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Pattern.java
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Pattern.java
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/*
* Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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
* by Oracle in the LICENSE file that accompanied this code.
*
* 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).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.regex;
import java.io.Serializable;
import java.text.Normalizer;
import java.text.Normalizer.Form;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
/**
* A compiled representation of a regular expression.
*
* <p> A regular expression, specified as a string, must first be compiled into
* an instance of this class. The resulting pattern can then be used to create
* a {@link Matcher} object that can match arbitrary {@linkplain
* java.lang.CharSequence character sequences} against the regular
* expression. All of the state involved in performing a match resides in the
* matcher, so many matchers can share the same pattern.
*
* <p> A typical invocation sequence is thus
*
* <blockquote><pre>
* Pattern p = Pattern.{@link #compile compile}("a*b");
* Matcher m = p.{@link #matcher matcher}("aaaaab");
* boolean b = m.{@link Matcher#matches matches}();</pre></blockquote>
*
* <p> A {@link #matches matches} method is defined by this class as a
* convenience for when a regular expression is used just once. This method
* compiles an expression and matches an input sequence against it in a single
* invocation. The statement
*
* <blockquote><pre>
* boolean b = Pattern.matches("a*b", "aaaaab");</pre></blockquote>
*
* is equivalent to the three statements above, though for repeated matches it
* is less efficient since it does not allow the compiled pattern to be reused.
*
* <p> Instances of this class are immutable and are safe for use by multiple
* concurrent threads. Instances of the {@link Matcher} class are not safe for
* such use.
*
*
* <h3><a id="sum">Summary of regular-expression constructs</a></h3>
*
* <table class="borderless">
* <caption style="display:none">Regular expression constructs, and what they match</caption>
* <thead style="text-align:left">
* <tr>
* <th id="construct">Construct</th>
* <th id="matches">Matches</th>
* </tr>
* </thead>
* <tbody style="text-align:left">
*
* <tr><th colspan="2" style="padding-top:20px" id="characters">Characters</th></tr>
*
* <tr><th style="vertical-align:top; font-weight: normal" id="x"><i>x</i></th>
* <td headers="matches characters x">The character <i>x</i></td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="backslash">{@code \\}</th>
* <td headers="matches characters backslash">The backslash character</td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="octal_n">{@code \0}<i>n</i></th>
* <td headers="matches characters octal_n">The character with octal value {@code 0}<i>n</i>
* (0 {@code <=} <i>n</i> {@code <=} 7)</td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="octal_nn">{@code \0}<i>nn</i></th>
* <td headers="matches characters octal_nn">The character with octal value {@code 0}<i>nn</i>
* (0 {@code <=} <i>n</i> {@code <=} 7)</td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="octal_nnn">{@code \0}<i>mnn</i></th>
* <td headers="matches characters octal_nnn">The character with octal value {@code 0}<i>mnn</i>
* (0 {@code <=} <i>m</i> {@code <=} 3,
* 0 {@code <=} <i>n</i> {@code <=} 7)</td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="hex_hh">{@code \x}<i>hh</i></th>
* <td headers="matches characters hex_hh">The character with hexadecimal value {@code 0x}<i>hh</i></td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="hex_hhhh"><code>\u</code><i>hhhh</i></th>
* <td headers="matches characters hex_hhhh">The character with hexadecimal value {@code 0x}<i>hhhh</i></td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="hex_h_h"><code>\x</code><i>{h...h}</i></th>
* <td headers="matches characters hex_h_h">The character with hexadecimal value {@code 0x}<i>h...h</i>
* ({@link java.lang.Character#MIN_CODE_POINT Character.MIN_CODE_POINT}
* <= {@code 0x}<i>h...h</i> <=
* {@link java.lang.Character#MAX_CODE_POINT Character.MAX_CODE_POINT})</td></tr>
* <tr><th style="vertical-align:top; font-weight: normal" id="unicode_name"><code>\N{</code><i>name</i><code>}</code></th>
* <td headers="matches characters unicode_name">The character with Unicode character name <i>'name'</i></td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="tab">{@code \t}</th>
* <td headers="matches characters tab">The tab character (<code>'\u0009'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="newline">{@code \n}</th>
* <td headers="matches characters newline">The newline (line feed) character (<code>'\u000A'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="return">{@code \r}</th>
* <td headers="matches characters return">The carriage-return character (<code>'\u000D'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="form_feed">{@code \f}</th>
* <td headers="matches characters form_feed">The form-feed character (<code>'\u000C'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="bell">{@code \a}</th>
* <td headers="matches characters bell">The alert (bell) character (<code>'\u0007'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="escape">{@code \e}</th>
* <td headers="matches characters escape">The escape character (<code>'\u001B'</code>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="ctrl_x">{@code \c}<i>x</i></th>
* <td headers="matches characters ctrl_x">The control character corresponding to <i>x</i></td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="classes">Character classes</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="simple">{@code [abc]}</th>
* <td headers="matches classes simple">{@code a}, {@code b}, or {@code c} (simple class)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="negation">{@code [^abc]}</th>
* <td headers="matches classes negation">Any character except {@code a}, {@code b}, or {@code c} (negation)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="range">{@code [a-zA-Z]}</th>
* <td headers="matches classes range">{@code a} through {@code z}
* or {@code A} through {@code Z}, inclusive (range)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="union">{@code [a-d[m-p]]}</th>
* <td headers="matches classes union">{@code a} through {@code d},
* or {@code m} through {@code p}: {@code [a-dm-p]} (union)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="intersection">{@code [a-z&&[def]]}</th>
