Matcher.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.util.regex;

import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * An engine that performs match operations on a {@linkplain
 * java.lang.CharSequence character sequence} by interpreting a {@link Pattern}.
 *
 * <p> A matcher is created from a pattern by invoking the pattern's {@link
 * Pattern#matcher matcher} method.  Once created, a matcher can be used to
 * perform three different kinds of match operations:
 *
 * <ul>
 *
 * <li><p> The {@link #matches matches} method attempts to match the entire
 * input sequence against the pattern.  </p></li>
 *
 * <li><p> The {@link #lookingAt lookingAt} method attempts to match the
 * input sequence, starting at the beginning, against the pattern.  </p></li>
 *
 * <li><p> The {@link #find find} method scans the input sequence looking
 * for the next subsequence that matches the pattern.  </p></li>
 *
 * </ul>
 *
 * <p> Each of these methods returns a boolean indicating success or failure.
 * More information about a successful match can be obtained by querying the
 * state of the matcher.
 *
 * <p> A matcher finds matches in a subset of its input called the
 * <i>region</i>. By default, the region contains all of the matcher's input.
 * The region can be modified via the {@link #region(int, int) region} method
 * and queried via the {@link #regionStart() regionStart} and {@link
 * #regionEnd() regionEnd} methods. The way that the region boundaries interact
 * with some pattern constructs can be changed. See {@link
 * #useAnchoringBounds(boolean) useAnchoringBounds} and {@link
 * #useTransparentBounds(boolean) useTransparentBounds} for more details.
 *
 * <p> This class also defines methods for replacing matched subsequences with
 * new strings whose contents can, if desired, be computed from the match
 * result.  The {@link #appendReplacement appendReplacement} and {@link
 * #appendTail appendTail} methods can be used in tandem in order to collect
 * the result into an existing string buffer or string builder. Alternatively,
 * the more convenient {@link #replaceAll replaceAll} method can be used to
 * create a string in which every matching subsequence in the input sequence
 * is replaced.
 *
 * <p> The explicit state of a matcher includes the start and end indices of
 * the most recent successful match.  It also includes the start and end
 * indices of the input subsequence captured by each <a
 * href="Pattern.html#cg">capturing group</a> in the pattern as well as a total
 * count of such subsequences.  As a convenience, methods are also provided for
 * returning these captured subsequences in string form.
 *
 * <p> The explicit state of a matcher is initially undefined; attempting to
 * query any part of it before a successful match will cause an {@link
 * IllegalStateException} to be thrown.  The explicit state of a matcher is
 * recomputed by every match operation.
 *
 * <p> The implicit state of a matcher includes the input character sequence as
 * well as the <i>append position</i>, which is initially zero and is updated
 * by the {@link #appendReplacement appendReplacement} method.
 *
 * <p> A matcher may be reset explicitly by invoking its {@link #reset()}
 * method or, if a new input sequence is desired, its {@link
 * #reset(java.lang.CharSequence) reset(CharSequence)} method.  Resetting a
 * matcher discards its explicit state information and sets the append position
 * to zero.
 *
 * <p> Instances of this class are not safe for use by multiple concurrent
 * threads. </p>
 *
 * @author Mike McCloskey
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @spec JSR-51
 * @since 1.4
 */
// 对接正则表达式与待检索字符串，以完成匹配任务
public final class Matcher implements MatchResult {
    
    /**
     * Matcher state used by the last node.
     * NOANCHOR is used when a match does not have to consume all of the input.
     * ENDANCHOR is the mode used for matching all the input.
     */
    static final int ENDANCHOR = 1;
    static final int NOANCHOR = 0;
    
    int acceptMode = NOANCHOR;
    
    /**
     * The Pattern object that created this Matcher.
     */
    Pattern parentPattern;
    
    /**
     * The storage used by groups. They may contain invalid values if
     * a group was skipped during the matching.
     */
    int[] groups;
    
    /**
     * The range within the sequence that is to be matched. Anchors
     * will match at these "hard" boundaries. Changing the region
     * changes these values.
     */
    int from, to;
    
    /**
     * Lookbehind uses this value to ensure that the subexpression
     * match ends at the point where the lookbehind was encountered.
     */
    int lookbehindTo;
    
    /**
     * The original string being matched.
     */
    CharSequence text;
    
    /**
     * The range of string that last matched the pattern. If the last
     * match failed then first is -1; last initially holds 0 then it
     * holds the index of the end of the last match (which is where the
     * next search starts).
     */
    int first = -1, last = 0;
    
    /**
     * The end index of what matched in the last match operation.
     */
    int oldLast = -1;
    
    /**
     * The index of the last position appended in a substitution.
     */
    int lastAppendPosition = 0;
    
    /**
     * Storage used by nodes to tell what repetition they are on in
     * a pattern, and where groups begin. The nodes themselves are stateless,
     * so they rely on this field to hold state during a match.
     */
    int[] locals;
    
    /**
     * Storage used by top greedy Loop node to store a specific hash set to
     * keep the beginning index of the failed repetition match. The nodes
     * themselves are stateless, so they rely on this field to hold state
     * during a match.
     */
    IntHashSet[] localsPos;
    
    /**
     * Boolean indicating whether or not more input could change
     * the results of the last match.
     *
     * If hitEnd is true, and a match was found, then more input
     * might cause a different match to be found.
     * If hitEnd is true and a match was not found, then more
     * input could cause a match to be found.
     * If hitEnd is false and a match was found, then more input
     * will not change the match.
     * If hitEnd is false and a match was not found, then more
     * input will not cause a match to be found.
     */
    boolean hitEnd;
    
    /**
     * Boolean indicating whether or not more input could change
     * a positive match into a negative one.
     *
     * If requireEnd is true, and a match was found, then more
     * input could cause the match to be lost.
     * If requireEnd is false and a match was found, then more
     * input might change the match but the match won't be lost.
     * If a match was not found, then requireEnd has no meaning.
     */
    boolean requireEnd;
    
    /**
     * If transparentBounds is true then the boundaries of this
     * matcher's region are transparent to lookahead, lookbehind,
     * and boundary matching constructs that try to see beyond them.
     */
    boolean transparentBounds = false;
    
    /**
     * If anchoringBounds is true then the boundaries of this
     * matcher's region match anchors such as ^ and $.
     */
    boolean anchoringBounds = true;
    
    /**
     * Number of times this matcher's state has been modified
     */
    int modCount;
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * No default constructor.
     */
    Matcher() {
    }
    
    /**
     * All matchers have the state used by Pattern during a match.
     */
    Matcher(Pattern parent, CharSequence text) {
        this.parentPattern = parent;
        this.text = text;
        
        // Allocate state storage
        int parentGroupCount = Math.max(parent.capturingGroupCount, 10);
        groups = new int[parentGroupCount * 2];
        locals = new int[parent.localCount];
        localsPos = new IntHashSet[parent.localTCNCount];
        
