1 /*
   2  * Copyright (c) 1994, 2015, 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.nio.charset.Charset;
  31 import java.util.ArrayList;
  32 import java.util.Arrays;
  33 import java.util.Comparator;
  34 import java.util.Formatter;
  35 import java.util.Locale;
  36 import java.util.Objects;
  37 import java.util.Spliterator;
  38 import java.util.StringJoiner;
  39 import java.util.function.ToIntFunction;
  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. String concatenation is implemented
  83  * through the {@code StringBuilder}(or {@code StringBuffer})
  84  * class and its {@code append} method.
  85  * String conversions are implemented through the method
  86  * {@code toString}, defined by {@code Object} and
  87  * inherited by all classes in Java. For additional information on
  88  * string concatenation and conversion, see Gosling, Joy, and Steele,
  89  * <i>The Java Language Specification</i>.
  90  *
  91  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  92  * or method in this class will cause a {@link NullPointerException} to be
  93  * thrown.
  94  *
  95  * <p>A {@code String} represents a string in the UTF-16 format
  96  * in which <em>supplementary characters</em> are represented by <em>surrogate
  97  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  98  * Character Representations</a> in the {@code Character} class for
  99  * more information).
 100  * Index values refer to {@code char} code units, so a supplementary
 101  * character uses two positions in a {@code String}.
 102  * <p>The {@code String} class provides methods for dealing with
 103  * Unicode code points (i.e., characters), in addition to those for
 104  * dealing with Unicode code units (i.e., {@code char} values).
 105  *
 106  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 107  * into account.  The {@link java.text.Collator} class provides methods for
 108  * finer-grain, locale-sensitive String comparison.
 109  *
 110  * @author  Lee Boynton
 111  * @author  Arthur van Hoff
 112  * @author  Martin Buchholz
 113  * @author  Ulf Zibis
 114  * @see     java.lang.Object#toString()
 115  * @see     java.lang.StringBuffer
 116  * @see     java.lang.StringBuilder
 117  * @see     java.nio.charset.Charset
 118  * @since   1.0
 119  */
 120 
 121 public final class String
 122     implements java.io.Serializable, Comparable<String>, CharSequence {
 123 
 124     /**
 125      * The value is used for character storage.
 126      *
 127      * @implNote This field is trusted by the VM, and is a subject to
 128      * constant folding if String instance is constant. Overwriting this
 129      * field after construction will cause problems.
 130      *
 131      * Additionally, it is marked with {@link Stable} to trust the contents
 132      * of the array. No other facility in JDK provides this functionality (yet).
 133      * {@link Stable} is safe here, because value is never null.
 134      */
 135     @Stable
 136     private final byte[] value;
 137 
 138     /**
 139      * The identifier of the encoding used to encode the bytes in
 140      * {@code value}. The supported values in this implementation are
 141      *
 142      * LATIN1
 143      * UTF16
 144      *
 145      * @implNote This field is trusted by the VM, and is a subject to
 146      * constant folding if String instance is constant. Overwriting this
 147      * field after construction will cause problems.
 148      */
 149     private final byte coder;
 150 
 151     /** Cache the hash code for the string */
 152     private int hash; // Default to 0
 153 
 154     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 155     private static final long serialVersionUID = -6849794470754667710L;
 156 
 157     /**
 158      * If String compaction is disabled, the bytes in {@code value} are
 159      * always encoded in UTF16.
 160      *
 161      * For methods with several possible implementation paths, when String
 162      * compaction is disabled, only one code path is taken.
 163      *
 164      * The instance field value is generally opaque to optimizing JIT
 165      * compilers. Therefore, in performance-sensitive place, an explicit
 166      * check of the static boolean {@code COMPACT_STRINGS} is done first
 167      * before checking the {@code coder} field since the static boolean
 168      * {@code COMPACT_STRINGS} would be constant folded away by an
 169      * optimizing JIT compiler. The idioms for these cases are as follows.
 170      *
 171      * For code such as:
 172      *
 173      *    if (coder == LATIN1) { ... }
 174      *
 175      * can be written more optimally as
 176      *
 177      *    if (coder() == LATIN1) { ... }
 178      *
 179      * or:
 180      *
 181      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 182      *
 183      * An optimizing JIT compiler can fold the above conditional as:
 184      *
 185      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 186      *    COMPACT_STRINGS == false => if (false)           { ... }
 187      *
 188      * @implNote
 189      * The actual value for this field is injected by JVM. The static
 190      * initialization block is used to set the value here to communicate
 191      * that this static final field is not statically foldable, and to
 192      * avoid any possible circular dependency during vm initialization.
 193      */
 194     static final boolean COMPACT_STRINGS;
 195 
 196     static {
 197         COMPACT_STRINGS = true;
 198     }
 199 
 200     /**
 201      * Class String is special cased within the Serialization Stream Protocol.
 202      *
 203      * A String instance is written into an ObjectOutputStream according to
 204      * <a href="{@docRoot}/../platform/serialization/spec/output.html">
 205      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 206      */
 207     private static final ObjectStreamField[] serialPersistentFields =
 208         new ObjectStreamField[0];
 209 
 210     /**
 211      * Initializes a newly created {@code String} object so that it represents
 212      * an empty character sequence.  Note that use of this constructor is
 213      * unnecessary since Strings are immutable.
 214      */
 215     public String() {
 216         this.value = "".value;
 217         this.coder = "".coder;
 218     }
 219 
 220     /**
 221      * Initializes a newly created {@code String} object so that it represents
 222      * the same sequence of characters as the argument; in other words, the
 223      * newly created string is a copy of the argument string. Unless an
 224      * explicit copy of {@code original} is needed, use of this constructor is
 225      * unnecessary since Strings are immutable.
 226      *
 227      * @param  original
 228      *         A {@code String}
 229      */
 230     @HotSpotIntrinsicCandidate
 231     public String(String original) {
 232         this.value = original.value;
 233         this.coder = original.coder;
 234         this.hash = original.hash;
 235     }
 236 
 237     /**
 238      * Allocates a new {@code String} so that it represents the sequence of
 239      * characters currently contained in the character array argument. The
 240      * contents of the character array are copied; subsequent modification of
 241      * the character array does not affect the newly created string.
 242      *
 243      * @param  value
 244      *         The initial value of the string
 245      */
 246     public String(char value[]) {
 247         this(value, 0, value.length, null);
 248     }
 249 
 250     /**
 251      * Allocates a new {@code String} that contains characters from a subarray
 252      * of the character array argument. The {@code offset} argument is the
 253      * index of the first character of the subarray and the {@code count}
 254      * argument specifies the length of the subarray. The contents of the
 255      * subarray are copied; subsequent modification of the character array does
 256      * not affect the newly created string.
 257      *
 258      * @param  value
 259      *         Array that is the source of characters
 260      *
 261      * @param  offset
 262      *         The initial offset
 263      *
 264      * @param  count
 265      *         The length
 266      *
 267      * @throws  IndexOutOfBoundsException
 268      *          If {@code offset} is negative, {@code count} is negative, or
 269      *          {@code offset} is greater than {@code value.length - count}
 270      */
 271     public String(char value[], int offset, int count) {
 272         this(value, offset, count, rangeCheck(value, offset, count));
 273     }
 274 
 275     private static Void rangeCheck(char[] value, int offset, int count) {
 276         checkBoundsOffCount(offset, count, value.length);
 277         return null;
 278     }
 279 
 280     /**
 281      * Allocates a new {@code String} that contains characters from a subarray
 282      * of the <a href="Character.html#unicode">Unicode code point</a> array
 283      * argument.  The {@code offset} argument is the index of the first code
 284      * point of the subarray and the {@code count} argument specifies the
 285      * length of the subarray.  The contents of the subarray are converted to
 286      * {@code char}s; subsequent modification of the {@code int} array does not
 287      * affect the newly created string.
 288      *
 289      * @param  codePoints
 290      *         Array that is the source of Unicode code points
 291      *
 292      * @param  offset
 293      *         The initial offset
 294      *
 295      * @param  count
 296      *         The length
 297      *
 298      * @throws  IllegalArgumentException
 299      *          If any invalid Unicode code point is found in {@code
 300      *          codePoints}
 301      *
 302      * @throws  IndexOutOfBoundsException
 303      *          If {@code offset} is negative, {@code count} is negative, or
 304      *          {@code offset} is greater than {@code codePoints.length - count}
 305      *
 306      * @since  1.5
 307      */
 308     public String(int[] codePoints, int offset, int count) {
 309         checkBoundsOffCount(offset, count, codePoints.length);
 310         if (count == 0) {
 311             this.value = "".value;
 312             this.coder = "".coder;
 313             return;
 314         }
 315         if (COMPACT_STRINGS) {
 316             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 317             if (val != null) {
 318                 this.coder = LATIN1;
 319                 this.value = val;
 320                 return;
 321             }
 322         }
 323         this.coder = UTF16;
 324         this.value = StringUTF16.toBytes(codePoints, offset, count);
 325     }
 326 
 327     /**
 328      * Allocates a new {@code String} constructed from a subarray of an array
 329      * of 8-bit integer values.
