1 /*
   2  * Copyright (c) 1994, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.ObjectStreamField;
  29 import java.io.UnsupportedEncodingException;
  30 import java.lang.annotation.Native;
  31 import java.nio.charset.Charset;
  32 import java.util.ArrayList;
  33 import java.util.Arrays;
  34 import java.util.Comparator;
  35 import java.util.Formatter;
  36 import java.util.Locale;
  37 import java.util.Objects;
  38 import java.util.Spliterator;
  39 import java.util.StringJoiner;
  40 import java.util.regex.Matcher;
  41 import java.util.regex.Pattern;
  42 import java.util.regex.PatternSyntaxException;
  43 import java.util.stream.IntStream;
  44 import java.util.stream.StreamSupport;
  45 import jdk.internal.HotSpotIntrinsicCandidate;
  46 import jdk.internal.vm.annotation.Stable;
  47 
  48 /**
  49  * The {@code String} class represents character strings. All
  50  * string literals in Java programs, such as {@code "abc"}, are
  51  * implemented as instances of this class.
  52  * <p>
  53  * Strings are constant; their values cannot be changed after they
  54  * are created. String buffers support mutable strings.
  55  * Because String objects are immutable they can be shared. For example:
  56  * <blockquote><pre>
  57  *     String str = "abc";
  58  * </pre></blockquote><p>
  59  * is equivalent to:
  60  * <blockquote><pre>
  61  *     char data[] = {'a', 'b', 'c'};
  62  *     String str = new String(data);
  63  * </pre></blockquote><p>
  64  * Here are some more examples of how strings can be used:
  65  * <blockquote><pre>
  66  *     System.out.println("abc");
  67  *     String cde = "cde";
  68  *     System.out.println("abc" + cde);
  69  *     String c = "abc".substring(2,3);
  70  *     String d = cde.substring(1, 2);
  71  * </pre></blockquote>
  72  * <p>
  73  * The class {@code String} includes methods for examining
  74  * individual characters of the sequence, for comparing strings, for
  75  * searching strings, for extracting substrings, and for creating a
  76  * copy of a string with all characters translated to uppercase or to
  77  * lowercase. Case mapping is based on the Unicode Standard version
  78  * specified by the {@link java.lang.Character Character} class.
  79  * <p>
  80  * The Java language provides special support for the string
  81  * concatenation operator (&nbsp;+&nbsp;), and for conversion of
  82  * other objects to strings. For additional information on string
  83  * concatenation and conversion, see <i>The Java&trade; Language Specification</i>.
  84  *
  85  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  86  * or method in this class will cause a {@link NullPointerException} to be
  87  * thrown.
  88  *
  89  * <p>A {@code String} represents a string in the UTF-16 format
  90  * in which <em>supplementary characters</em> are represented by <em>surrogate
  91  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  92  * Character Representations</a> in the {@code Character} class for
  93  * more information).
  94  * Index values refer to {@code char} code units, so a supplementary
  95  * character uses two positions in a {@code String}.
  96  * <p>The {@code String} class provides methods for dealing with
  97  * Unicode code points (i.e., characters), in addition to those for
  98  * dealing with Unicode code units (i.e., {@code char} values).
  99  *
 100  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 101  * into account.  The {@link java.text.Collator} class provides methods for
 102  * finer-grain, locale-sensitive String comparison.
 103  *
 104  * @implNote The implementation of the string concatenation operator is left to
 105  * the discretion of a Java compiler, as long as the compiler ultimately conforms
 106  * to <i>The Java&trade; Language Specification</i>. For example, the {@code javac} compiler
 107  * may implement the operator with {@code StringBuffer}, {@code StringBuilder},
 108  * or {@code java.lang.invoke.StringConcatFactory} depending on the JDK version. The
 109  * implementation of string conversion is typically through the method {@code toString},
 110  * defined by {@code Object} and inherited by all classes in Java.
 111  *
 112  * @author  Lee Boynton
 113  * @author  Arthur van Hoff
 114  * @author  Martin Buchholz
 115  * @author  Ulf Zibis
 116  * @see     java.lang.Object#toString()
 117  * @see     java.lang.StringBuffer
 118  * @see     java.lang.StringBuilder
 119  * @see     java.nio.charset.Charset
 120  * @since   1.0
 121  * @jls     15.18.1 String Concatenation Operator +
 122  */
 123 
 124 public final class String
 125     implements java.io.Serializable, Comparable<String>, CharSequence {
 126 
 127     /**
 128      * The value is used for character storage.
 129      *
 130      * @implNote This field is trusted by the VM, and is a subject to
 131      * constant folding if String instance is constant. Overwriting this
 132      * field after construction will cause problems.
 133      *
 134      * Additionally, it is marked with {@link Stable} to trust the contents
 135      * of the array. No other facility in JDK provides this functionality (yet).
 136      * {@link Stable} is safe here, because value is never null.
 137      */
 138     @Stable
 139     private final byte[] value;
 140 
 141     /**
 142      * The identifier of the encoding used to encode the bytes in
 143      * {@code value}. The supported values in this implementation are
 144      *
 145      * LATIN1
 146      * UTF16
 147      *
 148      * @implNote This field is trusted by the VM, and is a subject to
 149      * constant folding if String instance is constant. Overwriting this
 150      * field after construction will cause problems.
 151      */
 152     private final byte coder;
 153 
 154     /** Cache the hash code for the string */
 155     private int hash; // Default to 0
 156 
 157     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 158     private static final long serialVersionUID = -6849794470754667710L;
 159 
 160     /**
 161      * If String compaction is disabled, the bytes in {@code value} are
 162      * always encoded in UTF16.
 163      *
 164      * For methods with several possible implementation paths, when String
 165      * compaction is disabled, only one code path is taken.
 166      *
 167      * The instance field value is generally opaque to optimizing JIT
 168      * compilers. Therefore, in performance-sensitive place, an explicit
 169      * check of the static boolean {@code COMPACT_STRINGS} is done first
 170      * before checking the {@code coder} field since the static boolean
 171      * {@code COMPACT_STRINGS} would be constant folded away by an
 172      * optimizing JIT compiler. The idioms for these cases are as follows.
 173      *
 174      * For code such as:
 175      *
 176      *    if (coder == LATIN1) { ... }
 177      *
 178      * can be written more optimally as
 179      *
 180      *    if (coder() == LATIN1) { ... }
 181      *
 182      * or:
 183      *
 184      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 185      *
 186      * An optimizing JIT compiler can fold the above conditional as:
 187      *
 188      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 189      *    COMPACT_STRINGS == false => if (false)           { ... }
 190      *
 191      * @implNote
 192      * The actual value for this field is injected by JVM. The static
 193      * initialization block is used to set the value here to communicate
 194      * that this static final field is not statically foldable, and to
 195      * avoid any possible circular dependency during vm initialization.
 196      */
 197     static final boolean COMPACT_STRINGS;
 198 
 199     static {
 200         COMPACT_STRINGS = true;
 201     }
 202 
 203     /**
 204      * Class String is special cased within the Serialization Stream Protocol.
 205      *
 206      * A String instance is written into an ObjectOutputStream according to
 207      * <a href="{@docRoot}/../specs/serialization/protocol.html#stream-elements">
 208      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 209      */
 210     private static final ObjectStreamField[] serialPersistentFields =
 211         new ObjectStreamField[0];
 212 
 213     /**
 214      * Initializes a newly created {@code String} object so that it represents
 215      * an empty character sequence.  Note that use of this constructor is
 216      * unnecessary since Strings are immutable.
 217      */
 218     public String() {
 219         this.value = "".value;
 220         this.coder = "".coder;
 221     }
 222 
 223     /**
 224      * Initializes a newly created {@code String} object so that it represents
 225      * the same sequence of characters as the argument; in other words, the
 226      * newly created string is a copy of the argument string. Unless an
 227      * explicit copy of {@code original} is needed, use of this constructor is
 228      * unnecessary since Strings are immutable.
 229      *
 230      * @param  original
 231      *         A {@code String}
 232      */
 233     @HotSpotIntrinsicCandidate
 234     public String(String original) {
 235         this.value = original.value;
 236         this.coder = original.coder;
 237         this.hash = original.hash;
 238     }
 239 
 240     /**
 241      * Allocates a new {@code String} so that it represents the sequence of
 242      * characters currently contained in the character array argument. The
 243      * contents of the character array are copied; subsequent modification of
 244      * the character array does not affect the newly created string.
 245      *
 246      * @param  value
 247      *         The initial value of the string
 248      */
 249     public String(char value[]) {
 250         this(value, 0, value.length, null);
 251     }
 252 
 253     /**
 254      * Allocates a new {@code String} that contains characters from a subarray
 255      * of the character array argument. The {@code offset} argument is the
 256      * index of the first character of the subarray and the {@code count}
 257      * argument specifies the length of the subarray. The contents of the
 258      * subarray are copied; subsequent modification of the character array does
 259      * not affect the newly created string.
 260      *
 261      * @param  value
 262      *         Array that is the source of characters
 263      *
 264      * @param  offset
 265      *         The initial offset
 266      *
 267      * @param  count
 268      *         The length
 269      *
 270      * @throws  IndexOutOfBoundsException
 271      *          If {@code offset} is negative, {@code count} is negative, or
 272      *          {@code offset} is greater than {@code value.length - count}
 273      */
 274     public String(char value[], int offset, int count) {
 275         this(value, offset, count, rangeCheck(value, offset, count));
 276     }
 277 
 278     private static Void rangeCheck(char[] value, int offset, int count) {
 279         checkBoundsOffCount(offset, count, value.length);
 280         return null;
 281     }
 282 
 283     /**
 284      * Allocates a new {@code String} that contains characters from a subarray
 285      * of the <a href="Character.html#unicode">Unicode code point</a> array
 286      * argument.  The {@code offset} argument is the index of the first code
 287      * point of the subarray and the {@code count} argument specifies the
 288      * length of the subarray.  The contents of the subarray are converted to
 289      * {@code char}s; subsequent modification of the {@code int} array does not
 290      * affect the newly created string.
 291      *
 292      * @param  codePoints
 293      *         Array that is the source of Unicode code points
 294      *
 295      * @param  offset
 296      *         The initial offset
 297      *
 298      * @param  count
 299      *         The length
 300      *
 301      * @throws  IllegalArgumentException
 302      *          If any invalid Unicode code point is found in {@code
 303      *          codePoints}
 304      *
 305      * @throws  IndexOutOfBoundsException
 306      *          If {@code offset} is negative, {@code count} is negative, or
 307      *          {@code offset} is greater than {@code codePoints.length - count}
 308      *
 309      * @since  1.5
 310      */
 311     public String(int[] codePoints, int offset, int count) {
 312         checkBoundsOffCount(offset, count, codePoints.length);
 313         if (count == 0) {
 314             this.value = "".value;
 315             this.coder = "".coder;
 316             return;
 317         }
 318         if (COMPACT_STRINGS) {
 319             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 320             if (val != null) {
 321                 this.coder = LATIN1;
 322                 this.value = val;
 323                 return;
 324             }
 325         }
 326         this.coder = UTF16;
 327         this.value = StringUTF16.toBytes(codePoints, offset, count);
 328     }
 329 
 330     /**
 331      * Allocates a new {@code String} constructed from a subarray of an array
 332      * of 8-bit integer values.
 333      *
 334      * <p> The {@code offset} argument is the index of the first byte of the
 335      * subarray, and the {@code count} argument specifies the length of the
 336      * subarray.
 337      *
 338      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 339      * specified in the {@link #String(byte[],int) String(byte[],int)} constructor.
 340      *
 341      * @deprecated This method does not properly convert bytes into characters.
 342      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 343      * {@code String} constructors that take a {@link
 344      * java.nio.charset.Charset}, charset name, or that use the platform's
 345      * default charset.
 346      *
 347      * @param  ascii
 348      *         The bytes to be converted to characters
 349      *
 350      * @param  hibyte
 351      *         The top 8 bits of each 16-bit Unicode code unit
 352      *
 353      * @param  offset
 354      *         The initial offset
 355      * @param  count
 356      *         The length
 357      *
 358      * @throws  IndexOutOfBoundsException
 359      *          If {@code offset} is negative, {@code count} is negative, or
 360      *          {@code offset} is greater than {@code ascii.length - count}
 361      *
 362      * @see  #String(byte[], int)
 363      * @see  #String(byte[], int, int, java.lang.String)
 364      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 365      * @see  #String(byte[], int, int)
 366      * @see  #String(byte[], java.lang.String)
 367      * @see  #String(byte[], java.nio.charset.Charset)
 368      * @see  #String(byte[])
 369      */
 370     @Deprecated(since="1.1")
 371     public String(byte ascii[], int hibyte, int offset, int count) {
 372         checkBoundsOffCount(offset, count, ascii.length);
 373         if (count == 0) {
 374             this.value = "".value;
 375             this.coder = "".coder;
 376             return;
 377         }
 378         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 379             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 380             this.coder = LATIN1;
 381         } else {
 382             hibyte <<= 8;
 383             byte[] val = StringUTF16.newBytesFor(count);
 384             for (int i = 0; i < count; i++) {
 385                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 386             }
 387             this.value = val;
 388             this.coder = UTF16;
 389         }
 390     }
 391 
 392     /**
 393      * Allocates a new {@code String} containing characters constructed from
 394      * an array of 8-bit integer values. Each character <i>c</i> in the
 395      * resulting string is constructed from the corresponding component
 396      * <i>b</i> in the byte array such that:
 397      *
 398      * <blockquote><pre>
 399      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 400      *                         | (<b><i>b</i></b> &amp; 0xff))
 401      * </pre></blockquote>
 402      *
 403      * @deprecated  This method does not properly convert bytes into
 404      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 405      * {@code String} constructors that take a {@link
 406      * java.nio.charset.Charset}, charset name, or that use the platform's
 407      * default charset.
