rulebasedcollator.java

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/*
 * @(#)RuleBasedCollator.java	1.36 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996-1998 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.text;

import java.util.Vector;
import java.util.Locale;
import sun.text.Normalizer;
import sun.text.NormalizerUtilities;

/**
 * The <code>RuleBasedCollator</code> class is a concrete subclass of
 * <code>Collator</code> that provides a simple, data-driven, table
 * collator.  With this class you can create a customized table-based
 * <code>Collator</code>.  <code>RuleBasedCollator</code> maps
 * characters to sort keys.
 *
 * <p>
 * <code>RuleBasedCollator</code> has the following restrictions
 * for efficiency (other subclasses may be used for more complex languages) :
 * <ol>
 * <li>If a special collation rule controlled by a &lt;modifier&gt; is
      specified it applies to the whole collator object.
 * <li>All non-mentioned characters are at the end of the
 *     collation order.
 * </ol>
 *
 * <p>
 * The collation table is composed of a list of collation rules, where each
 * rule is of one of three forms:
 * <pre>
 *    &lt;modifier&gt;
 *    &lt;relation&gt; &lt;text-argument&gt;
 *    &lt;reset&gt; &lt;text-argument&gt;
 * </pre>
 * The definitions of the rule elements is as follows:
 * <UL Type=disc>
 *    <LI><strong>Text-Argument</strong>: 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. <code>b c</code> is treated as <code>bc</code>.
 *    <LI><strong>Modifier</strong>: There are currently two modifiers that 
 *        turn on special collation rules.
 *        <UL Type=square>
 *            <LI>'@' : Turns on backwards sorting of accents (secondary
 *                      differences), as in French.
 *            <LI>'!' : Turns on Thai/Lao vowel-consonant swapping.  If this
 *                      rule is in force when a Thai vowel of the range
 *                      &#92;U0E40-&#92;U0E44 precedes a Thai consonant of the range
 *                      &#92;U0E01-&#92;U0E2E OR a Lao vowel of the range &#92;U0EC0-&#92;U0EC4
 *                      precedes a Lao consonant of the range &#92;U0E81-&#92;U0EAE then
 *                      the vowel is placed after the consonant for collation
 *                      purposes.
 *        </UL>
 *        <p>'@' : Indicates that accents are sorted backwards, as in French.
 *    <LI><strong>Relation</strong>: The relations are the following:
 *        <UL Type=square>
 *            <LI>'&lt;' : Greater, as a letter difference (primary)
 *            <LI>';' : Greater, as an accent difference (secondary)
 *            <LI>',' : Greater, as a case difference (tertiary)
 *            <LI>'=' : Equal
 *        </UL>
 *    <LI><strong>Reset</strong>: 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.
 *        <p>'&' : Indicates that the next rule follows the position to where
 *            the reset text-argument would be sorted.
 * </UL>
 *
 * <p>
 * This sounds more complicated than it is in practice. For example, the
 * following are equivalent ways of expressing the same thing:
 * <blockquote>
 * <pre>
 * a &lt; b &lt; c
 * a &lt; b &amp; b &lt; c
 * a &lt; c &amp; a &lt; b
 * </pre>
 * </blockquote>
 * Notice that the order is important, as the subsequent item goes immediately
 * after the text-argument. The following are not equivalent:
 * <blockquote>
 * <pre>
 * a &lt; b &amp; a &lt; c
 * a &lt; c &amp; a &lt; b
 * </pre>
 * </blockquote>
 * 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 &lt; b &amp; ae &lt; 
 * 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 &lt; ch &lt; d"), while in traditional German
 * a-umlaut is treated as though it expanded to two characters
 * (expressed as "a,A &lt; b,B ... &amp;ae;&#92;u00e3&amp;AE;&#92;u00c3").
 * [&#92;u00e3 and &#92;u00c3 are, of course, the escape sequences for a-umlaut.]
 * <p>
 * <strong>Ignorable Characters</strong>
 * <p>
 * For ignorable characters, the first rule must start with a relation (the
 * examples we have used above are really fragments; "a &lt; b" really should be
 * "&lt; a &lt; b"). If, however, the first relation is not "&lt;", then all the all
 * text-arguments up to the first "&lt;" are ignorable. For example, ", - &lt; a &lt; 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.
 *
 * <p><strong>Normalization and Accents</strong>