 330      *
 331      * <p> The {@code offset} argument is the index of the first byte of the
 332      * subarray, and the {@code count} argument specifies the length of the
 333      * subarray.
 334      *
 335      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 336      * specified in the method above.
 337      *
 338      * @deprecated This method does not properly convert bytes into characters.
 339      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 340      * {@code String} constructors that take a {@link
 341      * java.nio.charset.Charset}, charset name, or that use the platform's
 342      * default charset.
 343      *
 344      * @param  ascii
 345      *         The bytes to be converted to characters
 346      *
 347      * @param  hibyte
 348      *         The top 8 bits of each 16-bit Unicode code unit
 349      *
 350      * @param  offset
 351      *         The initial offset
 352      * @param  count
 353      *         The length
 354      *
 355      * @throws  IndexOutOfBoundsException
 356      *          If {@code offset} is negative, {@code count} is negative, or
 357      *          {@code offset} is greater than {@code ascii.length - count}
 358      *
 359      * @see  #String(byte[], int)
 360      * @see  #String(byte[], int, int, java.lang.String)
 361      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 362      * @see  #String(byte[], int, int)
 363      * @see  #String(byte[], java.lang.String)
 364      * @see  #String(byte[], java.nio.charset.Charset)
 365      * @see  #String(byte[])
 366      */
 367     @Deprecated
 368     public String(byte ascii[], int hibyte, int offset, int count) {
 369         checkBoundsOffCount(offset, count, ascii.length);
 370         if (count == 0) {
 371             this.value = "".value;
 372             this.coder = "".coder;
 373             return;
 374         }
 375         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 376             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 377             this.coder = LATIN1;
 378         } else {
 379             hibyte <<= 8;
 380             byte[] val = StringUTF16.newBytesFor(count);
 381             for (int i = 0; i < count; i++) {
 382                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 383             }
 384             this.value = val;
 385             this.coder = UTF16;
 386         }
 387     }
 388 
 389     /**
 390      * Allocates a new {@code String} containing characters constructed from
 391      * an array of 8-bit integer values. Each character <i>c</i>in the
 392      * resulting string is constructed from the corresponding component
 393      * <i>b</i> in the byte array such that:
 394      *
 395      * <blockquote><pre>
 396      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 397      *                         | (<b><i>b</i></b> &amp; 0xff))
 398      * </pre></blockquote>
 399      *
 400      * @deprecated  This method does not properly convert bytes into
 401      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 402      * {@code String} constructors that take a {@link
 403      * java.nio.charset.Charset}, charset name, or that use the platform's
 404      * default charset.
 405      *
 406      * @param  ascii
 407      *         The bytes to be converted to characters
 408      *
 409      * @param  hibyte
 410      *         The top 8 bits of each 16-bit Unicode code unit
 411      *
 412      * @see  #String(byte[], int, int, java.lang.String)
 413      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 414      * @see  #String(byte[], int, int)
 415      * @see  #String(byte[], java.lang.String)
 416      * @see  #String(byte[], java.nio.charset.Charset)
 417      * @see  #String(byte[])
 418      */
 419     @Deprecated
 420     public String(byte ascii[], int hibyte) {
 421         this(ascii, hibyte, 0, ascii.length);
 422     }
 423 
 424     /**
 425      * Constructs a new {@code String} by decoding the specified subarray of
 426      * bytes using the specified charset.  The length of the new {@code String}
 427      * is a function of the charset, and hence may not be equal to the length
 428      * of the subarray.
 429      *
 430      * <p> The behavior of this constructor when the given bytes are not valid
 431      * in the given charset is unspecified.  The {@link
 432      * java.nio.charset.CharsetDecoder} class should be used when more control
 433      * over the decoding process is required.
 434      *
 435      * @param  bytes
 436      *         The bytes to be decoded into characters
 437      *
 438      * @param  offset
 439      *         The index of the first byte to decode
 440      *
 441      * @param  length
 442      *         The number of bytes to decode
 443 
 444      * @param  charsetName
 445      *         The name of a supported {@linkplain java.nio.charset.Charset
 446      *         charset}
 447      *
 448      * @throws  UnsupportedEncodingException
 449      *          If the named charset is not supported
 450      *
 451      * @throws  IndexOutOfBoundsException
 452      *          If {@code offset} is negative, {@code length} is negative, or
 453      *          {@code offset} is greater than {@code bytes.length - length}
 454      *
 455      * @since  1.1
 456      */
 457     public String(byte bytes[], int offset, int length, String charsetName)
 458             throws UnsupportedEncodingException {
 459         if (charsetName == null)
 460             throw new NullPointerException("charsetName");
 461         checkBoundsOffCount(offset, length, bytes.length);
 462         StringCoding.Result ret =
 463             StringCoding.decode(charsetName, bytes, offset, length);
 464         this.value = ret.value;
 465         this.coder = ret.coder;
 466     }
 467 
 468     /**
 469      * Constructs a new {@code String} by decoding the specified subarray of
 470      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 471      * The length of the new {@code String} is a function of the charset, and
 472      * hence may not be equal to the length of the subarray.
 473      *
 474      * <p> This method always replaces malformed-input and unmappable-character
 475      * sequences with this charset's default replacement string.  The {@link
 476      * java.nio.charset.CharsetDecoder} class should be used when more control
 477      * over the decoding process is required.
 478      *
 479      * @param  bytes
 480      *         The bytes to be decoded into characters
 481      *
 482      * @param  offset
 483      *         The index of the first byte to decode
 484      *
 485      * @param  length
 486      *         The number of bytes to decode
 487      *
 488      * @param  charset
 489      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 490      *         decode the {@code bytes}
 491      *
 492      * @throws  IndexOutOfBoundsException
 493      *          If {@code offset} is negative, {@code length} is negative, or
 494      *          {@code offset} is greater than {@code bytes.length - length}
 495      *
 496      * @since  1.6
 497      */
 498     public String(byte bytes[], int offset, int length, Charset charset) {
 499         if (charset == null)
 500             throw new NullPointerException("charset");
 501         checkBoundsOffCount(offset, length, bytes.length);
 502         StringCoding.Result ret =
 503             StringCoding.decode(charset, bytes, offset, length);
 504         this.value = ret.value;
 505         this.coder = ret.coder;
 506     }
 507 
 508     /**
 509      * Constructs a new {@code String} by decoding the specified array of bytes
 510      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 511      * length of the new {@code String} is a function of the charset, and hence
 512      * may not be equal to the length of the byte array.
 513      *
 514      * <p> The behavior of this constructor when the given bytes are not valid
 515      * in the given charset is unspecified.  The {@link
 516      * java.nio.charset.CharsetDecoder} class should be used when more control
 517      * over the decoding process is required.
 518      *
 519      * @param  bytes
 520      *         The bytes to be decoded into characters
 521      *
 522      * @param  charsetName
 523      *         The name of a supported {@linkplain java.nio.charset.Charset
 524      *         charset}
 525      *
 526      * @throws  UnsupportedEncodingException
 527      *          If the named charset is not supported
 528      *
 529      * @since  1.1
 530      */
 531     public String(byte bytes[], String charsetName)
 532             throws UnsupportedEncodingException {
 533         this(bytes, 0, bytes.length, charsetName);
 534     }
 535 
 536     /**
 537      * Constructs a new {@code String} by decoding the specified array of
 538      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 539      * The length of the new {@code String} is a function of the charset, and
 540      * hence may not be equal to the length of the byte array.
 541      *
 542      * <p> This method always replaces malformed-input and unmappable-character
 543      * sequences with this charset's default replacement string.  The {@link
 544      * java.nio.charset.CharsetDecoder} class should be used when more control
 545      * over the decoding process is required.
 546      *
 547      * @param  bytes
 548      *         The bytes to be decoded into characters
 549      *
 550      * @param  charset
 551      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 552      *         decode the {@code bytes}
 553      *
 554      * @since  1.6
 555      */
 556     public String(byte bytes[], Charset charset) {
 557         this(bytes, 0, bytes.length, charset);
 558     }
 559 
 560     /**
 561      * Constructs a new {@code String} by decoding the specified subarray of
 562      * bytes using the platform's default charset.  The length of the new
 563      * {@code String} is a function of the charset, and hence may not be equal
 564      * to the length of the subarray.
 565      *
 566      * <p> The behavior of this constructor when the given bytes are not valid
 567      * in the default charset is unspecified.  The {@link
 568      * java.nio.charset.CharsetDecoder} class should be used when more control
 569      * over the decoding process is required.
 570      *
 571      * @param  bytes
 572      *         The bytes to be decoded into characters
 573      *
 574      * @param  offset
 575      *         The index of the first byte to decode
 576      *
 577      * @param  length
 578      *         The number of bytes to decode
 579      *
 580      * @throws  IndexOutOfBoundsException
 581      *          If {@code offset} is negative, {@code length} is negative, or
 582      *          {@code offset} is greater than {@code bytes.length - length}
 583      *
 584      * @since  1.1
 585      */
 586     public String(byte bytes[], int offset, int length) {
 587         checkBoundsOffCount(offset, length, bytes.length);
 588         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 589         this.value = ret.value;
 590         this.coder = ret.coder;
 591     }
 592 
 593     /**
 594      * Constructs a new {@code String} by decoding the specified array of bytes
 595      * using the platform's default charset.  The length of the new {@code
 596      * String} is a function of the charset, and hence may not be equal to the
 597      * length of the byte array.