        // Put fields into initial states
        reset();
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 检索范围 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Sets the limits of this matcher's region. The region is the part of the
     * input sequence that will be searched to find a match. Invoking this
     * method resets the matcher, and then sets the region to start at the
     * index specified by the {@code start} parameter and end at the
     * index specified by the {@code end} parameter.
     *
     * <p>Depending on the transparency and anchoring being used (see
     * {@link #useTransparentBounds(boolean) useTransparentBounds} and
     * {@link #useAnchoringBounds(boolean) useAnchoringBounds}), certain
     * constructs such as anchors may behave differently at or around the
     * boundaries of the region.
     *
     * @param start The index to start searching at (inclusive)
     * @param end   The index to end searching at (exclusive)
     *
     * @return this matcher
     *
     * @throws IndexOutOfBoundsException If start or end is less than zero, if
     *                                   start is greater than the length of the input sequence, if
     *                                   end is greater than the length of the input sequence, or if
     *                                   start is greater than end.
     * @since 1.5
     */
    // 将matcher的检索范围设定在整个目标串的[start, end)之间
    public Matcher region(int start, int end) {
        if((start<0) || (start>getTextLength())) {
            throw new IndexOutOfBoundsException("start");
        }
        
        if((end<0) || (end>getTextLength())) {
            throw new IndexOutOfBoundsException("end");
        }
        
        if(start>end) {
            throw new IndexOutOfBoundsException("start > end");
        }
        
        reset();
        
        from = start;
        to = end;
        
        return this;
    }
    
    /**
     * Reports the start index of this matcher's region. The
     * searches this matcher conducts are limited to finding matches
     * within {@link #regionStart() regionStart} (inclusive) and
     * {@link #regionEnd() regionEnd} (exclusive).
     *
     * @return The starting point of this matcher's region
     *
     * @since 1.5
     */
    // 返回当前检索范围的起点
    public int regionStart() {
        return from;
    }
    
    /**
     * Reports the end index (exclusive) of this matcher's region.
     * The searches this matcher conducts are limited to finding matches
     * within {@link #regionStart() regionStart} (inclusive) and
     * {@link #regionEnd() regionEnd} (exclusive).
     *
     * @return the ending point of this matcher's region
     *
     * @since 1.5
     */
    // 返回当前检索范围的终点
    public int regionEnd() {
        return to;
    }
    
    /*▲ 检索范围 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 边界 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Sets the transparency of region bounds for this matcher.
     *
     * <p> Invoking this method with an argument of {@code true} will set this
     * matcher to use <i>transparent</i> bounds. If the boolean
     * argument is {@code false}, then <i>opaque</i> bounds will be used.
     *
     * <p> Using transparent bounds, the boundaries of this
     * matcher's region are transparent to lookahead, lookbehind,
     * and boundary matching constructs. Those constructs can see beyond the
     * boundaries of the region to see if a match is appropriate.
     *
     * <p> Using opaque bounds, the boundaries of this matcher's
     * region are opaque to lookahead, lookbehind, and boundary matching
     * constructs that may try to see beyond them. Those constructs cannot
     * look past the boundaries so they will fail to match anything outside
     * of the region.
     *
     * <p> By default, a matcher uses opaque bounds.
     *
     * @param b a boolean indicating whether to use opaque or transparent
     *          regions
     *
     * @return this matcher
     *
     * @see java.util.regex.Matcher#hasTransparentBounds
     * @since 1.5
     */
    /*
     * 设置是否使用透明边界（默认不使用透明边界，即使用不透明边界）
     * 使用不透明边界时（默认），前瞻、后顾、边界匹配这些操作不会越过检索范围去匹配
     * 换句话说，此时\b匹配到的边界未必是原文中真正的边界
     *
     * 例如使用"\bapple"去匹配"xapple"的[1, 6)范围：
     * 如果使用了透明边界，可以看到a之前还有个x，无法匹配到满足条件的边界
     * 如果使用了不透明边界，则索引1之前的x会被忽略，所以认为输入文本就是"apple"，此时可以匹配到边界
     */
    public Matcher useTransparentBounds(boolean b) {
        transparentBounds = b;
        return this;
    }
    
    /**
     * Queries the transparency of region bounds for this matcher.
     *
     * <p> This method returns {@code true} if this matcher uses
     * <i>transparent</i> bounds, {@code false} if it uses <i>opaque</i>
     * bounds.
     *
     * <p> See {@link #useTransparentBounds(boolean) useTransparentBounds} for a
     * description of transparent and opaque bounds.
     *
     * <p> By default, a matcher uses opaque region boundaries.
     *
     * @return {@code true} iff this matcher is using transparent bounds,
     * {@code false} otherwise.
     *
     * @see java.util.regex.Matcher#useTransparentBounds(boolean)
     * @since 1.5
     */
    // 判断是否使用了透明边界（默认为false）
    public boolean hasTransparentBounds() {
        return transparentBounds;
    }
    
    /**
     * Sets the anchoring of region bounds for this matcher.
     *
     * <p> Invoking this method with an argument of {@code true} will set this
     * matcher to use <i>anchoring</i> bounds. If the boolean
     * argument is {@code false}, then <i>non-anchoring</i> bounds will be
     * used.
     *
     * <p> Using anchoring bounds, the boundaries of this
     * matcher's region match anchors such as ^ and $.
     *
     * <p> Without anchoring bounds, the boundaries of this
     * matcher's region will not match anchors such as ^ and $.
     *
     * <p> By default, a matcher uses anchoring region boundaries.
     *
     * @param b a boolean indicating whether or not to use anchoring bounds.
     *
     * @return this matcher
     *
     * @see java.util.regex.Matcher#hasAnchoringBounds
     * @since 1.5
     */
    /*
     * 设置是否使用锚点边界（默认使用）
     * 使用锚点边界时，行锚点^、\A、$、\Z、\z能匹配检索范围的边界，即检索范围不等于整个字符串
     * 如果不使用锚点边界，则行锚点只能匹配检索范围内，整个目标字符串中符合规定的位置
     */
    public Matcher useAnchoringBounds(boolean b) {
        anchoringBounds = b;
        return this;
    }
    
    /**
     * Queries the anchoring of region bounds for this matcher.
     *
     * <p> This method returns {@code true} if this matcher uses
     * <i>anchoring</i> bounds, {@code false} otherwise.
     *
     * <p> See {@link #useAnchoringBounds(boolean) useAnchoringBounds} for a
     * description of anchoring bounds.
     *
     * <p> By default, a matcher uses anchoring region boundaries.
     *
     * @return {@code true} iff this matcher is using anchoring bounds,
     * {@code false} otherwise.
     *
     * @see java.util.regex.Matcher#useAnchoringBounds(boolean)
     * @since 1.5
     */
    // 判断是否使用了锚点边界（默认为true）
    public boolean hasAnchoringBounds() {
        return anchoringBounds;
    }
    
    /*▲ 边界 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 捕获组 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the number of capturing groups in this matcher's pattern.
     *
     * <p> Group zero denotes the entire pattern by convention. It is not
     * included in this count.
     *
     * <p> Any non-negative integer smaller than or equal to the value
     * returned by this method is guaranteed to be a valid group index for
     * this matcher.  </p>
     *
     * @return The number of capturing groups in this matcher's pattern
     */
    // 获取当前正则表达式中的捕获组数量（不考虑非捕获组）
    public int groupCount() {
        return parentPattern.capturingGroupCount - 1;
    }
    