* <td headers="matches classes intersection">{@code d}, {@code e}, or {@code f} (intersection)</tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="subtraction1">{@code [a-z&&[^bc]]}</th>
* <td headers="matches classes subtraction1">{@code a} through {@code z},
* except for {@code b} and {@code c}: {@code [ad-z]} (subtraction)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="subtraction2">{@code [a-z&&[^m-p]]}</th>
* <td headers="matches classes subtraction2">{@code a} through {@code z},
* and not {@code m} through {@code p}: {@code [a-lq-z]}(subtraction)</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="predef">Predefined character classes</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="any">{@code .}</th>
* <td headers="matches predef any">Any character (may or may not match <a href="#lt">line terminators</a>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="digit">{@code \d}</th>
* <td headers="matches predef digit">A digit: {@code [0-9]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_digit">{@code \D}</th>
* <td headers="matches predef non_digit">A non-digit: {@code [^0-9]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="horiz_white">{@code \h}</th>
* <td headers="matches predef horiz_white">A horizontal whitespace character:
* <code>[ \t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000]</code></td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_horiz_white">{@code \H}</th>
* <td headers="matches predef non_horiz_white">A non-horizontal whitespace character: {@code [^\h]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="white">{@code \s}</th>
* <td headers="matches predef white">A whitespace character: {@code [ \t\n\x0B\f\r]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_white">{@code \S}</th>
* <td headers="matches predef non_white">A non-whitespace character: {@code [^\s]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="vert_white">{@code \v}</th>
* <td headers="matches predef vert_white">A vertical whitespace character: <code>[\n\x0B\f\r\x85\u2028\u2029]</code>
* </td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_vert_white">{@code \V}</th>
* <td headers="matches predef non_vert_white">A non-vertical whitespace character: {@code [^\v]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="word">{@code \w}</th>
* <td headers="matches predef word">A word character: {@code [a-zA-Z_0-9]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_word">{@code \W}</th>
* <td headers="matches predef non_word">A non-word character: {@code [^\w]}</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="posix"><b>POSIX character classes (US-ASCII only)</b></th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="Lower">{@code \p{Lower}}</th>
* <td headers="matches posix Lower">A lower-case alphabetic character: {@code [a-z]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Upper">{@code \p{Upper}}</th>
* <td headers="matches posix Upper">An upper-case alphabetic character:{@code [A-Z]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="ASCII">{@code \p{ASCII}}</th>
* <td headers="matches posix ASCII">All ASCII:{@code [\x00-\x7F]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Alpha">{@code \p{Alpha}}</th>
* <td headers="matches posix Alpha">An alphabetic character:{@code [\p{Lower}\p{Upper}]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Digit">{@code \p{Digit}}</th>
* <td headers="matches posix Digit">A decimal digit: {@code [0-9]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Alnum">{@code \p{Alnum}}</th>
* <td headers="matches posix Alnum">An alphanumeric character:{@code [\p{Alpha}\p{Digit}]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Punct">{@code \p{Punct}}</th>
* <td headers="matches posix Punct">Punctuation: One of {@code !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~}</td></tr>
* <!-- {@code [\!"#\$%&'\(\)\*\+,\-\./:;\<=\>\?@\[\\\]\^_`\{\|\}~]}
* {@code [\X21-\X2F\X31-\X40\X5B-\X60\X7B-\X7E]} -->
* <tr><th style="vertical-align:top; font-weight:normal" id="Graph">{@code \p{Graph}}</th>
* <td headers="matches posix Graph">A visible character: {@code [\p{Alnum}\p{Punct}]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Print">{@code \p{Print}}</th>
* <td headers="matches posix Print">A printable character: {@code [\p{Graph}\x20]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Blank">{@code \p{Blank}}</th>
* <td headers="matches posix Blank">A space or a tab: {@code [ \t]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Cntrl">{@code \p{Cntrl}}</th>
* <td headers="matches posix Cntrl">A control character: {@code [\x00-\x1F\x7F]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="XDigit">{@code \p{XDigit}}</th>
* <td headers="matches posix XDigit">A hexadecimal digit: {@code [0-9a-fA-F]}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Space">{@code \p{Space}}</th>
* <td headers="matches posix Space">A whitespace character: {@code [ \t\n\x0B\f\r]}</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="java">java.lang.Character classes (simple <a href="#jcc">java character type</a>)</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="javaLowerCase">{@code \p{javaLowerCase}}</th>
* <td headers="matches java javaLowerCase">Equivalent to java.lang.Character.isLowerCase()</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="javaUpperCase">{@code \p{javaUpperCase}}</th>
* <td headers="matches java javaUpperCase">Equivalent to java.lang.Character.isUpperCase()</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="javaWhitespace">{@code \p{javaWhitespace}}</th>
* <td headers="matches java javaWhitespace">Equivalent to java.lang.Character.isWhitespace()</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="javaMirrored">{@code \p{javaMirrored}}</th>
* <td headers="matches java javaMirrored">Equivalent to java.lang.Character.isMirrored()</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="unicode">Classes for Unicode scripts, blocks, categories and binary properties</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="IsLatin">{@code \p{IsLatin}}</th>
* <td headers="matches unicode IsLatin">A Latin script character (<a href="#usc">script</a>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="InGreek">{@code \p{InGreek}}</th>
* <td headers="matches unicode InGreek">A character in the Greek block (<a href="#ubc">block</a>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Lu">{@code \p{Lu}}</th>
* <td headers="matches unicode Lu">An uppercase letter (<a href="#ucc">category</a>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="IsAlphabetic">{@code \p{IsAlphabetic}}</th>
* <td headers="matches unicode IsAlphabetic">An alphabetic character (<a href="#ubpc">binary property</a>)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="Sc">{@code \p{Sc}}</th>