 408      *
 409      * @param  ascii
 410      *         The bytes to be converted to characters
 411      *
 412      * @param  hibyte
 413      *         The top 8 bits of each 16-bit Unicode code unit
 414      *
 415      * @see  #String(byte[], int, int, java.lang.String)
 416      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 417      * @see  #String(byte[], int, int)
 418      * @see  #String(byte[], java.lang.String)
 419      * @see  #String(byte[], java.nio.charset.Charset)
 420      * @see  #String(byte[])
 421      */
 422     @Deprecated(since="1.1")
 423     public String(byte ascii[], int hibyte) {
 424         this(ascii, hibyte, 0, ascii.length);
 425     }
 426 
 427     /**
 428      * Constructs a new {@code String} by decoding the specified subarray of
 429      * bytes using the specified charset.  The length of the new {@code String}
 430      * is a function of the charset, and hence may not be equal to the length
 431      * of the subarray.
 432      *
 433      * <p> The behavior of this constructor when the given bytes are not valid
 434      * in the given charset is unspecified.  The {@link
 435      * java.nio.charset.CharsetDecoder} class should be used when more control
 436      * over the decoding process is required.
 437      *
 438      * @param  bytes
 439      *         The bytes to be decoded into characters
 440      *
 441      * @param  offset
 442      *         The index of the first byte to decode
 443      *
 444      * @param  length
 445      *         The number of bytes to decode
 446 
 447      * @param  charsetName
 448      *         The name of a supported {@linkplain java.nio.charset.Charset
 449      *         charset}
 450      *
 451      * @throws  UnsupportedEncodingException
 452      *          If the named charset is not supported
 453      *
 454      * @throws  IndexOutOfBoundsException
 455      *          If {@code offset} is negative, {@code length} is negative, or
 456      *          {@code offset} is greater than {@code bytes.length - length}
 457      *
 458      * @since  1.1
 459      */
 460     public String(byte bytes[], int offset, int length, String charsetName)
 461             throws UnsupportedEncodingException {
 462         if (charsetName == null)
 463             throw new NullPointerException("charsetName");
 464         checkBoundsOffCount(offset, length, bytes.length);
 465         StringCoding.Result ret =
 466             StringCoding.decode(charsetName, bytes, offset, length);
 467         this.value = ret.value;
 468         this.coder = ret.coder;
 469     }
 470 
 471     /**
 472      * Constructs a new {@code String} by decoding the specified subarray of
 473      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 474      * The length of the new {@code String} is a function of the charset, and
 475      * hence may not be equal to the length of the subarray.
 476      *
 477      * <p> This method always replaces malformed-input and unmappable-character
 478      * sequences with this charset's default replacement string.  The {@link
 479      * java.nio.charset.CharsetDecoder} class should be used when more control
 480      * over the decoding process is required.
 481      *
 482      * @param  bytes
 483      *         The bytes to be decoded into characters
 484      *
 485      * @param  offset
 486      *         The index of the first byte to decode
 487      *
 488      * @param  length
 489      *         The number of bytes to decode
 490      *
 491      * @param  charset
 492      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 493      *         decode the {@code bytes}
 494      *
 495      * @throws  IndexOutOfBoundsException
 496      *          If {@code offset} is negative, {@code length} is negative, or
 497      *          {@code offset} is greater than {@code bytes.length - length}
 498      *
 499      * @since  1.6
 500      */
 501     public String(byte bytes[], int offset, int length, Charset charset) {
 502         if (charset == null)
 503             throw new NullPointerException("charset");
 504         checkBoundsOffCount(offset, length, bytes.length);
 505         StringCoding.Result ret =
 506             StringCoding.decode(charset, bytes, offset, length);
 507         this.value = ret.value;
 508         this.coder = ret.coder;
 509     }
 510 
 511     /**
 512      * Constructs a new {@code String} by decoding the specified array of bytes
 513      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 514      * length of the new {@code String} is a function of the charset, and hence
 515      * may not be equal to the length of the byte array.
 516      *
 517      * <p> The behavior of this constructor when the given bytes are not valid
 518      * in the given charset is unspecified.  The {@link
 519      * java.nio.charset.CharsetDecoder} class should be used when more control
 520      * over the decoding process is required.
 521      *
 522      * @param  bytes
 523      *         The bytes to be decoded into characters
 524      *
 525      * @param  charsetName
 526      *         The name of a supported {@linkplain java.nio.charset.Charset
 527      *         charset}
 528      *
 529      * @throws  UnsupportedEncodingException
 530      *          If the named charset is not supported
 531      *
 532      * @since  1.1
 533      */
 534     public String(byte bytes[], String charsetName)
 535             throws UnsupportedEncodingException {
 536         this(bytes, 0, bytes.length, charsetName);
 537     }
 538 
 539     /**
 540      * Constructs a new {@code String} by decoding the specified array of
 541      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 542      * The length of the new {@code String} is a function of the charset, and
 543      * hence may not be equal to the length of the byte array.
 544      *
 545      * <p> This method always replaces malformed-input and unmappable-character
 546      * sequences with this charset's default replacement string.  The {@link
 547      * java.nio.charset.CharsetDecoder} class should be used when more control
 548      * over the decoding process is required.
 549      *
 550      * @param  bytes
 551      *         The bytes to be decoded into characters
 552      *
 553      * @param  charset
 554      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 555      *         decode the {@code bytes}
 556      *
 557      * @since  1.6
 558      */
 559     public String(byte bytes[], Charset charset) {
 560         this(bytes, 0, bytes.length, charset);
 561     }
 562 
 563     /**
 564      * Constructs a new {@code String} by decoding the specified subarray of
 565      * bytes using the platform's default charset.  The length of the new
 566      * {@code String} is a function of the charset, and hence may not be equal
 567      * to the length of the subarray.
 568      *
 569      * <p> The behavior of this constructor when the given bytes are not valid
 570      * in the default charset is unspecified.  The {@link
 571      * java.nio.charset.CharsetDecoder} class should be used when more control
 572      * over the decoding process is required.
 573      *
 574      * @param  bytes
 575      *         The bytes to be decoded into characters
 576      *
 577      * @param  offset
 578      *         The index of the first byte to decode
 579      *
 580      * @param  length
 581      *         The number of bytes to decode
 582      *
 583      * @throws  IndexOutOfBoundsException
 584      *          If {@code offset} is negative, {@code length} is negative, or
 585      *          {@code offset} is greater than {@code bytes.length - length}
 586      *
 587      * @since  1.1
 588      */
 589     public String(byte bytes[], int offset, int length) {
 590         checkBoundsOffCount(offset, length, bytes.length);
 591         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 592         this.value = ret.value;
 593         this.coder = ret.coder;
 594     }
 595 
 596     /**
 597      * Constructs a new {@code String} by decoding the specified array of bytes
 598      * using the platform's default charset.  The length of the new {@code
 599      * String} is a function of the charset, and hence may not be equal to the
 600      * length of the byte array.
 601      *
 602      * <p> The behavior of this constructor when the given bytes are not valid
 603      * in the default charset is unspecified.  The {@link
 604      * java.nio.charset.CharsetDecoder} class should be used when more control
 605      * over the decoding process is required.
 606      *
 607      * @param  bytes
 608      *         The bytes to be decoded into characters
 609      *
 610      * @since  1.1
 611      */
 612     public String(byte[] bytes) {
 613         this(bytes, 0, bytes.length);
 614     }
 615 
 616     /**
 617      * Allocates a new string that contains the sequence of characters
 618      * currently contained in the string buffer argument. The contents of the
 619      * string buffer are copied; subsequent modification of the string buffer
 620      * does not affect the newly created string.
 621      *
 622      * @param  buffer
 623      *         A {@code StringBuffer}
 624      */
 625     public String(StringBuffer buffer) {
 626         this(buffer.toString());
 627     }
 628 
 629     /**
 630      * Allocates a new string that contains the sequence of characters
 631      * currently contained in the string builder argument. The contents of the
 632      * string builder are copied; subsequent modification of the string builder
 633      * does not affect the newly created string.
 634      *
 635      * <p> This constructor is provided to ease migration to {@code
 636      * StringBuilder}. Obtaining a string from a string builder via the {@code
 637      * toString} method is likely to run faster and is generally preferred.
 638      *
 639      * @param   builder
 640      *          A {@code StringBuilder}
 641      *
 642      * @since  1.5
 643      */
 644     public String(StringBuilder builder) {
 645         this(builder, null);
 646     }
 647 
 648     /**
 649      * Returns the length of this string.
 650      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 651      * code units</a> in the string.
 652      *
 653      * @return  the length of the sequence of characters represented by this
 654      *          object.
 655      */
 656     public int length() {
 657         return value.length >> coder();
 658     }
 659 
 660     /**
 661      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 662      *
 663      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 664      * {@code false}
 665      *
 666      * @since 1.6
 667      */
 668     public boolean isEmpty() {
 669         return value.length == 0;
 670     }
 671 
 672     /**
 673      * Returns the {@code char} value at the
 674      * specified index. An index ranges from {@code 0} to
 675      * {@code length() - 1}. The first {@code char} value of the sequence
 676      * is at index {@code 0}, the next at index {@code 1},
 677      * and so on, as for array indexing.
 678      *
 679      * <p>If the {@code char} value specified by the index is a
 680      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 681      * value is returned.
 682      *
 683      * @param      index   the index of the {@code char} value.
 684      * @return     the {@code char} value at the specified index of this string.
 685      *             The first {@code char} value is at index {@code 0}.
 686      * @exception  IndexOutOfBoundsException  if the {@code index}
 687      *             argument is negative or not less than the length of this
 688      *             string.
 689      */
 690     public char charAt(int index) {
 691         if (isLatin1()) {
 692             return StringLatin1.charAt(value, index);
 693         } else {
 694             return StringUTF16.charAt(value, index);
 695         }
 696     }
 697 
 698     /**
 699      * Returns the character (Unicode code point) at the specified
 700      * index. The index refers to {@code char} values
 701      * (Unicode code units) and ranges from {@code 0} to
 702      * {@link #length()}{@code  - 1}.
 703      *
 704      * <p> If the {@code char} value specified at the given index
 705      * is in the high-surrogate range, the following index is less
 706      * than the length of this {@code String}, and the
 707      * {@code char} value at the following index is in the
 708      * low-surrogate range, then the supplementary code point
 709      * corresponding to this surrogate pair is returned. Otherwise,
 710      * the {@code char} value at the given index is returned.
 711      *
 712      * @param      index the index to the {@code char} values
 713      * @return     the code point value of the character at the
 714      *             {@code index}
 715      * @exception  IndexOutOfBoundsException  if the {@code index}
 716      *             argument is negative or not less than the length of this
 717      *             string.
 718      * @since      1.5
 719      */
 720     public int codePointAt(int index) {
 721         if (isLatin1()) {
 722             checkIndex(index, value.length);
 723             return value[index] & 0xff;
 724         }
 725         int length = value.length >> 1;
 726         checkIndex(index, length);
 727         return StringUTF16.codePointAt(value, index, length);
 728     }
 729 
 730     /**
 731      * Returns the character (Unicode code point) before the specified
 732      * index. The index refers to {@code char} values
 733      * (Unicode code units) and ranges from {@code 1} to {@link
 734      * CharSequence#length() length}.
 735      *
 736      * <p> If the {@code char} value at {@code (index - 1)}
 737      * is in the low-surrogate range, {@code (index - 2)} is not
 738      * negative, and the {@code char} value at {@code (index -
 739      * 2)} is in the high-surrogate range, then the
 740      * supplementary code point value of the surrogate pair is
 741      * returned. If the {@code char} value at {@code index -
 742      * 1} is an unpaired low-surrogate or a high-surrogate, the
 743      * surrogate value is returned.
 744      *
 745      * @param     index the index following the code point that should be returned
 746      * @return    the Unicode code point value before the given index.
 747      * @exception IndexOutOfBoundsException if the {@code index}
 748      *            argument is less than 1 or greater than the length
 749      *            of this string.
 750      * @since     1.5
 751      */
 752     public int codePointBefore(int index) {
 753         int i = index - 1;
 754         if (i < 0 || i >= length()) {
 755             throw new StringIndexOutOfBoundsException(index);
 756         }
 757         if (isLatin1()) {
 758             return (value[i] & 0xff);
 759         }
 760         return StringUTF16.codePointBefore(value, index);
 761     }
 762 
 763     /**
 764      * Returns the number of Unicode code points in the specified text
 765      * range of this {@code String}. The text range begins at the
 766      * specified {@code beginIndex} and extends to the
 767      * {@code char} at index {@code endIndex - 1}. Thus the
 768      * length (in {@code char}s) of the text range is
 769      * {@code endIndex-beginIndex}. Unpaired surrogates within
 770      * the text range count as one code point each.
 771      *
 772      * @param beginIndex the index to the first {@code char} of
 773      * the text range.
 774      * @param endIndex the index after the last {@code char} of
 775      * the text range.
 776      * @return the number of Unicode code points in the specified text
 777      * range
 778      * @exception IndexOutOfBoundsException if the
 779      * {@code beginIndex} is negative, or {@code endIndex}
 780      * is larger than the length of this {@code String}, or
 781      * {@code beginIndex} is larger than {@code endIndex}.
 782      * @since  1.5
 783      */
 784     public int codePointCount(int beginIndex, int endIndex) {
 785         if (beginIndex < 0 || beginIndex > endIndex ||
 786             endIndex > length()) {
 787             throw new IndexOutOfBoundsException();
 788         }
 789         if (isLatin1()) {
 790             return endIndex - beginIndex;
 791         }
 792         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 793     }
 794 
 795     /**
 796      * Returns the index within this {@code String} that is
 797      * offset from the given {@code index} by
 798      * {@code codePointOffset} code points. Unpaired surrogates
 799      * within the text range given by {@code index} and
 800      * {@code codePointOffset} count as one code point each.
