an additional weight is formed between the SECONDARY and TERTIARY weight, known as the case level.
void
setCaseLevelDefault()
Sets the case level mode to the initial mode set during construction of the RuleBasedCollator.
void
setDecompositionDefault()
Sets the decomposition mode to the initial mode set during construction of the RuleBasedCollator.
void
setFrenchCollation(boolean flag)
Sets the mode for the direction of SECONDARY weights to be used in French collation.
void
setFrenchCollationDefault()
Sets the French collation mode to the initial mode set during construction of the RuleBasedCollator.
void
setHiraganaQuaternary(boolean flag)
Sets the Hiragana Quaternary mode to be on or off.
void
setHiraganaQuaternaryDefault()
Sets the Hiragana Quaternary mode to the initial mode set during construction of the RuleBasedCollator.
void
setLowerCaseFirst(boolean lowerfirst)
Sets the orders of lower cased characters to sort before upper cased characters, in strength TERTIARY.
void
setNumericCollation(boolean flag)
When numeric collation is turned on, this Collator generates a collation key for the numeric value of substrings of digits.
void
setNumericCollationDefault()
Method to set numeric collation to its default value.
void
setStrength(int newStrength)
Sets this Collator's strength property.
void
setStrengthDefault()
Sets the collation strength to the initial mode set during the construction of the RuleBasedCollator.
void
setUpperCaseFirst(boolean upperfirst)
Sets whether uppercase characters sort before lowercase characters or vice versa, in strength TERTIARY.
int
setVariableTop(String varTop)
Variable top is a two byte primary value which causes all the codepoints with primary values that are less or equal than the variable top to be shifted when alternate handling is set to SHIFTED.
void
setVariableTop(int varTop)
Sets the variable top to a collation element value supplied.

Methods inherited from class com.ibm.icu.text.Collator

clone, compare, compare, equals, getAvailableLocales, getAvailableULocales, getCollationKey, getDecomposition, getDisplayName, getDisplayName, getDisplayName, getDisplayName, getFunctionalEquivalent, getFunctionalEquivalent, getInstance, getInstance, getInstance, getKeywordValues, getKeywords, getLocale, getRawCollationKey, getStrength, getTailoredSet, getUCAVersion, getVariableTop, getVersion, registerFactory, registerInstance, setDecomposition, setStrength, setVariableTop, setVariableTop, unregister

Constructor Details

RuleBasedCollator

public RuleBasedCollator(String rules)
            throws Exception
Parameters:
rules - the collation rules to build the collation table from.

Method Details

clone

public Object clone()
            throws CloneNotSupportedException
Clones the RuleBasedCollator
Overrides:
clone in interface Collator
Returns:
a new instance of this RuleBasedCollator object

compare

public int compare(String source,
                   String target)
Compares the source text String to the target text String according to the collation rules, strength and decomposition mode for this RuleBasedCollator. Returns an integer less than, equal to or greater than zero depending on whether the source String is less than, equal to or greater than the target String. See the Collator class description for an example of use.

General recommendation:
If comparison are to be done to the same String multiple times, it would be more efficient to generate CollationKeys for the Strings and use CollationKey.compareTo(CollationKey) for the comparisons. If speed performance is critical and object instantiation is to be reduced, further optimization may be achieved by generating a simpler key of the form RawCollationKey and reusing this RawCollationKey object with the method RuleBasedCollator.getRawCollationKey. Internal byte representation can be directly accessed via RawCollationKey and stored for future use. Like CollationKey, RawCollationKey provides a method RawCollationKey.compareTo for key comparisons. If the each Strings are compared to only once, using the method RuleBasedCollator.compare(String, String) will have a better performance.

Overrides:
compare in interface Collator
Parameters:
source - the source text String.
target - the target text String.
Returns:
Returns an integer value. Value is less than zero if source is less than target, value is zero if source and target are equal, value is greater than zero if source is greater than target.

equals

public boolean equals(Object obj)
Compares the equality of two RuleBasedCollator objects. RuleBasedCollator objects are equal if they have the same collation rules and the same attributes.
Parameters:
obj - the RuleBasedCollator to be compared to.
Returns:
true if this RuleBasedCollator has exactly the same collation behaviour as obj, false otherwise.

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(CharacterIterator source)
Return a CollationElementIterator for the given CharacterIterator. The source iterator's integrity will be preserved since a new copy will be created for use.

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(String source)
Return a CollationElementIterator for the given String.

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(UCharacterIterator source)
Return a CollationElementIterator for the given UCharacterIterator. The source iterator's integrity will be preserved since a new copy will be created for use.

getCollationKey

public CollationKey getCollationKey(String source)
Get a Collation key for the argument String source from this RuleBasedCollator.

General recommendation:
If comparison are to be done to the same String multiple times, it would be more efficient to generate CollationKeys for the Strings and use CollationKey.compareTo(CollationKey) for the comparisons. If the each Strings are compared to only once, using the method RuleBasedCollator.compare(String, String) will have a better performance.

