RuleBasedBreakIterator.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 *
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/*
 *
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 2002 - 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 sun.text;

import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.text.BreakIterator;
import java.text.CharacterIterator;
import java.text.StringCharacterIterator;
import java.util.MissingResourceException;

/**
 * <p>A subclass of BreakIterator whose behavior is specified using a list of rules.</p>
 *
 * <p>There are two kinds of rules, which are separated by semicolons: <i>substitutions</i>
 * and <i>regular expressions.</i></p>
 *
 * <p>A substitution rule defines a name that can be used in place of an expression. It
 * consists of a name, which is a string of characters contained in angle brackets, an equals
 * sign, and an expression. (There can be no whitespace on either side of the equals sign.)
 * To keep its syntactic meaning intact, the expression must be enclosed in parentheses or
 * square brackets. A substitution is visible after its definition, and is filled in using
 * simple textual substitution. Substitution definitions can contain other substitutions, as
 * long as those substitutions have been defined first. Substitutions are generally used to
 * make the regular expressions (which can get quite complex) shorted and easier to read.
 * They typically define either character categories or commonly-used subexpressions.</p>
 *
 * <p>There is one special substitution.&nbsp; If the description defines a substitution
 * called &quot;&lt;ignore&gt;&quot;, the expression must be a [] expression, and the
 * expression defines a set of characters (the &quot;<em>ignore characters</em>&quot;) that
 * will be transparent to the BreakIterator.&nbsp; A sequence of characters will break the
 * same way it would if any ignore characters it contains are taken out.&nbsp; Break
 * positions never occur befoer ignore characters.</p>
 *
 * <p>A regular expression uses a subset of the normal Unix regular-expression syntax, and
 * defines a sequence of characters to be kept together. With one significant exception, the
 * iterator uses a longest-possible-match algorithm when matching text to regular
 * expressions. The iterator also treats descriptions containing multiple regular expressions
 * as if they were ORed together (i.e., as if they were separated by |).</p>
 *
 * <p>The special characters recognized by the regular-expression parser are as follows:</p>
 *
 * <blockquote>
 * <table border="1" width="100%">
 * <tr>
 * <td width="6%">*</td>
 * <td width="94%">Specifies that the expression preceding the asterisk may occur any number
 * of times (including not at all).</td>
 * </tr>
 * <tr>
 * <td width="6%">{}</td>
 * <td width="94%">Encloses a sequence of characters that is optional.</td>
 * </tr>
 * <tr>
 * <td width="6%">()</td>
 * <td width="94%">Encloses a sequence of characters.&nbsp; If followed by *, the sequence
 * repeats.&nbsp; Otherwise, the parentheses are just a grouping device and a way to delimit
 * the ends of expressions containing |.</td>
 * </tr>
 * <tr>
 * <td width="6%">|</td>
 * <td width="94%">Separates two alternative sequences of characters.&nbsp; Either one
 * sequence or the other, but not both, matches this expression.&nbsp; The | character can
 * only occur inside ().</td>
 * </tr>
 * <tr>
 * <td width="6%">.</td>
 * <td width="94%">Matches any character.</td>
 * </tr>
 * <tr>
 * <td width="6%">*?</td>
 * <td width="94%">Specifies a non-greedy asterisk.&nbsp; *? works the same way as *, except
 * when there is overlap between the last group of characters in the expression preceding the
 * * and the first group of characters following the *.&nbsp; When there is this kind of
 * overlap, * will match the longest sequence of characters that match the expression before
 * the *, and *? will match the shortest sequence of characters matching the expression
 * before the *?.&nbsp; For example, if you have &quot;xxyxyyyxyxyxxyxyxyy&quot; in the text,
 * &quot;x[xy]*x&quot; will match through to the last x (i.e., &quot;<strong>xxyxyyyxyxyxxyxyx</strong>yy&quot;,
 * but &quot;x[xy]*?x&quot; will only match the first two xes (&quot;<strong>xx</strong>yxyyyxyxyxxyxyxyy&quot;).</td>
 * </tr>
 * <tr>
 * <td width="6%">[]</td>
 * <td width="94%">Specifies a group of alternative characters.&nbsp; A [] expression will
 * match any single character that is specified in the [] expression.&nbsp; For more on the
 * syntax of [] expressions, see below.</td>
 * </tr>
 * <tr>
 * <td width="6%">/</td>
 * <td width="94%">Specifies where the break position should go if text matches this
 * expression.&nbsp; (e.g., &quot;[a-z]&#42;/[:Zs:]*[1-0]&quot; will match if the iterator sees a run