 801      *
 802      * @param index the index to be offset
 803      * @param codePointOffset the offset in code points
 804      * @return the index within this {@code String}
 805      * @exception IndexOutOfBoundsException if {@code index}
 806      *   is negative or larger then the length of this
 807      *   {@code String}, or if {@code codePointOffset} is positive
 808      *   and the substring starting with {@code index} has fewer
 809      *   than {@code codePointOffset} code points,
 810      *   or if {@code codePointOffset} is negative and the substring
 811      *   before {@code index} has fewer than the absolute value
 812      *   of {@code codePointOffset} code points.
 813      * @since 1.5
 814      */
 815     public int offsetByCodePoints(int index, int codePointOffset) {
 816         if (index < 0 || index > length()) {
 817             throw new IndexOutOfBoundsException();
 818         }
 819         return Character.offsetByCodePoints(this, index, codePointOffset);
 820     }
 821 
 822     /**
 823      * Copies characters from this string into the destination character
 824      * array.
 825      * <p>
 826      * The first character to be copied is at index {@code srcBegin};
 827      * the last character to be copied is at index {@code srcEnd-1}
 828      * (thus the total number of characters to be copied is
 829      * {@code srcEnd-srcBegin}). The characters are copied into the
 830      * subarray of {@code dst} starting at index {@code dstBegin}
 831      * and ending at index:
 832      * <blockquote><pre>
 833      *     dstBegin + (srcEnd-srcBegin) - 1
 834      * </pre></blockquote>
 835      *
 836      * @param      srcBegin   index of the first character in the string
 837      *                        to copy.
 838      * @param      srcEnd     index after the last character in the string
 839      *                        to copy.
 840      * @param      dst        the destination array.
 841      * @param      dstBegin   the start offset in the destination array.
 842      * @exception IndexOutOfBoundsException If any of the following
 843      *            is true:
 844      *            <ul><li>{@code srcBegin} is negative.
 845      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 846      *            <li>{@code srcEnd} is greater than the length of this
 847      *                string
 848      *            <li>{@code dstBegin} is negative
 849      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 850      *                {@code dst.length}</ul>
 851      */
 852     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 853         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 854         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 855         if (isLatin1()) {
 856             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 857         } else {
 858             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 859         }
 860     }
 861 
 862     /**
 863      * Copies characters from this string into the destination byte array. Each
 864      * byte receives the 8 low-order bits of the corresponding character. The
 865      * eight high-order bits of each character are not copied and do not
 866      * participate in the transfer in any way.
 867      *
 868      * <p> The first character to be copied is at index {@code srcBegin}; the
 869      * last character to be copied is at index {@code srcEnd-1}.  The total
 870      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 871      * characters, converted to bytes, are copied into the subarray of {@code
 872      * dst} starting at index {@code dstBegin} and ending at index:
 873      *
 874      * <blockquote><pre>
 875      *     dstBegin + (srcEnd-srcBegin) - 1
 876      * </pre></blockquote>
 877      *
 878      * @deprecated  This method does not properly convert characters into
 879      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 880      * {@link #getBytes()} method, which uses the platform's default charset.
 881      *
 882      * @param  srcBegin
 883      *         Index of the first character in the string to copy
 884      *
 885      * @param  srcEnd
 886      *         Index after the last character in the string to copy
 887      *
 888      * @param  dst
 889      *         The destination array
 890      *
 891      * @param  dstBegin
 892      *         The start offset in the destination array
 893      *
 894      * @throws  IndexOutOfBoundsException
 895      *          If any of the following is true:
 896      *          <ul>
 897      *            <li> {@code srcBegin} is negative
 898      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 899      *            <li> {@code srcEnd} is greater than the length of this String
 900      *            <li> {@code dstBegin} is negative
 901      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 902      *                 dst.length}
 903      *          </ul>
 904      */
 905     @Deprecated(since="1.1")
 906     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 907         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 908         Objects.requireNonNull(dst);
 909         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 910         if (isLatin1()) {
 911             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 912         } else {
 913             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 914         }
 915     }
 916 
 917     /**
 918      * Encodes this {@code String} into a sequence of bytes using the named
 919      * charset, storing the result into a new byte array.
 920      *
 921      * <p> The behavior of this method when this string cannot be encoded in
 922      * the given charset is unspecified.  The {@link
 923      * java.nio.charset.CharsetEncoder} class should be used when more control
 924      * over the encoding process is required.
 925      *
 926      * @param  charsetName
 927      *         The name of a supported {@linkplain java.nio.charset.Charset
 928      *         charset}
 929      *
 930      * @return  The resultant byte array
 931      *
 932      * @throws  UnsupportedEncodingException
 933      *          If the named charset is not supported
 934      *
 935      * @since  1.1
 936      */
 937     public byte[] getBytes(String charsetName)
 938             throws UnsupportedEncodingException {
 939         if (charsetName == null) throw new NullPointerException();
 940         return StringCoding.encode(charsetName, coder(), value);
 941     }
 942 
 943     /**
 944      * Encodes this {@code String} into a sequence of bytes using the given
 945      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 946      * new byte array.
 947      *
 948      * <p> This method always replaces malformed-input and unmappable-character
 949      * sequences with this charset's default replacement byte array.  The
 950      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 951      * control over the encoding process is required.
 952      *
 953      * @param  charset
 954      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 955      *         the {@code String}
 956      *
 957      * @return  The resultant byte array
 958      *
 959      * @since  1.6
 960      */
 961     public byte[] getBytes(Charset charset) {
 962         if (charset == null) throw new NullPointerException();
 963         return StringCoding.encode(charset, coder(), value);
 964      }
 965 
 966     /**
 967      * Encodes this {@code String} into a sequence of bytes using the
 968      * platform's default charset, storing the result into a new byte array.
 969      *
 970      * <p> The behavior of this method when this string cannot be encoded in
 971      * the default charset is unspecified.  The {@link
 972      * java.nio.charset.CharsetEncoder} class should be used when more control
 973      * over the encoding process is required.
 974      *
 975      * @return  The resultant byte array
 976      *
 977      * @since      1.1
 978      */
 979     public byte[] getBytes() {
 980         return StringCoding.encode(coder(), value);
 981     }
 982 
 983     /**
 984      * Compares this string to the specified object.  The result is {@code
 985      * true} if and only if the argument is not {@code null} and is a {@code
 986      * String} object that represents the same sequence of characters as this
 987      * object.
 988      *
 989      * <p>For finer-grained String comparison, refer to
 990      * {@link java.text.Collator}.
 991      *
 992      * @param  anObject
 993      *         The object to compare this {@code String} against
 994      *
 995      * @return  {@code true} if the given object represents a {@code String}
 996      *          equivalent to this string, {@code false} otherwise
 997      *
 998      * @see  #compareTo(String)
 999      * @see  #equalsIgnoreCase(String)
1000      */
1001     public boolean equals(Object anObject) {
1002         if (this == anObject) {
1003             return true;
1004         }
1005         if (anObject instanceof String) {
1006             String aString = (String)anObject;
1007             if (coder() == aString.coder()) {
1008                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1009                                   : StringUTF16.equals(value, aString.value);
1010             }
1011         }
1012         return false;
1013     }
1014 
1015     /**
1016      * Compares this string to the specified {@code StringBuffer}.  The result
1017      * is {@code true} if and only if this {@code String} represents the same
1018      * sequence of characters as the specified {@code StringBuffer}. This method
1019      * synchronizes on the {@code StringBuffer}.
1020      *
1021      * <p>For finer-grained String comparison, refer to
1022      * {@link java.text.Collator}.
1023      *
1024      * @param  sb
1025      *         The {@code StringBuffer} to compare this {@code String} against
1026      *
1027      * @return  {@code true} if this {@code String} represents the same
1028      *          sequence of characters as the specified {@code StringBuffer},
1029      *          {@code false} otherwise
1030      *
1031      * @since  1.4
1032      */
1033     public boolean contentEquals(StringBuffer sb) {
1034         return contentEquals((CharSequence)sb);
1035     }
1036 
1037     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1038         int len = length();
1039         if (len != sb.length()) {
1040             return false;
1041         }
1042         byte v1[] = value;
1043         byte v2[] = sb.getValue();
1044         if (coder() == sb.getCoder()) {
1045             int n = v1.length;
1046             for (int i = 0; i < n; i++) {
1047                 if (v1[i] != v2[i]) {
1048                     return false;
1049                 }
1050             }
1051         } else {
1052             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1053                 return false;
1054             }
1055             return StringUTF16.contentEquals(v1, v2, len);
1056         }
1057         return true;
1058     }
1059 
1060     /**
1061      * Compares this string to the specified {@code CharSequence}.  The
1062      * result is {@code true} if and only if this {@code String} represents the
1063      * same sequence of char values as the specified sequence. Note that if the
1064      * {@code CharSequence} is a {@code StringBuffer} then the method
1065      * synchronizes on it.
1066      *
1067      * <p>For finer-grained String comparison, refer to
1068      * {@link java.text.Collator}.
1069      *
1070      * @param  cs
1071      *         The sequence to compare this {@code String} against
1072      *
1073      * @return  {@code true} if this {@code String} represents the same
1074      *          sequence of char values as the specified sequence, {@code
1075      *          false} otherwise
1076      *
1077      * @since  1.5
1078      */
1079     public boolean contentEquals(CharSequence cs) {
1080         // Argument is a StringBuffer, StringBuilder
1081         if (cs instanceof AbstractStringBuilder) {
1082             if (cs instanceof StringBuffer) {
1083                 synchronized(cs) {
1084                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1085                 }
1086             } else {
1087                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1088             }
1089         }
1090         // Argument is a String
1091         if (cs instanceof String) {
1092             return equals(cs);
1093         }
1094         // Argument is a generic CharSequence
1095         int n = cs.length();
1096         if (n != length()) {
1097             return false;
1098         }
1099         byte[] val = this.value;
1100         if (isLatin1()) {
1101             for (int i = 0; i < n; i++) {
1102                 if ((val[i] & 0xff) != cs.charAt(i)) {
1103                     return false;
1104                 }
1105             }
1106         } else {
1107             if (!StringUTF16.contentEquals(val, cs, n)) {
1108                 return false;
1109             }
1110         }
1111         return true;
1112     }
1113 
1114     /**
1115      * Compares this {@code String} to another {@code String}, ignoring case
1116      * considerations.  Two strings are considered equal ignoring case if they
1117      * are of the same length and corresponding characters in the two strings
1118      * are equal ignoring case.
1119      *
1120      * <p> Two characters {@code c1} and {@code c2} are considered the same
1121      * ignoring case if at least one of the following is true:
1122      * <ul>
1123      *   <li> The two characters are the same (as compared by the
1124      *        {@code ==} operator)
1125      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1126      *        on each character produces the same result
1127      * </ul>
1128      *
1129      * <p>Note that this method does <em>not</em> take locale into account, and
1130      * will result in unsatisfactory results for certain locales.  The
1131      * {@link java.text.Collator} class provides locale-sensitive comparison.
1132      *
1133      * @param  anotherString
1134      *         The {@code String} to compare this {@code String} against
1135      *
1136      * @return  {@code true} if the argument is not {@code null} and it
1137      *          represents an equivalent {@code String} ignoring case; {@code
1138      *          false} otherwise
1139      *
1140      * @see  #equals(Object)
1141      */
1142     public boolean equalsIgnoreCase(String anotherString) {
1143         return (this == anotherString) ? true
1144                 : (anotherString != null)
1145                 && (anotherString.length() == length())
1146                 && regionMatches(true, 0, anotherString, 0, length());
1147     }
1148 
1149     /**
1150      * Compares two strings lexicographically.
1151      * The comparison is based on the Unicode value of each character in
1152      * the strings. The character sequence represented by this
1153      * {@code String} object is compared lexicographically to the
1154      * character sequence represented by the argument string. The result is
1155      * a negative integer if this {@code String} object
1156      * lexicographically precedes the argument string. The result is a
1157      * positive integer if this {@code String} object lexicographically
1158      * follows the argument string. The result is zero if the strings
1159      * are equal; {@code compareTo} returns {@code 0} exactly when
1160      * the {@link #equals(Object)} method would return {@code true}.
1161      * <p>
1162      * This is the definition of lexicographic ordering. If two strings are
1163      * different, then either they have different characters at some index
1164      * that is a valid index for both strings, or their lengths are different,
1165      * or both. If they have different characters at one or more index
1166      * positions, let <i>k</i> be the smallest such index; then the string
1167      * whose character at position <i>k</i> has the smaller value, as
1168      * determined by using the {@code <} operator, lexicographically precedes the
1169      * other string. In this case, {@code compareTo} returns the
1170      * difference of the two character values at position {@code k} in
1171      * the two string -- that is, the value:
1172      * <blockquote><pre>
1173      * this.charAt(k)-anotherString.charAt(k)
1174      * </pre></blockquote>
1175      * If there is no index position at which they differ, then the shorter
1176      * string lexicographically precedes the longer string. In this case,
1177      * {@code compareTo} returns the difference of the lengths of the
1178      * strings -- that is, the value:
1179      * <blockquote><pre>
1180      * this.length()-anotherString.length()
1181      * </pre></blockquote>
1182      *
1183      * <p>For finer-grained String comparison, refer to
1184      * {@link java.text.Collator}.
1185      *
1186      * @param   anotherString   the {@code String} to be compared.
1187      * @return  the value {@code 0} if the argument string is equal to
1188      *          this string; a value less than {@code 0} if this string
1189      *          is lexicographically less than the string argument; and a
1190      *          value greater than {@code 0} if this string is
1191      *          lexicographically greater than the string argument.
1192      */
1193     public int compareTo(String anotherString) {
1194         byte v1[] = value;
1195         byte v2[] = anotherString.value;
1196         if (coder() == anotherString.coder()) {
1197             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1198                               : StringUTF16.compareTo(v1, v2);
1199         }
1200         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1201                           : StringUTF16.compareToLatin1(v1, v2);
1202      }
1203 
1204     /**
1205      * A Comparator that orders {@code String} objects as by
1206      * {@code compareToIgnoreCase}. This comparator is serializable.