 598      *
 599      * <p> The behavior of this constructor when the given bytes are not valid
 600      * in the default charset is unspecified.  The {@link
 601      * java.nio.charset.CharsetDecoder} class should be used when more control
 602      * over the decoding process is required.
 603      *
 604      * @param  bytes
 605      *         The bytes to be decoded into characters
 606      *
 607      * @since  1.1
 608      */
 609     public String(byte[] bytes) {
 610         this(bytes, 0, bytes.length);
 611     }
 612 
 613     /**
 614      * Allocates a new string that contains the sequence of characters
 615      * currently contained in the string buffer argument. The contents of the
 616      * string buffer are copied; subsequent modification of the string buffer
 617      * does not affect the newly created string.
 618      *
 619      * @param  buffer
 620      *         A {@code StringBuffer}
 621      */
 622     public String(StringBuffer buffer) {
 623         this(buffer.toString());
 624     }
 625 
 626     /**
 627      * Allocates a new string that contains the sequence of characters
 628      * currently contained in the string builder argument. The contents of the
 629      * string builder are copied; subsequent modification of the string builder
 630      * does not affect the newly created string.
 631      *
 632      * <p> This constructor is provided to ease migration to {@code
 633      * StringBuilder}. Obtaining a string from a string builder via the {@code
 634      * toString} method is likely to run faster and is generally preferred.
 635      *
 636      * @param   builder
 637      *          A {@code StringBuilder}
 638      *
 639      * @since  1.5
 640      */
 641     public String(StringBuilder builder) {
 642         this(builder, null);
 643     }
 644 
 645    /*
 646     * Package private constructor which shares value array for speed.
 647     * this constructor is always expected to be called with share==true.
 648     * a separate constructor is needed because we already have a public
 649     * String(char[]) constructor that makes a copy of the given char[].
 650     */
 651     // TBD: this is kept for package internal use (Thread/System),
 652     // should be removed if they all have a byte[] version
 653     String(char[] val, boolean share) {
 654         // assert share : "unshared not supported";
 655         this(val, 0, val.length, null);
 656     }
 657 
 658     /**
 659      * Returns the length of this string.
 660      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 661      * code units</a> in the string.
 662      *
 663      * @return  the length of the sequence of characters represented by this
 664      *          object.
 665      */
 666     public int length() {
 667         return value.length >> coder();
 668     }
 669 
 670     /**
 671      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 672      *
 673      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 674      * {@code false}
 675      *
 676      * @since 1.6
 677      */
 678     public boolean isEmpty() {
 679         return value.length == 0;
 680     }
 681 
 682     /**
 683      * Returns the {@code char} value at the
 684      * specified index. An index ranges from {@code 0} to
 685      * {@code length() - 1}. The first {@code char} value of the sequence
 686      * is at index {@code 0}, the next at index {@code 1},
 687      * and so on, as for array indexing.
 688      *
 689      * <p>If the {@code char} value specified by the index is a
 690      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 691      * value is returned.
 692      *
 693      * @param      index   the index of the {@code char} value.
 694      * @return     the {@code char} value at the specified index of this string.
 695      *             The first {@code char} value is at index {@code 0}.
 696      * @exception  IndexOutOfBoundsException  if the {@code index}
 697      *             argument is negative or not less than the length of this
 698      *             string.
 699      */
 700     public char charAt(int index) {
 701         if (isLatin1()) {
 702             return StringLatin1.charAt(value, index);
 703         } else {
 704             return StringUTF16.charAt(value, index);
 705         }
 706     }
 707 
 708     /**
 709      * Returns the character (Unicode code point) at the specified
 710      * index. The index refers to {@code char} values
 711      * (Unicode code units) and ranges from {@code 0} to
 712      * {@link #length()}{@code  - 1}.
 713      *
 714      * <p> If the {@code char} value specified at the given index
 715      * is in the high-surrogate range, the following index is less
 716      * than the length of this {@code String}, and the
 717      * {@code char} value at the following index is in the
 718      * low-surrogate range, then the supplementary code point
 719      * corresponding to this surrogate pair is returned. Otherwise,
 720      * the {@code char} value at the given index is returned.
 721      *
 722      * @param      index the index to the {@code char} values
 723      * @return     the code point value of the character at the
 724      *             {@code index}
 725      * @exception  IndexOutOfBoundsException  if the {@code index}
 726      *             argument is negative or not less than the length of this
 727      *             string.
 728      * @since      1.5
 729      */
 730     public int codePointAt(int index) {
 731         if (isLatin1()) {
 732             checkIndex(index, value.length);
 733             return value[index] & 0xff;
 734         }
 735         int length = value.length >> 1;
 736         checkIndex(index, length);
 737         return StringUTF16.codePointAt(value, index, length);
 738     }
 739 
 740     /**
 741      * Returns the character (Unicode code point) before the specified
 742      * index. The index refers to {@code char} values
 743      * (Unicode code units) and ranges from {@code 1} to {@link
 744      * CharSequence#length() length}.
 745      *
 746      * <p> If the {@code char} value at {@code (index - 1)}
 747      * is in the low-surrogate range, {@code (index - 2)} is not
 748      * negative, and the {@code char} value at {@code (index -
 749      * 2)} is in the high-surrogate range, then the
 750      * supplementary code point value of the surrogate pair is
 751      * returned. If the {@code char} value at {@code index -
 752      * 1} is an unpaired low-surrogate or a high-surrogate, the
 753      * surrogate value is returned.
 754      *
 755      * @param     index the index following the code point that should be returned
 756      * @return    the Unicode code point value before the given index.
 757      * @exception IndexOutOfBoundsException if the {@code index}
 758      *            argument is less than 1 or greater than the length
 759      *            of this string.
 760      * @since     1.5
 761      */
 762     public int codePointBefore(int index) {
 763         int i = index - 1;
 764         if (i < 0 || i >= length()) {
 765             throw new StringIndexOutOfBoundsException(index);
 766         }
 767         if (isLatin1()) {
 768             return (value[i] & 0xff);
 769         }
 770         return StringUTF16.codePointBefore(value, index);
 771     }
 772 
 773     /**
 774      * Returns the number of Unicode code points in the specified text
 775      * range of this {@code String}. The text range begins at the
 776      * specified {@code beginIndex} and extends to the
 777      * {@code char} at index {@code endIndex - 1}. Thus the
 778      * length (in {@code char}s) of the text range is
 779      * {@code endIndex-beginIndex}. Unpaired surrogates within
 780      * the text range count as one code point each.
 781      *
 782      * @param beginIndex the index to the first {@code char} of
 783      * the text range.
 784      * @param endIndex the index after the last {@code char} of
 785      * the text range.
 786      * @return the number of Unicode code points in the specified text
 787      * range
 788      * @exception IndexOutOfBoundsException if the
 789      * {@code beginIndex} is negative, or {@code endIndex}
 790      * is larger than the length of this {@code String}, or
 791      * {@code beginIndex} is larger than {@code endIndex}.
 792      * @since  1.5
 793      */
 794     public int codePointCount(int beginIndex, int endIndex) {
 795         if (beginIndex < 0 || beginIndex > endIndex ||
 796             endIndex > length()) {
 797             throw new IndexOutOfBoundsException();
 798         }
 799         if (isLatin1()) {
 800             return endIndex - beginIndex;
 801         }
 802         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 803     }
 804 
 805     /**
 806      * Returns the index within this {@code String} that is
 807      * offset from the given {@code index} by
 808      * {@code codePointOffset} code points. Unpaired surrogates
 809      * within the text range given by {@code index} and
 810      * {@code codePointOffset} count as one code point each.
 811      *
 812      * @param index the index to be offset
 813      * @param codePointOffset the offset in code points
 814      * @return the index within this {@code String}
 815      * @exception IndexOutOfBoundsException if {@code index}
 816      *   is negative or larger then the length of this
 817      *   {@code String}, or if {@code codePointOffset} is positive
 818      *   and the substring starting with {@code index} has fewer
 819      *   than {@code codePointOffset} code points,
 820      *   or if {@code codePointOffset} is negative and the substring
 821      *   before {@code index} has fewer than the absolute value
 822      *   of {@code codePointOffset} code points.
 823      * @since 1.5
 824      */
 825     public int offsetByCodePoints(int index, int codePointOffset) {
 826         if (index < 0 || index > length()) {
 827             throw new IndexOutOfBoundsException();
 828         }
 829         return Character.offsetByCodePoints(this, index, codePointOffset);
 830     }
 831 
 832     /**
 833      * Copies characters from this string into the destination character
 834      * array.