    /**
     * Returns the input subsequence matched by the previous match.
     *
     * <p> For a matcher <i>m</i> with input sequence <i>s</i>,
     * the expressions <i>m.</i>{@code group()} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(),}&nbsp;<i>m.</i>
     * {@code end())} are equivalent.  </p>
     *
     * <p> Note that some patterns, for example {@code a*}, match the empty
     * string.  This method will return the empty string when the pattern
     * successfully matches the empty string in the input.  </p>
     *
     * @return The (possibly empty) subsequence matched by the previous match,
     * in string form
     *
     * @throws IllegalStateException If no match has yet been attempted,
     *                               or if the previous match operation failed
     */
    // 获取整个正则表达式匹配到的目标串
    public String group() {
        return group(0);
    }
    
    /**
     * Returns the input subsequence captured by the given group during the
     * previous match operation.
     *
     * <p> For a matcher <i>m</i>, input sequence <i>s</i>, and group index
     * <i>g</i>, the expressions <i>m.</i>{@code group(}<i>g</i>{@code )} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(}<i>g</i>{@code
     * ),}&nbsp;<i>m.</i>{@code end(}<i>g</i>{@code ))}
     * are equivalent.  </p>
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression {@code m.group(0)} is equivalent to {@code m.group()}.
     * </p>
     *
     * <p> If the match was successful but the group specified failed to match
     * any part of the input sequence, then {@code null} is returned. Note
     * that some groups, for example {@code (a*)}, match the empty string.
     * This method will return the empty string when such a group successfully
     * matches the empty string in the input.  </p>
     *
     * @param group The index of a capturing group in this matcher's pattern
     *
     * @return The (possibly empty) subsequence captured by the group
     * during the previous match, or {@code null} if the group
     * failed to match part of the input
     *
     * @throws IllegalStateException     If no match has yet been attempted,
     *                                   or if the previous match operation failed
     * @throws IndexOutOfBoundsException If there is no capturing group in the pattern
     *                                   with the given index
     */
    // 获取正则表达式中第group个捕获组匹配到的目标串（group为0时，效果同group()）
    public String group(int group) {
        if(first<0) {
            throw new IllegalStateException("No match found");
        }
    
        if(group<0 || group>groupCount()) {
            throw new IndexOutOfBoundsException("No group " + group);
        }
    
        if((groups[group * 2] == -1) || (groups[group * 2 + 1] == -1)) {
            return null;
        }
    
        return getSubSequence(groups[group * 2], groups[group * 2 + 1]).toString();
    }
    
    /**
     * Returns the input subsequence captured by the given
     * <a href="Pattern.html#groupname">named-capturing group</a> during the
     * previous match operation.
     *
     * <p> If the match was successful but the group specified failed to match
     * any part of the input sequence, then {@code null} is returned. Note
     * that some groups, for example {@code (a*)}, match the empty string.
     * This method will return the empty string when such a group successfully
     * matches the empty string in the input.  </p>
     *
     * @param name The name of a named-capturing group in this matcher's pattern
     *
     * @return The (possibly empty) subsequence captured by the named group
     * during the previous match, or {@code null} if the group
     * failed to match part of the input
     *
     * @throws IllegalStateException    If no match has yet been attempted,
     *                                  or if the previous match operation failed
     * @throws IllegalArgumentException If there is no capturing group in the pattern
     *                                  with the given name
     * @since 1.7
     */
    // 获取正则表达式中名称为name的捕获组匹配到的目标串
    public String group(String name) {
        int group = getMatchedGroupIndex(name);
        if((groups[group * 2] == -1) || (groups[group * 2 + 1] == -1))
            return null;
        return getSubSequence(groups[group * 2], groups[group * 2 + 1]).toString();
    }
    
    /*▲ 捕获组 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 匹配 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Attempts to match the entire region against the pattern.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return {@code true} if, and only if, the entire region sequence
     * matches this matcher's pattern
     */
    /*
     * 判断当前的正则表达式与当前的目标字符串是否完全匹配
     * 该方法受检索范围的影响
     */
    public boolean matches() {
        return match(from, ENDANCHOR);
    }
    
    /**
     * Attempts to match the input sequence, starting at the beginning of the
     * region, against the pattern.
     *
     * <p> Like the {@link #matches matches} method, this method always starts
     * at the beginning of the region; unlike that method, it does not
     * require that the entire region be matched.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return {@code true} if, and only if, a prefix of the input
     * sequence matches this matcher's pattern
     */
    /*
     * 判断当前的正则表达式能否在当前的目标字符串中找到匹配
     * 与matches不同的是，该方法不要求正则表达式与目标字符串"完全匹配"
     */
    public boolean lookingAt() {
        return match(from, NOANCHOR);
    }
    
    /**
     * Attempts to find the next subsequence of the input sequence that matches
     * the pattern.
     *
     * <p> This method starts at the beginning of this matcher's region, or, if
     * a previous invocation of the method was successful and the matcher has
     * not since been reset, at the first character not matched by the previous
     * match.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return {@code true} if, and only if, a subsequence of the input
     * sequence matches this matcher's pattern
     */
    /*
     * 在目标字符串的当前检索范围中应用Matcher的正则表达式，返回的boolean值表示是否能找到匹配
     * 如果多次调用，则每次都在上次的匹配位置之后尝试新的匹配
     * 无参数的find只使用当前的检索范围
     */
    public boolean find() {
        int nextSearchIndex = last;
        if(nextSearchIndex == first)
            nextSearchIndex++;
        
        // If next search starts before region, start it at region
        if(nextSearchIndex<from)
            nextSearchIndex = from;
        
        // If next search starts beyond region then it fails
        if(nextSearchIndex>to) {
            for(int i = 0; i<groups.length; i++)
                groups[i] = -1;
            return false;
        }
        return search(nextSearchIndex);
    }
    
    /**
     * Resets this matcher and then attempts to find the next subsequence of
     * the input sequence that matches the pattern, starting at the specified
     * index.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods, and subsequent
     * invocations of the {@link #find()} method will start at the first
     * character not matched by this match.  </p>
     *
     * @param start the index to start searching for a match
     *
     * @return {@code true} if, and only if, a subsequence of the input
     * sequence starting at the given index matches this matcher's
     * pattern
     *
     * @throws IndexOutOfBoundsException If start is less than zero or if start is greater than the
     *                                   length of the input sequence.
     */
    /*
     * 该方法与无参数的find的不同之处在于：匹配会尝试从距离目标字符串开头ofset个字符的位置开始
     * 如果ofset为负数或超出了目标字符串的长度，会抛出IndexoutofBoundsException异常
     * 这种形式的find不会受当前检索范围的影响，而会把它设置为整个"目标字符串"
     */
    public boolean find(int start) {
        int limit = getTextLength();
        if((start<0) || (start>limit))
            throw new IndexOutOfBoundsException("Illegal start index");
        reset();
        return search(start);
    }
    
    
    /**
     * Returns the start index of the previous match.
     *
     * @return The index of the first character matched
     *
     * @throws IllegalStateException If no match has yet been attempted,
     *                               or if the previous match operation failed
     */
    // 获取上次匹配到的文本起点（包含）
    public int start() {
        if(first<0)
            throw new IllegalStateException("No match available");
        return first;
    }
    
    /**
     * Returns the offset after the last character matched.
     *
     * @return The offset after the last character matched
     *
     * @throws IllegalStateException If no match has yet been attempted,
     *                               or if the previous match operation failed
     */
    // 获取上次匹配到的文本终点（不包含）
    public int end() {
        if(first<0)
            throw new IllegalStateException("No match available");
        return last;
    }
    