1207      * <p>
1208      * Note that this Comparator does <em>not</em> take locale into account,
1209      * and will result in an unsatisfactory ordering for certain locales.
1210      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1211      *
1212      * @see     java.text.Collator
1213      * @since   1.2
1214      */
1215     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1216                                          = new CaseInsensitiveComparator();
1217     private static class CaseInsensitiveComparator
1218             implements Comparator<String>, java.io.Serializable {
1219         // use serialVersionUID from JDK 1.2.2 for interoperability
1220         private static final long serialVersionUID = 8575799808933029326L;
1221 
1222         public int compare(String s1, String s2) {
1223             byte v1[] = s1.value;
1224             byte v2[] = s2.value;
1225             if (s1.coder() == s2.coder()) {
1226                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1227                                      : StringUTF16.compareToCI(v1, v2);
1228             }
1229             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1230                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1231         }
1232 
1233         /** Replaces the de-serialized object. */
1234         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1235     }
1236 
1237     /**
1238      * Compares two strings lexicographically, ignoring case
1239      * differences. This method returns an integer whose sign is that of
1240      * calling {@code compareTo} with normalized versions of the strings
1241      * where case differences have been eliminated by calling
1242      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1243      * each character.
1244      * <p>
1245      * Note that this method does <em>not</em> take locale into account,
1246      * and will result in an unsatisfactory ordering for certain locales.
1247      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1248      *
1249      * @param   str   the {@code String} to be compared.
1250      * @return  a negative integer, zero, or a positive integer as the
1251      *          specified String is greater than, equal to, or less
1252      *          than this String, ignoring case considerations.
1253      * @see     java.text.Collator
1254      * @since   1.2
1255      */
1256     public int compareToIgnoreCase(String str) {
1257         return CASE_INSENSITIVE_ORDER.compare(this, str);
1258     }
1259 
1260     /**
1261      * Tests if two string regions are equal.
1262      * <p>
1263      * A substring of this {@code String} object is compared to a substring
1264      * of the argument other. The result is true if these substrings
1265      * represent identical character sequences. The substring of this
1266      * {@code String} object to be compared begins at index {@code toffset}
1267      * and has length {@code len}. The substring of other to be compared
1268      * begins at index {@code ooffset} and has length {@code len}. The
1269      * result is {@code false} if and only if at least one of the following
1270      * is true:
1271      * <ul><li>{@code toffset} is negative.
1272      * <li>{@code ooffset} is negative.
1273      * <li>{@code toffset+len} is greater than the length of this
1274      * {@code String} object.
1275      * <li>{@code ooffset+len} is greater than the length of the other
1276      * argument.
1277      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1278      * such that:
1279      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1280      * <i>k</i>{@code )}
1281      * </ul>
1282      *
1283      * <p>Note that this method does <em>not</em> take locale into account.  The
1284      * {@link java.text.Collator} class provides locale-sensitive comparison.
1285      *
1286      * @param   toffset   the starting offset of the subregion in this string.
1287      * @param   other     the string argument.
1288      * @param   ooffset   the starting offset of the subregion in the string
1289      *                    argument.
1290      * @param   len       the number of characters to compare.
1291      * @return  {@code true} if the specified subregion of this string
1292      *          exactly matches the specified subregion of the string argument;
1293      *          {@code false} otherwise.
1294      */
1295     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1296         byte tv[] = value;
1297         byte ov[] = other.value;
1298         // Note: toffset, ooffset, or len might be near -1>>>1.
1299         if ((ooffset < 0) || (toffset < 0) ||
1300              (toffset > (long)length() - len) ||
1301              (ooffset > (long)other.length() - len)) {
1302             return false;
1303         }
1304         if (coder() == other.coder()) {
1305             if (!isLatin1() && (len > 0)) {
1306                 toffset = toffset << 1;
1307                 ooffset = ooffset << 1;
1308                 len = len << 1;
1309             }
1310             while (len-- > 0) {
1311                 if (tv[toffset++] != ov[ooffset++]) {
1312                     return false;
1313                 }
1314             }
1315         } else {
1316             if (coder() == LATIN1) {
1317                 while (len-- > 0) {
1318                     if (StringLatin1.getChar(tv, toffset++) !=
1319                         StringUTF16.getChar(ov, ooffset++)) {
1320                         return false;
1321                     }
1322                 }
1323             } else {
1324                 while (len-- > 0) {
1325                     if (StringUTF16.getChar(tv, toffset++) !=
1326                         StringLatin1.getChar(ov, ooffset++)) {
1327                         return false;
1328                     }
1329                 }
1330             }
1331         }
1332         return true;
1333     }
1334 
1335     /**
1336      * Tests if two string regions are equal.
1337      * <p>
1338      * A substring of this {@code String} object is compared to a substring
1339      * of the argument {@code other}. The result is {@code true} if these
1340      * substrings represent character sequences that are the same, ignoring
1341      * case if and only if {@code ignoreCase} is true. The substring of
1342      * this {@code String} object to be compared begins at index
1343      * {@code toffset} and has length {@code len}. The substring of
1344      * {@code other} to be compared begins at index {@code ooffset} and
1345      * has length {@code len}. The result is {@code false} if and only if
1346      * at least one of the following is true:
1347      * <ul><li>{@code toffset} is negative.
1348      * <li>{@code ooffset} is negative.
1349      * <li>{@code toffset+len} is greater than the length of this
1350      * {@code String} object.
1351      * <li>{@code ooffset+len} is greater than the length of the other
1352      * argument.
1353      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1354      * integer <i>k</i> less than {@code len} such that:
1355      * <blockquote><pre>
1356      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1357      * </pre></blockquote>
1358      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1359      * integer <i>k</i> less than {@code len} such that:
1360      * <blockquote><pre>
1361      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1362      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1363      * </pre></blockquote>
1364      * </ul>
1365      *
1366      * <p>Note that this method does <em>not</em> take locale into account,
1367      * and will result in unsatisfactory results for certain locales when
1368      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1369      * provides locale-sensitive comparison.
1370      *
1371      * @param   ignoreCase   if {@code true}, ignore case when comparing
1372      *                       characters.
1373      * @param   toffset      the starting offset of the subregion in this
1374      *                       string.
1375      * @param   other        the string argument.
1376      * @param   ooffset      the starting offset of the subregion in the string
1377      *                       argument.
1378      * @param   len          the number of characters to compare.
1379      * @return  {@code true} if the specified subregion of this string
1380      *          matches the specified subregion of the string argument;
1381      *          {@code false} otherwise. Whether the matching is exact
1382      *          or case insensitive depends on the {@code ignoreCase}
1383      *          argument.
1384      */
1385     public boolean regionMatches(boolean ignoreCase, int toffset,
1386             String other, int ooffset, int len) {
1387         if (!ignoreCase) {
1388             return regionMatches(toffset, other, ooffset, len);
1389         }
1390         // Note: toffset, ooffset, or len might be near -1>>>1.
1391         if ((ooffset < 0) || (toffset < 0)
1392                 || (toffset > (long)length() - len)
1393                 || (ooffset > (long)other.length() - len)) {
1394             return false;
1395         }
1396         byte tv[] = value;
1397         byte ov[] = other.value;
1398         if (coder() == other.coder()) {
1399             return isLatin1()
1400               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1401               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1402         }
1403         return isLatin1()
1404               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1405               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1406     }
1407 
1408     /**
1409      * Tests if the substring of this string beginning at the
1410      * specified index starts with the specified prefix.
1411      *
1412      * @param   prefix    the prefix.
1413      * @param   toffset   where to begin looking in this string.
1414      * @return  {@code true} if the character sequence represented by the
1415      *          argument is a prefix of the substring of this object starting
1416      *          at index {@code toffset}; {@code false} otherwise.
1417      *          The result is {@code false} if {@code toffset} is
1418      *          negative or greater than the length of this
1419      *          {@code String} object; otherwise the result is the same
1420      *          as the result of the expression
1421      *          <pre>
1422      *          this.substring(toffset).startsWith(prefix)
1423      *          </pre>
1424      */
1425     public boolean startsWith(String prefix, int toffset) {
1426         // Note: toffset might be near -1>>>1.
1427         if (toffset < 0 || toffset > length() - prefix.length()) {
1428             return false;
1429         }
1430         byte ta[] = value;
1431         byte pa[] = prefix.value;
1432         int po = 0;
1433         int pc = pa.length;
1434         if (coder() == prefix.coder()) {
1435             int to = isLatin1() ? toffset : toffset << 1;
1436             while (po < pc) {
1437                 if (ta[to++] != pa[po++]) {
1438                     return false;
1439                 }
1440             }
1441         } else {
1442             if (isLatin1()) {  // && pcoder == UTF16
1443                 return false;
1444             }
1445             // coder == UTF16 && pcoder == LATIN1)
1446             while (po < pc) {
1447                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1448                     return false;
1449                }
1450             }
1451         }
1452         return true;
1453     }
1454 
1455     /**
1456      * Tests if this string starts with the specified prefix.
1457      *
1458      * @param   prefix   the prefix.
1459      * @return  {@code true} if the character sequence represented by the
1460      *          argument is a prefix of the character sequence represented by
1461      *          this string; {@code false} otherwise.
1462      *          Note also that {@code true} will be returned if the
1463      *          argument is an empty string or is equal to this
1464      *          {@code String} object as determined by the
1465      *          {@link #equals(Object)} method.
1466      * @since   1.0
1467      */
1468     public boolean startsWith(String prefix) {
1469         return startsWith(prefix, 0);
1470     }
1471 
1472     /**
1473      * Tests if this string ends with the specified suffix.
1474      *
1475      * @param   suffix   the suffix.
1476      * @return  {@code true} if the character sequence represented by the
1477      *          argument is a suffix of the character sequence represented by
1478      *          this object; {@code false} otherwise. Note that the
1479      *          result will be {@code true} if the argument is the
1480      *          empty string or is equal to this {@code String} object
1481      *          as determined by the {@link #equals(Object)} method.
1482      */
1483     public boolean endsWith(String suffix) {
1484         return startsWith(suffix, length() - suffix.length());
1485     }
1486 
1487     /**
1488      * Returns a hash code for this string. The hash code for a
1489      * {@code String} object is computed as
1490      * <blockquote><pre>
1491      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1492      * </pre></blockquote>
1493      * using {@code int} arithmetic, where {@code s[i]} is the
1494      * <i>i</i>th character of the string, {@code n} is the length of
1495      * the string, and {@code ^} indicates exponentiation.
1496      * (The hash value of the empty string is zero.)
1497      *
1498      * @return  a hash code value for this object.
1499      */
1500     public int hashCode() {
1501         int h = hash;
1502         if (h == 0 && value.length > 0) {
1503             hash = h = isLatin1() ? StringLatin1.hashCode(value)
1504                                   : StringUTF16.hashCode(value);
1505         }
1506         return h;
1507     }
1508 
1509     /**
1510      * Returns the index within this string of the first occurrence of
1511      * the specified character. If a character with value
1512      * {@code ch} occurs in the character sequence represented by
1513      * this {@code String} object, then the index (in Unicode
1514      * code units) of the first such occurrence is returned. For
1515      * values of {@code ch} in the range from 0 to 0xFFFF
1516      * (inclusive), this is the smallest value <i>k</i> such that:
1517      * <blockquote><pre>
1518      * this.charAt(<i>k</i>) == ch
1519      * </pre></blockquote>
1520      * is true. For other values of {@code ch}, it is the
1521      * smallest value <i>k</i> such that:
1522      * <blockquote><pre>
1523      * this.codePointAt(<i>k</i>) == ch
1524      * </pre></blockquote>
1525      * is true. In either case, if no such character occurs in this
1526      * string, then {@code -1} is returned.
1527      *
1528      * @param   ch   a character (Unicode code point).
1529      * @return  the index of the first occurrence of the character in the
1530      *          character sequence represented by this object, or
1531      *          {@code -1} if the character does not occur.
1532      */
1533     public int indexOf(int ch) {
1534         return indexOf(ch, 0);
1535     }
1536 
1537     /**
1538      * Returns the index within this string of the first occurrence of the
1539      * specified character, starting the search at the specified index.
1540      * <p>
1541      * If a character with value {@code ch} occurs in the
1542      * character sequence represented by this {@code String}
1543      * object at an index no smaller than {@code fromIndex}, then
1544      * the index of the first such occurrence is returned. For values
1545      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1546      * this is the smallest value <i>k</i> such that:
1547      * <blockquote><pre>
1548      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1549      * </pre></blockquote>
1550      * is true. For other values of {@code ch}, it is the
1551      * smallest value <i>k</i> such that:
1552      * <blockquote><pre>
1553      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1554      * </pre></blockquote>
1555      * is true. In either case, if no such character occurs in this
1556      * string at or after position {@code fromIndex}, then
1557      * {@code -1} is returned.
1558      *
1559      * <p>
1560      * There is no restriction on the value of {@code fromIndex}. If it
1561      * is negative, it has the same effect as if it were zero: this entire
1562      * string may be searched. If it is greater than the length of this
1563      * string, it has the same effect as if it were equal to the length of
1564      * this string: {@code -1} is returned.
1565      *
1566      * <p>All indices are specified in {@code char} values
1567      * (Unicode code units).
1568      *
1569      * @param   ch          a character (Unicode code point).
1570      * @param   fromIndex   the index to start the search from.
1571      * @return  the index of the first occurrence of the character in the
1572      *          character sequence represented by this object that is greater
1573      *          than or equal to {@code fromIndex}, or {@code -1}
1574      *          if the character does not occur.