 835      * <p>
 836      * The first character to be copied is at index {@code srcBegin};
 837      * the last character to be copied is at index {@code srcEnd-1}
 838      * (thus the total number of characters to be copied is
 839      * {@code srcEnd-srcBegin}). The characters are copied into the
 840      * subarray of {@code dst} starting at index {@code dstBegin}
 841      * and ending at index:
 842      * <blockquote><pre>
 843      *     dstBegin + (srcEnd-srcBegin) - 1
 844      * </pre></blockquote>
 845      *
 846      * @param      srcBegin   index of the first character in the string
 847      *                        to copy.
 848      * @param      srcEnd     index after the last character in the string
 849      *                        to copy.
 850      * @param      dst        the destination array.
 851      * @param      dstBegin   the start offset in the destination array.
 852      * @exception IndexOutOfBoundsException If any of the following
 853      *            is true:
 854      *            <ul><li>{@code srcBegin} is negative.
 855      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 856      *            <li>{@code srcEnd} is greater than the length of this
 857      *                string
 858      *            <li>{@code dstBegin} is negative
 859      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 860      *                {@code dst.length}</ul>
 861      */
 862     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 863         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 864         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 865         if (isLatin1()) {
 866             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 867         } else {
 868             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 869         }
 870     }
 871 
 872     /**
 873      * Copies characters from this string into the destination byte array. Each
 874      * byte receives the 8 low-order bits of the corresponding character. The
 875      * eight high-order bits of each character are not copied and do not
 876      * participate in the transfer in any way.
 877      *
 878      * <p> The first character to be copied is at index {@code srcBegin}; the
 879      * last character to be copied is at index {@code srcEnd-1}.  The total
 880      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 881      * characters, converted to bytes, are copied into the subarray of {@code
 882      * dst} starting at index {@code dstBegin} and ending at index:
 883      *
 884      * <blockquote><pre>
 885      *     dstBegin + (srcEnd-srcBegin) - 1
 886      * </pre></blockquote>
 887      *
 888      * @deprecated  This method does not properly convert characters into
 889      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 890      * {@link #getBytes()} method, which uses the platform's default charset.
 891      *
 892      * @param  srcBegin
 893      *         Index of the first character in the string to copy
 894      *
 895      * @param  srcEnd
 896      *         Index after the last character in the string to copy
 897      *
 898      * @param  dst
 899      *         The destination array
 900      *
 901      * @param  dstBegin
 902      *         The start offset in the destination array
 903      *
 904      * @throws  IndexOutOfBoundsException
 905      *          If any of the following is true:
 906      *          <ul>
 907      *            <li> {@code srcBegin} is negative
 908      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 909      *            <li> {@code srcEnd} is greater than the length of this String
 910      *            <li> {@code dstBegin} is negative
 911      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 912      *                 dst.length}
 913      *          </ul>
 914      */
 915     @Deprecated
 916     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 917         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 918         Objects.requireNonNull(dst);
 919         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 920         if (isLatin1()) {
 921             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 922         } else {
 923             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 924         }
 925     }
 926 
 927     /**
 928      * Encodes this {@code String} into a sequence of bytes using the named
 929      * charset, storing the result into a new byte array.
 930      *
 931      * <p> The behavior of this method when this string cannot be encoded in
 932      * the given charset is unspecified.  The {@link
 933      * java.nio.charset.CharsetEncoder} class should be used when more control
 934      * over the encoding process is required.
 935      *
 936      * @param  charsetName
 937      *         The name of a supported {@linkplain java.nio.charset.Charset
 938      *         charset}
 939      *
 940      * @return  The resultant byte array
 941      *
 942      * @throws  UnsupportedEncodingException
 943      *          If the named charset is not supported
 944      *
 945      * @since  1.1
 946      */
 947     public byte[] getBytes(String charsetName)
 948             throws UnsupportedEncodingException {
 949         if (charsetName == null) throw new NullPointerException();
 950         return StringCoding.encode(charsetName, coder(), value);
 951     }
 952 
 953     /**
 954      * Encodes this {@code String} into a sequence of bytes using the given
 955      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 956      * new byte array.
 957      *
 958      * <p> This method always replaces malformed-input and unmappable-character
 959      * sequences with this charset's default replacement byte array.  The
 960      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 961      * control over the encoding process is required.
 962      *
 963      * @param  charset
 964      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 965      *         the {@code String}
 966      *
 967      * @return  The resultant byte array
 968      *
 969      * @since  1.6
 970      */
 971     public byte[] getBytes(Charset charset) {
 972         if (charset == null) throw new NullPointerException();
 973         return StringCoding.encode(charset, coder(), value);
 974      }
 975 
 976     /**
 977      * Encodes this {@code String} into a sequence of bytes using the
 978      * platform's default charset, storing the result into a new byte array.
 979      *
 980      * <p> The behavior of this method when this string cannot be encoded in
 981      * the default charset is unspecified.  The {@link
 982      * java.nio.charset.CharsetEncoder} class should be used when more control
 983      * over the encoding process is required.
 984      *
 985      * @return  The resultant byte array
 986      *
 987      * @since      1.1
 988      */
 989     public byte[] getBytes() {
 990         return StringCoding.encode(coder(), value);
 991     }
 992 
 993     /**
 994      * Compares this string to the specified object.  The result is {@code
 995      * true} if and only if the argument is not {@code null} and is a {@code
 996      * String} object that represents the same sequence of characters as this
 997      * object.
 998      *
 999      * <p>For finer-grained String comparison, refer to
1000      * {@link java.text.Collator}.
1001      *
1002      * @param  anObject
1003      *         The object to compare this {@code String} against
1004      *
1005      * @return  {@code true} if the given object represents a {@code String}
1006      *          equivalent to this string, {@code false} otherwise
1007      *
1008      * @see  #compareTo(String)
1009      * @see  #equalsIgnoreCase(String)
1010      */
1011     public boolean equals(Object anObject) {
1012         if (this == anObject) {
1013             return true;
1014         }
1015         if (anObject instanceof String) {
1016             String aString = (String)anObject;
1017             if (coder() == aString.coder()) {
1018                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1019                                   : StringUTF16.equals(value, aString.value);
1020             }
1021         }
1022         return false;
1023     }
1024 
1025     /**
1026      * Compares this string to the specified {@code StringBuffer}.  The result
1027      * is {@code true} if and only if this {@code String} represents the same
1028      * sequence of characters as the specified {@code StringBuffer}. This method
1029      * synchronizes on the {@code StringBuffer}.
1030      *
1031      * <p>For finer-grained String comparison, refer to
1032      * {@link java.text.Collator}.
1033      *
1034      * @param  sb
1035      *         The {@code StringBuffer} to compare this {@code String} against
1036      *
1037      * @return  {@code true} if this {@code String} represents the same
1038      *          sequence of characters as the specified {@code StringBuffer},
1039      *          {@code false} otherwise
1040      *
1041      * @since  1.4
1042      */
1043     public boolean contentEquals(StringBuffer sb) {
1044         return contentEquals((CharSequence)sb);
1045     }
1046 
1047     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1048         int len = length();
1049         if (len != sb.length()) {
1050             return false;
1051         }
1052         byte v1[] = value;
1053         byte v2[] = sb.getValue();
1054         if (coder() == sb.getCoder()) {
1055             int n = v1.length;
1056             for (int i = 0; i < n; i++) {
1057                 if (v1[i] != v2[i]) {
1058                     return false;
1059                 }
1060             }
1061         } else {
1062             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1063                 return false;
1064             }
1065             for (int i = 0; i < len; i++) {
1066                 if ((char)(v1[i] & 0xff) != StringUTF16.getChar(v2, i)) {
1067                     return false;
1068                 }
1069             }
1070         }
1071         return true;
1072     }
1073 
1074     /**
1075      * Compares this string to the specified {@code CharSequence}.  The
1076      * result is {@code true} if and only if this {@code String} represents the
1077      * same sequence of char values as the specified sequence. Note that if the
1078      * {@code CharSequence} is a {@code StringBuffer} then the method
1079      * synchronizes on it.
1080      *
1081      * <p>For finer-grained String comparison, refer to
1082      * {@link java.text.Collator}.
1083      *
1084      * @param  cs
1085      *         The sequence to compare this {@code String} against
1086      *
1087      * @return  {@code true} if this {@code String} represents the same
1088      *          sequence of char values as the specified sequence, {@code
1089      *          false} otherwise
1090      *
1091      * @since  1.5
1092      */
1093     public boolean contentEquals(CharSequence cs) {
1094         // Argument is a StringBuffer, StringBuilder
1095         if (cs instanceof AbstractStringBuilder) {
1096             if (cs instanceof StringBuffer) {
1097                 synchronized(cs) {
1098                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1099                 }
1100             } else {
1101                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1102             }
1103         }
1104         // Argument is a String
1105         if (cs instanceof String) {
1106             return equals(cs);
1107         }
1108         // Argument is a generic CharSequence
1109         int n = cs.length();
1110         if (n != length()) {
1111             return false;
1112         }
1113         byte[] val = this.value;
1114         if (isLatin1()) {
1115             for (int i = 0; i < n; i++) {
1116                 if ((val[i] & 0xff) != cs.charAt(i)) {
1117                     return false;
1118                 }
1119             }
1120         } else {
1121             for (int i = 0; i < n; i++) {
1122                 if (StringUTF16.getChar(val, i) != cs.charAt(i)) {
1123                     return false;
1124                 }
1125             }
1126         }
1127         return true;
1128     }
1129 
1130     /**
1131      * Compares this {@code String} to another {@code String}, ignoring case
1132      * considerations.  Two strings are considered equal ignoring case if they
1133      * are of the same length and corresponding characters in the two strings
1134      * are equal ignoring case.