 * <p>
 * <code>RuleBasedCollator</code> 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.
 * <p>
 * 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.
 *
 * <p><strong>Errors</strong>
 * <p>
 * The following are errors:
 * <UL Type=disc>
 *     <LI>A text-argument contains unquoted punctuation symbols
 *        (e.g. "a &lt; b-c &lt; d").
 *     <LI>A relation or reset character not followed by a text-argument
 *        (e.g. "a &lt; ,b").
 *     <LI>A reset where the text-argument (or an initial substring of the
 *         text-argument) is not already in the sequence.
 *         (e.g. "a &lt; b &amp; e &lt; f")
 * </UL>
 * If you produce one of these errors, a <code>RuleBasedCollator</code> throws
 * a <code>ParseException</code>.
 * 
 * <p><strong>Examples</strong>
 * <p>Simple:     "&lt; a &lt; b &lt; c &lt; d"
 * <p>Norwegian:  "&lt; a,A&lt; b,B&lt; c,C&lt; d,D&lt; e,E&lt; f,F&lt; g,G&lt; h,H&lt; i,I&lt; j,J
 *                 &lt; k,K&lt; l,L&lt; m,M&lt; n,N&lt; o,O&lt; p,P&lt; q,Q&lt; r,R&lt; s,S&lt; t,T
 *                 &lt; u,U&lt; v,V&lt; w,W&lt; x,X&lt; y,Y&lt; z,Z
 *                 &lt; &#92;u00E5=a&#92;u030A,&#92;u00C5=A&#92;u030A
 *                 ;aa,AA&lt; &#92;u00E6,&#92;u00C6&lt; &#92;u00F8,&#92;u00D8"
 *
 * <p>
 * Normally, to create a rule-based Collator object, you will use
 * <code>Collator</code>'s factory method <code>getInstance</code>.
 * However, to create a rule-based Collator object with specialized
 * rules tailored to your needs, you construct the <code>RuleBasedCollator</code>
 * with the rules contained in a <code>String</code> object. For example:
 * <blockquote>
 * <pre>
 * String Simple = "&lt; a&lt; b&lt; c&lt; d";
 * RuleBasedCollator mySimple = new RuleBasedCollator(Simple);
 * </pre>
 * </blockquote>
 * Or:
 * <blockquote>
 * <pre>
 * String Norwegian = "&lt; a,A&lt; b,B&lt; c,C&lt; d,D&lt; e,E&lt; f,F&lt; g,G&lt; h,H&lt; i,I&lt; j,J" +
 *                 "&lt; k,K&lt; l,L&lt; m,M&lt; n,N&lt; o,O&lt; p,P&lt; q,Q&lt; r,R&lt; s,S&lt; t,T" +
 *                 "&lt; u,U&lt; v,V&lt; w,W&lt; x,X&lt; y,Y&lt; z,Z" +
 *                 "&lt; &#92;u00E5=a&#92;u030A,&#92;u00C5=A&#92;u030A" +
 *                 ";aa,AA&lt; &#92;u00E6,&#92;u00C6&lt; &#92;u00F8,&#92;u00D8";
 * RuleBasedCollator myNorwegian = new RuleBasedCollator(Norwegian);
 * </pre>
 * </blockquote>
 *
 * <p>
 * Combining <code>Collator</code>s is as simple as concatenating strings.
 * Here's an example that combines two <code>Collator</code>s from two
 * different locales:
 * <blockquote>
 * <pre>
 * // 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
 * </pre>
 * </blockquote>
 *
 * <p>
 * Another more interesting example would be to make changes on an existing
 * table to create a new <code>Collator</code> object.  For example, add
 * "&amp;C&lt; ch, cH, Ch, CH" to the <code>en_USCollator</code> object to create
 * your own:
 * <blockquote>
 * <pre>
 * // Create a new Collator object with additional rules
 * String addRules = "&amp;C&lt; ch, cH, Ch, CH";
 * RuleBasedCollator myCollator =
 *     new RuleBasedCollator(en_USCollator + addRules);
 * // myCollator contains the new rules
 * </pre>
 * </blockquote>
 *
 * <p>
 * The following example demonstrates how to change the order of
 * non-spacing accents,
 * <blockquote>
 * <pre>
 * // old rule
 * String oldRules = "=&#92;u0301;&#92;u0300;&#92;u0302;&#92;u0308"    // main accents
 *                 + ";&#92;u0327;&#92;u0303;&#92;u0304;&#92;u0305"    // main accents
 *                 + ";&#92;u0306;&#92;u0307;&#92;u0309;&#92;u030A"    // main accents
 *                 + ";&#92;u030B;&#92;u030C;&#92;u030D;&#92;u030E"    // main accents
 *                 + ";&#92;u030F;&#92;u0310;&#92;u0311;&#92;u0312"    // main accents
 *                 + "&lt; a , A ; ae, AE ; &#92;u00e6 , &#92;u00c6"
 *                 + "&lt; b , B &lt; c, C &lt; e, E & C &lt; d, D";
 * // change the order of accent characters
 * String addOn = "& &#92;u0300 ; &#92;u0308 ; &#92;u0302";
 * RuleBasedCollator myCollator = new RuleBasedCollator(oldRules + addOn);
 * </pre>
 * </blockquote>
 *
 * <p>
 * The last example shows how to put new primary ordering in before the
 * default setting. For example, in Japanese <code>Collator</code>, you
 * can either sort English characters before or after Japanese characters,
 * <blockquote>
 * <pre>