com.ibm.icu.text
Class RuleBasedCollator

java.lang.Object
  |
  +--com.ibm.icu.text.Collator
        |
        +--com.ibm.icu.text.RuleBasedCollator
All Implemented Interfaces:
java.lang.Cloneable, java.util.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);
 

Since:
release 2.2, April 18 2002
Author:
Syn Wee Quek

Fields inherited from class com.ibm.icu.text.Collator
CANONICAL_DECOMPOSITION, IDENTICAL, NO_DECOMPOSITION, PRIMARY, QUATERNARY, SECONDARY, TERTIARY
 
Constructor Summary
RuleBasedCollator(java.lang.String rules)
           Constructor that takes the argument rules for customization.
 
Method Summary
 java.lang.Object clone()
          Clones the RuleBasedCollator
 int compare(java.lang.String source, java.lang.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(java.lang.Object obj)
          Compares the equality of two RuleBasedCollator objects.
 CollationElementIterator getCollationElementIterator(java.text.CharacterIterator source)
          Return a CollationElementIterator for the given CharacterIterator.
 CollationElementIterator getCollationElementIterator(java.lang.String source)
          Return a CollationElementIterator for the given String.
 CollationKey getCollationKey(java.lang.String source)
           Get a Collation key for the argument String source from this RuleBasedCollator.
 java.lang.String getRules()
          Gets the collation rules for this RuleBasedCollator.
 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 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.
 
Methods inherited from class com.ibm.icu.text.Collator
compare, equals, getDecomposition, getInstance, getInstance, getStrength, setDecomposition
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

RuleBasedCollator

public RuleBasedCollator(java.lang.String rules)
                  throws java.lang.Exception

Constructor that takes the argument rules for customization. The collator will be based on UCA, with the attributes and re-ordering of the characters specified in the argument rules.

See the user guide's section on Collation Customization for details on the rule syntax.

Parameters:
rules - the collation rules to build the collation table from.
Throws:
ParseException - and IOException thrown. ParseException thrown when argument rules have an invalid syntax. IOException thrown when an error occured while reading internal data.
Method Detail

clone

public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException
Clones the RuleBasedCollator
Overrides:
clone in class java.lang.Object
Returns:
a new instance of this RuleBasedCollator object

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(java.lang.String source)
Return a CollationElementIterator for the given String.
See Also:
CollationElementIterator

getCollationElementIterator

public CollationElementIterator getCollationElementIterator(java.text.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.
See Also:
CollationElementIterator

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
See Also:
setHiraganaQuaternaryDefault(), isHiraganaQuaternary()

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.
See Also:
setHiraganaQuaternary(boolean), isHiraganaQuaternary()

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
See Also:
isLowerCaseFirst(), isUpperCaseFirst(), setLowerCaseFirst(boolean), setCaseFirstDefault()

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.
See Also:
isLowerCaseFirst(), isUpperCaseFirst(), setUpperCaseFirst(boolean), setCaseFirstDefault()

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.
See Also:
isLowerCaseFirst(), isUpperCaseFirst(), setLowerCaseFirst(boolean), setUpperCaseFirst(boolean)

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.
See Also:
setAlternateHandlingShifted(boolean), isAlternateHandlingShifted()

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.
See Also:
setCaseLevel(boolean), isCaseLevel()

setDecompositionDefault

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

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.
See Also:
isFrenchCollation(), setFrenchCollation(boolean)

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), Collator.getStrength()

setFrenchCollation

public void setFrenchCollation(boolean flag)
Sets the mode for the direction of SECONDARY weights to be used in French collation. The default value is false, which treats SECONDARY weights in the order they appear. If set to true, the SECONDARY weights will be sorted backwards. See the section on French collation for more information.
Parameters:
flag - true to set the French collation on, false to set it off
See Also:
isFrenchCollation(), setFrenchCollationDefault()

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.
See Also:
isAlternateHandlingShifted(), setAlternateHandlingDefault()

setCaseLevel

public 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. The case level is used to distinguish large and small Japanese Kana characters. Case level could also be used in other situations. For example to distinguish certain Pinyin characters. The default value is false, which means the case level is not generated. The contents of the case level are affected by the case first mode. A simple way to ignore accent differences in a string is to set the strength to PRIMARY and enable case level.

See the section on case level for more information.

Parameters:
flag - true if case level sorting is required, false otherwise
See Also:
setCaseLevelDefault(), isCaseLevel()

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 class Collator
Parameters:
the - new strength value.
Throws:
java.lang.IllegalArgumentException - If the new strength value is not one of PRIMARY, SECONDARY, TERTIARY, QUATERNARY or IDENTICAL.
See Also:
Collator.getStrength(), setStrengthDefault(), Collator.PRIMARY, Collator.SECONDARY, Collator.TERTIARY, Collator.QUATERNARY, Collator.IDENTICAL

getRules

public java.lang.String getRules()
Gets the collation rules for this RuleBasedCollator.
Returns:
returns the collation rules

getCollationKey

public CollationKey getCollationKey(java.lang.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 class 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.
See Also:
CollationKey, compare(String, String)

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
See Also:
setUpperCaseFirst(boolean), setLowerCaseFirst(boolean), isLowerCaseFirst(), setCaseFirstDefault()

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
See Also:
setUpperCaseFirst(boolean), setLowerCaseFirst(boolean), isUpperCaseFirst(), setCaseFirstDefault()

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
See Also:
setAlternateHandlingShifted(boolean), setAlternateHandlingDefault()

isCaseLevel

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

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
See Also:
setFrenchCollation(boolean), setFrenchCollationDefault()

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
See Also:
setHiraganaQuaternaryDefault(), setHiraganaQuaternary(boolean)

equals

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

hashCode

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

compare

public int compare(java.lang.String source,
                   java.lang.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 the each Strings are compared to only once, using the method RuleBasedCollator.compare(String, String) will have a better performance.

Overrides:
compare in class 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.
See Also:
CollationKey, getCollationKey(java.lang.String)


Copyright (c) 2002 IBM Corporation and others.