* <td headers="matches unicode Sc">A currency symbol</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="not_InGreek">{@code \P{InGreek}}</th>
* <td headers="matches unicode not_InGreek">Any character except one in the Greek block (negation)</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="not_uppercase">{@code [\p{L}&&[^\p{Lu}]]}</th>
* <td headers="matches unicode not_uppercase">Any letter except an uppercase letter (subtraction)</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="bounds">Boundary matchers</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="begin_line">{@code ^}</th>
* <td headers="matches bounds begin_line">The beginning of a line</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="end_line">{@code $}</th>
* <td headers="matches bounds end_line">The end of a line</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="word_boundary">{@code \b}</th>
* <td headers="matches bounds word_boundary">A word boundary</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="grapheme_cluster_boundary">{@code \b{g}}</th>
* <td headers="matches bounds grapheme_cluster_boundary">A Unicode extended grapheme cluster boundary</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_word_boundary">{@code \B}</th>
* <td headers="matches bounds non_word_boundary">A non-word boundary</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="begin_input">{@code \A}</th>
* <td headers="matches bounds begin_input">The beginning of the input</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="end_prev_match">{@code \G}</th>
* <td headers="matches bounds end_prev_match">The end of the previous match</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="end_input_except_term">{@code \Z}</th>
* <td headers="matches bounds end_input_except_term">The end of the input but for the final
* <a href="#lt">terminator</a>, if any</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="end_input">{@code \z}</th>
* <td headers="matches bounds end_input">The end of the input</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="linebreak">Linebreak matcher</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="any_unicode_linebreak">{@code \R}</th>
* <td headers="matches linebreak any_unicode_linebreak">Any Unicode linebreak sequence, is equivalent to
* <code>\u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]
* </code></td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="grapheme">Unicode Extended Grapheme matcher</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="grapheme_any">{@code \X}</th>
* <td headers="matches grapheme grapheme_any">Any Unicode extended grapheme cluster</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="greedy">Greedy quantifiers</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_once_or_not"><i>X</i>{@code ?}</th>
* <td headers="matches greedy greedy_once_or_not"><i>X</i>, once or not at all</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_zero_or_more"><i>X</i>{@code *}</th>
* <td headers="matches greedy greedy_zero_or_more"><i>X</i>, zero or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_one_or_more"><i>X</i>{@code +}</th>
* <td headers="matches greedy greedy_one_or_more"><i>X</i>, one or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_exactly"><i>X</i><code>{</code><i>n</i><code>}</code></th>
* <td headers="matches greedy greedy_exactly"><i>X</i>, exactly <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_at_least"><i>X</i><code>{</code><i>n</i>{@code ,}}</th>
* <td headers="matches greedy greedy_at_least"><i>X</i>, at least <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="greedy_at_least_up_to"><i>X</i><code>{</code><i>n</i>{@code ,}<i>m</i><code>}</code></th>
* <td headers="matches greedy greedy_at_least_up_to"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="reluc">Reluctant quantifiers</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_once_or_not"><i>X</i>{@code ??}</th>
* <td headers="matches reluc reluc_once_or_not"><i>X</i>, once or not at all</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_zero_or_more"><i>X</i>{@code *?}</th>
* <td headers="matches reluc reluc_zero_or_more"><i>X</i>, zero or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_one_or_more"><i>X</i>{@code +?}</th>
* <td headers="matches reluc reluc_one_or_more"><i>X</i>, one or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_exactly"><i>X</i><code>{</code><i>n</i><code>}?</code></th>
* <td headers="matches reluc reluc_exactly"><i>X</i>, exactly <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_at_least"><i>X</i><code>{</code><i>n</i><code>,}?</code></th>
* <td headers="matches reluc reluc_at_least"><i>X</i>, at least <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="reluc_at_least_up_to"><i>X</i><code>{</code><i>n</i>{@code ,}<i>m</i><code>}?</code></th>
* <td headers="matches reluc reluc_at_least_up_to"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="poss">Possessive quantifiers</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_once_or_not"><i>X</i>{@code ?+}</th>
* <td headers="matches poss poss_once_or_not"><i>X</i>, once or not at all</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_zero_or_more"><i>X</i>{@code *+}</th>
* <td headers="matches poss poss_zero_or_more"><i>X</i>, zero or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_one_or_more"><i>X</i>{@code ++}</th>
* <td headers="matches poss poss_one_or_more"><i>X</i>, one or more times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_exactly"><i>X</i><code>{</code><i>n</i><code>}+</code></th>
* <td headers="matches poss poss_exactly"><i>X</i>, exactly <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_at_least"><i>X</i><code>{</code><i>n</i><code>,}+</code></th>
* <td headers="matches poss poss_at_least"><i>X</i>, at least <i>n</i> times</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="poss_at_least_up_to"><i>X</i><code>{</code><i>n</i>{@code ,}<i>m</i><code>}+</code></th>
* <td headers="matches poss poss_at_least_up_to"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="logical">Logical operators</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="concat"><i>XY</i></th>
* <td headers="matches logical concat"><i>X</i> followed by <i>Y</i></td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="alternate"><i>X</i>{@code |}<i>Y</i></th>
* <td headers="matches logical alternate">Either <i>X</i> or <i>Y</i></td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="group">{@code (}<i>X</i>{@code )}</th>