    /**
     * Returns the start index of the subsequence captured by the given group
     * during the previous match operation.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code start(0)} is equivalent to
     * <i>m.</i>{@code start()}.  </p>
     *
     * @param group The index of a capturing group in this matcher's pattern
     *
     * @return The index of the first character captured by the group,
     * or {@code -1} if the match was successful but the group
     * itself did not match anything
     *
     * @throws IllegalStateException     If no match has yet been attempted,
     *                                   or if the previous match operation failed
     * @throws IndexOutOfBoundsException If there is no capturing group in the pattern
     *                                   with the given index
     */
    // 获取group捕获组中上次匹配到的文本起点（包含）
    public int start(int group) {
        if(first<0)
            throw new IllegalStateException("No match available");
        if(group<0 || group>groupCount())
            throw new IndexOutOfBoundsException("No group " + group);
        return groups[group * 2];
    }
    
    /**
     * Returns the offset after the last character of the subsequence
     * captured by the given group during the previous match operation.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code end(0)} is equivalent to
     * <i>m.</i>{@code end()}.  </p>
     *
     * @param group The index of a capturing group in this matcher's pattern
     *
     * @return The offset after the last character captured by the group,
     * or {@code -1} if the match was successful
     * but the group itself did not match anything
     *
     * @throws IllegalStateException     If no match has yet been attempted,
     *                                   or if the previous match operation failed
     * @throws IndexOutOfBoundsException If there is no capturing group in the pattern
     *                                   with the given index
     */
    // 获取group捕获组中上次匹配到的文本终点（不包含）
    public int end(int group) {
        if(first<0)
            throw new IllegalStateException("No match available");
        if(group<0 || group>groupCount())
            throw new IndexOutOfBoundsException("No group " + group);
        return groups[group * 2 + 1];
    }
    
    /**
     * Returns the start index of the subsequence captured by the given
     * <a href="Pattern.html#groupname">named-capturing group</a> during the
     * previous match operation.
     *
     * @param name The name of a named-capturing group in this matcher's pattern
     *
     * @return The index of the first character captured by the group,
     * or {@code -1} if the match was successful but the group
     * itself did not match anything
     *
     * @throws IllegalStateException    If no match has yet been attempted,
     *                                  or if the previous match operation failed
     * @throws IllegalArgumentException If there is no capturing group in the pattern
     *                                  with the given name
     * @since 1.8
     */
    // 获取name捕获组中上次匹配到的文本起点（包含）
    public int start(String name) {
        return groups[getMatchedGroupIndex(name) * 2];
    }
    
    /**
     * Returns the offset after the last character of the subsequence
     * captured by the given <a href="Pattern.html#groupname">named-capturing
     * group</a> during the previous match operation.
     *
     * @param name The name of a named-capturing group in this matcher's pattern
     *
     * @return The offset after the last character captured by the group,
     * or {@code -1} if the match was successful
     * but the group itself did not match anything
     *
     * @throws IllegalStateException    If no match has yet been attempted,
     *                                  or if the previous match operation failed
     * @throws IllegalArgumentException If there is no capturing group in the pattern
     *                                  with the given name
     * @since 1.8
     */
    // 获取name捕获组中上次匹配到的文本终点（不包含）
    public int end(String name) {
        return groups[getMatchedGroupIndex(name) * 2 + 1];
    }
    
    /*▲ 匹配 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 简单替换 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /*
     * replacement参数的预处理：
     * 1> $1、$2之类的捕获组引用会被替换为对应位置的捕获组匹配到的目标文本
     * 2> 如果$之后不是数字，会抛异常
     * 3> $之后的数字，只会应用"有意义"的部分
     * 4> 反斜杠用来转义后面的字符
     */
    
    /**
     * Replaces every subsequence of the input sequence that matches the
     * pattern with the given replacement string.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for matches of the pattern.  Characters that are not
     * part of any match are appended directly to the result string; each match
     * is replaced in the result by the replacement string.  The replacement
     * string may contain references to captured subsequences as in the {@link
     * #appendReplacement appendReplacement} method.
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code a*b}, the input
     * {@code "aabfooaabfooabfoob"}, and the replacement string
     * {@code "-"}, an invocation of this method on a matcher for that
     * expression would yield the string {@code "-foo-foo-foo-"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * @param replacement The replacement string
     *
     * @return The string constructed by replacing each matching subsequence
     * by the replacement string, substituting captured subsequences
     * as needed
     */
    // 使用replacement中的内容替换当前正则表达式匹配到的【所有】目标串，返回原字符串被替换后的副本（不受检索范围的限制）
    public String replaceAll(String replacement) {
        reset();
        boolean result = find();
        if(result) {
            StringBuilder sb = new StringBuilder();
            do {
                appendReplacement(sb, replacement);
                result = find();
            } while(result);
            appendTail(sb);
            return sb.toString();
        }
        return text.toString();
    }
    
    /**
     * Replaces the first subsequence of the input sequence that matches the
     * pattern with the given replacement string.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for a match of the pattern.  Characters that are not
     * part of the match are appended directly to the result string; the match
     * is replaced in the result by the replacement string.  The replacement
     * string may contain references to captured subsequences as in the {@link
     * #appendReplacement appendReplacement} method.
     *
     * <p>Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the replacement string
     * {@code "cat"}, an invocation of this method on a matcher for that
     * expression would yield the string {@code "zzzcatzzzdogzzz"}.  </p>
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * @param replacement The replacement string
     *
     * @return The string constructed by replacing the first matching
     * subsequence by the replacement string, substituting captured
     * subsequences as needed
     */
    // 使用replacement中的内容替换当前正则表达式匹配到的【首个】目标串，返回原字符串被替换后的副本（不受检索范围的限制）
    public String replaceFirst(String replacement) {
        if(replacement == null)
            throw new NullPointerException("replacement");
        reset();
        if(!find())
            return text.toString();
        StringBuilder sb = new StringBuilder();
        appendReplacement(sb, replacement);
        appendTail(sb);
        return sb.toString();
    }
    
    /**
     * Replaces every subsequence of the input sequence that matches the
     * pattern with the result of applying the given replacer function to the
     * match result of this matcher corresponding to that subsequence.
     * Exceptions thrown by the function are relayed to the caller.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for matches of the pattern.  Characters that are not
     * part of any match are appended directly to the result string; each match
     * is replaced in the result by the applying the replacer function that
     * returns a replacement string.  Each replacement string may contain
     * references to captured subsequences as in the {@link #appendReplacement
     * appendReplacement} method.
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * a replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the function
     * {@code mr -> mr.group().toUpperCase()}, an invocation of this method on
     * a matcher for that expression would yield the string
     * {@code "zzzDOGzzzDOGzzz"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * <p> The replacer function should not modify this matcher's state during
     * replacement.  This method will, on a best-effort basis, throw a
     * {@link java.util.ConcurrentModificationException} if such modification is
     * detected.
     *
     * <p> The state of each match result passed to the replacer function is
     * guaranteed to be constant only for the duration of the replacer function
     * call and only if the replacer function does not modify this matcher's
     * state.
     *
     * @param replacer The function to be applied to the match result of this matcher
     *                 that returns a replacement string.
     *
     * @return The string constructed by replacing each matching subsequence
     * with the result of applying the replacer function to that
     * matched subsequence, substituting captured subsequences as
     * needed.
     *
     * @throws NullPointerException            if the replacer function is null
     * @throws ConcurrentModificationException if it is detected, on a
     *                                         best-effort basis, that the replacer function modified this
     *                                         matcher's state
     * @implNote This implementation applies the replacer function to this matcher, which
     * is an instance of {@code MatchResult}.
     * @since 9
     */
    // 作用与replaceAll(String)一致，但replacement由replacer计算而来
    public String replaceAll(Function<MatchResult, String> replacer) {
        Objects.requireNonNull(replacer);
        reset();
        boolean result = find();
        if(result) {
            StringBuilder sb = new StringBuilder();
            do {
                int ec = modCount;
                String replacement = replacer.apply(this);
                if(ec != modCount)
                    throw new ConcurrentModificationException();
                appendReplacement(sb, replacement);
                result = find();
            } while(result);
            appendTail(sb);
            return sb.toString();
        }
        return text.toString();
    }
    