 * of letters, followed by a run of whitespace, followed by a digit, but the break position
 * will actually go before the whitespace).&nbsp; Expressions that don't contain / put the
 * break position at the end of the matching text.</td>
 * </tr>
 * <tr>
 * <td width="6%">\</td>
 * <td width="94%">Escape character.&nbsp; The \ itself is ignored, but causes the next
 * character to be treated as literal character.&nbsp; This has no effect for many
 * characters, but for the characters listed above, this deprives them of their special
 * meaning.&nbsp; (There are no special escape sequences for Unicode characters, or tabs and
 * newlines; these are all handled by a higher-level protocol.&nbsp; In a Java string,
 * &quot;\n&quot; will be converted to a literal newline character by the time the
 * regular-expression parser sees it.&nbsp; Of course, this means that \ sequences that are
 * visible to the regexp parser must be written as \\ when inside a Java string.)&nbsp; All
 * characters in the ASCII range except for letters, digits, and control characters are
 * reserved characters to the parser and must be preceded by \ even if they currently don't
 * mean anything.</td>
 * </tr>
 * <tr>
 * <td width="6%">!</td>
 * <td width="94%">If ! appears at the beginning of a regular expression, it tells the regexp
 * parser that this expression specifies the backwards-iteration behavior of the iterator,
 * and not its normal iteration behavior.&nbsp; This is generally only used in situations
 * where the automatically-generated backwards-iteration brhavior doesn't produce
 * satisfactory results and must be supplemented with extra client-specified rules.</td>
 * </tr>
 * <tr>
 * <td width="6%"><em>(all others)</em></td>
 * <td width="94%">All other characters are treated as literal characters, which must match
 * the corresponding character(s) in the text exactly.</td>
 * </tr>
 * </table>
 * </blockquote>
 *
 * <p>Within a [] expression, a number of other special characters can be used to specify
 * groups of characters:</p>
 *
 * <blockquote>
 * <table border="1" width="100%">
 * <tr>
 * <td width="6%">-</td>
 * <td width="94%">Specifies a range of matching characters.&nbsp; For example
 * &quot;[a-p]&quot; matches all lowercase Latin letters from a to p (inclusive).&nbsp; The -
 * sign specifies ranges of continuous Unicode numeric values, not ranges of characters in a
 * language's alphabetical order: &quot;[a-z]&quot; doesn't include capital letters, nor does
 * it include accented letters such as a-umlaut.</td>
 * </tr>
 * <tr>
 * <td width="6%">::</td>
 * <td width="94%">A pair of colons containing a one- or two-letter code matches all
 * characters in the corresponding Unicode category.&nbsp; The two-letter codes are the same
 * as the two-letter codes in the Unicode database (for example, &quot;[:Sc::Sm:]&quot;
 * matches all currency symbols and all math symbols).&nbsp; Specifying a one-letter code is
 * the same as specifying all two-letter codes that begin with that letter (for example,
 * &quot;[:L:]&quot; matches all letters, and is equivalent to
 * &quot;[:Lu::Ll::Lo::Lm::Lt:]&quot;).&nbsp; Anything other than a valid two-letter Unicode
 * category code or a single letter that begins a Unicode category code is illegal within
 * colons.</td>
 * </tr>
 * <tr>
 * <td width="6%">[]</td>
 * <td width="94%">[] expressions can nest.&nbsp; This has no effect, except when used in
 * conjunction with the ^ token.</td>
 * </tr>
 * <tr>
 * <td width="6%">^</td>
 * <td width="94%">Excludes the character (or the characters in the [] expression) following
 * it from the group of characters.&nbsp; For example, &quot;[a-z^p]&quot; matches all Latin
 * lowercase letters except p.&nbsp; &quot;[:L:^[&#92;u4e00-&#92;u9fff]]&quot; matches all letters
 * except the Han ideographs.</td>
 * </tr>
 * <tr>
 * <td width="6%"><em>(all others)</em></td>
 * <td width="94%">All other characters are treated as literal characters.&nbsp; (For
 * example, &quot;[aeiou]&quot; specifies just the letters a, e, i, o, and u.)</td>
 * </tr>
 * </table>
 * </blockquote>
 *
 * <p>For a more complete explanation, see <a
 * href="http://www.ibm.com/java/education/boundaries/boundaries.html">http://www.ibm.com/java/education/boundaries/boundaries.html</a>.
 * &nbsp; For examples, see the resource data (which is annotated).</p>
 *
 * @author Richard Gillam
 */
/*
 * BreakIterator的子类，使用指定的规则文件指导如何解析文本。
 *
 * 【由于对解析文本的规则文件未知，所以对某些方法及字段的理解还不到位...】
 *
 * 使用方式参考BreakIterator的测试用例
 */
public class RuleBasedBreakIterator extends BreakIterator {
    
    /**
     * A token used as a character-category value to identify ignore characters
     */
    protected static final byte IGNORE = -1;
    