See the class documentation for an explanation about CollationKeys.

Overrides:
getCollationKey in interface Collator
Parameters:
source - the text String to be transformed into a collation key.
Returns:
the CollationKey for the given String based on this RuleBasedCollator's collation rules. If the source String is null, a null CollationKey is returned.

getContractionsAndExpansions

public void getContractionsAndExpansions(UnicodeSet contractions,
                                         UnicodeSet expansions,
                                         boolean addPrefixes)
            throws Exception
Gets unicode sets containing contractions and/or expansions of a collator
Parameters:
contractions - if not null, set to contain contractions
expansions - if not null, set to contain expansions
addPrefixes - add the prefix contextual elements to contractions

getNumericCollation

public boolean getNumericCollation()
Method to retrieve the numeric collation value. When numeric collation is turned on, this Collator generates a collation key for the numeric value of substrings of digits. This is a way to get '100' to sort AFTER '2'
Returns:
true if numeric collation is turned on, false otherwise

getRawCollationKey

public RawCollationKey getRawCollationKey(String source,
                                          RawCollationKey key)
Gets the simpler form of a CollationKey for the String source following the rules of this Collator and stores the result into the user provided argument key. If key has a internal byte array of length that's too small for the result, the internal byte array will be grown to the exact required size.
Overrides:
getRawCollationKey in interface Collator
Parameters:
source - the text String to be transformed into a RawCollationKey
key - output RawCollationKey to store results
Returns:
If key is null, a new instance of RawCollationKey will be created and returned, otherwise the user provided key will be returned.

getRules

public String getRules()
Gets the collation rules for this RuleBasedCollator. Equivalent to String getRules(RuleOption.FULL_RULES).
Returns:
returns the collation rules

getRules

public String getRules(boolean fullrules)
Returns current rules. The argument defines whether full rules (UCA + tailored) rules are returned or just the tailoring.
Parameters:
fullrules - true if the rules that defines the full set of collation order is required, otherwise false for returning only the tailored rules
Returns:
the current rules that defines this Collator.

getTailoredSet

public UnicodeSet getTailoredSet()
Get an UnicodeSet that contains all the characters and sequences tailored in this collator.
Overrides:
getTailoredSet in interface Collator
Returns:
a pointer to a UnicodeSet object containing all the code points and sequences that may sort differently than in the UCA.

getUCAVersion

public VersionInfo getUCAVersion()
Get the UCA version of this collator object.
Overrides:
getUCAVersion in interface Collator
Returns:
the version object associated with this collator

getVariableTop

public int getVariableTop()
Gets the variable top value of a Collator. Lower 16 bits are undefined and should be ignored.
Overrides:
getVariableTop in interface Collator
Returns:
the variable top value of a Collator.
See Also:
setVariableTop

getVersion

public VersionInfo getVersion()
Get the version of this collator object.
Overrides:
getVersion in interface Collator
Returns:
the version object associated with this collator

hashCode

public int hashCode()
Generates a unique hash code for this RuleBasedCollator.
Returns:
the unique hash code for this Collator

isAlternateHandlingShifted

public boolean isAlternateHandlingShifted()
Checks if the alternate handling behaviour is the UCA defined SHIFTED or NON_IGNORABLE. If return value is true, then the alternate handling attribute for the Collator is SHIFTED. Otherwise if return value is false, then the alternate handling attribute for the Collator is NON_IGNORABLE See setAlternateHandlingShifted(boolean) for more details.
Returns:
true or false

isCaseLevel

public boolean isCaseLevel()
Checks if case level is set to true. See setCaseLevel(boolean) for details.
Returns:
the case level mode

isFrenchCollation

public boolean isFrenchCollation()
Checks if French Collation is set to true. See setFrenchCollation(boolean) for details.
Returns:
true if French Collation is set to true, false otherwise

isHiraganaQuaternary

public boolean isHiraganaQuaternary()
Checks if the Hiragana Quaternary mode is set on. See setHiraganaQuaternary(boolean) for more details.
Returns:
flag true if Hiragana Quaternary mode is on, false otherwise

isLowerCaseFirst

public boolean isLowerCaseFirst()
Return true if a lowercase character is sorted before the corresponding uppercase character. See setCaseFirst(boolean) for details.
Returns:
true lower cased characters are sorted before upper cased characters, false otherwise

isUpperCaseFirst

public boolean isUpperCaseFirst()
Return true if an uppercase character is sorted before the corresponding lowercase character. See setCaseFirst(boolean) for details.
Returns:
true if upper cased characters are sorted before lower cased characters, false otherwise

setAlternateHandlingDefault

public void setAlternateHandlingDefault()
Sets the alternate handling mode to the initial mode set during construction of the RuleBasedCollator. See setAlternateHandling(boolean) for more details.