* <td headers="matches logical group">X, as a <a href="#cg">capturing group</a></td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="backref">Back references</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="back_nth">{@code \}<i>n</i></th>
* <td headers="matches backref back_nth">Whatever the <i>n</i><sup>th</sup>
* <a href="#cg">capturing group</a> matched</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="back_named">{@code \}<i>k</i><<i>name</i>></th>
* <td headers="matches backref back_named">Whatever the
* <a href="#groupname">named-capturing group</a> "name" matched</td></tr>
*
* <tr><th colspan="2" style="padding-top:20px" id="quote">Quotation</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="quote_follow">{@code \}</th>
* <td headers="matches quote quote_follow">Nothing, but quotes the following character</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="quote_begin">{@code \Q}</th>
* <td headers="matches quote quote_begin">Nothing, but quotes all characters until {@code \E}</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="quote_end">{@code \E}</th>
* <td headers="matches quote quote_end">Nothing, but ends quoting started by {@code \Q}</td></tr>
* <!-- Metachars: !$()*+.<>?[\]^{|} -->
*
* <tr><th colspan="2" style="padding-top:20px" id="special">Special constructs (named-capturing and non-capturing)</th></tr>
*
* <tr><th style="vertical-align:top; font-weight:normal" id="named_group"><code>(?<<a href="#groupname">name</a>></code><i>X</i>{@code )}</th>
* <td headers="matches special named_group"><i>X</i>, as a named-capturing group</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_capture_group">{@code (?:}<i>X</i>{@code )}</th>
* <td headers="matches special non_capture_group"><i>X</i>, as a non-capturing group</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="flags"><code>(?idmsuxU-idmsuxU) </code></th>
* <td headers="matches special flags">Nothing, but turns match flags <a href="#CASE_INSENSITIVE">i</a>
* <a href="#UNIX_LINES">d</a> <a href="#MULTILINE">m</a> <a href="#DOTALL">s</a>
* <a href="#UNICODE_CASE">u</a> <a href="#COMMENTS">x</a> <a href="#UNICODE_CHARACTER_CLASS">U</a>
* on - off</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="non_capture_group_flags"><code>(?idmsux-idmsux:</code><i>X</i>{@code )} </th>
* <td headers="matches special non_capture_group_flags"><i>X</i>, as a <a href="#cg">non-capturing group</a> with the
* given flags <a href="#CASE_INSENSITIVE">i</a> <a href="#UNIX_LINES">d</a>
* <a href="#MULTILINE">m</a> <a href="#DOTALL">s</a> <a href="#UNICODE_CASE">u</a >
* <a href="#COMMENTS">x</a> on - off</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="pos_lookahead">{@code (?=}<i>X</i>{@code )}</th>
* <td headers="matches special pos_lookahead"><i>X</i>, via zero-width positive lookahead</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="neg_lookahead">{@code (?!}<i>X</i>{@code )}</th>
* <td headers="matches special neg_lookahead"><i>X</i>, via zero-width negative lookahead</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="pos_lookbehind">{@code (?<=}<i>X</i>{@code )}</th>
* <td headers="matches special pos_lookbehind"><i>X</i>, via zero-width positive lookbehind</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="neg_lookbehind">{@code (?<!}<i>X</i>{@code )}</th>
* <td headers="matches special neg_lookbehind"><i>X</i>, via zero-width negative lookbehind</td></tr>
* <tr><th style="vertical-align:top; font-weight:normal" id="indep_non_capture_group">{@code (?>}<i>X</i>{@code )}</th>
* <td headers="matches special indep_non_capture_group"><i>X</i>, as an independent, non-capturing group</td></tr>
*
* </tbody>
* </table>
*
* <hr>
*
*
* <h3><a id="bs">Backslashes, escapes, and quoting</a></h3>
*
* <p> The backslash character ({@code '\'}) serves to introduce escaped
* constructs, as defined in the table above, as well as to quote characters
* that otherwise would be interpreted as unescaped constructs. Thus the
* expression {@code \\} matches a single backslash and <code>\{</code> matches a
* left brace.
*
* <p> It is an error to use a backslash prior to any alphabetic character that
* does not denote an escaped construct; these are reserved for future
* extensions to the regular-expression language. A backslash may be used
* prior to a non-alphabetic character regardless of whether that character is
* part of an unescaped construct.
*
* <p> Backslashes within string literals in Java source code are interpreted
* as required by
* <cite>The Java™ Language Specification</cite>
* as either Unicode escapes (section 3.3) or other character escapes (section 3.10.6)
* It is therefore necessary to double backslashes in string
* literals that represent regular expressions to protect them from
* interpretation by the Java bytecode compiler. The string literal
* <code>"\b"</code>, for example, matches a single backspace character when
* interpreted as a regular expression, while {@code "\\b"} matches a
* word boundary. The string literal {@code "\(hello\)"} is illegal
* and leads to a compile-time error; in order to match the string
* {@code (hello)} the string literal {@code "\\(hello\\)"}
* must be used.
*
* <h3><a id="cc">Character Classes</a></h3>
*
* <p> Character classes may appear within other character classes, and
* may be composed by the union operator (implicit) and the intersection
* operator ({@code &&}).
* The union operator denotes a class that contains every character that is
* in at least one of its operand classes. The intersection operator
* denotes a class that contains every character that is in both of its
* operand classes.
*
* <p> The precedence of character-class operators is as follows, from
* highest to lowest:
*
* <table class="striped" style="margin-left: 2em;">
* <caption style="display:none">Precedence of character class operators.</caption>
* <thead>
* <tr><th scope="col">Precedence<th scope="col">Name<th scope="col">Example
* </thead>
* <tbody>
* <tr><th scope="row">1</th>
* <td>Literal escape </td>
* <td>{@code \x}</td></tr>
* <tr><th scope="row">2</th>
* <td>Grouping</td>
* <td>{@code [...]}</td></tr>
* <tr><th scope="row">3</th>
* <td>Range</td>
* <td>{@code a-z}</td></tr>
* <tr><th scope="row">4</th>
* <td>Union</td>
* <td>{@code [a-e][i-u]}</td></tr>
* <tr><th scope="row">5</th>
* <td>Intersection</td>
* <td>{@code [a-z&&[aeiou]]}</td></tr>
* </tbody>
* </table>
*
* <p> Note that a different set of metacharacters are in effect inside
* a character class than outside a character class. For instance, the
* regular expression {@code .} loses its special meaning inside a
* character class, while the expression {@code -} becomes a range
* forming metacharacter.