    /**
     * Magic number for the BreakIterator data file format.
     */
    // 校验规则文件用到的魔数
    static final byte[] LABEL = {(byte) 'B', (byte) 'I', (byte) 'd', (byte) 'a', (byte) 't', (byte) 'a', (byte) '\0'};
    static final int LABEL_LENGTH = LABEL.length;
    
    /**
     * Version number of the dictionary that was read in.
     */
    // 校验规则文件用到的版本信息
    static final byte supportedVersion = 1;
    
    /**
     * The state number of the starting state
     */
    private static final short START_STATE = 1;
    /**
     * The state-transition value indicating "stop"
     */
    private static final short STOP_STATE = 0;
    /**
     * An array length of indices for BMP characters
     */
    private static final int BMP_INDICES_LENGTH = 512;
    
    /**
     * Tables that indexes from character values to character category numbers
     */
    /*
     * CompactByteArray和SupplementaryCharacterData作为辅助类，
     * 用来存放从BreakIterator这类分词器使用的规则文件中提取的Unicode增补字符集类别信息。
     */
    private CompactByteArray charCategoryTable = null;
    private SupplementaryCharacterData supplementaryCharCategoryTable = null;
    
    /**
     * The table of state transitions used for forward iteration
     */
    // 状态转换表，用于前向迭代
    private short[] stateTable = null;
    
    /**
     * The table of state transitions used to sync up the iterator with the text in backwards and random-access iteration
     */
    // 状态转换表，用于将迭代器与向后和随机访问迭代中的文本同步
    private short[] backwardsStateTable = null;
    
    /**
     * A list of flags indicating which states in the state table are accepting ("end") states
     */
    // 一个状态标记列表，用来指示状态转换表中哪些状态是accepting ("end")状态
    private boolean[] endStates = null;
    
    /**
     * A list of flags indicating which states in the state table are lookahead states (states which turn lookahead on and off)
     */
    // 一个状态标记列表，用来只是状态转换表中哪些状态是lookahead状态
    private boolean[] lookaheadStates = null;
    
    /**
     * A table for additional data. May be used by a subclass of RuleBasedBreakIterator.
     */
    // 附加数据表。可以由RuleBasedBreakIterator的子类使用。
    private byte[] additionalData = null;
    
    /**
     * The number of character categories (and, thus, the number of columns in the state tables)
     */
    // 字符类别的数量（同时也是状态状态表中的列数）
    private int numCategories;
    
    /**
     * The character iterator through which this BreakIterator accesses the text
     */
    // 通过该字符迭代器访问分词器中关联的文本
    private CharacterIterator text = null;
    
    /**
     * A CRC32 value of all data in datafile
     */
    // 数据文件的循环冗余校验码，用来保证数据的完整性
    private long checksum;
    
    private int cachedLastKnownBreak = BreakIterator.DONE;
    
    /**
     * Constructs a RuleBasedBreakIterator using the given rule data.
     *
     * @throws MissingResourceException if the rule data is invalid or corrupted
     */
    /*
     * 使用给定的规则文件构造RuleBasedBreakIterator，以字符分词器为例：
     * 规则文件名ruleFile==CharacterBreakIteratorData，ruleData是从规则文件sun/text/resources/CharacterBreakIteratorData中加载的规则信息。
     */
    public RuleBasedBreakIterator(String ruleFile, byte[] ruleData) {
        ByteBuffer bb = ByteBuffer.wrap(ruleData);
        try {
            validateRuleData(ruleFile, bb);
            // 使用规则文件中的数据设置状态装换表信息
            setupTables(ruleFile, bb);
        } catch(BufferUnderflowException bue) {
            MissingResourceException e;
            e = new MissingResourceException("Corrupted rule data file", ruleFile, "");
            e.initCause(bue);
            throw e;
        }
    }
    
    
    
    /**
     * Returns the current iteration position.
     *
     * @return The current iteration position.
     */
    // 返回游标当前的索引
    @Override
    public int current() {
        return getText().getIndex();
    }
    
    /**
     * Sets the current iteration position to the beginning of the text.
     * (i.e., the CharacterIterator's starting offset).
     *
     * @return The offset of the beginning of the text.
     */
    // 返回整个文本的起点索引，并将游标设置到起点
    @Override
    public int first() {
        CharacterIterator t = getText();
        t.first();
        return t.getIndex();
    }
    
    /**
     * Sets the current iteration position to the end of the text.
     * (i.e., the CharacterIterator's ending offset).
     *
     * @return The text's past-the-end offset.
     */
    // 返回整个文本的终点索引（此处由DONE标记），并将游标设置到终点
    @Override
    public int last() {
        CharacterIterator t = getText();
        // I'm not sure why, but t.last() returns the offset of the last character, rather than the past-the-end offset
        t.setIndex(t.getEndIndex());
        return t.getIndex();
    }
    