    /**
     * Replaces the first subsequence of the input sequence that matches the
     * pattern with the result of applying the given replacer function to the
     * match result of this matcher corresponding to that subsequence.
     * Exceptions thrown by the replace function are relayed to the caller.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for a match of the pattern.  Characters that are not
     * part of the match are appended directly to the result string; the match
     * is replaced in the result by the applying the replacer function that
     * returns a replacement string.  The replacement string may contain
     * references to captured subsequences as in the {@link #appendReplacement
     * appendReplacement} method.
     *
     * <p>Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the function
     * {@code mr -> mr.group().toUpperCase()}, an invocation of this method on
     * a matcher for that expression would yield the string
     * {@code "zzzDOGzzzdogzzz"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.
     *
     * <p> The replacer function should not modify this matcher's state during
     * replacement.  This method will, on a best-effort basis, throw a
     * {@link java.util.ConcurrentModificationException} if such modification is
     * detected.
     *
     * <p> The state of the match result passed to the replacer function is
     * guaranteed to be constant only for the duration of the replacer function
     * call and only if the replacer function does not modify this matcher's
     * state.
     *
     * @param replacer The function to be applied to the match result of this matcher
     *                 that returns a replacement string.
     *
     * @return The string constructed by replacing the first matching
     * subsequence with the result of applying the replacer function to
     * the matched subsequence, substituting captured subsequences as
     * needed.
     *
     * @throws NullPointerException            if the replacer function is null
     * @throws ConcurrentModificationException if it is detected, on a
     *                                         best-effort basis, that the replacer function modified this
     *                                         matcher's state
     * @implNote This implementation applies the replacer function to this matcher, which
     * is an instance of {@code MatchResult}.
     * @since 9
     */
    // 作用与replaceFirst(String)一致，但replacement由replacer计算而来
    public String replaceFirst(Function<MatchResult, String> replacer) {
        Objects.requireNonNull(replacer);
        reset();
        if(!find())
            return text.toString();
        StringBuilder sb = new StringBuilder();
        int ec = modCount;
        String replacement = replacer.apply(this);
        if(ec != modCount)
            throw new ConcurrentModificationException();
        appendReplacement(sb, replacement);
        appendTail(sb);
        return sb.toString();
    }
    
    /**
     * Returns a literal replacement {@code String} for the specified
     * {@code String}.
     *
     * This method produces a {@code String} that will work
     * as a literal replacement {@code s} in the
     * {@code appendReplacement} method of the {@link Matcher} class.
     * The {@code String} produced will match the sequence of characters
     * in {@code s} treated as a literal sequence. Slashes ('\') and
     * dollar signs ('$') will be given no special meaning.
     *
     * @param s The string to be literalized
     *
     * @return A literal string replacement
     *
     * @since 1.5
     */
    // 将replacement转换为字面值
    public static String quoteReplacement(String s) {
        if((s.indexOf('\\') == -1) && (s.indexOf('$') == -1))
            return s;
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i<s.length(); i++) {
            char c = s.charAt(i);
            if(c == '\\' || c == '$') {
                sb.append('\\');
            }
            sb.append(c);
        }
        return sb.toString();
    }
    
    /*▲ 简单替换 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 高级替换 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /*
     * 使用示例
     *
     * String text = "123#456#789";
     * String regex = "[^\\d]";
     *
     * Pattern pattern = Pattern.compile(regex);
     * Matcher matcher = pattern.matcher(text);
     *
     * StringBuffer sb = new StringBuffer();
     *
     * while(matcher.find()){
     *    matcher.appendReplacement(sb, "-");
     *    // 第一次输出123-，第二次输出123-456-
     *    System.out.println(sb);
     * }
     *
     * matcher.appendTail(sb);
     * // 最后输出123-456-789
     * System.out.println(sb);
     */
    
    /**
     * Implements a non-terminal append-and-replace step.
     *
     * <p> This method performs the following actions: </p>
     *
     * <ol>
     *
     * <li><p> It reads characters from the input sequence, starting at the
     * append position, and appends them to the given string buffer.  It
     * stops after reading the last character preceding the previous match,
     * that is, the character at index {@link
     * #start()}&nbsp;{@code -}&nbsp;{@code 1}.  </p></li>
     *
     * <li><p> It appends the given replacement string to the string buffer.
     * </p></li>
     *
     * <li><p> It sets the append position of this matcher to the index of
     * the last character matched, plus one, that is, to {@link #end()}.
     * </p></li>
     *
     * </ol>
     *
     * <p> The replacement string may contain references to subsequences
     * captured during the previous match: Each occurrence of
     * <code>${</code><i>name</i><code>}</code> or {@code $}<i>g</i>
     * will be replaced by the result of evaluating the corresponding
     * {@link #group(String) group(name)} or {@link #group(int) group(g)}
     * respectively. For {@code $}<i>g</i>,
     * the first number after the {@code $} is always treated as part of
     * the group reference. Subsequent numbers are incorporated into g if
     * they would form a legal group reference. Only the numerals '0'
     * through '9' are considered as potential components of the group
     * reference. If the second group matched the string {@code "foo"}, for
     * example, then passing the replacement string {@code "$2bar"} would
     * cause {@code "foobar"} to be appended to the string buffer. A dollar
     * sign ({@code $}) may be included as a literal in the replacement
     * string by preceding it with a backslash ({@code \$}).
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> This method is intended to be used in a loop together with the
     * {@link #appendTail(StringBuffer) appendTail} and {@link #find() find}
     * methods.  The following code, for example, writes {@code one dog two dogs
     * in the yard} to the standard-output stream: </p>
     *
     * <blockquote><pre>
     * Pattern p = Pattern.compile("cat");
     * Matcher m = p.matcher("one cat two cats in the yard");
     * StringBuffer sb = new StringBuffer();
     * while (m.find()) {
     *     m.appendReplacement(sb, "dog");
     * }
     * m.appendTail(sb);
     * System.out.println(sb.toString());</pre></blockquote>
     *
     * @param sb          The target string buffer
     * @param replacement The replacement string
     *
     * @return This matcher
     *
     * @throws IllegalStateException     If no match has yet been attempted,
     *                                   or if the previous match operation failed
     * @throws IllegalArgumentException  If the replacement string refers to a named-capturing
     *                                   group that does not exist in the pattern
     * @throws IndexOutOfBoundsException If the replacement string refers to a capturing group
     *                                   that does not exist in the pattern
     */
    // 一般在find()过程中调用，将上次的替换结果存到sb中
    public Matcher appendReplacement(StringBuffer sb, String replacement) {
        // If no match, return error
        if(first<0)
            throw new IllegalStateException("No match available");
        StringBuilder result = new StringBuilder();
        appendExpandedReplacement(replacement, result);
        // Append the intervening text
        sb.append(text, lastAppendPosition, first);
        // Append the match substitution
        sb.append(result);
        lastAppendPosition = last;
        modCount++;
        return this;
    }
    
