java.text.RuleBasedCollator Maven / Gradle / Ivy
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package java.text;
import java.util.Vector;
import java.util.Locale;
/**
* 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) :
*
* - If a special collation rule controlled by a <modifier> is
* specified it applies to the whole collator object.
*
- 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>
*
* The definitions of the rule elements is as follows:
*
* - 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
*
*
* Notice that the order is important, as the subsequent item goes immediately
* after the text-argument. The following are not equivalent:
*
*
* a < b & a < c
* a < c & a < b
*
*
* Either the text-argument must already be present in the sequence, or some
* initial substring of the text-argument must be present. (e.g. "a < b & ae <
* e" is valid since "a" is present in the sequence before "ae" is reset). In
* this latter case, "ae" is not entered and treated as a single character;
* instead, "e" is sorted as if it were expanded to two characters: "a"
* followed by an "e". This difference appears in natural languages: in
* traditional Spanish "ch" is treated as though it contracts to a single
* character (expressed as "c < ch < d"), while in traditional German
* a-umlaut is treated as though it expanded to two characters
* (expressed as "a,A < b,B ... &ae;\u00e3&AE;\u00c3").
* [\u00e3 and \u00c3 are, of course, the escape sequences for a-umlaut.]
*
* 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")
*
* If you produce one of these errors, a RuleBasedCollator throws
* a ParseException.
*
* 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
* < \u00E5=a\u030A,\u00C5=A\u030A
* ;aa,AA< \u00E6,\u00C6< \u00F8,\u00D8"
*
*
* Normally, to create a rule-based Collator object, you will use
* Collator's factory method getInstance.
* However, to create a rule-based Collator 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);
*
*
* Or:
*
*
* 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 myNorwegian = new RuleBasedCollator(Norwegian);
*
*
*
*
* Combining Collators is as simple as concatenating strings.
* Here's an example that combines two Collators from two
* different locales:
*
*
* // 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
*
*
*
*
* Another more interesting example would be to make changes on an existing
* table to create a new Collator object. For example, add
* "&C< ch, cH, Ch, CH" to the en_USCollator object to create
* your own:
*
*
* // 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
*
*
*
*
* 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);
*
*
*
*
* The last example shows how to put new primary ordering in before the
* default setting. For example, in Japanese Collator, you
* can either sort English characters before or after Japanese characters,
*
*
* // get en_US Collator rules
* RuleBasedCollator en_USCollator = (RuleBasedCollator)Collator.getInstance(Locale.US);
* // add a few Japanese character 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);
*
*
*
* @see Collator
* @see CollationElementIterator
* @version 1.25 07/24/98
* @author Helena Shih, Laura Werner, Richard Gillam
*/
public class RuleBasedCollator extends Collator
{
/**
* RuleBasedCollator constructor. This takes the table rules and builds
* a collation table out of them. Please see RuleBasedCollator class
* description for more details on the collation rule syntax.
* @see java.util.Locale
* @param rules the collation rules to build the collation table from.
* @exception ParseException A format exception
* will be thrown if the build process of the rules fails. For
* example, build rule "a < ? < d" will cause the constructor to
* throw the ParseException because the '?' is not quoted.
*/
public RuleBasedCollator(String rules) throws ParseException { }
/**
* Gets the table-based rules for the collation object.
* @return returns the collation rules that the table collation object
* was created from.
*/
public String getRules() {
return null;
}
/**
* Return a CollationElementIterator for the given String.
* @see java.text.CollationElementIterator
*/
public CollationElementIterator getCollationElementIterator(String source) {
return null;
}
/**
* Return a CollationElementIterator for the given String.
* @see java.text.CollationElementIterator
* @since 1.2
*/
public CollationElementIterator
getCollationElementIterator(CharacterIterator source)
{
return null;
}
/**
* Compares the character data stored in two different strings based on the
* collation rules. Returns information about whether a string is less
* than, greater than or equal to another string in a language.
* This can be overriden in a subclass.
*/
public synchronized int compare(String source, String target) {
return 0;
}
/**
* Transforms the string into a series of characters that can be compared
* with CollationKey.compareTo. This overrides java.text.Collator.getCollationKey.
* It can be overriden in a subclass.
*/
public synchronized CollationKey getCollationKey(String source) {
return null;
}
/**
* Standard override; no change in semantics.
*/
public Object clone() {
return null;
}
/**
* Compares the equality of two collation objects.
* @param obj the table-based collation object to be compared with this.
* @return true if the current table-based collation object is the same
* as the table-based collation object obj; false otherwise.
*/
public boolean equals(Object obj) {
return false;
}
/**
* Generates the hash code for the table-based collation object
*/
public int hashCode() {
return 0;
}
}