1135      *
1136      * <p> Two characters {@code c1} and {@code c2} are considered the same
1137      * ignoring case if at least one of the following is true:
1138      * <ul>
1139      *   <li> The two characters are the same (as compared by the
1140      *        {@code ==} operator)
1141      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1142      *        on each character produces the same result
1143      * </ul>
1144      *
1145      * <p>Note that this method does <em>not</em> take locale into account, and
1146      * will result in unsatisfactory results for certain locales.  The
1147      * {@link java.text.Collator} class provides locale-sensitive comparison.
1148      *
1149      * @param  anotherString
1150      *         The {@code String} to compare this {@code String} against
1151      *
1152      * @return  {@code true} if the argument is not {@code null} and it
1153      *          represents an equivalent {@code String} ignoring case; {@code
1154      *          false} otherwise
1155      *
1156      * @see  #equals(Object)
1157      */
1158     public boolean equalsIgnoreCase(String anotherString) {
1159         return (this == anotherString) ? true
1160                 : (anotherString != null)
1161                 && (anotherString.length() == length())
1162                 && regionMatches(true, 0, anotherString, 0, length());
1163     }
1164 
1165     /**
1166      * Compares two strings lexicographically.
1167      * The comparison is based on the Unicode value of each character in
1168      * the strings. The character sequence represented by this
1169      * {@code String} object is compared lexicographically to the
1170      * character sequence represented by the argument string. The result is
1171      * a negative integer if this {@code String} object
1172      * lexicographically precedes the argument string. The result is a
1173      * positive integer if this {@code String} object lexicographically
1174      * follows the argument string. The result is zero if the strings
1175      * are equal; {@code compareTo} returns {@code 0} exactly when
1176      * the {@link #equals(Object)} method would return {@code true}.
1177      * <p>
1178      * This is the definition of lexicographic ordering. If two strings are
1179      * different, then either they have different characters at some index
1180      * that is a valid index for both strings, or their lengths are different,
1181      * or both. If they have different characters at one or more index
1182      * positions, let <i>k</i> be the smallest such index; then the string
1183      * whose character at position <i>k</i> has the smaller value, as
1184      * determined by using the {@code <} operator, lexicographically precedes the
1185      * other string. In this case, {@code compareTo} returns the
1186      * difference of the two character values at position {@code k} in
1187      * the two string -- that is, the value:
1188      * <blockquote><pre>
1189      * this.charAt(k)-anotherString.charAt(k)
1190      * </pre></blockquote>
1191      * If there is no index position at which they differ, then the shorter
1192      * string lexicographically precedes the longer string. In this case,
1193      * {@code compareTo} returns the difference of the lengths of the
1194      * strings -- that is, the value:
1195      * <blockquote><pre>
1196      * this.length()-anotherString.length()
1197      * </pre></blockquote>
1198      *
1199      * <p>For finer-grained String comparison, refer to
1200      * {@link java.text.Collator}.
1201      *
1202      * @param   anotherString   the {@code String} to be compared.
1203      * @return  the value {@code 0} if the argument string is equal to
1204      *          this string; a value less than {@code 0} if this string
1205      *          is lexicographically less than the string argument; and a
1206      *          value greater than {@code 0} if this string is
1207      *          lexicographically greater than the string argument.
1208      */
1209     public int compareTo(String anotherString) {
1210         byte v1[] = value;
1211         byte v2[] = anotherString.value;
1212         if (coder() == anotherString.coder()) {
1213             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1214                               : StringUTF16.compareTo(v1, v2);
1215         }
1216         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1217                           : StringUTF16.compareToLatin1(v1, v2);
1218      }
1219 
1220     /**
1221      * A Comparator that orders {@code String} objects as by
1222      * {@code compareToIgnoreCase}. This comparator is serializable.
1223      * <p>
1224      * Note that this Comparator does <em>not</em> take locale into account,
1225      * and will result in an unsatisfactory ordering for certain locales.
1226      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1227      *
1228      * @see     java.text.Collator
1229      * @since   1.2
1230      */
1231     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1232                                          = new CaseInsensitiveComparator();
1233 
1234     /**
1235      * A hashCode computing function that is consistent with
1236      * {@link #CASE_INSENSITIVE_ORDER} {@code Comparator}.
1237      *
1238      * @since 9
1239      */
1240     @SuppressWarnings("unchecked")
1241     public static final ToIntFunction<String> CASE_INSENSITIVE_HASHER
1242         = (ToIntFunction<String>) CASE_INSENSITIVE_ORDER;
1243 
1244     private static class CaseInsensitiveComparator
1245             implements Comparator<String>, java.io.Serializable,
1246                        ToIntFunction<String> /* hasher */ {
1247         // use serialVersionUID from JDK 1.2.2 for interoperability
1248         private static final long serialVersionUID = 8575799808933029326L;
1249 
1250         @Override
1251         public int compare(String s1, String s2) {
1252             byte v1[] = s1.value;
1253             byte v2[] = s2.value;
1254             if (s1.coder() == s2.coder()) {
1255                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1256                                      : StringUTF16.compareToCI(v1, v2);
1257             }
1258             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1259                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1260         }
1261 
1262         /**
1263          * Compute hashCode consistent with {@link #compare(String, String)}
1264          */
1265         @Override
1266         public int applyAsInt(String s) {
1267             return s.isLatin1() ? StringLatin1.hashCodeCI(s.value)
1268                                 : StringUTF16.hashCodeCI(s.value);
1269         }
1270 
1271         /** Replaces the de-serialized object. */
1272         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1273     }
1274 
1275     /**
1276      * Compares two strings lexicographically, ignoring case
1277      * differences. This method returns an integer whose sign is that of
1278      * calling {@code compareTo} with normalized versions of the strings
1279      * where case differences have been eliminated by calling
1280      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1281      * each character.
1282      * <p>
1283      * Note that this method does <em>not</em> take locale into account,
1284      * and will result in an unsatisfactory ordering for certain locales.
1285      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1286      *
1287      * @param   str   the {@code String} to be compared.
1288      * @return  a negative integer, zero, or a positive integer as the
1289      *          specified String is greater than, equal to, or less
1290      *          than this String, ignoring case considerations.
1291      * @see     java.text.Collator
1292      * @since   1.2
1293      */
1294     public int compareToIgnoreCase(String str) {
1295         return CASE_INSENSITIVE_ORDER.compare(this, str);
1296     }
1297 
1298     /**
1299      * Tests if two string regions are equal.
1300      * <p>
1301      * A substring of this {@code String} object is compared to a substring
1302      * of the argument other. The result is true if these substrings
1303      * represent identical character sequences. The substring of this
1304      * {@code String} object to be compared begins at index {@code toffset}
1305      * and has length {@code len}. The substring of other to be compared
1306      * begins at index {@code ooffset} and has length {@code len}. The
1307      * result is {@code false} if and only if at least one of the following
1308      * is true:
1309      * <ul><li>{@code toffset} is negative.
1310      * <li>{@code ooffset} is negative.
1311      * <li>{@code toffset+len} is greater than the length of this
1312      * {@code String} object.
1313      * <li>{@code ooffset+len} is greater than the length of the other
1314      * argument.
1315      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1316      * such that:
1317      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1318      * <i>k</i>{@code )}
1319      * </ul>
1320      *
1321      * <p>Note that this method does <em>not</em> take locale into account.  The
1322      * {@link java.text.Collator} class provides locale-sensitive comparison.
1323      *
1324      * @param   toffset   the starting offset of the subregion in this string.
1325      * @param   other     the string argument.
1326      * @param   ooffset   the starting offset of the subregion in the string
1327      *                    argument.
1328      * @param   len       the number of characters to compare.
1329      * @return  {@code true} if the specified subregion of this string
1330      *          exactly matches the specified subregion of the string argument;
1331      *          {@code false} otherwise.
1332      */
1333     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1334         byte tv[] = value;
1335         byte ov[] = other.value;
1336         // Note: toffset, ooffset, or len might be near -1>>>1.