    /**
     * Advances the iterator backwards, to the last boundary preceding this one.
     *
     * @return The position of the last boundary position preceding this one.
     */
    // 返回前一个最近的左边界（当游标位于某个元素中间时，返回的就是当前元素的左边界）
    @Override
    public int previous() {
        // 如果已经在文本的起点，则返回DONE
        CharacterIterator text = getText();
        if(current() == text.getBeginIndex()) {
            return BreakIterator.DONE;
        }
        
        // set things up.
        // handlePrevious() will back us up to some valid break position before the current position
        // (we back our internal iterator up one step to prevent handlePrevious() from returning the current position),
        // but not necessarily the last one before where we started
        
        // 返回当前索引
        int start = current();
        int lastResult = cachedLastKnownBreak;
        if(lastResult >= start || lastResult <= BreakIterator.DONE) {
            // 返回前一个Unicode符号码点值，且游标值也挪到前一个Unicode符号的起始部位
            getPrevious();
            lastResult = handlePrevious();
        } else {
            // it might be better to check if handlePrevious() give us closer safe value but handlePrevious() is slow too So, this has to be done carefully
            text.setIndex(lastResult);
        }
        int result = lastResult;
        
        // iterate forward from the known break position until we pass our starting point.
        // The last break position before the starting point is our return value
        while(result != BreakIterator.DONE && result < start) {
            lastResult = result;
            result = handleNext();
        }
        
        // set the current iteration position to be the last break position before where we started, and then return that value
        text.setIndex(lastResult);
        cachedLastKnownBreak = lastResult;
        return lastResult;
    }
    
    /**
     * Advances the iterator to the next boundary position.
     *
     * @return The position of the first boundary after this one.
     */
    // 返回当前索引所在的元素的下一个元素（字符/单词/行/句子）的左边界索引，且游标也要后移。
    @Override
    public int next() {
        return handleNext();
    }
    
    /**
     * Advances the iterator either forward or backward the specified number of steps.
     * Negative values move backward, and positive values move forward.  This is
     * equivalent to repeatedly calling next() or previous().
     *
     * @param n The number of steps to move.  The sign indicates the direction
     *          (negative is backwards, and positive is forwards).
     *
     * @return The character offset of the boundary position n boundaries away from
     * the current one.
     */
    // 返回游标前进/后退n个元素后的左边界索引，并将游标挪到相应的新位置。
    @Override
    public int next(int n) {
        // 找到游标的当前索引
        int result = current();
        
        while(n > 0) {
            result = handleNext();
            --n;
        }
        
        while(n < 0) {
            result = previous();
            ++n;
        }
        return result;
    }
    
    /**
     * Sets the iterator to refer to the first boundary position following
     * the specified position.
     *
     * @return The position of the first break after the current position.
     *
     * @offset The position from which to begin searching for a break position.
     */
    // 返回offset索引所在的元素的下一个元素的左边界，游标也会跟着移动。
    @Override
    public int following(int offset) {
        
        CharacterIterator text = getText();
        checkOffset(offset, text);
        
        // Set our internal iteration position (temporarily)
        // to the position passed in.  If this is the _beginning_ position,
        // then we can just use next() to get our return value
        text.setIndex(offset);
        if(offset == text.getBeginIndex()) {
            cachedLastKnownBreak = handleNext();
            return cachedLastKnownBreak;
        }
        
        // otherwise, we have to sync up first.  Use handlePrevious() to back
        // us up to a known break position before the specified position (if
        // we can determine that the specified position is a break position,
        // we don't back up at all).  This may or may not be the last break
        // position at or before our starting position.  Advance forward
        // from here until we've passed the starting position.  The position
        // we stop on will be the first break position after the specified one.
        int result = cachedLastKnownBreak;
        if(result >= offset || result <= BreakIterator.DONE) {
            result = handlePrevious();
        } else {
            //it might be better to check if handlePrevious() give us closer
            //safe value but handlePrevious() is slow too
            //So, this has to be done carefully
            text.setIndex(result);
        }
        while(result != BreakIterator.DONE && result <= offset) {
            result = handleNext();
        }
        cachedLastKnownBreak = result;
        return result;
    }
    
    /**
     * Sets the iterator to refer to the last boundary position before the
     * specified position.
     *
     * @return The position of the last boundary before the starting position.
     *
     * @offset The position to begin searching for a break from.
     */
    // 返回offset索引左侧出现的最近一个左边界
    @Override
    public int preceding(int offset) {
        // if we start by updating the current iteration position to the
        // position specified by the caller, we can just use previous()
        // to carry out this operation
        CharacterIterator text = getText();
        checkOffset(offset, text);
        text.setIndex(offset);
        return previous();
    }
    