1575      */
1576     public int indexOf(int ch, int fromIndex) {
1577         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1578                           : StringUTF16.indexOf(value, ch, fromIndex);
1579     }
1580 
1581     /**
1582      * Returns the index within this string of the last occurrence of
1583      * the specified character. For values of {@code ch} in the
1584      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1585      * units) returned is the largest value <i>k</i> such that:
1586      * <blockquote><pre>
1587      * this.charAt(<i>k</i>) == ch
1588      * </pre></blockquote>
1589      * is true. For other values of {@code ch}, it is the
1590      * largest value <i>k</i> such that:
1591      * <blockquote><pre>
1592      * this.codePointAt(<i>k</i>) == ch
1593      * </pre></blockquote>
1594      * is true.  In either case, if no such character occurs in this
1595      * string, then {@code -1} is returned.  The
1596      * {@code String} is searched backwards starting at the last
1597      * character.
1598      *
1599      * @param   ch   a character (Unicode code point).
1600      * @return  the index of the last occurrence of the character in the
1601      *          character sequence represented by this object, or
1602      *          {@code -1} if the character does not occur.
1603      */
1604     public int lastIndexOf(int ch) {
1605         return lastIndexOf(ch, length() - 1);
1606     }
1607 
1608     /**
1609      * Returns the index within this string of the last occurrence of
1610      * the specified character, searching backward starting at the
1611      * specified index. For values of {@code ch} in the range
1612      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1613      * value <i>k</i> such that:
1614      * <blockquote><pre>
1615      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1616      * </pre></blockquote>
1617      * is true. For other values of {@code ch}, it is the
1618      * largest value <i>k</i> such that:
1619      * <blockquote><pre>
1620      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1621      * </pre></blockquote>
1622      * is true. In either case, if no such character occurs in this
1623      * string at or before position {@code fromIndex}, then
1624      * {@code -1} is returned.
1625      *
1626      * <p>All indices are specified in {@code char} values
1627      * (Unicode code units).
1628      *
1629      * @param   ch          a character (Unicode code point).
1630      * @param   fromIndex   the index to start the search from. There is no
1631      *          restriction on the value of {@code fromIndex}. If it is
1632      *          greater than or equal to the length of this string, it has
1633      *          the same effect as if it were equal to one less than the
1634      *          length of this string: this entire string may be searched.
1635      *          If it is negative, it has the same effect as if it were -1:
1636      *          -1 is returned.
1637      * @return  the index of the last occurrence of the character in the
1638      *          character sequence represented by this object that is less
1639      *          than or equal to {@code fromIndex}, or {@code -1}
1640      *          if the character does not occur before that point.
1641      */
1642     public int lastIndexOf(int ch, int fromIndex) {
1643         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1644                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1645     }
1646 
1647     /**
1648      * Returns the index within this string of the first occurrence of the
1649      * specified substring.
1650      *
1651      * <p>The returned index is the smallest value {@code k} for which:
1652      * <pre>{@code
1653      * this.startsWith(str, k)
1654      * }</pre>
1655      * If no such value of {@code k} exists, then {@code -1} is returned.
1656      *
1657      * @param   str   the substring to search for.
1658      * @return  the index of the first occurrence of the specified substring,
1659      *          or {@code -1} if there is no such occurrence.
1660      */
1661     public int indexOf(String str) {
1662         if (coder() == str.coder()) {
1663             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1664                               : StringUTF16.indexOf(value, str.value);
1665         }
1666         if (coder() == LATIN1) {  // str.coder == UTF16
1667             return -1;
1668         }
1669         return StringUTF16.indexOfLatin1(value, str.value);
1670     }
1671 
1672     /**
1673      * Returns the index within this string of the first occurrence of the
1674      * specified substring, starting at the specified index.
1675      *
1676      * <p>The returned index is the smallest value {@code k} for which:
1677      * <pre>{@code
1678      *     k >= Math.min(fromIndex, this.length()) &&
1679      *                   this.startsWith(str, k)
1680      * }</pre>
1681      * If no such value of {@code k} exists, then {@code -1} is returned.
1682      *
1683      * @param   str         the substring to search for.
1684      * @param   fromIndex   the index from which to start the search.
1685      * @return  the index of the first occurrence of the specified substring,
1686      *          starting at the specified index,
1687      *          or {@code -1} if there is no such occurrence.
1688      */
1689     public int indexOf(String str, int fromIndex) {
1690         return indexOf(value, coder(), length(), str, fromIndex);
1691     }
1692 
1693     /**
1694      * Code shared by String and AbstractStringBuilder to do searches. The
1695      * source is the character array being searched, and the target
1696      * is the string being searched for.
1697      *
1698      * @param   src       the characters being searched.
1699      * @param   srcCoder  the coder of the source string.
1700      * @param   srcCount  length of the source string.
1701      * @param   tgtStr    the characters being searched for.
1702      * @param   fromIndex the index to begin searching from.
1703      */
1704     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1705                        String tgtStr, int fromIndex) {
1706         byte[] tgt    = tgtStr.value;
1707         byte tgtCoder = tgtStr.coder();
1708         int tgtCount  = tgtStr.length();
1709 
1710         if (fromIndex >= srcCount) {
1711             return (tgtCount == 0 ? srcCount : -1);
1712         }
1713         if (fromIndex < 0) {
1714             fromIndex = 0;
1715         }
1716         if (tgtCount == 0) {
1717             return fromIndex;
1718         }
1719         if (tgtCount > srcCount) {
1720             return -1;
1721         }
1722         if (srcCoder == tgtCoder) {
1723             return srcCoder == LATIN1
1724                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1725                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1726         }
1727         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1728             return -1;
1729         }
1730         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1731         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1732     }
1733 
1734     /**
1735      * Returns the index within this string of the last occurrence of the
1736      * specified substring.  The last occurrence of the empty string ""
1737      * is considered to occur at the index value {@code this.length()}.
1738      *
1739      * <p>The returned index is the largest value {@code k} for which:
1740      * <pre>{@code
1741      * this.startsWith(str, k)
1742      * }</pre>
1743      * If no such value of {@code k} exists, then {@code -1} is returned.
1744      *
1745      * @param   str   the substring to search for.
1746      * @return  the index of the last occurrence of the specified substring,
1747      *          or {@code -1} if there is no such occurrence.
1748      */
1749     public int lastIndexOf(String str) {
1750         return lastIndexOf(str, length());
1751     }
1752 
1753     /**
1754      * Returns the index within this string of the last occurrence of the
1755      * specified substring, searching backward starting at the specified index.
1756      *
1757      * <p>The returned index is the largest value {@code k} for which:
1758      * <pre>{@code
1759      *     k <= Math.min(fromIndex, this.length()) &&
1760      *                   this.startsWith(str, k)
1761      * }</pre>
1762      * If no such value of {@code k} exists, then {@code -1} is returned.
1763      *
1764      * @param   str         the substring to search for.
1765      * @param   fromIndex   the index to start the search from.
1766      * @return  the index of the last occurrence of the specified substring,
1767      *          searching backward from the specified index,
1768      *          or {@code -1} if there is no such occurrence.
1769      */
1770     public int lastIndexOf(String str, int fromIndex) {
1771         return lastIndexOf(value, coder(), length(), str, fromIndex);
1772     }
1773 
1774     /**
1775      * Code shared by String and AbstractStringBuilder to do searches. The
1776      * source is the character array being searched, and the target
1777      * is the string being searched for.
1778      *
1779      * @param   src         the characters being searched.
1780      * @param   srcCoder    coder handles the mapping between bytes/chars
1781      * @param   srcCount    count of the source string.
1782      * @param   tgt         the characters being searched for.
1783      * @param   fromIndex   the index to begin searching from.
1784      */
1785     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1786                            String tgtStr, int fromIndex) {
1787         byte[] tgt = tgtStr.value;
1788         byte tgtCoder = tgtStr.coder();
1789         int tgtCount = tgtStr.length();
1790         /*
1791          * Check arguments; return immediately where possible. For
1792          * consistency, don't check for null str.
1793          */
1794         int rightIndex = srcCount - tgtCount;
1795         if (fromIndex > rightIndex) {
1796             fromIndex = rightIndex;
1797         }
1798         if (fromIndex < 0) {
1799             return -1;
1800         }
1801         /* Empty string always matches. */
1802         if (tgtCount == 0) {
1803             return fromIndex;
1804         }
1805         if (srcCoder == tgtCoder) {
1806             return srcCoder == LATIN1
1807                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1808                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1809         }
1810         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1811             return -1;
1812         }
1813         // srcCoder == UTF16 && tgtCoder == LATIN1
1814         return StringUTF16.lastIndexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1815     }
1816 
1817     /**
1818      * Returns a string that is a substring of this string. The
1819      * substring begins with the character at the specified index and
1820      * extends to the end of this string. <p>
1821      * Examples:
1822      * <blockquote><pre>
1823      * "unhappy".substring(2) returns "happy"
1824      * "Harbison".substring(3) returns "bison"
1825      * "emptiness".substring(9) returns "" (an empty string)
1826      * </pre></blockquote>
1827      *
1828      * @param      beginIndex   the beginning index, inclusive.
1829      * @return     the specified substring.
1830      * @exception  IndexOutOfBoundsException  if
1831      *             {@code beginIndex} is negative or larger than the
1832      *             length of this {@code String} object.
1833      */
1834     public String substring(int beginIndex) {
1835         if (beginIndex < 0) {
1836             throw new StringIndexOutOfBoundsException(beginIndex);
1837         }
1838         int subLen = length() - beginIndex;
1839         if (subLen < 0) {
1840             throw new StringIndexOutOfBoundsException(subLen);
1841         }
1842         if (beginIndex == 0) {
1843             return this;
1844         }
1845         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1846                           : StringUTF16.newString(value, beginIndex, subLen);
1847     }
1848 
1849     /**
1850      * Returns a string that is a substring of this string. The
1851      * substring begins at the specified {@code beginIndex} and
1852      * extends to the character at index {@code endIndex - 1}.
1853      * Thus the length of the substring is {@code endIndex-beginIndex}.
1854      * <p>
1855      * Examples:
1856      * <blockquote><pre>
1857      * "hamburger".substring(4, 8) returns "urge"
1858      * "smiles".substring(1, 5) returns "mile"
1859      * </pre></blockquote>
1860      *
1861      * @param      beginIndex   the beginning index, inclusive.
1862      * @param      endIndex     the ending index, exclusive.
1863      * @return     the specified substring.
1864      * @exception  IndexOutOfBoundsException  if the
1865      *             {@code beginIndex} is negative, or
1866      *             {@code endIndex} is larger than the length of
1867      *             this {@code String} object, or
1868      *             {@code beginIndex} is larger than
1869      *             {@code endIndex}.
1870      */
1871     public String substring(int beginIndex, int endIndex) {
1872         int length = length();
1873         checkBoundsBeginEnd(beginIndex, endIndex, length);
1874         int subLen = endIndex - beginIndex;
1875         if (beginIndex == 0 && endIndex == length) {
1876             return this;
1877         }
1878         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1879                           : StringUTF16.newString(value, beginIndex, subLen);
1880     }
1881 
1882     /**
1883      * Returns a character sequence that is a subsequence of this sequence.
1884      *
1885      * <p> An invocation of this method of the form
1886      *
1887      * <blockquote><pre>
1888      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1889      *
1890      * behaves in exactly the same way as the invocation
1891      *
1892      * <blockquote><pre>
1893      * str.substring(begin,&nbsp;end)</pre></blockquote>
1894      *
1895      * @apiNote
1896      * This method is defined so that the {@code String} class can implement
1897      * the {@link CharSequence} interface.
1898      *
1899      * @param   beginIndex   the begin index, inclusive.
1900      * @param   endIndex     the end index, exclusive.
1901      * @return  the specified subsequence.
1902      *
1903      * @throws  IndexOutOfBoundsException
1904      *          if {@code beginIndex} or {@code endIndex} is negative,
1905      *          if {@code endIndex} is greater than {@code length()},
1906      *          or if {@code beginIndex} is greater than {@code endIndex}
1907      *
1908      * @since 1.4
1909      * @spec JSR-51
1910      */
1911     public CharSequence subSequence(int beginIndex, int endIndex) {
1912         return this.substring(beginIndex, endIndex);
1913     }
1914 
1915     /**
1916      * Concatenates the specified string to the end of this string.
1917      * <p>
1918      * If the length of the argument string is {@code 0}, then this
1919      * {@code String} object is returned. Otherwise, a
1920      * {@code String} object is returned that represents a character
1921      * sequence that is the concatenation of the character sequence
1922      * represented by this {@code String} object and the character
1923      * sequence represented by the argument string.<p>
1924      * Examples:
1925      * <blockquote><pre>
1926      * "cares".concat("s") returns "caress"
1927      * "to".concat("get").concat("her") returns "together"
1928      * </pre></blockquote>
1929      *
1930      * @param   str   the {@code String} that is concatenated to the end
1931      *                of this {@code String}.
1932      * @return  a string that represents the concatenation of this object's
1933      *          characters followed by the string argument's characters.
1934      */
1935     public String concat(String str) {
1936         int olen = str.length();
1937         if (olen == 0) {
1938             return this;
1939         }
1940         if (coder() == str.coder()) {
1941             byte[] val = this.value;
1942             byte[] oval = str.value;
1943             int len = val.length + oval.length;
1944             byte[] buf = Arrays.copyOf(val, len);
1945             System.arraycopy(oval, 0, buf, val.length, oval.length);
1946             return new String(buf, coder);
1947         }
1948         int len = length();
1949         byte[] buf = StringUTF16.newBytesFor(len + olen);
1950         getBytes(buf, 0, UTF16);
1951         str.getBytes(buf, len, UTF16);
1952         return new String(buf, UTF16);
1953     }
1954 
1955     /**
1956      * Returns a string resulting from replacing all occurrences of
1957      * {@code oldChar} in this string with {@code newChar}.
1958      * <p>
1959      * If the character {@code oldChar} does not occur in the
1960      * character sequence represented by this {@code String} object,
1961      * then a reference to this {@code String} object is returned.