    /**
     * Implements a terminal append-and-replace step.
     *
     * <p> This method reads characters from the input sequence, starting at
     * the append position, and appends them to the given string buffer.  It is
     * intended to be invoked after one or more invocations of the {@link
     * #appendReplacement(StringBuffer, String) appendReplacement} method in
     * order to copy the remainder of the input sequence.  </p>
     *
     * @param sb The target string buffer
     *
     * @return The target string buffer
     */
    // 一般在find()结束后调用，将剩余的字符串存到sb中
    public StringBuffer appendTail(StringBuffer sb) {
        sb.append(text, lastAppendPosition, getTextLength());
        return sb;
    }
    
    /**
     * Implements a non-terminal append-and-replace step.
     *
     * <p> This method performs the following actions: </p>
     *
     * <ol>
     *
     * <li><p> It reads characters from the input sequence, starting at the
     * append position, and appends them to the given string builder.  It
     * stops after reading the last character preceding the previous match,
     * that is, the character at index {@link
     * #start()}&nbsp;{@code -}&nbsp;{@code 1}.  </p></li>
     *
     * <li><p> It appends the given replacement string to the string builder.
     * </p></li>
     *
     * <li><p> It sets the append position of this matcher to the index of
     * the last character matched, plus one, that is, to {@link #end()}.
     * </p></li>
     *
     * </ol>
     *
     * <p> The replacement string may contain references to subsequences
     * captured during the previous match: Each occurrence of
     * {@code $}<i>g</i> will be replaced by the result of
     * evaluating {@link #group(int) group}{@code (}<i>g</i>{@code )}.
     * The first number after the {@code $} is always treated as part of
     * the group reference. Subsequent numbers are incorporated into g if
     * they would form a legal group reference. Only the numerals '0'
     * through '9' are considered as potential components of the group
     * reference. If the second group matched the string {@code "foo"}, for
     * example, then passing the replacement string {@code "$2bar"} would
     * cause {@code "foobar"} to be appended to the string builder. A dollar
     * sign ({@code $}) may be included as a literal in the replacement
     * string by preceding it with a backslash ({@code \$}).
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> This method is intended to be used in a loop together with the
     * {@link #appendTail(StringBuilder) appendTail} and
     * {@link #find() find} methods. The following code, for example, writes
     * {@code one dog two dogs in the yard} to the standard-output stream: </p>
     *
     * <blockquote><pre>
     * Pattern p = Pattern.compile("cat");
     * Matcher m = p.matcher("one cat two cats in the yard");
     * StringBuilder sb = new StringBuilder();
     * while (m.find()) {
     *     m.appendReplacement(sb, "dog");
     * }
     * m.appendTail(sb);
     * System.out.println(sb.toString());</pre></blockquote>
     *
     * @param sb          The target string builder
     * @param replacement The replacement string
     *
     * @return This matcher
     *
     * @throws IllegalStateException     If no match has yet been attempted,
     *                                   or if the previous match operation failed
     * @throws IllegalArgumentException  If the replacement string refers to a named-capturing
     *                                   group that does not exist in the pattern
     * @throws IndexOutOfBoundsException If the replacement string refers to a capturing group
     *                                   that does not exist in the pattern
     * @since 9
     */
    // 参见appendReplacement(StringBuffer, String)
    public Matcher appendReplacement(StringBuilder sb, String replacement) {
        // If no match, return error
        if(first<0)
            throw new IllegalStateException("No match available");
        StringBuilder result = new StringBuilder();
        appendExpandedReplacement(replacement, result);
        // Append the intervening text
        sb.append(text, lastAppendPosition, first);
        // Append the match substitution
        sb.append(result);
        lastAppendPosition = last;
        modCount++;
        return this;
    }
    
    /**
     * Implements a terminal append-and-replace step.
     *
     * <p> This method reads characters from the input sequence, starting at
     * the append position, and appends them to the given string builder.  It is
     * intended to be invoked after one or more invocations of the {@link
     * #appendReplacement(StringBuilder, String)
     * appendReplacement} method in order to copy the remainder of the input
     * sequence.  </p>
     *
     * @param sb The target string builder
     *
     * @return The target string builder
     *
     * @since 9
     */
    // 参见appendTail(StringBuffer)
    public StringBuilder appendTail(StringBuilder sb) {
        sb.append(text, lastAppendPosition, getTextLength());
        return sb;
    }
    
    /*▲ 高级替换 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ MatchResult ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the match state of this matcher as a {@link MatchResult}.
     * The result is unaffected by subsequent operations performed upon this
     * matcher.
     *
     * @return a {@code MatchResult} with the state of this matcher
     *
     * @since 1.5
     */
    // 获取上次匹配到的目标串的匹配信息
    public MatchResult toMatchResult() {
        return toMatchResult(text.toString());
    }
    
    /**
     * Returns a stream of match results for each subsequence of the input
     * sequence that matches the pattern.  The match results occur in the
     * same order as the matching subsequences in the input sequence.
     *
     * <p> Each match result is produced as if by {@link #toMatchResult()}.
     *
     * <p> This method does not reset this matcher.  Matching starts on
     * initiation of the terminal stream operation either at the beginning of
     * this matcher's region, or, if the matcher has not since been reset, at
     * the first character not matched by a previous match.
     *
     * <p> If the matcher is to be used for further matching operations after
     * the terminal stream operation completes then it should be first reset.
     *
     * <p> This matcher's state should not be modified during execution of the
     * returned stream's pipeline.  The returned stream's source
     * {@code Spliterator} is <em>fail-fast</em> and will, on a best-effort
     * basis, throw a {@link java.util.ConcurrentModificationException} if such
     * modification is detected.
     *
     * @return a sequential stream of match results.
     *
     * @since 9
     */
    // 将所有匹配结果存入流中并返回（不存储匹配到的文本，只是存储匹配文本的起点和终点）
    public Stream<MatchResult> results() {
        class MatchResultIterator implements Iterator<MatchResult> {
            // -ve for call to find, 0 for not found, 1 for found
            int state = -1;
            // State for concurrent modification checking
            // -1 for uninitialized
            int expectedCount = -1;
            // The input sequence as a string, set once only after first find
            // Avoids repeated conversion from CharSequence for each match
            String textAsString;
    
            @Override
            public MatchResult next() {
                if(expectedCount >= 0 && expectedCount != modCount)
                    throw new ConcurrentModificationException();
        
                if(!hasNext())
                    throw new NoSuchElementException();
        
                state = -1;
                return toMatchResult(textAsString);
            }
    
            @Override
            public boolean hasNext() {
                if(state >= 0)
                    return state == 1;
        