    /**
     * Returns true if the specified position is a boundary position.  As a side
     * effect, leaves the iterator pointing to the first boundary position at
     * or after "offset".
     *
     * @param offset the offset to check.
     *
     * @return True if "offset" is a boundary position.
     */
    // 判断offset索引处是否是一个（左）边界。
    @Override
    public boolean isBoundary(int offset) {
        CharacterIterator text = getText();
        checkOffset(offset, text);
        if(offset == text.getBeginIndex()) {
            return true;
        } else {
            // to check whether this is a boundary,
            // we can use following() on the position before the specified one and return true if the position we get back is the one the user specified
            return following(offset - 1) == offset;
        }
    }
    
    /**
     * Return a CharacterIterator over the text being analyzed.  This version
     * of this method returns the actual CharacterIterator we're using internally.
     * Changing the state of this iterator can have undefined consequences.  If
     * you need to change it, clone it first.
     *
     * @return An iterator over the text being analyzed.
     */
    // 返回分词器关联的文本迭代器
    @Override
    public CharacterIterator getText() {
        // The iterator is initialized pointing to no text at all, so if this
        // function is called while we're in that state, we have to fudge an
        // iterator to return.
        if(text == null) {
            text = new StringCharacterIterator("");
        }
        return text;
    }
    
    /**
     * Set the iterator to analyze a new piece of text.  This function resets
     * the current iteration position to the beginning of the text.
     *
     * @param newText An iterator over the text to analyze.
     */
    // 为分词器设置文本迭代器
    @Override
    public void setText(CharacterIterator newText) {
        // Test iterator to see if we need to wrap it in a SafeCharIterator.
        // The correct behavior for CharacterIterators is to allow the position to be set to the endpoint of the iterator.
        // Many CharacterIterators do not uphold this, so this is a workaround to permit them to use this class.
        // 返回文本迭代器的终点
        int end = newText.getEndIndex();
        boolean goodIterator;
        try {
            // 检测使用的迭代器是否为一个安全的迭代器（意味着游标可以定位到终点）
            newText.setIndex(end);  // some buggy iterators throw an exception here
            goodIterator = newText.getIndex() == end;
        } catch(IllegalArgumentException e) {
            goodIterator = false;
        }
    
        // 如果是一个安全的迭代器，将其设置给分词器
        if(goodIterator) {
            text = newText;
        } else {
            // 如果不是一个安全的迭代器，将其包装到“安全迭代器”中
            text = new SafeCharIterator(newText);
        }
        
        // 重置游标到文本起点
        text.first();
        
        // 缓存最近一次已知的边界为DONE
        cachedLastKnownBreak = BreakIterator.DONE;
    }
    
    
    
    /**
     * This method is the actual implementation of the next() method.
     * All iteration vectors through here.
     * This method initializes the state machine to state 1 and advances through the text character by character
     * until we reach the end of the text or the state machine transitions to state 0.
     * We update our return value every time the state machine passes through a possible end state.
     */
    // next方法的具体实现
    protected int handleNext() {
        // if we're already at the end of the text, return DONE.
        CharacterIterator text = getText();
        if(text.getIndex() == text.getEndIndex()) {
            return BreakIterator.DONE;
        }
        
        // no matter what, we always advance at least one character forward
        int result = getNextIndex();
        int lookaheadResult = 0;
        
        // begin in state 1
        int state = START_STATE;
        int category;
        int c = getCurrent();
        
        // loop until we reach the end of the text or transition to state 0
        while(c != CharacterIterator.DONE && state != STOP_STATE) {
            
            // look up the current character's character category (which tells us
            // which column in the state table to look at)
            category = lookupCategory(c);
            
            // if the character isn't an ignore character, look up a state
            // transition in the state table
            if(category != IGNORE) {
                state = lookupState(state, category);
            }
            
            // if the state we've just transitioned to is a lookahead state,
            // (but not also an end state), save its position.  If it's
            // both a lookahead state and an end state, update the break position
            // to the last saved lookup-state position
            if(lookaheadStates[state]) {
                if(endStates[state]) {
                    result = lookaheadResult;
                } else {
                    lookaheadResult = getNextIndex();
                }
            }
            
            // otherwise, if the state we've just transitioned to is an accepting
            // state, update the break position to be the current iteration position
            else {
                if(endStates[state]) {
                    result = getNextIndex();
                }
            }
            
            c = getNext();
        }
        
        // if we've run off the end of the text, and the very last character took us into
        // a lookahead state, advance the break position to the lookahead position
        // (the theory here is that if there are no characters at all after the lookahead
        // position, that always matches the lookahead criteria)
        if(c == CharacterIterator.DONE && lookaheadResult == text.getEndIndex()) {
            result = lookaheadResult;
        }
        
        text.setIndex(result);
        return result;
    }
    
    /**
     * This method backs the iterator back up to a "safe position" in the text.
     * This is a position that we know, without any context, must be a break position.
     * The various calling methods then iterate forward from this safe position to the appropriate position to return.
     * (For more information, see the description of buildBackwardsStateTable() in RuleBasedBreakIterator.Builder.)
     */
    // 将迭代器游标备份回"安全位置"
    protected int handlePrevious() {
        CharacterIterator text = getText();
        int state = START_STATE;
        int category = 0;
        int lastCategory = 0;
        int c = getCurrent();
        