1962      * Otherwise, a {@code String} object is returned that
1963      * represents a character sequence identical to the character sequence
1964      * represented by this {@code String} object, except that every
1965      * occurrence of {@code oldChar} is replaced by an occurrence
1966      * of {@code newChar}.
1967      * <p>
1968      * Examples:
1969      * <blockquote><pre>
1970      * "mesquite in your cellar".replace('e', 'o')
1971      *         returns "mosquito in your collar"
1972      * "the war of baronets".replace('r', 'y')
1973      *         returns "the way of bayonets"
1974      * "sparring with a purple porpoise".replace('p', 't')
1975      *         returns "starring with a turtle tortoise"
1976      * "JonL".replace('q', 'x') returns "JonL" (no change)
1977      * </pre></blockquote>
1978      *
1979      * @param   oldChar   the old character.
1980      * @param   newChar   the new character.
1981      * @return  a string derived from this string by replacing every
1982      *          occurrence of {@code oldChar} with {@code newChar}.
1983      */
1984     public String replace(char oldChar, char newChar) {
1985         if (oldChar != newChar) {
1986             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
1987                                     : StringUTF16.replace(value, oldChar, newChar);
1988             if (ret != null) {
1989                 return ret;
1990             }
1991         }
1992         return this;
1993     }
1994 
1995     /**
1996      * Tells whether or not this string matches the given <a
1997      * href="../util/regex/Pattern.html#sum">regular expression</a>.
1998      *
1999      * <p> An invocation of this method of the form
2000      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2001      * same result as the expression
2002      *
2003      * <blockquote>
2004      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2005      * matches(<i>regex</i>, <i>str</i>)}
2006      * </blockquote>
2007      *
2008      * @param   regex
2009      *          the regular expression to which this string is to be matched
2010      *
2011      * @return  {@code true} if, and only if, this string matches the
2012      *          given regular expression
2013      *
2014      * @throws  PatternSyntaxException
2015      *          if the regular expression's syntax is invalid
2016      *
2017      * @see java.util.regex.Pattern
2018      *
2019      * @since 1.4
2020      * @spec JSR-51
2021      */
2022     public boolean matches(String regex) {
2023         return Pattern.matches(regex, this);
2024     }
2025 
2026     /**
2027      * Returns true if and only if this string contains the specified
2028      * sequence of char values.
2029      *
2030      * @param s the sequence to search for
2031      * @return true if this string contains {@code s}, false otherwise
2032      * @since 1.5
2033      */
2034     public boolean contains(CharSequence s) {
2035         return indexOf(s.toString()) >= 0;
2036     }
2037 
2038     /**
2039      * Replaces the first substring of this string that matches the given <a
2040      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2041      * given replacement.
2042      *
2043      * <p> An invocation of this method of the form
2044      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2045      * yields exactly the same result as the expression
2046      *
2047      * <blockquote>
2048      * <code>
2049      * {@link java.util.regex.Pattern}.{@link
2050      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2051      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2052      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2053      * </code>
2054      * </blockquote>
2055      *
2056      *<p>
2057      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2058      * replacement string may cause the results to be different than if it were
2059      * being treated as a literal replacement string; see
2060      * {@link java.util.regex.Matcher#replaceFirst}.
2061      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2062      * meaning of these characters, if desired.
2063      *
2064      * @param   regex
2065      *          the regular expression to which this string is to be matched
2066      * @param   replacement
2067      *          the string to be substituted for the first match
2068      *
2069      * @return  The resulting {@code String}
2070      *
2071      * @throws  PatternSyntaxException
2072      *          if the regular expression's syntax is invalid
2073      *
2074      * @see java.util.regex.Pattern
2075      *
2076      * @since 1.4
2077      * @spec JSR-51
2078      */
2079     public String replaceFirst(String regex, String replacement) {
2080         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2081     }
2082 
2083     /**
2084      * Replaces each substring of this string that matches the given <a
2085      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2086      * given replacement.
2087      *
2088      * <p> An invocation of this method of the form
2089      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2090      * yields exactly the same result as the expression
2091      *
2092      * <blockquote>
2093      * <code>
2094      * {@link java.util.regex.Pattern}.{@link
2095      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2096      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2097      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2098      * </code>
2099      * </blockquote>
2100      *
2101      *<p>
2102      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2103      * replacement string may cause the results to be different than if it were
2104      * being treated as a literal replacement string; see
2105      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2106      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2107      * meaning of these characters, if desired.
2108      *
2109      * @param   regex
2110      *          the regular expression to which this string is to be matched
2111      * @param   replacement
2112      *          the string to be substituted for each match
2113      *
2114      * @return  The resulting {@code String}
2115      *
2116      * @throws  PatternSyntaxException
2117      *          if the regular expression's syntax is invalid
2118      *
2119      * @see java.util.regex.Pattern
2120      *
2121      * @since 1.4
2122      * @spec JSR-51
2123      */
2124     public String replaceAll(String regex, String replacement) {
2125         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2126     }
2127 
2128     /**
2129      * Replaces each substring of this string that matches the literal target
2130      * sequence with the specified literal replacement sequence. The
2131      * replacement proceeds from the beginning of the string to the end, for
2132      * example, replacing "aa" with "b" in the string "aaa" will result in
2133      * "ba" rather than "ab".
2134      *
2135      * @param  target The sequence of char values to be replaced
2136      * @param  replacement The replacement sequence of char values
2137      * @return  The resulting string
2138      * @since 1.5
2139      */
2140     public String replace(CharSequence target, CharSequence replacement) {
2141         String tgtStr = target.toString();
2142         String replStr = replacement.toString();
2143         int j = indexOf(tgtStr);
2144         if (j < 0) {
2145             return this;
2146         }
2147         int tgtLen = tgtStr.length();
2148         int tgtLen1 = Math.max(tgtLen, 1);
2149         int thisLen = length();
2150 
2151         int newLenHint = thisLen - tgtLen + replStr.length();
2152         if (newLenHint < 0) {
2153             throw new OutOfMemoryError();
2154         }
2155         StringBuilder sb = new StringBuilder(newLenHint);
2156         int i = 0;
2157         do {
2158             sb.append(this, i, j).append(replStr);
2159             i = j + tgtLen;
2160         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2161         return sb.append(this, i, thisLen).toString();
2162     }
2163 
2164     /**
2165      * Splits this string around matches of the given
2166      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2167      *
2168      * <p> The array returned by this method contains each substring of this
2169      * string that is terminated by another substring that matches the given
2170      * expression or is terminated by the end of the string.  The substrings in
2171      * the array are in the order in which they occur in this string.  If the
2172      * expression does not match any part of the input then the resulting array
2173      * has just one element, namely this string.
2174      *
2175      * <p> When there is a positive-width match at the beginning of this
2176      * string then an empty leading substring is included at the beginning
2177      * of the resulting array. A zero-width match at the beginning however
2178      * never produces such empty leading substring.
2179      *
2180      * <p> The {@code limit} parameter controls the number of times the
2181      * pattern is applied and therefore affects the length of the resulting
2182      * array.  If the limit <i>n</i> is greater than zero then the pattern
2183      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2184      * length will be no greater than <i>n</i>, and the array's last entry
2185      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2186      * is non-positive then the pattern will be applied as many times as
2187      * possible and the array can have any length.  If <i>n</i> is zero then
2188      * the pattern will be applied as many times as possible, the array can
2189      * have any length, and trailing empty strings will be discarded.
2190      *
2191      * <p> The string {@code "boo:and:foo"}, for example, yields the
2192      * following results with these parameters:
2193      *
2194      * <blockquote><table class="plain">
2195      * <caption style="display:none">Split example showing regex, limit, and result</caption>
2196      * <thead>
2197      * <tr>
2198      *     <th scope="col">Regex</th>
2199      *     <th scope="col">Limit</th>
2200      *     <th scope="col">Result</th>
2201      * </tr>
2202      * </thead>
2203      * <tbody>
2204      * <tr><th scope="row" rowspan="3" style="font-weight:normal">:</th>
2205      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">2</th>
2206      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2207      * <tr><!-- : -->
2208      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">5</th>
2209      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2210      * <tr><!-- : -->
2211      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">-2</th>
2212      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2213      * <tr><th scope="row" rowspan="3" style="font-weight:normal">o</th>
2214      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">5</th>
2215      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2216      * <tr><!-- o -->
2217      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">-2</th>
2218      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2219      * <tr><!-- o -->
2220      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">0</th>
2221      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2222      * </tbody>
2223      * </table></blockquote>
2224      *
2225      * <p> An invocation of this method of the form
2226      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2227      * yields the same result as the expression
2228      *
2229      * <blockquote>
2230      * <code>
2231      * {@link java.util.regex.Pattern}.{@link
2232      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2233      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2234      * </code>
2235      * </blockquote>
2236      *
2237      *
2238      * @param  regex
2239      *         the delimiting regular expression
2240      *
2241      * @param  limit
2242      *         the result threshold, as described above
2243      *
2244      * @return  the array of strings computed by splitting this string
2245      *          around matches of the given regular expression
2246      *
2247      * @throws  PatternSyntaxException
2248      *          if the regular expression's syntax is invalid
2249      *
2250      * @see java.util.regex.Pattern
2251      *
2252      * @since 1.4
2253      * @spec JSR-51
2254      */
2255     public String[] split(String regex, int limit) {
2256         /* fastpath if the regex is a
2257          (1)one-char String and this character is not one of the
2258             RegEx's meta characters ".$|()[{^?*+\\", or
2259          (2)two-char String and the first char is the backslash and
2260             the second is not the ascii digit or ascii letter.
2261          */
2262         char ch = 0;
2263         if (((regex.length() == 1 &&
2264              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2265              (regex.length() == 2 &&
2266               regex.charAt(0) == '\\' &&
2267               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2268               ((ch-'a')|('z'-ch)) < 0 &&
2269               ((ch-'A')|('Z'-ch)) < 0)) &&
2270             (ch < Character.MIN_HIGH_SURROGATE ||
2271              ch > Character.MAX_LOW_SURROGATE))
2272         {
2273             int off = 0;
2274             int next = 0;
2275             boolean limited = limit > 0;
2276             ArrayList<String> list = new ArrayList<>();
2277             while ((next = indexOf(ch, off)) != -1) {
2278                 if (!limited || list.size() < limit - 1) {
2279                     list.add(substring(off, next));
2280                     off = next + 1;
2281                 } else {    // last one
2282                     //assert (list.size() == limit - 1);
2283                     int last = length();
2284                     list.add(substring(off, last));
2285                     off = last;
2286                     break;
2287                 }
2288             }
2289             // If no match was found, return this
2290             if (off == 0)
2291                 return new String[]{this};
2292 
2293             // Add remaining segment
2294             if (!limited || list.size() < limit)
2295                 list.add(substring(off, length()));
2296 
2297             // Construct result
2298             int resultSize = list.size();
2299             if (limit == 0) {
2300                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2301                     resultSize--;
2302                 }
2303             }
2304             String[] result = new String[resultSize];
2305             return list.subList(0, resultSize).toArray(result);
2306         }
2307         return Pattern.compile(regex).split(this, limit);
2308     }
2309 
2310     /**
2311      * Splits this string around matches of the given <a
2312      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2313      *
2314      * <p> This method works as if by invoking the two-argument {@link
2315      * #split(String, int) split} method with the given expression and a limit
2316      * argument of zero.  Trailing empty strings are therefore not included in
2317      * the resulting array.
2318      *
2319      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2320      * results with these expressions:
2321      *
2322      * <blockquote><table class="plain">
2323      * <caption style="display:none">Split examples showing regex and result</caption>
2324      * <thead>
2325      * <tr>
2326      *  <th scope="col">Regex</th>
2327      *  <th scope="col">Result</th>
2328      * </tr>
2329      * </thead>
2330      * <tbody>
2331      * <tr><th scope="row" style="text-weight:normal">:</th>
2332      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2333      * <tr><th scope="row" style="text-weight:normal">o</th>
2334      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2335      * </tbody>
2336      * </table></blockquote>
2337      *
2338      *
2339      * @param  regex
2340      *         the delimiting regular expression
2341      *
2342      * @return  the array of strings computed by splitting this string
2343      *          around matches of the given regular expression
2344      *
2345      * @throws  PatternSyntaxException
2346      *          if the regular expression's syntax is invalid
2347      *
2348      * @see java.util.regex.Pattern
2349      *
2350      * @since 1.4
2351      * @spec JSR-51
2352      */
2353     public String[] split(String regex) {
2354         return split(regex, 0);
2355     }
2356 
2357     /**
2358      * Returns a new String composed of copies of the
2359      * {@code CharSequence elements} joined together with a copy of
2360      * the specified {@code delimiter}.
2361      *
2362      * <blockquote>For example,
2363      * <pre>{@code
2364      *     String message = String.join("-", "Java", "is", "cool");
2365      *     // message returned is: "Java-is-cool"
2366      * }</pre></blockquote>
2367      *
2368      * Note that if an element is null, then {@code "null"} is added.
2369      *
2370      * @param  delimiter the delimiter that separates each element
2371      * @param  elements the elements to join together.
2372      *
2373      * @return a new {@code String} that is composed of the {@code elements}
2374      *         separated by the {@code delimiter}
2375      *
2376      * @throws NullPointerException If {@code delimiter} or {@code elements}
2377      *         is {@code null}
2378      *
2379      * @see java.util.StringJoiner
2380      * @since 1.8
2381      */
2382     public static String join(CharSequence delimiter, CharSequence... elements) {
2383         Objects.requireNonNull(delimiter);
2384         Objects.requireNonNull(elements);
2385         // Number of elements not likely worth Arrays.stream overhead.
2386         StringJoiner joiner = new StringJoiner(delimiter);
2387         for (CharSequence cs: elements) {
2388             joiner.add(cs);
2389         }
2390         return joiner.toString();
2391     }
2392 
2393     /**
2394      * Returns a new {@code String} composed of copies of the
2395      * {@code CharSequence elements} joined together with a copy of the
2396      * specified {@code delimiter}.