*
* <h3><a id="lt">Line terminators</a></h3>
*
* <p> A <i>line terminator</i> is a one- or two-character sequence that marks
* the end of a line of the input character sequence. The following are
* recognized as line terminators:
*
* <ul>
*
* <li> A newline (line feed) character ({@code '\n'}),
*
* <li> A carriage-return character followed immediately by a newline
* character ({@code "\r\n"}),
*
* <li> A standalone carriage-return character ({@code '\r'}),
*
* <li> A next-line character (<code>'\u0085'</code>),
*
* <li> A line-separator character (<code>'\u2028'</code>), or
*
* <li> A paragraph-separator character (<code>'\u2029'</code>).
*
* </ul>
* <p>If {@link #UNIX_LINES} mode is activated, then the only line terminators
* recognized are newline characters.
*
* <p> The regular expression {@code .} matches any character except a line
* terminator unless the {@link #DOTALL} flag is specified.
*
* <p> By default, the regular expressions {@code ^} and {@code $} ignore
* line terminators and only match at the beginning and the end, respectively,
* of the entire input sequence. If {@link #MULTILINE} mode is activated then
* {@code ^} matches at the beginning of input and after any line terminator
* except at the end of input. When in {@link #MULTILINE} mode {@code $}
* matches just before a line terminator or the end of the input sequence.
*
* <h3><a id="cg">Groups and capturing</a></h3>
*
* <h4><a id="gnumber">Group number</a></h4>
* <p> Capturing groups are numbered by counting their opening parentheses from
* left to right. In the expression {@code ((A)(B(C)))}, for example, there
* are four such groups: </p>
*
* <ol style="margin-left:2em;">
* <li> {@code ((A)(B(C)))}
* <li> {@code (A)}
* <li> {@code (B(C))}
* <li> {@code (C)}
* </ol>
*
* <p> Group zero always stands for the entire expression.
*
* <p> Capturing groups are so named because, during a match, each subsequence
* of the input sequence that matches such a group is saved. The captured
* subsequence may be used later in the expression, via a back reference, and
* may also be retrieved from the matcher once the match operation is complete.
*
* <h4><a id="groupname">Group name</a></h4>
* <p>A capturing group can also be assigned a "name", a {@code named-capturing group},
* and then be back-referenced later by the "name". Group names are composed of
* the following characters. The first character must be a {@code letter}.
*
* <ul>
* <li> The uppercase letters {@code 'A'} through {@code 'Z'}
* (<code>'\u0041'</code> through <code>'\u005a'</code>),
* <li> The lowercase letters {@code 'a'} through {@code 'z'}
* (<code>'\u0061'</code> through <code>'\u007a'</code>),
* <li> The digits {@code '0'} through {@code '9'}
* (<code>'\u0030'</code> through <code>'\u0039'</code>),
* </ul>
*
* <p> A {@code named-capturing group} is still numbered as described in
* <a href="#gnumber">Group number</a>.
*
* <p> The captured input associated with a group is always the subsequence
* that the group most recently matched. If a group is evaluated a second time
* because of quantification then its previously-captured value, if any, will
* be retained if the second evaluation fails. Matching the string
* {@code "aba"} against the expression {@code (a(b)?)+}, for example, leaves
* group two set to {@code "b"}. All captured input is discarded at the
* beginning of each match.
*
* <p> Groups beginning with {@code (?} are either pure, <i>non-capturing</i> groups
* that do not capture text and do not count towards the group total, or
* <i>named-capturing</i> group.
*
* <h3> Unicode support </h3>
*
* <p> This class is in conformance with Level 1 of <a
* href="http://www.unicode.org/reports/tr18/"><i>Unicode Technical
* Standard #18: Unicode Regular Expression</i></a>, plus RL2.1
* Canonical Equivalents.
* <p>
* <b>Unicode escape sequences</b> such as <code>\u2014</code> in Java source code
* are processed as described in section 3.3 of
* <cite>The Java™ Language Specification</cite>.
* Such escape sequences are also implemented directly by the regular-expression
* parser so that Unicode escapes can be used in expressions that are read from
* files or from the keyboard. Thus the strings <code>"\u2014"</code> and
* {@code "\\u2014"}, while not equal, compile into the same pattern, which
* matches the character with hexadecimal value {@code 0x2014}.
* <p>
* A Unicode character can also be represented by using its <b>Hex notation</b>
* (hexadecimal code point value) directly as described in construct
* <code>\x{...}</code>, for example a supplementary character U+2011F can be
* specified as <code>\x{2011F}</code>, instead of two consecutive Unicode escape
* sequences of the surrogate pair <code>\uD840</code><code>\uDD1F</code>.
* <p>
* <b>Unicode character names</b> are supported by the named character construct
* <code>\N{</code>...<code>}</code>, for example, <code>\N{WHITE SMILING FACE}</code>
* specifies character <code>\u263A</code>. The character names supported
* by this class are the valid Unicode character names matched by
* {@link java.lang.Character#codePointOf(String) Character.codePointOf(name)}.
* <p>
* <a href="http://www.unicode.org/reports/tr18/#Default_Grapheme_Clusters">
* <b>Unicode extended grapheme clusters</b></a> are supported by the grapheme
* cluster matcher {@code \X} and the corresponding boundary matcher {@code \b{g}}.