                // Defer throwing ConcurrentModificationException to when next
                // or forEachRemaining is called.  The is consistent with other
                // fail-fast implementations.
                if(expectedCount >= 0 && expectedCount != modCount)
                    return true;
        
                boolean found = find();
                // Capture the input sequence as a string on first find
                if(found && state<0)
                    textAsString = text.toString();
                state = found ? 1 : 0;
                expectedCount = modCount;
                return found;
            }
    
            @Override
            public void forEachRemaining(Consumer<? super MatchResult> action) {
                if(expectedCount >= 0 && expectedCount != modCount)
                    throw new ConcurrentModificationException();
        
                int s = state;
                if(s == 0)
                    return;
        
                // Set state to report no more elements on further operations
                state = 0;
                expectedCount = -1;
        
                // Perform a first find if required
                if(s<0 && !find())
                    return;
        
                // Capture the input sequence as a string on first find
                textAsString = text.toString();
        
                do {
                    int ec = modCount;
                    action.accept(toMatchResult(textAsString));
                    if(ec != modCount)
                        throw new ConcurrentModificationException();
                } while(find());
            }
        }
    
        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(new MatchResultIterator(), Spliterator.ORDERED | Spliterator.NONNULL), false);
    }
    
    /*▲ MatchResult ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ Pattern ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the pattern that is interpreted by this matcher.
     *
     * @return The pattern for which this matcher was created
     */
    // 获取当前Matcher关联的Pattern
    public Pattern pattern() {
        return parentPattern;
    }
    
    /**
     * Changes the {@code Pattern} that this {@code Matcher} uses to
     * find matches with.
     *
     * <p> This method causes this matcher to lose information
     * about the groups of the last match that occurred. The
     * matcher's position in the input is maintained and its
     * last append position is unaffected.</p>
     *
     * @param newPattern The new pattern used by this matcher
     *
     * @return This matcher
     *
     * @throws IllegalArgumentException If newPattern is {@code null}
     * @since 1.5
     */
    /*
     * 对当前Matcher使用新的Pattern（中途更换正则表达式）
     * 该方法不会重置Matcher，所以能够在文本的当前位置使用不同的Pattern
     */
    public Matcher usePattern(Pattern newPattern) {
        if(newPattern == null)
            throw new IllegalArgumentException("Pattern cannot be null");
        parentPattern = newPattern;
        
        // Reallocate state storage
        int parentGroupCount = Math.max(newPattern.capturingGroupCount, 10);
        groups = new int[parentGroupCount * 2];
        locals = new int[newPattern.localCount];
        for(int i = 0; i<groups.length; i++)
            groups[i] = -1;
        for(int i = 0; i<locals.length; i++)
            locals[i] = -1;
        localsPos = new IntHashSet[parentPattern.localTCNCount];
        modCount++;
        return this;
    }
    
    /*▲ Pattern ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 重置 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Resets this matcher.
     *
     * <p> Resetting a matcher discards all of its explicit state information
     * and sets its append position to zero. The matcher's region is set to the
     * default region, which is its entire character sequence. The anchoring
     * and transparency of this matcher's region boundaries are unaffected.
     *
     * @return This matcher
     */
    /**
     * 将检索范围重置为整个文本，并丢弃之前的匹配信息
     * 注：透明边界跟锚点边界不会变化
     */
    public Matcher reset() {
        first = -1;
        last = 0;
        oldLast = -1;
        for(int i = 0; i<groups.length; i++)
            groups[i] = -1;
        for(int i = 0; i<locals.length; i++)
            locals[i] = -1;
        for(int i = 0; i<localsPos.length; i++) {
            if(localsPos[i] != null)
                localsPos[i].clear();
        }
        lastAppendPosition = 0;
        from = 0;
        to = getTextLength();
        modCount++;
        return this;
    }
    
    /**
     * Resets this matcher with a new input sequence.
     *
     * <p> Resetting a matcher discards all of its explicit state information
     * and sets its append position to zero.  The matcher's region is set to
     * the default region, which is its entire character sequence.  The
     * anchoring and transparency of this matcher's region boundaries are
     * unaffected.
     *
     * @param input The new input character sequence
     *
     * @return This matcher
     */
    // 除了发挥reset()的作用之外，还会更换新的待检索文本
    public Matcher reset(CharSequence input) {
        text = input;
        return reset();
    }
    
    /*▲ 重置 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 构建扫描程序 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * <p>Returns true if the end of input was hit by the search engine in
     * the last match operation performed by this matcher.
     *
     * <p>When this method returns true, then it is possible that more input
     * would have changed the result of the last search.
     *
     * @return true iff the end of input was hit in the last match; false
     * otherwise
     *
     * @since 1.5
     */
    /*
     * 此方法表示，正则引擎在上一次匹配尝试中，是否检查了输入数据结束之后的数据（无论上一次匹配是否成功），其中包含\b和$之类的边界检查
     * 如果hitEnd返回true，则输入更多数据可能会改变匹配结果（匹配成功变为匹配失败，匹配失败变为匹配成功，或者匹配文本发生变化）
     * 相反，如果返回false，则匹配结果已经确定，输入更多的数据也不会改变匹配结果
     *
     * 常见的应用是，如果匹配成功，而hitEnd返回true，则必须等待更多的输入数据才能最后做出决定
     * 如果匹配失败，而hitEnd返回false，应该期待更多的输入数据，而不是报告语法错误
     *
     * 举例：在输入表达式中遇到<时，必须继续等待后续输入，以判断是否含有=号，进而决定表达式应当使用<还是<=
     *
     * 该方法会受到检索范围的影响
     */
    public boolean hitEnd() {
        return hitEnd;
    }
    
    /**
     * <p>Returns true if more input could change a positive match into a
     * negative one.
     *
     * <p>If this method returns true, and a match was found, then more
     * input could cause the match to be lost. If this method returns false
     * and a match was found, then more input might change the match but the
     * match won't be lost. If a match was not found, then requireEnd has no
     * meaning.
     *
     * @return true iff more input could change a positive match into a
     * negative one.
     *
     * @since 1.5
     */
    /*
     * 此方法只有在匹配成功之后才有意义，它表示正则引擎的匹配成功与否是否受输入数据结尾的影响
     * 也就是说，如果requireEnd返回true，更多的输入数据可能导致匹配尝试失败，如果返回false，更多的输入数据可能改变匹配的细节，但不会导致匹配失败
     *
     * 常见的应用是：如果requireEnd返回true，在最后做出决定之前，必须接受更多的输入数据
     *
     * 该方法会受到检索范围的影响
     */
    public boolean requireEnd() {
        return requireEnd;
    }
    
    /*▲ 构建扫描程序 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * <p>Returns the string representation of this matcher. The
     * string representation of a {@code Matcher} contains information
     * that may be useful for debugging. The exact format is unspecified.
     *
     * @return The string representation of this matcher
     *
     * @since 1.5
     */
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("java.util.regex.Matcher").append("[pattern=").append(pattern()).append(" region=").append(regionStart()).append(',').append(regionEnd()).append(" lastmatch=");
        if((first >= 0) && (group() != null)) {
            sb.append(group());
        }
        sb.append(']');
        return sb.toString();
    }
    