2397      *
2398      * <blockquote>For example,
2399      * <pre>{@code
2400      *     List<String> strings = List.of("Java", "is", "cool");
2401      *     String message = String.join(" ", strings);
2402      *     //message returned is: "Java is cool"
2403      *
2404      *     Set<String> strings =
2405      *         new LinkedHashSet<>(List.of("Java", "is", "very", "cool"));
2406      *     String message = String.join("-", strings);
2407      *     //message returned is: "Java-is-very-cool"
2408      * }</pre></blockquote>
2409      *
2410      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2411      *
2412      * @param  delimiter a sequence of characters that is used to separate each
2413      *         of the {@code elements} in the resulting {@code String}
2414      * @param  elements an {@code Iterable} that will have its {@code elements}
2415      *         joined together.
2416      *
2417      * @return a new {@code String} that is composed from the {@code elements}
2418      *         argument
2419      *
2420      * @throws NullPointerException If {@code delimiter} or {@code elements}
2421      *         is {@code null}
2422      *
2423      * @see    #join(CharSequence,CharSequence...)
2424      * @see    java.util.StringJoiner
2425      * @since 1.8
2426      */
2427     public static String join(CharSequence delimiter,
2428             Iterable<? extends CharSequence> elements) {
2429         Objects.requireNonNull(delimiter);
2430         Objects.requireNonNull(elements);
2431         StringJoiner joiner = new StringJoiner(delimiter);
2432         for (CharSequence cs: elements) {
2433             joiner.add(cs);
2434         }
2435         return joiner.toString();
2436     }
2437 
2438     /**
2439      * Converts all of the characters in this {@code String} to lower
2440      * case using the rules of the given {@code Locale}.  Case mapping is based
2441      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2442      * class. Since case mappings are not always 1:1 char mappings, the resulting
2443      * {@code String} may be a different length than the original {@code String}.
2444      * <p>
2445      * Examples of lowercase  mappings are in the following table:
2446      * <table class="plain">
2447      * <caption style="display:none">Lowercase mapping examples showing language code of locale, upper case, lower case, and description</caption>
2448      * <thead>
2449      * <tr>
2450      *   <th scope="col">Language Code of Locale</th>
2451      *   <th scope="col">Upper Case</th>
2452      *   <th scope="col">Lower Case</th>
2453      *   <th scope="col">Description</th>
2454      * </tr>
2455      * </thead>
2456      * <tbody>
2457      * <tr>
2458      *   <td>tr (Turkish)</td>
2459      *   <th scope="row" style="font-weight:normal; text-align:left">\u0130</th>
2460      *   <td>\u0069</td>
2461      *   <td>capital letter I with dot above -&gt; small letter i</td>
2462      * </tr>
2463      * <tr>
2464      *   <td>tr (Turkish)</td>
2465      *   <th scope="row" style="font-weight:normal; text-align:left">\u0049</th>
2466      *   <td>\u0131</td>
2467      *   <td>capital letter I -&gt; small letter dotless i </td>
2468      * </tr>
2469      * <tr>
2470      *   <td>(all)</td>
2471      *   <th scope="row" style="font-weight:normal; text-align:left">French Fries</th>
2472      *   <td>french fries</td>
2473      *   <td>lowercased all chars in String</td>
2474      * </tr>
2475      * <tr>
2476      *   <td>(all)</td>
2477      *   <th scope="row" style="font-weight:normal; text-align:left">
2478      *       &Iota;&Chi;&Theta;&Upsilon;&Sigma;</th>
2479      *   <td>&iota;&chi;&theta;&upsilon;&sigma;</td>
2480      *   <td>lowercased all chars in String</td>
2481      * </tr>
2482      * </tbody>
2483      * </table>
2484      *
2485      * @param locale use the case transformation rules for this locale
2486      * @return the {@code String}, converted to lowercase.
2487      * @see     java.lang.String#toLowerCase()
2488      * @see     java.lang.String#toUpperCase()
2489      * @see     java.lang.String#toUpperCase(Locale)
2490      * @since   1.1
2491      */
2492     public String toLowerCase(Locale locale) {
2493         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2494                           : StringUTF16.toLowerCase(this, value, locale);
2495     }
2496 
2497     /**
2498      * Converts all of the characters in this {@code String} to lower
2499      * case using the rules of the default locale. This is equivalent to calling
2500      * {@code toLowerCase(Locale.getDefault())}.
2501      * <p>
2502      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2503      * results if used for strings that are intended to be interpreted locale
2504      * independently.
2505      * Examples are programming language identifiers, protocol keys, and HTML
2506      * tags.
2507      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2508      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2509      * LATIN SMALL LETTER DOTLESS I character.
2510      * To obtain correct results for locale insensitive strings, use
2511      * {@code toLowerCase(Locale.ROOT)}.
2512      *
2513      * @return  the {@code String}, converted to lowercase.
2514      * @see     java.lang.String#toLowerCase(Locale)
2515      */
2516     public String toLowerCase() {
2517         return toLowerCase(Locale.getDefault());
2518     }
2519 
2520     /**
2521      * Converts all of the characters in this {@code String} to upper
2522      * case using the rules of the given {@code Locale}. Case mapping is based
2523      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2524      * class. Since case mappings are not always 1:1 char mappings, the resulting
2525      * {@code String} may be a different length than the original {@code String}.
2526      * <p>
2527      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2528      *
2529      * <table class="plain">
2530      * <caption style="display:none">Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.</caption>
2531      * <thead>
2532      * <tr>
2533      *   <th scope="col">Language Code of Locale</th>
2534      *   <th scope="col">Lower Case</th>
2535      *   <th scope="col">Upper Case</th>
2536      *   <th scope="col">Description</th>
2537      * </tr>
2538      * </thead>
2539      * <tbody>
2540      * <tr>
2541      *   <td>tr (Turkish)</td>
2542      *   <th scope="row" style="font-weight:normal; text-align:left">\u0069</th>
2543      *   <td>\u0130</td>
2544      *   <td>small letter i -&gt; capital letter I with dot above</td>
2545      * </tr>
2546      * <tr>
2547      *   <td>tr (Turkish)</td>
2548      *   <th scope="row" style="font-weight:normal; text-align:left">\u0131</th>
2549      *   <td>\u0049</td>
2550      *   <td>small letter dotless i -&gt; capital letter I</td>
2551      * </tr>
2552      * <tr>
2553      *   <td>(all)</td>
2554      *   <th scope="row" style="font-weight:normal; text-align:left">\u00df</th>
2555      *   <td>\u0053 \u0053</td>
2556      *   <td>small letter sharp s -&gt; two letters: SS</td>
2557      * </tr>
2558      * <tr>
2559      *   <td>(all)</td>
2560      *   <th scope="row" style="font-weight:normal; text-align:left">Fahrvergn&uuml;gen</th>
2561      *   <td>FAHRVERGN&Uuml;GEN</td>
2562      *   <td></td>
2563      * </tr>
2564      * </tbody>
2565      * </table>
2566      * @param locale use the case transformation rules for this locale
2567      * @return the {@code String}, converted to uppercase.
2568      * @see     java.lang.String#toUpperCase()
2569      * @see     java.lang.String#toLowerCase()
2570      * @see     java.lang.String#toLowerCase(Locale)
2571      * @since   1.1
2572      */
2573     public String toUpperCase(Locale locale) {
2574         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2575                           : StringUTF16.toUpperCase(this, value, locale);
2576     }
2577 
2578     /**
2579      * Converts all of the characters in this {@code String} to upper
2580      * case using the rules of the default locale. This method is equivalent to
2581      * {@code toUpperCase(Locale.getDefault())}.
2582      * <p>
2583      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2584      * results if used for strings that are intended to be interpreted locale
2585      * independently.
2586      * Examples are programming language identifiers, protocol keys, and HTML
2587      * tags.
2588      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2589      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2590      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2591      * To obtain correct results for locale insensitive strings, use
2592      * {@code toUpperCase(Locale.ROOT)}.
2593      *
2594      * @return  the {@code String}, converted to uppercase.
2595      * @see     java.lang.String#toUpperCase(Locale)
2596      */
2597     public String toUpperCase() {
2598         return toUpperCase(Locale.getDefault());
2599     }
2600 
2601     /**
2602      * Returns a string whose value is this string, with any leading and trailing
2603      * whitespace removed.
2604      * <p>
2605      * If this {@code String} object represents an empty character
2606      * sequence, or the first and last characters of character sequence
2607      * represented by this {@code String} object both have codes
2608      * greater than {@code '\u005Cu0020'} (the space character), then a
2609      * reference to this {@code String} object is returned.
2610      * <p>
2611      * Otherwise, if there is no character with a code greater than
2612      * {@code '\u005Cu0020'} in the string, then a
2613      * {@code String} object representing an empty string is
2614      * returned.
2615      * <p>
2616      * Otherwise, let <i>k</i> be the index of the first character in the
2617      * string whose code is greater than {@code '\u005Cu0020'}, and let
2618      * <i>m</i> be the index of the last character in the string whose code
2619      * is greater than {@code '\u005Cu0020'}. A {@code String}
2620      * object is returned, representing the substring of this string that
2621      * begins with the character at index <i>k</i> and ends with the
2622      * character at index <i>m</i>-that is, the result of
2623      * {@code this.substring(k, m + 1)}.
2624      * <p>
2625      * This method may be used to trim whitespace (as defined above) from
2626      * the beginning and end of a string.
2627      *
2628      * @return  A string whose value is this string, with any leading and trailing white
2629      *          space removed, or this string if it has no leading or
2630      *          trailing white space.
2631      */
2632     public String trim() {
2633         String ret = isLatin1() ? StringLatin1.trim(value)
2634                                 : StringUTF16.trim(value);
2635         return ret == null ? this : ret;
2636     }
2637 
2638     /**
2639      * This object (which is already a string!) is itself returned.
2640      *
2641      * @return  the string itself.
2642      */
2643     public String toString() {
2644         return this;
2645     }
2646 
2647     /**
2648      * Returns a stream of {@code int} zero-extending the {@code char} values
2649      * from this sequence.  Any char which maps to a <a
2650      * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
2651      * point</a> is passed through uninterpreted.
2652      *
2653      * @return an IntStream of char values from this sequence
2654      * @since 9
2655      */
2656     @Override
2657     public IntStream chars() {
2658         return StreamSupport.intStream(
2659             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2660                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
2661             false);
2662     }
2663 
2664 
2665     /**
2666      * Returns a stream of code point values from this sequence.  Any surrogate
2667      * pairs encountered in the sequence are combined as if by {@linkplain
2668      * Character#toCodePoint Character.toCodePoint} and the result is passed
2669      * to the stream. Any other code units, including ordinary BMP characters,
2670      * unpaired surrogates, and undefined code units, are zero-extended to
2671      * {@code int} values which are then passed to the stream.
2672      *
2673      * @return an IntStream of Unicode code points from this sequence
2674      * @since 9
2675      */
2676     @Override
2677     public IntStream codePoints() {
2678         return StreamSupport.intStream(
2679             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2680                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
2681             false);
2682     }
2683 
2684     /**
2685      * Converts this string to a new character array.
2686      *
2687      * @return  a newly allocated character array whose length is the length
2688      *          of this string and whose contents are initialized to contain
2689      *          the character sequence represented by this string.
2690      */
2691     public char[] toCharArray() {
2692         return isLatin1() ? StringLatin1.toChars(value)
2693                           : StringUTF16.toChars(value);
2694     }
2695 
2696     /**
2697      * Returns a formatted string using the specified format string and
2698      * arguments.
2699      *
2700      * <p> The locale always used is the one returned by {@link
2701      * java.util.Locale#getDefault(java.util.Locale.Category)
2702      * Locale.getDefault(Locale.Category)} with
2703      * {@link java.util.Locale.Category#FORMAT FORMAT} category specified.
2704      *
2705      * @param  format
2706      *         A <a href="../util/Formatter.html#syntax">format string</a>
2707      *
2708      * @param  args
2709      *         Arguments referenced by the format specifiers in the format
2710      *         string.  If there are more arguments than format specifiers, the
2711      *         extra arguments are ignored.  The number of arguments is
2712      *         variable and may be zero.  The maximum number of arguments is
2713      *         limited by the maximum dimension of a Java array as defined by
2714      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2715      *         The behaviour on a
2716      *         {@code null} argument depends on the <a
2717      *         href="../util/Formatter.html#syntax">conversion</a>.
2718      *
2719      * @throws  java.util.IllegalFormatException
2720      *          If a format string contains an illegal syntax, a format
2721      *          specifier that is incompatible with the given arguments,
2722      *          insufficient arguments given the format string, or other
2723      *          illegal conditions.  For specification of all possible
2724      *          formatting errors, see the <a
2725      *          href="../util/Formatter.html#detail">Details</a> section of the
2726      *          formatter class specification.
2727      *
2728      * @return  A formatted string
2729      *
2730      * @see  java.util.Formatter
2731      * @since  1.5
2732      */
2733     public static String format(String format, Object... args) {
2734         return new Formatter().format(format, args).toString();
2735     }
2736 
2737     /**
2738      * Returns a formatted string using the specified locale, format string,
2739      * and arguments.
2740      *
2741      * @param  l
2742      *         The {@linkplain java.util.Locale locale} to apply during
2743      *         formatting.  If {@code l} is {@code null} then no localization
2744      *         is applied.