setAlternateHandlingShifted

public void setAlternateHandlingShifted(boolean shifted)
Sets the alternate handling for QUATERNARY strength to be either shifted or non-ignorable. See the UCA definition on Alternate Weighting. This attribute will only be effective when QUATERNARY strength is set. The default value for this mode is false, corresponding to the NON_IGNORABLE mode in UCA. In the NON-IGNORABLE mode, the RuleBasedCollator will treats all the codepoints with non-ignorable primary weights in the same way. If the mode is set to true, the behaviour corresponds to SHIFTED defined in UCA, this causes codepoints with PRIMARY orders that are equal or below the variable top value to be ignored in PRIMARY order and moved to the QUATERNARY order.
Parameters:
shifted - true if SHIFTED behaviour for alternate handling is desired, false for the NON_IGNORABLE behaviour.

setCaseFirstDefault

public final void setCaseFirstDefault()
Sets the case first mode to the initial mode set during construction of the RuleBasedCollator. See setUpperCaseFirst(boolean) and setLowerCaseFirst(boolean) for more details.

setCaseLevel

public void setCaseLevel(boolean flag)
Parameters:
flag - true if case level sorting is required, false otherwise

setCaseLevelDefault

public void setCaseLevelDefault()
Sets the case level mode to the initial mode set during construction of the RuleBasedCollator. See setCaseLevel(boolean) for more details.

setDecompositionDefault

public void setDecompositionDefault()
Sets the decomposition mode to the initial mode set during construction of the RuleBasedCollator. See setDecomposition(int) for more details.

setFrenchCollation

public void setFrenchCollation(boolean flag)
Parameters:
flag - true to set the French collation on, false to set it off

setFrenchCollationDefault

public void setFrenchCollationDefault()
Sets the French collation mode to the initial mode set during construction of the RuleBasedCollator. See setFrenchCollation(boolean) for more details.

setHiraganaQuaternary

public void setHiraganaQuaternary(boolean flag)
Sets the Hiragana Quaternary mode to be on or off. When the Hiragana Quaternary mode is turned on, the collator positions Hiragana characters before all non-ignorable characters in QUATERNARY strength. This is to produce a correct JIS collation order, distinguishing between Katakana and Hiragana characters.
Parameters:
flag - true if Hiragana Quaternary mode is to be on, false otherwise

setHiraganaQuaternaryDefault

public void setHiraganaQuaternaryDefault()
Sets the Hiragana Quaternary mode to the initial mode set during construction of the RuleBasedCollator. See setHiraganaQuaternary(boolean) for more details.

setLowerCaseFirst

public void setLowerCaseFirst(boolean lowerfirst)
Sets the orders of lower cased characters to sort before upper cased characters, in strength TERTIARY. The default mode is false. If true is set, the RuleBasedCollator will sort lower cased characters before the upper cased ones. Otherwise, if false is set, the RuleBasedCollator will ignore case preferences.
Parameters:
lowerfirst - true for sorting lower cased characters before upper cased characters, false to ignore case preferences.

setNumericCollation

public void setNumericCollation(boolean flag)
When numeric collation is turned on, this Collator generates a collation key for the numeric value of substrings of digits. This is a way to get '100' to sort AFTER '2'
Parameters:
flag - true to turn numeric collation on and false to turn it off

setNumericCollationDefault

public void setNumericCollationDefault()
Method to set numeric collation to its default value. When numeric collation is turned on, this Collator generates a collation key for the numeric value of substrings of digits. This is a way to get '100' to sort AFTER '2'

setStrength

public void setStrength(int newStrength)
Sets this Collator's strength property. The strength property determines the minimum level of difference considered significant during comparison.

See the Collator class description for an example of use.

Overrides:
setStrength in interface Collator
Parameters:
newStrength - the new strength value.

setStrengthDefault

public void setStrengthDefault()
Sets the collation strength to the initial mode set during the construction of the RuleBasedCollator. See setStrength(int) for more details.
See Also:
setStrength(int), RuleBasedCollator

setUpperCaseFirst

public void setUpperCaseFirst(boolean upperfirst)
Sets whether uppercase characters sort before lowercase characters or vice versa, in strength TERTIARY. The default mode is false, and so lowercase characters sort before uppercase characters. If true, sort upper case characters first.
Parameters:
upperfirst - true to sort uppercase characters before lowercase characters, false to sort lowercase characters before uppercase characters

setVariableTop

public int setVariableTop(String varTop)
Variable top is a two byte primary value which causes all the codepoints with primary values that are less or equal than the variable top to be shifted when alternate handling is set to SHIFTED.

Sets the variable top to a collation element value of a string supplied.

Overrides:
setVariableTop in interface Collator
Parameters:
varTop - one or more (if contraction) characters to which the variable top should be set
Returns:
a int value containing the value of the variable top in upper 16 bits. Lower 16 bits are undefined.

setVariableTop

public void setVariableTop(int varTop)
Sets the variable top to a collation element value supplied. Variable top is set to the upper 16 bits. Lower 16 bits are ignored.
Overrides:
setVariableTop in interface Collator
Parameters:
varTop - Collation element value, as returned by setVariableTop or getVariableTop

Copyright (c) 2006 IBM Corporation and others.