    
    /**
     * Initiates a search to find a Pattern within the given bounds.
     * The groups are filled with default values and the match of the root
     * of the state machine is called. The state machine will hold the state
     * of the match as it proceeds in this matcher.
     *
     * Matcher.from is not set here, because it is the "hard" boundary
     * of the start of the search which anchors will set to. The from param
     * is the "soft" boundary of the start of the search, meaning that the
     * regex tries to match at that index but ^ won't match there. Subsequent
     * calls to the search methods start at a new "soft" boundary which is
     * the end of the previous match.
     */
    boolean search(int from) {
        this.hitEnd = false;
        this.requireEnd = false;
        from = Math.max(from, 0);
        this.first = from;
        this.oldLast = oldLast<0 ? from : oldLast;
        Arrays.fill(groups, -1);
        for(IntHashSet localsPo : localsPos) {
            if(localsPo != null) {
                localsPo.clear();
            }
        }
        acceptMode = NOANCHOR;
        boolean result = parentPattern.root.match(this, from, text);
        if(!result) {
            this.first = -1;
        }
        this.oldLast = this.last;
        this.modCount++;
        return result;
    }
    
    /**
     * Initiates a search for an anchored match to a Pattern within the given
     * bounds. The groups are filled with default values and the match of the
     * root of the state machine is called. The state machine will hold the
     * state of the match as it proceeds in this matcher.
     */
    boolean match(int from, int anchor) {
        this.hitEnd = false;
        this.requireEnd = false;
        from = Math.max(from, 0);
        this.first = from;
        this.oldLast = oldLast<0 ? from : oldLast;
        Arrays.fill(groups, -1);
        for(IntHashSet localsPo : localsPos) {
            if(localsPo != null) {
                localsPo.clear();
            }
        }
        acceptMode = anchor;
        boolean result = parentPattern.matchRoot.match(this, from, text);
        if(!result) {
            this.first = -1;
        }
        this.oldLast = this.last;
        this.modCount++;
        return result;
    }
    
    /**
     * Returns the end index of the text.
     *
     * @return the index after the last character in the text
     */
    int getTextLength() {
        return text.length();
    }
    
    /**
     * Generates a String from this matcher's input in the specified range.
     *
     * @param beginIndex the beginning index, inclusive
     * @param endIndex   the ending index, exclusive
     *
     * @return A String generated from this matcher's input
     */
    CharSequence getSubSequence(int beginIndex, int endIndex) {
        return text.subSequence(beginIndex, endIndex);
    }
    
    /**
     * Returns this matcher's input character at index i.
     *
     * @return A char from the specified index
     */
    char charAt(int i) {
        return text.charAt(i);
    }
    
    /**
     * Returns the group index of the matched capturing group.
     *
     * @return the index of the named-capturing group
     */
    int getMatchedGroupIndex(String name) {
        Objects.requireNonNull(name, "Group name");
        if(first<0)
            throw new IllegalStateException("No match found");
        if(!parentPattern.namedGroups().containsKey(name))
            throw new IllegalArgumentException("No group with name <" + name + ">");
        return parentPattern.namedGroups().get(name);
    }
    
    private MatchResult toMatchResult(String text) {
        return new ImmutableMatchResult(this.first, this.last, groupCount(), this.groups.clone(), text);
    }
    
    /**
     * Processes replacement string to replace group references with
     * groups.
     */
    private StringBuilder appendExpandedReplacement(String replacement, StringBuilder result) {
        int cursor = 0;
        while(cursor<replacement.length()) {
            char nextChar = replacement.charAt(cursor);
            if(nextChar == '\\') {
                cursor++;
                if(cursor == replacement.length())
                    throw new IllegalArgumentException("character to be escaped is missing");
                nextChar = replacement.charAt(cursor);
                result.append(nextChar);
                cursor++;
            } else if(nextChar == '$') {
                // Skip past $
                cursor++;
                // Throw IAE if this "$" is the last character in replacement
                if(cursor == replacement.length())
                    throw new IllegalArgumentException("Illegal group reference: group index is missing");
                nextChar = replacement.charAt(cursor);
                int refNum = -1;
                if(nextChar == '{') {
                    cursor++;
                    StringBuilder gsb = new StringBuilder();
                    while(cursor<replacement.length()) {
                        nextChar = replacement.charAt(cursor);
                        if(ASCII.isLower(nextChar) || ASCII.isUpper(nextChar) || ASCII.isDigit(nextChar)) {
                            gsb.append(nextChar);
                            cursor++;
                        } else {
                            break;
                        }
                    }
                    if(gsb.length() == 0)
                        throw new IllegalArgumentException("named capturing group has 0 length name");
                    if(nextChar != '}')
                        throw new IllegalArgumentException("named capturing group is missing trailing '}'");
                    String gname = gsb.toString();
                    if(ASCII.isDigit(gname.charAt(0)))
                        throw new IllegalArgumentException("capturing group name {" + gname + "} starts with digit character");
                    if(!parentPattern.namedGroups().containsKey(gname))
                        throw new IllegalArgumentException("No group with name {" + gname + "}");
                    refNum = parentPattern.namedGroups().get(gname);
                    cursor++;
                } else {
                    // The first number is always a group
                    refNum = nextChar - '0';
                    if((refNum<0) || (refNum>9))
                        throw new IllegalArgumentException("Illegal group reference");
                    cursor++;
                    // Capture the largest legal group string
                    boolean done = false;
                    while(!done) {
                        if(cursor >= replacement.length()) {
                            break;
                        }
                        int nextDigit = replacement.charAt(cursor) - '0';
                        if((nextDigit<0) || (nextDigit>9)) { // not a number
                            break;
                        }
                        int newRefNum = (refNum * 10) + nextDigit;
                        if(groupCount()<newRefNum) {
                            done = true;
                        } else {
                            refNum = newRefNum;
                            cursor++;
                        }
                    }
                }
                // Append group
                if(start(refNum) != -1 && end(refNum) != -1)
                    result.append(text, start(refNum), end(refNum));
            } else {
                result.append(nextChar);
                cursor++;
            }
        }
        return result;
    }
    
    private static class ImmutableMatchResult implements MatchResult {
        private final int first;
        private final int last;
        private final int[] groups;
        private final int groupCount;
        private final String text;
        
        ImmutableMatchResult(int first, int last, int groupCount, int[] groups, String text) {
            this.first = first;
            this.last = last;
            this.groupCount = groupCount;
            this.groups = groups;
            this.text = text;
        }
        
        @Override
        public int start() {
            checkMatch();
            return first;
        }
        
        @Override
        public int start(int group) {
            checkMatch();
            if(group<0 || group>groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            return groups[group * 2];
        }
        
        @Override
        public int end() {
            checkMatch();
            return last;
        }
        
        @Override
        public int end(int group) {
            checkMatch();
            if(group<0 || group>groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            return groups[group * 2 + 1];
        }
        
        @Override
        public int groupCount() {
            return groupCount;
        }
        
        @Override
        public String group() {
            checkMatch();
            return group(0);
        }
        
        @Override
        public String group(int group) {
            checkMatch();
            if(group<0 || group>groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            if((groups[group * 2] == -1) || (groups[group * 2 + 1] == -1))
                return null;
            return text.subSequence(groups[group * 2], groups[group * 2 + 1]).toString();
        }
        
        private void checkMatch() {
            if(first<0)
                throw new IllegalStateException("No match found");
            
        }
    }
}