RuleBasedCollator

public class RuleBasedCollator
extends Collator

The RuleBasedCollator class is a concrete subclass of Collator that provides a simple, data-driven, table collator. With this class you can create a customized table-based Collator. RuleBasedCollator maps characters to sort keys.

RuleBasedCollator has the following restrictions for efficiency (other subclasses may be used for more complex languages) :

1. If a special collation rule controlled by a <modifier> is specified it applies to the whole collator object.
2. All non-mentioned characters are at the end of the collation order.

The collation table is composed of a list of collation rules, where each rule is of one of three forms:

    <modifier>
    <relation> <text-argument>
    <reset> <text-argument>
 

• Text-Argument: A text-argument is any sequence of characters, excluding special characters (that is, common whitespace characters [0009-000D, 0020] and rule syntax characters [0021-002F, 003A-0040, 005B-0060, 007B-007E]). If those characters are desired, you can put them in single quotes (e.g. ampersand => '&'). Note that unquoted white space characters are ignored; e.g. b c is treated as bc.
• Modifier: There are currently two modifiers that turn on special collation rules.
  • '@' : Turns on backwards sorting of accents (secondary differences), as in French.
  • '!' : Turns on Thai/Lao vowel-consonant swapping. If this rule is in force when a Thai vowel of the range \U0E40-\U0E44 precedes a Thai consonant of the range \U0E01-\U0E2E OR a Lao vowel of the range \U0EC0-\U0EC4 precedes a Lao consonant of the range \U0E81-\U0EAE then the vowel is placed after the consonant for collation purposes.

  '@' : Indicates that accents are sorted backwards, as in French.

• Relation: The relations are the following:
  • '<' : Greater, as a letter difference (primary)
  • ';' : Greater, as an accent difference (secondary)
  • ',' : Greater, as a case difference (tertiary)
  • '=' : Equal
• Reset: There is a single reset which is used primarily for contractions and expansions, but which can also be used to add a modification at the end of a set of rules.

  '&' : Indicates that the next rule follows the position to where the reset text-argument would be sorted.

This sounds more complicated than it is in practice. For example, the following are equivalent ways of expressing the same thing:

 a < b < c
 a < b & b < c
 a < c & a < b
 

 a < b & a < c
 a < c & a < b
 

Ignorable Characters

For ignorable characters, the first rule must start with a relation (the examples we have used above are really fragments; "a < b" really should be "< a < b"). If, however, the first relation is not "<", then all the all text-arguments up to the first "<" are ignorable. For example, ", - < a < b" makes "-" an ignorable character, as we saw earlier in the word "black-birds". In the samples for different languages, you see that most accents are ignorable.

Normalization and Accents

RuleBasedCollator automatically processes its rule table to include both pre-composed and combining-character versions of accented characters. Even if the provided rule string contains only base characters and separate combining accent characters, the pre-composed accented characters matching all canonical combinations of characters from the rule string will be entered in the table.

This allows you to use a RuleBasedCollator to compare accented strings even when the collator is set to NO_DECOMPOSITION. There are two caveats, however. First, if the strings to be collated contain combining sequences that may not be in canonical order, you should set the collator to CANONICAL_DECOMPOSITION or FULL_DECOMPOSITION to enable sorting of combining sequences. Second, if the strings contain characters with compatibility decompositions (such as full-width and half-width forms), you must use FULL_DECOMPOSITION, since the rule tables only include canonical mappings.

Errors

The following are errors:

• A text-argument contains unquoted punctuation symbols (e.g. "a < b-c < d").
• A relation or reset character not followed by a text-argument (e.g. "a < ,b").
• A reset where the text-argument (or an initial substring of the text-argument) is not already in the sequence. (e.g. "a < b & e < f")

Examples

Simple: "< a < b < c < d"

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 < \u00E6, \u00C6 < \u00F8, \u00D8 < \u00E5 = a\u030A, \u00C5 = A\u030A; aa, AA"

To create a RuleBasedCollator object with specialized rules tailored to your needs, you construct the RuleBasedCollator with the rules contained in a String object. For example:

 String simple = "< a< b< c< d";
 RuleBasedCollator mySimple = 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" +
                    "< \u00E6, \u00C6" +     // Latin letter ae & AE
                    "< \u00F8, \u00D8" +     // Latin letter o & O with stroke
                    "< \u00E5 = a\u030A," +  // Latin letter a with ring above
                    "  \u00C5 = A\u030A;" +  // Latin letter A with ring above
                    "  aa, AA";
 RuleBasedCollator myNorwegian = new RuleBasedCollator(Norwegian);
 

A new collation rules string can be created by concatenating rules strings. For example, the rules returned by getRules() could be concatenated to combine multiple RuleBasedCollators.