        // 循环，直到我们到达文本的开头或转换到状态为0
        while(c != CharacterIterator.DONE && state != STOP_STATE) {
            
            // save the last character's category and look up the current character's category
            lastCategory = category;
            category = lookupCategory(c);   // 查找字符类别
            
            // if the current character isn't an ignore character, look up a state transition in the backwards state table
            // 如果当前字符不是一个可忽略字符，则在backwardsStateTable中查找其状态转换信息
            if(category != IGNORE) {
                // 给定当前状态和字符类别，在backwardsStateTable中查找要转换到的下一个状态。
                state = lookupBackwardState(state, category);
            }
            
            // 返回前一个Unicode符号码点值，且游标值也挪到前一个Unicode符号的起始部位
            c = getPrevious();
        }
        
        // if we didn't march off the beginning of the text, we're either one or two positions away from the real break position.
        // (One because of the call to previous() at the end of the loop above,
        // and another because the character that takes us into the stop state will always be the character BEFORE the break position.)
        if(c != CharacterIterator.DONE) {
            if(lastCategory != IGNORE) {
                getNext();
                getNext();
            } else {
                getNext();
            }
        }
        
        return text.getIndex();
    }
    
    /**
     * Looks up a character's category (i.e., its category for breaking purposes, not its Unicode category)
     */
    // 查找字符类别（由规则文件决定）
    protected int lookupCategory(int c) {
        if(c < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
            return charCategoryTable.elementAt((char) c);
        } else {
            return supplementaryCharCategoryTable.getValue(c);
        }
    }
    
    /**
     * Given a current state and a character category, looks up the next state to transition to in the state table.
     */
    // 给定当前状态和字符类别，在stateTable中查找要转换到的下一个状态。
    protected int lookupState(int state, int category) {
        return stateTable[state * numCategories + category];
    }
    
    /**
     * Given a current state and a character category, looks up the next state to transition to in the backwards state table.
     */
    // 给定当前状态和字符类别，在backwardsStateTable中查找要转换到的下一个状态。
    protected int lookupBackwardState(int state, int category) {
        return backwardsStateTable[state * numCategories + category];
    }
    
    /**
     * Returns current character
     */
    // 返回当前索引处的Unicode符号的编码
    int getCurrent() {
        char c1 = text.current();
        if(Character.isHighSurrogate(c1) && text.getIndex() < text.getEndIndex()) {
            char c2 = text.next();
            text.previous();
            if(Character.isLowSurrogate(c2)) {
                return Character.toCodePoint(c1, c2);
            }
        }
        return (int) c1;
    }
    
    /**
     * Returns next character
     */
    // 返回下一个索引处的Unicode符号的编码
    int getNext() {
        int index = text.getIndex();
        int endIndex = text.getEndIndex();
        if(index == endIndex || (index += getCurrentCodePointCount()) >= endIndex) {
            return CharacterIterator.DONE;
        }
        text.setIndex(index);
        return getCurrent();
    }
    
    /**
     * Returns previous character
     */
    // 返回前一个Unicode符号码点值，且游标值也挪到前一个Unicode符号的起始部位
    private int getPrevious() {
        char c2 = text.previous();
        if(Character.isLowSurrogate(c2) && text.getIndex() > text.getBeginIndex()) {
            char c1 = text.previous();
            if(Character.isHighSurrogate(c1)) {
                return Character.toCodePoint(c1, c2);
            } else {
                text.next();
            }
        }
        return (int) c2;
    }
    
    /**
     * Returns the count of next character.
     */
    // 返回当前索引处的Unicode符号所占的码元(char)个数
    private int getCurrentCodePointCount() {
        char c1 = text.current();
        if(Character.isHighSurrogate(c1) && text.getIndex() < text.getEndIndex()) {
            char c2 = text.next();
            text.previous();
            if(Character.isLowSurrogate(c2)) {
                return 2;
            }
        }
        return 1;
    }
    
    /**
     * Returns the position of next character.
     */
    // 返回下一个Unicode符号的索引
    private int getNextIndex() {
        int index = text.getIndex() + getCurrentCodePointCount();
        int endIndex = text.getEndIndex();
        if(index > endIndex) {
            return endIndex;
        } else {
            return index;
        }
    }
    
    
    