* <p>
* Unicode scripts, blocks, categories and binary properties are written with
* the {@code \p} and {@code \P} constructs as in Perl.
* <code>\p{</code><i>prop</i><code>}</code> matches if
* the input has the property <i>prop</i>, while <code>\P{</code><i>prop</i><code>}</code>
* does not match if the input has that property.
* <p>
* Scripts, blocks, categories and binary properties can be used both inside
* and outside of a character class.
*
* <p>
* <b><a id="usc">Scripts</a></b> are specified either with the prefix {@code Is}, as in
* {@code IsHiragana}, or by using the {@code script} keyword (or its short
* form {@code sc}) as in {@code script=Hiragana} or {@code sc=Hiragana}.
* <p>
* The script names supported by {@code Pattern} are the valid script names
* accepted and defined by
* {@link java.lang.Character.UnicodeScript#forName(String) UnicodeScript.forName}.
*
* <p>
* <b><a id="ubc">Blocks</a></b> are specified with the prefix {@code In}, as in
* {@code InMongolian}, or by using the keyword {@code block} (or its short
* form {@code blk}) as in {@code block=Mongolian} or {@code blk=Mongolian}.
* <p>
* The block names supported by {@code Pattern} are the valid block names
* accepted and defined by
* {@link java.lang.Character.UnicodeBlock#forName(String) UnicodeBlock.forName}.
* <p>
*
* <b><a id="ucc">Categories</a></b> may be specified with the optional prefix {@code Is}:
* Both {@code \p{L}} and {@code \p{IsL}} denote the category of Unicode
* letters. Same as scripts and blocks, categories can also be specified
* by using the keyword {@code general_category} (or its short form
* {@code gc}) as in {@code general_category=Lu} or {@code gc=Lu}.
* <p>
* The supported categories are those of
* <a href="http://www.unicode.org/unicode/standard/standard.html">
* <i>The Unicode Standard</i></a> in the version specified by the
* {@link java.lang.Character Character} class. The category names are those
* defined in the Standard, both normative and informative.
* <p>
*
* <b><a id="ubpc">Binary properties</a></b> are specified with the prefix {@code Is}, as in
* {@code IsAlphabetic}. The supported binary properties by {@code Pattern}
* are
* <ul>
* <li> Alphabetic
* <li> Ideographic
* <li> Letter
* <li> Lowercase
* <li> Uppercase
* <li> Titlecase
* <li> Punctuation
* <Li> Control
* <li> White_Space
* <li> Digit
* <li> Hex_Digit
* <li> Join_Control
* <li> Noncharacter_Code_Point
* <li> Assigned
* </ul>
* <p>
* The following <b>Predefined Character classes</b> and <b>POSIX character classes</b>
* are in conformance with the recommendation of <i>Annex C: Compatibility Properties</i>
* of <a href="http://www.unicode.org/reports/tr18/"><i>Unicode Regular Expression
* </i></a>, when {@link #UNICODE_CHARACTER_CLASS} flag is specified.
*
* <table class="striped">
* <caption style="display:none">predefined and posix character classes in Unicode mode</caption>
* <thead>
* <tr>
* <th scope="col" id="predef_classes">Classes</th>
* <th scope="col" id="predef_matches">Matches</th>
* </tr>
* </thead>
* <tbody>
* <tr><th scope="row">{@code \p{Lower}}</th>
* <td>A lowercase character:{@code \p{IsLowercase}}</td></tr>
* <tr><th scope="row">{@code \p{Upper}}</th>
* <td>An uppercase character:{@code \p{IsUppercase}}</td></tr>
* <tr><th scope="row">{@code \p{ASCII}}</th>
* <td>All ASCII:{@code [\x00-\x7F]}</td></tr>
* <tr><th scope="row">{@code \p{Alpha}}</th>
* <td>An alphabetic character:{@code \p{IsAlphabetic}}</td></tr>
* <tr><th scope="row">{@code \p{Digit}}</th>
* <td>A decimal digit character:{@code \p{IsDigit}}</td></tr>
* <tr><th scope="row">{@code \p{Alnum}}</th>
* <td>An alphanumeric character:{@code [\p{IsAlphabetic}\p{IsDigit}]}</td></tr>
* <tr><th scope="row">{@code \p{Punct}}</th>
* <td>A punctuation character:{@code \p{IsPunctuation}}</td></tr>
* <tr><th scope="row">{@code \p{Graph}}</th>
* <td>A visible character: {@code [^\p{IsWhite_Space}\p{gc=Cc}\p{gc=Cs}\p{gc=Cn}]}</td></tr>
* <tr><th scope="row">{@code \p{Print}}</th>
* <td>A printable character: {@code [\p{Graph}\p{Blank}&&[^\p{Cntrl}]]}</td></tr>
* <tr><th scope="row">{@code \p{Blank}}</th>
* <td>A space or a tab: {@code [\p{IsWhite_Space}&&[^\p{gc=Zl}\p{gc=Zp}\x0a\x0b\x0c\x0d\x85]]}</td></tr>
* <tr><th scope="row">{@code \p{Cntrl}}</th>
* <td>A control character: {@code \p{gc=Cc}}</td></tr>
* <tr><th scope="row">{@code \p{XDigit}}</th>
* <td>A hexadecimal digit: {@code [\p{gc=Nd}\p{IsHex_Digit}]}</td></tr>
* <tr><th scope="row">{@code \p{Space}}</th>
* <td>A whitespace character:{@code \p{IsWhite_Space}}</td></tr>
* <tr><th scope="row">{@code \d}</th>
* <td>A digit: {@code \p{IsDigit}}</td></tr>
* <tr><th scope="row">{@code \D}</th>
* <td>A non-digit: {@code [^\d]}</td></tr>
* <tr><th scope="row">{@code \s}</th>
* <td>A whitespace character: {@code \p{IsWhite_Space}}</td></tr>
* <tr><th scope="row">{@code \S}</th>
* <td>A non-whitespace character: {@code [^\s]}</td></tr>
* <tr><th scope="row">{@code \w}</th>
* <td>A word character: {@code [\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}\p{IsJoin_Control}]}</td></tr>
* <tr><th scope="row">{@code \W}</th>
* <td>A non-word character: {@code [^\w]}</td></tr>
* </tbody>
* </table>
* <p>
* <a id="jcc">
* Categories that behave like the java.lang.Character
* boolean is<i>methodname</i> methods (except for the deprecated ones) are
* available through the same <code>\p{</code><i>prop</i><code>}</code> syntax where
* the specified property has the name <code>java<i>methodname</i></code></a>.