1337         if ((ooffset < 0) || (toffset < 0) ||
1338              (toffset > (long)length() - len) ||
1339              (ooffset > (long)other.length() - len)) {
1340             return false;
1341         }
1342         if (coder() == other.coder()) {
1343             if (!isLatin1() && (len > 0)) {
1344                 toffset = toffset << 1;
1345                 ooffset = ooffset << 1;
1346                 len = len << 1;
1347             }
1348             while (len-- > 0) {
1349                 if (tv[toffset++] != ov[ooffset++]) {
1350                     return false;
1351                 }
1352             }
1353         } else {
1354             if (coder() == LATIN1) {
1355                 while (len-- > 0) {
1356                     if (StringLatin1.getChar(tv, toffset++) !=
1357                         StringUTF16.getChar(ov, ooffset++)) {
1358                         return false;
1359                     }
1360                 }
1361             } else {
1362                 while (len-- > 0) {
1363                     if (StringUTF16.getChar(tv, toffset++) !=
1364                         StringLatin1.getChar(ov, ooffset++)) {
1365                         return false;
1366                     }
1367                 }
1368             }
1369         }
1370         return true;
1371     }
1372 
1373     /**
1374      * Tests if two string regions are equal.
1375      * <p>
1376      * A substring of this {@code String} object is compared to a substring
1377      * of the argument {@code other}. The result is {@code true} if these
1378      * substrings represent character sequences that are the same, ignoring
1379      * case if and only if {@code ignoreCase} is true. The substring of
1380      * this {@code String} object to be compared begins at index
1381      * {@code toffset} and has length {@code len}. The substring of
1382      * {@code other} to be compared begins at index {@code ooffset} and
1383      * has length {@code len}. The result is {@code false} if and only if
1384      * at least one of the following is true:
1385      * <ul><li>{@code toffset} is negative.
1386      * <li>{@code ooffset} is negative.
1387      * <li>{@code toffset+len} is greater than the length of this
1388      * {@code String} object.
1389      * <li>{@code ooffset+len} is greater than the length of the other
1390      * argument.
1391      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1392      * integer <i>k</i> less than {@code len} such that:
1393      * <blockquote><pre>
1394      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1395      * </pre></blockquote>
1396      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1397      * integer <i>k</i> less than {@code len} such that:
1398      * <blockquote><pre>
1399      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1400      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1401      * </pre></blockquote>
1402      * </ul>
1403      *
1404      * <p>Note that this method does <em>not</em> take locale into account,
1405      * and will result in unsatisfactory results for certain locales when
1406      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1407      * provides locale-sensitive comparison.
1408      *
1409      * @param   ignoreCase   if {@code true}, ignore case when comparing
1410      *                       characters.
1411      * @param   toffset      the starting offset of the subregion in this
1412      *                       string.
1413      * @param   other        the string argument.
1414      * @param   ooffset      the starting offset of the subregion in the string
1415      *                       argument.
1416      * @param   len          the number of characters to compare.
1417      * @return  {@code true} if the specified subregion of this string
1418      *          matches the specified subregion of the string argument;
1419      *          {@code false} otherwise. Whether the matching is exact
1420      *          or case insensitive depends on the {@code ignoreCase}
1421      *          argument.
1422      */
1423     public boolean regionMatches(boolean ignoreCase, int toffset,
1424             String other, int ooffset, int len) {
1425         if (!ignoreCase) {
1426             return regionMatches(toffset, other, ooffset, len);
1427         }
1428         // Note: toffset, ooffset, or len might be near -1>>>1.
1429         if ((ooffset < 0) || (toffset < 0)
1430                 || (toffset > (long)length() - len)
1431                 || (ooffset > (long)other.length() - len)) {
1432             return false;
1433         }
1434         byte tv[] = value;
1435         byte ov[] = other.value;
1436         if (coder() == other.coder()) {
1437             return isLatin1()
1438               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1439               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1440         }
1441         return isLatin1()
1442               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1443               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1444     }
1445 
1446     /**
1447      * Tests if the substring of this string beginning at the
1448      * specified index starts with the specified prefix.
1449      *
1450      * @param   prefix    the prefix.
1451      * @param   toffset   where to begin looking in this string.
1452      * @return  {@code true} if the character sequence represented by the
1453      *          argument is a prefix of the substring of this object starting
1454      *          at index {@code toffset}; {@code false} otherwise.
1455      *          The result is {@code false} if {@code toffset} is
1456      *          negative or greater than the length of this
1457      *          {@code String} object; otherwise the result is the same
1458      *          as the result of the expression
1459      *          <pre>
1460      *          this.substring(toffset).startsWith(prefix)
1461      *          </pre>
1462      */
1463     public boolean startsWith(String prefix, int toffset) {
1464         // Note: toffset might be near -1>>>1.
1465         if (toffset < 0 || toffset > length() - prefix.length()) {
1466             return false;
1467         }
1468         byte ta[] = value;
1469         byte pa[] = prefix.value;
1470         int po = 0;
1471         int pc = pa.length;
1472         if (coder() == prefix.coder()) {
1473             int to = isLatin1() ? toffset : toffset << 1;
1474             while (po < pc) {
1475                 if (ta[to++] != pa[po++]) {
1476                     return false;
1477                 }
1478             }
1479         } else {
1480             if (isLatin1()) {  // && pcoder == UTF16
1481                 return false;
1482             }
1483             // coder == UTF16 && pcoder == LATIN1)
1484             while (po < pc) {
1485                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1486                     return false;
1487                }
1488             }
1489         }
1490         return true;
1491     }
1492 
1493     /**
1494      * Tests if this string starts with the specified prefix.
1495      *
1496      * @param   prefix   the prefix.
1497      * @return  {@code true} if the character sequence represented by the
1498      *          argument is a prefix of the character sequence represented by
1499      *          this string; {@code false} otherwise.
1500      *          Note also that {@code true} will be returned if the
1501      *          argument is an empty string or is equal to this
1502      *          {@code String} object as determined by the
1503      *          {@link #equals(Object)} method.
1504      * @since   1.0
1505      */
1506     public boolean startsWith(String prefix) {
1507         return startsWith(prefix, 0);
1508     }
1509 
1510     /**
1511      * Tests if this string ends with the specified suffix.
1512      *
1513      * @param   suffix   the suffix.
1514      * @return  {@code true} if the character sequence represented by the
1515      *          argument is a suffix of the character sequence represented by
1516      *          this object; {@code false} otherwise. Note that the
1517      *          result will be {@code true} if the argument is the
1518      *          empty string or is equal to this {@code String} object
1519      *          as determined by the {@link #equals(Object)} method.
1520      */
1521     public boolean endsWith(String suffix) {
1522         return startsWith(suffix, length() - suffix.length());
1523     }
1524 
1525     /**
1526      * Returns a hash code for this string. The hash code for a
1527      * {@code String} object is computed as
1528      * <blockquote><pre>
1529      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1530      * </pre></blockquote>
1531      * using {@code int} arithmetic, where {@code s[i]} is the
1532      * <i>i</i>th character of the string, {@code n} is the length of
1533      * the string, and {@code ^} indicates exponentiation.
1534      * (The hash value of the empty string is zero.)
1535      *
1536      * @return  a hash code value for this object.
1537      */
1538     public int hashCode() {
1539         if (hash == 0 && value.length > 0) {
1540             hash = isLatin1() ? StringLatin1.hashCode(value)
1541                               : StringUTF16.hashCode(value);
1542         }
1543         return hash;
1544     }
1545 
1546     /**
1547      * Returns the index within this string of the first occurrence of
1548      * the specified character. If a character with value
1549      * {@code ch} occurs in the character sequence represented by
1550      * this {@code String} object, then the index (in Unicode
1551      * code units) of the first such occurrence is returned. For
1552      * values of {@code ch} in the range from 0 to 0xFFFF
1553      * (inclusive), this is the smallest value <i>k</i> such that:
1554      * <blockquote><pre>
1555      * this.charAt(<i>k</i>) == ch
1556      * </pre></blockquote>
1557      * is true. For other values of {@code ch}, it is the
1558      * smallest value <i>k</i> such that:
1559      * <blockquote><pre>
1560      * this.codePointAt(<i>k</i>) == ch
1561      * </pre></blockquote>
1562      * is true. In either case, if no such character occurs in this
1563      * string, then {@code -1} is returned.
1564      *
1565      * @param   ch   a character (Unicode code point).
1566      * @return  the index of the first occurrence of the character in the
1567      *          character sequence represented by this object, or
1568      *          {@code -1} if the character does not occur.
1569      */
1570     public int indexOf(int ch) {
1571         return indexOf(ch, 0);
1572     }
1573 
1574     /**
1575      * Returns the index within this string of the first occurrence of the
1576      * specified character, starting the search at the specified index.
1577      * <p>
1578      * If a character with value {@code ch} occurs in the
1579      * character sequence represented by this {@code String}
1580      * object at an index no smaller than {@code fromIndex}, then
1581      * the index of the first such occurrence is returned. For values
1582      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1583      * this is the smallest value <i>k</i> such that:
1584      * <blockquote><pre>
1585      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1586      * </pre></blockquote>
1587      * is true. For other values of {@code ch}, it is the
1588      * smallest value <i>k</i> such that:
1589      * <blockquote><pre>
1590      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1591      * </pre></blockquote>
1592      * is true. In either case, if no such character occurs in this
1593      * string at or after position {@code fromIndex}, then
1594      * {@code -1} is returned.