    /**
     * Validates the magic number, version, and the length of the given data.
     *
     * @throws BufferUnderflowException if the end-of-data is reached while validating data
     * @throws MissingResourceException if valification failed
     */
    // 校验规则文件数据完整性
    void validateRuleData(String ruleFile, ByteBuffer bb) {
        /* Verify the magic number. */
        for(int i = 0; i < LABEL_LENGTH; i++) {
            if(bb.get() != LABEL[i]) {
                throw new MissingResourceException("Wrong magic number", ruleFile, "");
            }
        }
        
        /* Verify the version number. */
        byte version = bb.get();
        if(version != supportedVersion) {
            throw new MissingResourceException("Unsupported version(" + version + ")", ruleFile, "");
        }
        
        // Check the length of the rest of data
        int len = bb.getInt();
        if(bb.position() + len != bb.limit()) {
            throw new MissingResourceException("Wrong data length", ruleFile, "");
        }
    }
    
    /**
     * Initializes the fields with the given rule data.
     * The data format is as follows:
     * <pre>
     *   BreakIteratorData {
     *       u1           magic[7];
     *       u1           version;
     *       u4           totalDataSize;
     *       header_info  header;
     *       body         value;
     *   }
     * </pre>
     * <code>totalDataSize</code> is the summation of the size of
     * <code>header_info</code> and <code>body</code> in byte count.
     * <p>
     * In <code>header</code>, each field except for checksum implies the
     * length of each field. Since <code>BMPdataLength</code> is a fixed-length
     * data(512 entries), its length isn't included in <code>header</code>.
     * <code>checksum</code> is a CRC32 value of all in <code>body</code>.
     * <pre>
     *   header_info {
     *       u4           stateTableLength;
     *       u4           backwardsStateTableLength;
     *       u4           endStatesLength;
     *       u4           lookaheadStatesLength;
     *       u4           BMPdataLength;
     *       u4           nonBMPdataLength;
     *       u4           additionalDataLength;
     *       u8           checksum;
     *   }
     * </pre>
     * <p>
     *
     * Finally, <code>BMPindices</code> and <code>BMPdata</code> are set to
     * <code>charCategoryTable</code>. <code>nonBMPdata</code> is set to
     * <code>supplementaryCharCategoryTable</code>.
     * <pre>
     *   body {
     *       u2           stateTable[stateTableLength];
     *       u2           backwardsStateTable[backwardsStateTableLength];
     *       u1           endStates[endStatesLength];
     *       u1           lookaheadStates[lookaheadStatesLength];
     *       u2           BMPindices[512];
     *       u1           BMPdata[BMPdataLength];
     *       u4           nonBMPdata[numNonBMPdataLength];
     *       u1           additionalData[additionalDataLength];
     *   }
     * </pre>
     *
     * @throws BufferUnderflowException if the end-of-data is reached before
     *                                  setting up all the tables
     */
    // 使用规则文件中的数据设置状态装换表信息
    private void setupTables(String ruleFile, ByteBuffer bb) {
        /* Read header_info. */
        int stateTableLength = bb.getInt();
        int backwardsStateTableLength = bb.getInt();
        int endStatesLength = bb.getInt();
        int lookaheadStatesLength = bb.getInt();
        int BMPdataLength = bb.getInt();
        int nonBMPdataLength = bb.getInt();
        int additionalDataLength = bb.getInt();
        checksum = bb.getLong();
        
        /* Read stateTable[numCategories * numRows] */
        stateTable = new short[stateTableLength];
        for(int i = 0; i < stateTableLength; i++) {
            stateTable[i] = bb.getShort();
        }
        
        /* Read backwardsStateTable[numCategories * numRows] */
        backwardsStateTable = new short[backwardsStateTableLength];
        for(int i = 0; i < backwardsStateTableLength; i++) {
            backwardsStateTable[i] = bb.getShort();
        }
        
        /* Read endStates[numRows] */
        endStates = new boolean[endStatesLength];
        for(int i = 0; i < endStatesLength; i++) {
            endStates[i] = bb.get() == 1;
        }
        
        /* Read lookaheadStates[numRows] */
        lookaheadStates = new boolean[lookaheadStatesLength];
        for(int i = 0; i < lookaheadStatesLength; i++) {
            lookaheadStates[i] = bb.get() == 1;
        }
        
        /* Read a category table and indices for BMP characters. */
        short[] temp1 = new short[BMP_INDICES_LENGTH];  // BMPindices
        for(int i = 0; i < BMP_INDICES_LENGTH; i++) {
            temp1[i] = bb.getShort();
        }
        byte[] temp2 = new byte[BMPdataLength];  // BMPdata
        bb.get(temp2);
        charCategoryTable = new CompactByteArray(temp1, temp2);
        
        /* Read a category table for non-BMP characters. */
        int[] temp3 = new int[nonBMPdataLength];
        for(int i = 0; i < nonBMPdataLength; i++) {
            temp3[i] = bb.getInt();
        }
        supplementaryCharCategoryTable = new SupplementaryCharacterData(temp3);
        