*
* <h3> Comparison to Perl 5 </h3>
*
* <p>The {@code Pattern} engine performs traditional NFA-based matching
* with ordered alternation as occurs in Perl 5.
*
* <p> Perl constructs not supported by this class: </p>
*
* <ul>
* <li><p> The backreference constructs, <code>\g{</code><i>n</i><code>}</code> for
* the <i>n</i><sup>th</sup><a href="#cg">capturing group</a> and
* <code>\g{</code><i>name</i><code>}</code> for
* <a href="#groupname">named-capturing group</a>.
* </p></li>
*
* <li><p> The conditional constructs
* {@code (?(}<i>condition</i>{@code )}<i>X</i>{@code )} and
* {@code (?(}<i>condition</i>{@code )}<i>X</i>{@code |}<i>Y</i>{@code )},
* </p></li>
*
* <li><p> The embedded code constructs <code>(?{</code><i>code</i><code>})</code>
* and <code>(??{</code><i>code</i><code>})</code>,</p></li>
*
* <li><p> The embedded comment syntax {@code (?#comment)}, and </p></li>
*
* <li><p> The preprocessing operations {@code \l} <code>\u</code>,
* {@code \L}, and {@code \U}. </p></li>
*
* </ul>
*
* <p> Constructs supported by this class but not by Perl: </p>
*
* <ul>
*
* <li><p> Character-class union and intersection as described
* <a href="#cc">above</a>.</p></li>
*
* </ul>
*
* <p> Notable differences from Perl: </p>
*
* <ul>
*
* <li><p> In Perl, {@code \1} through {@code \9} are always interpreted
* as back references; a backslash-escaped number greater than {@code 9} is
* treated as a back reference if at least that many subexpressions exist,
* otherwise it is interpreted, if possible, as an octal escape. In this
* class octal escapes must always begin with a zero. In this class,
* {@code \1} through {@code \9} are always interpreted as back
* references, and a larger number is accepted as a back reference if at
* least that many subexpressions exist at that point in the regular
* expression, otherwise the parser will drop digits until the number is
* smaller or equal to the existing number of groups or it is one digit.
* </p></li>
*
* <li><p> Perl uses the {@code g} flag to request a match that resumes
* where the last match left off. This functionality is provided implicitly
* by the {@link Matcher} class: Repeated invocations of the {@link
* Matcher#find find} method will resume where the last match left off,
* unless the matcher is reset. </p></li>
*
* <li><p> In Perl, embedded flags at the top level of an expression affect
* the whole expression. In this class, embedded flags always take effect
* at the point at which they appear, whether they are at the top level or
* within a group; in the latter case, flags are restored at the end of the
* group just as in Perl. </p></li>
*
* </ul>
*
*
* <p> For a more precise description of the behavior of regular expression
* constructs, please see <a href="http://www.oreilly.com/catalog/regex3/">
* <i>Mastering Regular Expressions, 3nd Edition</i>, Jeffrey E. F. Friedl,
* O'Reilly and Associates, 2006.</a>
* </p>
*
* @author Mike McCloskey
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @spec JSR-51
* @see java.lang.String#split(String, int)
* @see java.lang.String#split(String)
* @since 1.4
*/
// 正则表达式对象
public final class Pattern implements Serializable {
/** use serialVersionUID from Merlin b59 for interoperability */
private static final long serialVersionUID = 5073258162644648461L;
/*
* Regular expression modifier values. Instead of being passed as
* arguments, they can also be passed as inline modifiers.
* For example, the following statements have the same effect.
* <pre>
* Pattern p1 = Pattern.compile("abc", Pattern.CASE_INSENSITIVE|Pattern.MULTILINE);
* Pattern p2 = Pattern.compile("(?im)abc", 0);
* </pre>
*/
/**
* Enables Unix lines mode.
*
* <p> In this mode, only the {@code '\n'} line terminator is recognized
* in the behavior of {@code .}, {@code ^}, and {@code $}.
*
* <p> Unix lines mode can also be enabled via the embedded flag
* expression {@code (?d)}.
*/
public static final int UNIX_LINES = 0x01; // (?d)，只使用Unix行终止符'\n'
/**
* Enables case-insensitive matching.
*
* <p> By default, case-insensitive matching assumes that only characters
* in the US-ASCII charset are being matched. Unicode-aware
* case-insensitive matching can be enabled by specifying the {@link
* #UNICODE_CASE} flag in conjunction with this flag.
*
* <p> Case-insensitive matching can also be enabled via the embedded flag
* expression {@code (?i)}.
*
* <p> Specifying this flag may impose a slight performance penalty. </p>
*/
public static final int CASE_INSENSITIVE = 0x02; // (?i)，不区分大小写
/**
* Permits whitespace and comments in pattern.
*
* <p> In this mode, whitespace is ignored, and embedded comments starting
* with {@code #} are ignored until the end of a line.