1595      *
1596      * <p>
1597      * There is no restriction on the value of {@code fromIndex}. If it
1598      * is negative, it has the same effect as if it were zero: this entire
1599      * string may be searched. If it is greater than the length of this
1600      * string, it has the same effect as if it were equal to the length of
1601      * this string: {@code -1} is returned.
1602      *
1603      * <p>All indices are specified in {@code char} values
1604      * (Unicode code units).
1605      *
1606      * @param   ch          a character (Unicode code point).
1607      * @param   fromIndex   the index to start the search from.
1608      * @return  the index of the first occurrence of the character in the
1609      *          character sequence represented by this object that is greater
1610      *          than or equal to {@code fromIndex}, or {@code -1}
1611      *          if the character does not occur.
1612      */
1613     public int indexOf(int ch, int fromIndex) {
1614         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1615                           : StringUTF16.indexOf(value, ch, fromIndex);
1616     }
1617 
1618     /**
1619      * Returns the index within this string of the last occurrence of
1620      * the specified character. For values of {@code ch} in the
1621      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1622      * units) returned is the largest value <i>k</i> such that:
1623      * <blockquote><pre>
1624      * this.charAt(<i>k</i>) == ch
1625      * </pre></blockquote>
1626      * is true. For other values of {@code ch}, it is the
1627      * largest value <i>k</i> such that:
1628      * <blockquote><pre>
1629      * this.codePointAt(<i>k</i>) == ch
1630      * </pre></blockquote>
1631      * is true.  In either case, if no such character occurs in this
1632      * string, then {@code -1} is returned.  The
1633      * {@code String} is searched backwards starting at the last
1634      * character.
1635      *
1636      * @param   ch   a character (Unicode code point).
1637      * @return  the index of the last occurrence of the character in the
1638      *          character sequence represented by this object, or
1639      *          {@code -1} if the character does not occur.
1640      */
1641     public int lastIndexOf(int ch) {
1642         return lastIndexOf(ch, length() - 1);
1643     }
1644 
1645     /**
1646      * Returns the index within this string of the last occurrence of
1647      * the specified character, searching backward starting at the
1648      * specified index. For values of {@code ch} in the range
1649      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1650      * value <i>k</i> such that:
1651      * <blockquote><pre>
1652      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1653      * </pre></blockquote>
1654      * is true. For other values of {@code ch}, it is the
1655      * largest value <i>k</i> such that:
1656      * <blockquote><pre>
1657      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1658      * </pre></blockquote>
1659      * is true. In either case, if no such character occurs in this
1660      * string at or before position {@code fromIndex}, then
1661      * {@code -1} is returned.
1662      *
1663      * <p>All indices are specified in {@code char} values
1664      * (Unicode code units).
1665      *
1666      * @param   ch          a character (Unicode code point).
1667      * @param   fromIndex   the index to start the search from. There is no
1668      *          restriction on the value of {@code fromIndex}. If it is
1669      *          greater than or equal to the length of this string, it has
1670      *          the same effect as if it were equal to one less than the
1671      *          length of this string: this entire string may be searched.
1672      *          If it is negative, it has the same effect as if it were -1:
1673      *          -1 is returned.
1674      * @return  the index of the last occurrence of the character in the
1675      *          character sequence represented by this object that is less
1676      *          than or equal to {@code fromIndex}, or {@code -1}
1677      *          if the character does not occur before that point.
1678      */
1679     public int lastIndexOf(int ch, int fromIndex) {
1680         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1681                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1682     }
1683 
1684     /**
1685      * Returns the index within this string of the first occurrence of the
1686      * specified substring.
1687      *
1688      * <p>The returned index is the smallest value {@code k} for which:
1689      * <pre>{@code
1690      * this.startsWith(str, k)
1691      * }</pre>
1692      * If no such value of {@code k} exists, then {@code -1} is returned.
1693      *
1694      * @param   str   the substring to search for.
1695      * @return  the index of the first occurrence of the specified substring,
1696      *          or {@code -1} if there is no such occurrence.
1697      */
1698     public int indexOf(String str) {
1699         if (coder() == str.coder()) {
1700             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1701                               : StringUTF16.indexOf(value, str.value);
1702         }
1703         if (coder() == LATIN1) {  // str.coder == UTF16
1704             return -1;
1705         }
1706         return StringUTF16.indexOfLatin1(value, str.value);
1707     }
1708 
1709     /**
1710      * Returns the index within this string of the first occurrence of the
1711      * specified substring, starting at the specified index.
1712      *
1713      * <p>The returned index is the smallest value {@code k} for which:
1714      * <pre>{@code
1715      *     k >= Math.min(fromIndex, this.length()) &&
1716      *                   this.startsWith(str, k)
1717      * }</pre>
1718      * If no such value of {@code k} exists, then {@code -1} is returned.
1719      *
1720      * @param   str         the substring to search for.
1721      * @param   fromIndex   the index from which to start the search.
1722      * @return  the index of the first occurrence of the specified substring,
1723      *          starting at the specified index,
1724      *          or {@code -1} if there is no such occurrence.
1725      */
1726     public int indexOf(String str, int fromIndex) {
1727         return indexOf(value, coder(), length(), str, fromIndex);
1728     }
1729 
1730     /**
1731      * Code shared by String and AbstractStringBuilder to do searches. The
1732      * source is the character array being searched, and the target
1733      * is the string being searched for.
1734      *
1735      * @param   src       the characters being searched.
1736      * @param   srcCoder  the coder of the source string.
1737      * @param   srcCount  length of the source string.
1738      * @param   tgtStr    the characters being searched for.
1739      * @param   fromIndex the index to begin searching from.
1740      */
1741     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1742                        String tgtStr, int fromIndex) {
1743         byte[] tgt    = tgtStr.value;
1744         byte tgtCoder = tgtStr.coder();
1745         int tgtCount  = tgtStr.length();
1746 
1747         if (fromIndex >= srcCount) {
1748             return (tgtCount == 0 ? srcCount : -1);
1749         }
1750         if (fromIndex < 0) {
1751             fromIndex = 0;
1752         }
1753         if (tgtCount == 0) {
1754             return fromIndex;
1755         }
1756         if (srcCoder == tgtCoder) {
1757             return srcCoder == LATIN1
1758                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1759                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1760         }
1761         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1762             return -1;
1763         }
1764         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1765         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1766     }
1767 
1768     /**
1769      * Returns the index within this string of the last occurrence of the
1770      * specified substring.  The last occurrence of the empty string ""
1771      * is considered to occur at the index value {@code this.length()}.
1772      *
1773      * <p>The returned index is the largest value {@code k} for which:
1774      * <pre>{@code
1775      * this.startsWith(str, k)
1776      * }</pre>
1777      * If no such value of {@code k} exists, then {@code -1} is returned.
1778      *
1779      * @param   str   the substring to search for.
1780      * @return  the index of the last occurrence of the specified substring,
1781      *          or {@code -1} if there is no such occurrence.
1782      */
1783     public int lastIndexOf(String str) {
1784         return lastIndexOf(str, length());
1785     }
1786 
1787     /**
1788      * Returns the index within this string of the last occurrence of the
1789      * specified substring, searching backward starting at the specified index.
1790      *
1791      * <p>The returned index is the largest value {@code k} for which:
1792      * <pre>{@code
1793      *     k <= Math.min(fromIndex, this.length()) &&
1794      *                   this.startsWith(str, k)
1795      * }</pre>
1796      * If no such value of {@code k} exists, then {@code -1} is returned.
1797      *
1798      * @param   str         the substring to search for.
1799      * @param   fromIndex   the index to start the search from.
1800      * @return  the index of the last occurrence of the specified substring,
1801      *          searching backward from the specified index,
1802      *          or {@code -1} if there is no such occurrence.
1803      */
1804     public int lastIndexOf(String str, int fromIndex) {
1805         return lastIndexOf(value, coder(), length(), str, fromIndex);
1806     }
1807 
1808     /**
1809      * Code shared by String and AbstractStringBuilder to do searches. The
1810      * source is the character array being searched, and the target
1811      * is the string being searched for.
1812      *
1813      * @param   src         the characters being searched.
1814      * @param   srcCoder  coder handles the mapping between bytes/chars
1815      * @param   srcCount    count of the source string.
1816      * @param   tgt         the characters being searched for.
1817      * @param   fromIndex   the index to begin searching from.
1818      */
1819     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1820                            String tgtStr, int fromIndex) {
1821         byte[] tgt = tgtStr.value;
1822         byte tgtCoder = tgtStr.coder();
1823         int tgtCount = tgtStr.length();
1824         /*
1825          * Check arguments; return immediately where possible. For
1826          * consistency, don't check for null str.