The following example demonstrates how to change the order of non-spacing accents,

 // old rule
 String oldRules = "=\u0301;\u0300;\u0302;\u0308"    // main accents
                 + ";\u0327;\u0303;\u0304;\u0305"    // main accents
                 + ";\u0306;\u0307;\u0309;\u030A"    // main accents
                 + ";\u030B;\u030C;\u030D;\u030E"    // main accents
                 + ";\u030F;\u0310;\u0311;\u0312"    // main accents
                 + "< 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);
 

Summary

Inherited constants
From class java.text.Collator int CANONICAL_DECOMPOSITION Decomposition mode value. int FULL_DECOMPOSITION Decomposition mode value. int IDENTICAL Collator strength value. int NO_DECOMPOSITION Decomposition mode value. int PRIMARY Collator strength value. int SECONDARY Collator strength value. int TERTIARY Collator strength value.

Inherited methods
From class java.text.Collator Object clone() Returns a new collator with the same decomposition mode and strength value as this collator. int compare(Object o1, Object o2) Compares its two arguments for order. abstract int compare(String source, String target) Compares the source string to the target string according to the collation rules for this Collator. boolean equals(String source, String target) Convenience method for comparing the equality of two strings based on this Collator's collation rules. boolean equals(Object that) Compares the equality of two Collators. static Locale[] getAvailableLocales() Returns an array of all locales for which the getInstance methods of this class can return localized instances. abstract CollationKey getCollationKey(String source) Transforms the String into a series of bits that can be compared bitwise to other CollationKeys. int getDecomposition() Get the decomposition mode of this Collator. static Collator getInstance() Gets the Collator for the current default locale. static Collator getInstance(Locale desiredLocale) Gets the Collator for the desired locale. int getStrength() Returns this Collator's strength property. abstract int hashCode() Generates the hash code for this Collator. void setDecomposition(int decompositionMode) Set the decomposition mode of this Collator. void setStrength(int newStrength) Sets this Collator's strength property.
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 millis, 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 millis) 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.
From interface java.util.Comparator abstract int compare(Object o1, Object o2) Compares its two arguments for order. static <T, U> Comparator<Object> comparing(Function<? super T, ? extends U> keyExtractor, Comparator<? super U> keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Comparator. static <T, U extends Comparable<? super U>> Comparator<Object> comparing(Function<? super T, ? extends U> keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key. static <T> Comparator<Object> comparingDouble(ToDoubleFunction<? super T> keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator<T> that compares by that sort key. static <T> Comparator<Object> comparingInt(ToIntFunction<? super T> keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator<T> that compares by that sort key. static <T> Comparator<Object> comparingLong(ToLongFunction<? super T> keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator<T> that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static <T extends Comparable<? super T>> Comparator<T> naturalOrder() Returns a comparator that compares Comparable objects in natural order. static <T> Comparator<Object> nullsFirst(Comparator<? super T> comparator) Returns a null-friendly comparator that considers null to be less than non-null. static <T> Comparator<Object> nullsLast(Comparator<? super T> comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static <T extends Comparable<? super T>> Comparator<T> reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator<Object> reversed() Returns a comparator that imposes the reverse ordering of this comparator. default <U extends Comparable<? super U>> Comparator<Object> thenComparing(Function<? super T, ? extends U> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default <U> Comparator<Object> thenComparing(Function<? super T, ? extends U> keyExtractor, Comparator<? super U> keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator<Object> thenComparing(Comparator<? super T> other) Returns a lexicographic-order comparator with another comparator. default Comparator<Object> thenComparingDouble(ToDoubleFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator<Object> thenComparingInt(ToIntFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a int sort key. default Comparator<Object> thenComparingLong(ToLongFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key.

Public constructors

RuleBasedCollator (String rules)

Public methods

Object clone ()

int compare (String source, 
                String target)

boolean equals (Object obj)

CollationElementIterator getCollationElementIterator (String source)

CollationElementIterator getCollationElementIterator (CharacterIterator source)

CollationKey getCollationKey (String source)

String getRules ()

int hashCode ()