*
* <p> Comments mode can also be enabled via the embedded flag
* expression {@code (?x)}.
*/
public static final int COMMENTS = 0x04; // (?x)，忽略空格和#开头的注释
/**
* Enables multiline mode.
*
* <p> In multiline mode the expressions {@code ^} and {@code $} match
* just after or just before, respectively, a line terminator or the end of
* the input sequence. By default these expressions only match at the
* beginning and the end of the entire input sequence.
*
* <p> Multiline mode can also be enabled via the embedded flag
* expression {@code (?m)}. </p>
*/
public static final int MULTILINE = 0x08; // (?m)，多行模式
/**
* Enables literal parsing of the pattern.
*
* <p> When this flag is specified then the input string that specifies
* the pattern is treated as a sequence of literal characters.
* Metacharacters or escape sequences in the input sequence will be
* given no special meaning.
*
* <p>The flags CASE_INSENSITIVE and UNICODE_CASE retain their impact on
* matching when used in conjunction with this flag. The other flags
* become superfluous.
*
* <p> There is no embedded flag character for enabling literal parsing.
*
* @since 1.5
*/
public static final int LITERAL = 0x10; // \Q...\E
/**
* Enables dotall mode.
*
* <p> In dotall mode, the expression {@code .} matches any character,
* including a line terminator. By default this expression does not match
* line terminators.
*
* <p> Dotall mode can also be enabled via the embedded flag
* expression {@code (?s)}. (The {@code s} is a mnemonic for
* "single-line" mode, which is what this is called in Perl.) </p>
*/
public static final int DOTALL = 0x20; // (?s)，.可以匹配任意字符，包括行终止符
/**
* Enables Unicode-aware case folding.
*
* <p> When this flag is specified then case-insensitive matching, when
* enabled by the {@link #CASE_INSENSITIVE} flag, is done in a manner
* consistent with the Unicode Standard. By default, case-insensitive
* matching assumes that only characters in the US-ASCII charset are being
* matched.
*
* <p> Unicode-aware case folding can also be enabled via the embedded flag
* expression {@code (?u)}.
*
* <p> Specifying this flag may impose a performance penalty. </p>
*/
public static final int UNICODE_CASE = 0x40; // (?u)，正确识别码点大于0xFFFF的Unicode字符和大括号{}表示的Unicode字符
/**
* Enables canonical equivalence.
*
* <p> When this flag is specified then two characters will be considered
* to match if, and only if, their full canonical decompositions match.
* The expression <code>"a\u030A"</code>, for example, will match the
* string <code>"\u00E5"</code> when this flag is specified. By default,
* matching does not take canonical equivalence into account.
*
* <p> There is no embedded flag character for enabling canonical
* equivalence.
*
* <p> Specifying this flag may impose a performance penalty. </p>
*/
public static final int CANON_EQ = 0x80; // 启用规范等价模式
/**
* Enables the Unicode version of <i>Predefined character classes</i> and
* <i>POSIX character classes</i>.
*
* <p> When this flag is specified then the (US-ASCII only)
* <i>Predefined character classes</i> and <i>POSIX character classes</i>
* are in conformance with
* <a href="http://www.unicode.org/reports/tr18/"><i>Unicode Technical
* Standard #18: Unicode Regular Expression</i></a>
* <i>Annex C: Compatibility Properties</i>.
* <p>
* The UNICODE_CHARACTER_CLASS mode can also be enabled via the embedded
* flag expression {@code (?U)}.
* <p>
* The flag implies UNICODE_CASE, that is, it enables Unicode-aware case
* folding.
* <p>
* Specifying this flag may impose a performance penalty. </p>
* @since 1.7
*/
public static final int UNICODE_CHARACTER_CLASS = 0x100; // (?U)，启用对预定义字符和POSIX字符的Unicode支持(包含了(?u)的功能)
/**
* Contains all possible flags for compile(regex, flags).
*/
private static final int ALL_FLAGS = CASE_INSENSITIVE | MULTILINE | DOTALL | UNICODE_CASE | CANON_EQ | UNIX_LINES | LITERAL | UNICODE_CHARACTER_CLASS | COMMENTS;
static final int MAX_REPS = 0x7FFFFFFF;
/* Pattern has only two serialized components: The pattern string
* and the flags, which are all that is needed to recompile the pattern
* when it is deserialized.
*/
/**
* This must be the very first initializer.
*/
static final Node accept = new Node();
static final Node lastAccept = new LastNode();
/**
* For use with lookbehinds; matches the position where the lookbehind
* was encountered.
*/
static Node lookbehindEnd = new Node() {
boolean match(Matcher matcher, int i, CharSequence seq) {
return i == matcher.lookbehindTo;
}
};
/**
* Map the "name" of the "named capturing group" to its group id
* node.
*/
transient volatile Map<String, Integer> namedGroups;
/**
* The starting point of state machine for the find operation. This allows
* a match to start anywhere in the input.
*/
transient Node root;
/**
* The root of object tree for a match operation. The pattern is matched
* at the beginning. This may include a find that uses BnM or a First
* node.
*/
transient Node matchRoot;
/**
* Temporary storage used by parsing pattern slice.
*/
transient int[] buffer;
/**
* A temporary storage used for predicate for double return.
*/
transient CharPredicate predicate;
/**
* Temporary storage used while parsing group references.
*/
transient GroupHead[] groupNodes;
/**
* Temporary storage used to store the top level closure nodes.
*/
transient List<Node> topClosureNodes;
/**
* The number of top greedy closure nodes in this Pattern. Used by
* matchers to allocate storage needed for a IntHashSet to keep the
* beginning pos {@code i} of all failed match.
*/
transient int localTCNCount;