        /* Read additional data */
        if(additionalDataLength > 0) {
            additionalData = new byte[additionalDataLength];
            bb.get(additionalData);
        }
        assert bb.position() == bb.limit();
        
        /* Set numCategories */
        numCategories = stateTable.length / endStates.length;
    }
    
    byte[] getAdditionalData() {
        return additionalData;
    }
    
    void setAdditionalData(byte[] b) {
        additionalData = b;
    }
    
    
    
    /**
     * Clones this iterator.
     *
     * @return A newly-constructed RuleBasedBreakIterator with the same
     * behavior as this one.
     */
    @Override
    public Object clone() {
        RuleBasedBreakIterator result = (RuleBasedBreakIterator) super.clone();
        if(text != null) {
            result.text = (CharacterIterator) text.clone();
        }
        return result;
    }
    
    /**
     * Returns true if both BreakIterators are of the same class, have the same
     * rules, and iterate over the same text.
     */
    @Override
    public boolean equals(Object that) {
        try {
            if(that == null) {
                return false;
            }
            
            RuleBasedBreakIterator other = (RuleBasedBreakIterator) that;
            if(checksum != other.checksum) {
                return false;
            }
            if(text == null) {
                return other.text == null;
            } else {
                return text.equals(other.text);
            }
        } catch(ClassCastException e) {
            return false;
        }
    }
    
    /**
     * Returns text
     */
    @Override
    public String toString() {
        return "[checksum=0x" + Long.toHexString(checksum) + ']';
    }
    
    /**
     * Compute a hashcode for this BreakIterator
     *
     * @return A hash code
     */
    @Override
    public int hashCode() {
        return (int) checksum;
    }
    
    
    
    /**
     * Throw IllegalArgumentException unless begin <= offset < end.
     */
    // 越界检查
    protected static final void checkOffset(int offset, CharacterIterator text) {
        if(offset < text.getBeginIndex() || offset > text.getEndIndex()) {
            throw new IllegalArgumentException("offset out of bounds");
        }
    }
    
    
    /**
     * This class exists to work around a bug in incorrect implementations of CharacterIterator, which incorrectly handle setIndex(endIndex).
     * This iterator relies only on base.setIndex(n) where n is less than endIndex.
     *
     * One caveat:  if the base iterator's begin and end indices change the change will not be reflected by this wrapper.
     * Does that matter?
     */
    // TODO: Review this class to see if it's still required.
    /* 用来包装可能不安全的文本迭代器，即包装那些游标不支持定位到终点（有效元素的下一个位置）的迭代器 */
    private static final class SafeCharIterator implements CharacterIterator, Cloneable {
        
        private CharacterIterator base;
        
        private int rangeStart;     // 迭代器中游标的起点
        private int rangeLimit;     // 迭代器中游标的终点
        private int currentIndex;   // 迭代器中游标当前索引
        
        SafeCharIterator(CharacterIterator base) {
            this.base = base;
            this.rangeStart = base.getBeginIndex();
            this.rangeLimit = base.getEndIndex();
            this.currentIndex = base.getIndex();
        }
        
        @Override
        public char first() {
            return setIndex(rangeStart);
        }
        
        @Override
        public char last() {
            return setIndex(rangeLimit - 1);
        }
        
        @Override
        public char current() {
            if(currentIndex < rangeStart || currentIndex >= rangeLimit) {
                return DONE;
            } else {
                return base.setIndex(currentIndex);
            }
        }
        
        @Override
        public char next() {
            
            currentIndex++;
            if(currentIndex >= rangeLimit) {
                currentIndex = rangeLimit;
                return DONE;
            } else {
                return base.setIndex(currentIndex);
            }
        }
        
        @Override
        public char previous() {
            
            currentIndex--;
            if(currentIndex < rangeStart) {
                currentIndex = rangeStart;
                return DONE;
            } else {
                return base.setIndex(currentIndex);
            }
        }
        
        @Override
        public char setIndex(int i) {
            
            if(i < rangeStart || i > rangeLimit) {
                throw new IllegalArgumentException("Invalid position");
            }
            currentIndex = i;
            return current();
        }
        
        @Override
        public int getBeginIndex() {
            return rangeStart;
        }
        
        @Override
        public int getEndIndex() {
            return rangeLimit;
        }
        
        @Override
        public int getIndex() {
            return currentIndex;
        }
        
        @Override
        public Object clone() {
            
            SafeCharIterator copy = null;
            try {
                copy = (SafeCharIterator) super.clone();
            } catch(CloneNotSupportedException e) {
                throw new Error("Clone not supported: " + e);
            }
            
            CharacterIterator copyOfBase = (CharacterIterator) base.clone();
            copy.base = copyOfBase;
            return copy;
        }
    }
}