2745      *
2746      * @param  format
2747      *         A <a href="../util/Formatter.html#syntax">format string</a>
2748      *
2749      * @param  args
2750      *         Arguments referenced by the format specifiers in the format
2751      *         string.  If there are more arguments than format specifiers, the
2752      *         extra arguments are ignored.  The number of arguments is
2753      *         variable and may be zero.  The maximum number of arguments is
2754      *         limited by the maximum dimension of a Java array as defined by
2755      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2756      *         The behaviour on a
2757      *         {@code null} argument depends on the
2758      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2759      *
2760      * @throws  java.util.IllegalFormatException
2761      *          If a format string contains an illegal syntax, a format
2762      *          specifier that is incompatible with the given arguments,
2763      *          insufficient arguments given the format string, or other
2764      *          illegal conditions.  For specification of all possible
2765      *          formatting errors, see the <a
2766      *          href="../util/Formatter.html#detail">Details</a> section of the
2767      *          formatter class specification
2768      *
2769      * @return  A formatted string
2770      *
2771      * @see  java.util.Formatter
2772      * @since  1.5
2773      */
2774     public static String format(Locale l, String format, Object... args) {
2775         return new Formatter(l).format(format, args).toString();
2776     }
2777 
2778     /**
2779      * Returns the string representation of the {@code Object} argument.
2780      *
2781      * @param   obj   an {@code Object}.
2782      * @return  if the argument is {@code null}, then a string equal to
2783      *          {@code "null"}; otherwise, the value of
2784      *          {@code obj.toString()} is returned.
2785      * @see     java.lang.Object#toString()
2786      */
2787     public static String valueOf(Object obj) {
2788         return (obj == null) ? "null" : obj.toString();
2789     }
2790 
2791     /**
2792      * Returns the string representation of the {@code char} array
2793      * argument. The contents of the character array are copied; subsequent
2794      * modification of the character array does not affect the returned
2795      * string.
2796      *
2797      * @param   data     the character array.
2798      * @return  a {@code String} that contains the characters of the
2799      *          character array.
2800      */
2801     public static String valueOf(char data[]) {
2802         return new String(data);
2803     }
2804 
2805     /**
2806      * Returns the string representation of a specific subarray of the
2807      * {@code char} array argument.
2808      * <p>
2809      * The {@code offset} argument is the index of the first
2810      * character of the subarray. The {@code count} argument
2811      * specifies the length of the subarray. The contents of the subarray
2812      * are copied; subsequent modification of the character array does not
2813      * affect the returned string.
2814      *
2815      * @param   data     the character array.
2816      * @param   offset   initial offset of the subarray.
2817      * @param   count    length of the subarray.
2818      * @return  a {@code String} that contains the characters of the
2819      *          specified subarray of the character array.
2820      * @exception IndexOutOfBoundsException if {@code offset} is
2821      *          negative, or {@code count} is negative, or
2822      *          {@code offset+count} is larger than
2823      *          {@code data.length}.
2824      */
2825     public static String valueOf(char data[], int offset, int count) {
2826         return new String(data, offset, count);
2827     }
2828 
2829     /**
2830      * Equivalent to {@link #valueOf(char[], int, int)}.
2831      *
2832      * @param   data     the character array.
2833      * @param   offset   initial offset of the subarray.
2834      * @param   count    length of the subarray.
2835      * @return  a {@code String} that contains the characters of the
2836      *          specified subarray of the character array.
2837      * @exception IndexOutOfBoundsException if {@code offset} is
2838      *          negative, or {@code count} is negative, or
2839      *          {@code offset+count} is larger than
2840      *          {@code data.length}.
2841      */
2842     public static String copyValueOf(char data[], int offset, int count) {
2843         return new String(data, offset, count);
2844     }
2845 
2846     /**
2847      * Equivalent to {@link #valueOf(char[])}.
2848      *
2849      * @param   data   the character array.
2850      * @return  a {@code String} that contains the characters of the
2851      *          character array.
2852      */
2853     public static String copyValueOf(char data[]) {
2854         return new String(data);
2855     }
2856 
2857     /**
2858      * Returns the string representation of the {@code boolean} argument.
2859      *
2860      * @param   b   a {@code boolean}.
2861      * @return  if the argument is {@code true}, a string equal to
2862      *          {@code "true"} is returned; otherwise, a string equal to
2863      *          {@code "false"} is returned.
2864      */
2865     public static String valueOf(boolean b) {
2866         return b ? "true" : "false";
2867     }
2868 
2869     /**
2870      * Returns the string representation of the {@code char}
2871      * argument.
2872      *
2873      * @param   c   a {@code char}.
2874      * @return  a string of length {@code 1} containing
2875      *          as its single character the argument {@code c}.
2876      */
2877     public static String valueOf(char c) {
2878         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
2879             return new String(StringLatin1.toBytes(c), LATIN1);
2880         }
2881         return new String(StringUTF16.toBytes(c), UTF16);
2882     }
2883 
2884     /**
2885      * Returns the string representation of the {@code int} argument.
2886      * <p>
2887      * The representation is exactly the one returned by the
2888      * {@code Integer.toString} method of one argument.
2889      *
2890      * @param   i   an {@code int}.
2891      * @return  a string representation of the {@code int} argument.
2892      * @see     java.lang.Integer#toString(int, int)
2893      */
2894     public static String valueOf(int i) {
2895         return Integer.toString(i);
2896     }
2897 
2898     /**
2899      * Returns the string representation of the {@code long} argument.
2900      * <p>
2901      * The representation is exactly the one returned by the
2902      * {@code Long.toString} method of one argument.
2903      *
2904      * @param   l   a {@code long}.
2905      * @return  a string representation of the {@code long} argument.
2906      * @see     java.lang.Long#toString(long)
2907      */
2908     public static String valueOf(long l) {
2909         return Long.toString(l);
2910     }
2911 
2912     /**
2913      * Returns the string representation of the {@code float} argument.
2914      * <p>
2915      * The representation is exactly the one returned by the
2916      * {@code Float.toString} method of one argument.
2917      *
2918      * @param   f   a {@code float}.
2919      * @return  a string representation of the {@code float} argument.
2920      * @see     java.lang.Float#toString(float)
2921      */
2922     public static String valueOf(float f) {
2923         return Float.toString(f);
2924     }
2925 
2926     /**
2927      * Returns the string representation of the {@code double} argument.
2928      * <p>
2929      * The representation is exactly the one returned by the
2930      * {@code Double.toString} method of one argument.
2931      *
2932      * @param   d   a {@code double}.
2933      * @return  a  string representation of the {@code double} argument.
2934      * @see     java.lang.Double#toString(double)
2935      */
2936     public static String valueOf(double d) {
2937         return Double.toString(d);
2938     }
2939 
2940     /**
2941      * Returns a canonical representation for the string object.
2942      * <p>
2943      * A pool of strings, initially empty, is maintained privately by the
2944      * class {@code String}.
2945      * <p>
2946      * When the intern method is invoked, if the pool already contains a
2947      * string equal to this {@code String} object as determined by
2948      * the {@link #equals(Object)} method, then the string from the pool is
2949      * returned. Otherwise, this {@code String} object is added to the
2950      * pool and a reference to this {@code String} object is returned.
2951      * <p>
2952      * It follows that for any two strings {@code s} and {@code t},
2953      * {@code s.intern() == t.intern()} is {@code true}
2954      * if and only if {@code s.equals(t)} is {@code true}.
2955      * <p>
2956      * All literal strings and string-valued constant expressions are
2957      * interned. String literals are defined in section 3.10.5 of the
2958      * <cite>The Java&trade; Language Specification</cite>.
2959      *
2960      * @return  a string that has the same contents as this string, but is
2961      *          guaranteed to be from a pool of unique strings.
2962      * @jls 3.10.5 String Literals
2963      */
2964     public native String intern();
2965 
2966     /**
2967      * Returns a string whose value is the concatenation of this
2968      * string repeated {@code count} times.
2969      * <p>
2970      * If this string is empty or count is zero then the empty
2971      * string is returned.
2972      *
2973      * @param   count number of times to repeat
2974      *
2975      * @return  A string composed of this string repeated
2976      *          {@code count} times or the empty string if this
2977      *          string is empty or count is zero
2978      *
2979      * @throws  IllegalArgumentException if the {@code count} is
2980      *          negative.
2981      *
2982      * @since 11
2983      */
2984     public String repeat(int count) {
2985         if (count < 0) {
2986             throw new IllegalArgumentException("count is negative: " + count);
2987         }
2988         if (count == 1) {
2989             return this;
2990         }
2991         final int len = value.length;
2992         if (len == 0 || count == 0) {
2993             return "";
2994         }
2995         if (len == 1) {
2996             final byte[] single = new byte[count];
2997             Arrays.fill(single, value[0]);
2998             return new String(single, coder);
2999         }
3000         if (Integer.MAX_VALUE / count < len) {
3001             throw new OutOfMemoryError("Repeating " + len + " bytes String " + count +
3002                     " times will produce a String exceeding maximum size.");
3003         }
3004         final int limit = len * count;
3005         final byte[] multiple = new byte[limit];
3006         System.arraycopy(value, 0, multiple, 0, len);
3007         int copied = len;
3008         for (; copied < limit - copied; copied <<= 1) {
3009             System.arraycopy(multiple, 0, multiple, copied, copied);
3010         }
3011         System.arraycopy(multiple, 0, multiple, copied, limit - copied);
3012         return new String(multiple, coder);
3013     }
3014 
3015     ////////////////////////////////////////////////////////////////
3016 
3017     /**
3018      * Copy character bytes from this string into dst starting at dstBegin.
3019      * This method doesn't perform any range checking.
3020      *
3021      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
3022      * coders are different, and dst is big enough (range check)
3023      *
3024      * @param dstBegin  the char index, not offset of byte[]
3025      * @param coder     the coder of dst[]
3026      */
3027     void getBytes(byte dst[], int dstBegin, byte coder) {
3028         if (coder() == coder) {
3029             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
3030         } else {    // this.coder == LATIN && coder == UTF16
3031             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
3032         }
3033     }
3034 
3035     /*
3036      * Package private constructor. Trailing Void argument is there for
3037      * disambiguating it against other (public) constructors.
3038      *
3039      * Stores the char[] value into a byte[] that each byte represents
3040      * the8 low-order bits of the corresponding character, if the char[]
3041      * contains only latin1 character. Or a byte[] that stores all
3042      * characters in their byte sequences defined by the {@code StringUTF16}.
3043      */
3044     String(char[] value, int off, int len, Void sig) {
3045         if (len == 0) {
3046             this.value = "".value;
3047             this.coder = "".coder;
3048             return;
3049         }
3050         if (COMPACT_STRINGS) {
3051             byte[] val = StringUTF16.compress(value, off, len);
3052             if (val != null) {
3053                 this.value = val;
3054                 this.coder = LATIN1;
3055                 return;
3056             }
3057         }
3058         this.coder = UTF16;
3059         this.value = StringUTF16.toBytes(value, off, len);
3060     }
3061 
3062     /*
3063      * Package private constructor. Trailing Void argument is there for
3064      * disambiguating it against other (public) constructors.
3065      */
3066     String(AbstractStringBuilder asb, Void sig) {
3067         byte[] val = asb.getValue();
3068         int length = asb.length();
3069         if (asb.isLatin1()) {
3070             this.coder = LATIN1;
3071             this.value = Arrays.copyOfRange(val, 0, length);
3072         } else {
3073             if (COMPACT_STRINGS) {
3074                 byte[] buf = StringUTF16.compress(val, 0, length);
3075                 if (buf != null) {
3076                     this.coder = LATIN1;
3077                     this.value = buf;
3078                     return;
3079                 }
3080             }
3081             this.coder = UTF16;
3082             this.value = Arrays.copyOfRange(val, 0, length << 1);
3083         }
3084     }
3085 
3086    /*
3087     * Package private constructor which shares value array for speed.
3088     */
3089     String(byte[] value, byte coder) {
3090         this.value = value;
3091         this.coder = coder;
3092     }
3093 
3094     byte coder() {
3095         return COMPACT_STRINGS ? coder : UTF16;
3096     }
3097 
3098     byte[] value() {
3099         return value;
3100     }
3101 
3102     private boolean isLatin1() {
3103         return COMPACT_STRINGS && coder == LATIN1;
3104     }
3105 
3106     @Native static final byte LATIN1 = 0;
3107     @Native static final byte UTF16  = 1;
3108 
3109     /*
3110      * StringIndexOutOfBoundsException  if {@code index} is
3111      * negative or greater than or equal to {@code length}.
3112      */
3113     static void checkIndex(int index, int length) {
3114         if (index < 0 || index >= length) {
3115             throw new StringIndexOutOfBoundsException("index " + index +
3116                                                       ",length " + length);
3117         }
3118     }
3119 
3120     /*
3121      * StringIndexOutOfBoundsException  if {@code offset}
3122      * is negative or greater than {@code length}.
3123      */
3124     static void checkOffset(int offset, int length) {
3125         if (offset < 0 || offset > length) {
3126             throw new StringIndexOutOfBoundsException("offset " + offset +
3127                                                       ",length " + length);
3128         }
3129     }
3130 
3131     /*
3132      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3133      * bounds.
3134      *
3135      * @throws  StringIndexOutOfBoundsException
3136      *          If {@code offset} is negative, {@code count} is negative,
3137      *          or {@code offset} is greater than {@code length - count}
3138      */
3139     static void checkBoundsOffCount(int offset, int count, int length) {
3140         if (offset < 0 || count < 0 || offset > length - count) {
3141             throw new StringIndexOutOfBoundsException(
3142                 "offset " + offset + ", count " + count + ", length " + length);
3143         }
3144     }
3145 
3146     /*
3147      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3148      * bounds.
3149      *
3150      * @throws  StringIndexOutOfBoundsException
3151      *          If {@code begin} is negative, {@code begin} is greater than
3152      *          {@code end}, or {@code end} is greater than {@code length}.
3153      */
3154     static void checkBoundsBeginEnd(int begin, int end, int length) {
3155         if (begin < 0 || begin > end || end > length) {
3156             throw new StringIndexOutOfBoundsException(
3157                 "begin " + begin + ", end " + end + ", length " + length);
3158         }
3159     }
3160 }