1827          */
1828         int rightIndex = srcCount - tgtCount;
1829         if (fromIndex < 0) {
1830             return -1;
1831         }
1832         if (fromIndex > rightIndex) {
1833             fromIndex = rightIndex;
1834         }
1835         /* Empty string always matches. */
1836         if (tgtCount == 0) {
1837             return fromIndex;
1838         }
1839         if (srcCoder == tgtCoder) {
1840             return srcCoder == LATIN1
1841                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1842                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1843         }
1844         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1845             return -1;
1846         }
1847                                      // srcCoder == UTF16 && tgtCoder == LATIN1
1848         int min = tgtCount - 1;
1849         int i = min + fromIndex;
1850         int strLastIndex = tgtCount - 1;
1851 
1852         char strLastChar = (char)(tgt[strLastIndex] & 0xff);
1853     startSearchForLastChar:
1854         while (true) {
1855             while (i >= min && StringUTF16.getChar(src, i) != strLastChar) {
1856                 i--;
1857             }
1858             if (i < min) {
1859                 return -1;
1860             }
1861             int j = i - 1;
1862             int start = j - strLastIndex;
1863             int k = strLastIndex - 1;
1864             while (j > start) {
1865                 if (StringUTF16.getChar(src, j--) != (tgt[k--] & 0xff)) {
1866                     i--;
1867                     continue startSearchForLastChar;
1868                 }
1869             }
1870             return start + 1;
1871         }
1872     }
1873 
1874     /**
1875      * Returns a string that is a substring of this string. The
1876      * substring begins with the character at the specified index and
1877      * extends to the end of this string. <p>
1878      * Examples:
1879      * <blockquote><pre>
1880      * "unhappy".substring(2) returns "happy"
1881      * "Harbison".substring(3) returns "bison"
1882      * "emptiness".substring(9) returns "" (an empty string)
1883      * </pre></blockquote>
1884      *
1885      * @param      beginIndex   the beginning index, inclusive.
1886      * @return     the specified substring.
1887      * @exception  IndexOutOfBoundsException  if
1888      *             {@code beginIndex} is negative or larger than the
1889      *             length of this {@code String} object.
1890      */
1891     public String substring(int beginIndex) {
1892         if (beginIndex < 0) {
1893             throw new StringIndexOutOfBoundsException(beginIndex);
1894         }
1895         int subLen = length() - beginIndex;
1896         if (subLen < 0) {
1897             throw new StringIndexOutOfBoundsException(subLen);
1898         }
1899         if (beginIndex == 0) {
1900             return this;
1901         }
1902         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1903                           : StringUTF16.newString(value, beginIndex, subLen);
1904     }
1905 
1906     /**
1907      * Returns a string that is a substring of this string. The
1908      * substring begins at the specified {@code beginIndex} and
1909      * extends to the character at index {@code endIndex - 1}.
1910      * Thus the length of the substring is {@code endIndex-beginIndex}.
1911      * <p>
1912      * Examples:
1913      * <blockquote><pre>
1914      * "hamburger".substring(4, 8) returns "urge"
1915      * "smiles".substring(1, 5) returns "mile"
1916      * </pre></blockquote>
1917      *
1918      * @param      beginIndex   the beginning index, inclusive.
1919      * @param      endIndex     the ending index, exclusive.
1920      * @return     the specified substring.
1921      * @exception  IndexOutOfBoundsException  if the
1922      *             {@code beginIndex} is negative, or
1923      *             {@code endIndex} is larger than the length of
1924      *             this {@code String} object, or
1925      *             {@code beginIndex} is larger than
1926      *             {@code endIndex}.
1927      */
1928     public String substring(int beginIndex, int endIndex) {
1929         int length = length();
1930         checkBoundsBeginEnd(beginIndex, endIndex, length);
1931         int subLen = endIndex - beginIndex;
1932         if (beginIndex == 0 && endIndex == length) {
1933             return this;
1934         }
1935         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1936                           : StringUTF16.newString(value, beginIndex, subLen);
1937     }
1938 
1939     /**
1940      * Returns a character sequence that is a subsequence of this sequence.
1941      *
1942      * <p> An invocation of this method of the form
1943      *
1944      * <blockquote><pre>
1945      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1946      *
1947      * behaves in exactly the same way as the invocation
1948      *
1949      * <blockquote><pre>
1950      * str.substring(begin,&nbsp;end)</pre></blockquote>
1951      *
1952      * @apiNote
1953      * This method is defined so that the {@code String} class can implement
1954      * the {@link CharSequence} interface.
1955      *
1956      * @param   beginIndex   the begin index, inclusive.
1957      * @param   endIndex     the end index, exclusive.
1958      * @return  the specified subsequence.
1959      *
1960      * @throws  IndexOutOfBoundsException
1961      *          if {@code beginIndex} or {@code endIndex} is negative,
1962      *          if {@code endIndex} is greater than {@code length()},
1963      *          or if {@code beginIndex} is greater than {@code endIndex}
1964      *
1965      * @since 1.4
1966      * @spec JSR-51
1967      */
1968     public CharSequence subSequence(int beginIndex, int endIndex) {
1969         return this.substring(beginIndex, endIndex);
1970     }
1971 
1972     /**
1973      * Concatenates the specified string to the end of this string.
1974      * <p>
1975      * If the length of the argument string is {@code 0}, then this
1976      * {@code String} object is returned. Otherwise, a
1977      * {@code String} object is returned that represents a character
1978      * sequence that is the concatenation of the character sequence
1979      * represented by this {@code String} object and the character
1980      * sequence represented by the argument string.<p>
1981      * Examples:
1982      * <blockquote><pre>
1983      * "cares".concat("s") returns "caress"
1984      * "to".concat("get").concat("her") returns "together"
1985      * </pre></blockquote>
1986      *
1987      * @param   str   the {@code String} that is concatenated to the end
1988      *                of this {@code String}.
1989      * @return  a string that represents the concatenation of this object's
1990      *          characters followed by the string argument's characters.
1991      */
1992     public String concat(String str) {
1993         int olen = str.length();
1994         if (olen == 0) {
1995             return this;
1996         }
1997         if (coder() == str.coder()) {
1998             byte[] val = this.value;
1999             byte[] oval = str.value;
2000             int len = val.length + oval.length;
2001             byte[] buf = Arrays.copyOf(val, len);
2002             System.arraycopy(oval, 0, buf, val.length, oval.length);
2003             return new String(buf, coder);
2004         }
2005         int len = length();
2006         byte[] buf = StringUTF16.newBytesFor(len + olen);
2007         getBytes(buf, 0, UTF16);
2008         str.getBytes(buf, len, UTF16);
2009         return new String(buf, UTF16);
2010     }
2011 
2012     /**
2013      * Returns a string resulting from replacing all occurrences of
2014      * {@code oldChar} in this string with {@code newChar}.
2015      * <p>
2016      * If the character {@code oldChar} does not occur in the
2017      * character sequence represented by this {@code String} object,
2018      * then a reference to this {@code String} object is returned.
2019      * Otherwise, a {@code String} object is returned that
2020      * represents a character sequence identical to the character sequence
2021      * represented by this {@code String} object, except that every
2022      * occurrence of {@code oldChar} is replaced by an occurrence
2023      * of {@code newChar}.
2024      * <p>
2025      * Examples:
2026      * <blockquote><pre>
2027      * "mesquite in your cellar".replace('e', 'o')
2028      *         returns "mosquito in your collar"
2029      * "the war of baronets".replace('r', 'y')
2030      *         returns "the way of bayonets"
2031      * "sparring with a purple porpoise".replace('p', 't')
2032      *         returns "starring with a turtle tortoise"
2033      * "JonL".replace('q', 'x') returns "JonL" (no change)
2034      * </pre></blockquote>
2035      *
2036      * @param   oldChar   the old character.
2037      * @param   newChar   the new character.
2038      * @return  a string derived from this string by replacing every
2039      *          occurrence of {@code oldChar} with {@code newChar}.
2040      */
2041     public String replace(char oldChar, char newChar) {
2042         if (oldChar != newChar) {
2043             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
2044                                     : StringUTF16.replace(value, oldChar, newChar);
2045             if (ret != null) {
2046                 return ret;
2047             }
2048         }
2049         return this;
2050     }
2051 
2052     /**
2053      * Tells whether or not this string matches the given <a
2054      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2055      *
2056      * <p> An invocation of this method of the form
2057      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2058      * same result as the expression
2059      *
2060      * <blockquote>
2061      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2062      * matches(<i>regex</i>, <i>str</i>)}
2063      * </blockquote>
2064      *
2065      * @param   regex
2066      *          the regular expression to which this string is to be matched
2067      *
2068      * @return  {@code true} if, and only if, this string matches the
2069      *          given regular expression
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 boolean matches(String regex) {
2080         return Pattern.matches(regex, this);
2081     }
2082 
2083     /**
2084      * Returns true if and only if this string contains the specified
2085      * sequence of char values.
2086      *
2087      * @param s the sequence to search for
2088      * @return true if this string contains {@code s}, false otherwise
2089      * @since 1.5
2090      */
2091     public boolean contains(CharSequence s) {
2092         return indexOf(s.toString()) >= 0;
2093     }
2094 
2095     /**
2096      * Replaces the first substring of this string that matches the given <a
2097      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2098      * given replacement.
2099      *
2100      * <p> An invocation of this method of the form
2101      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2102      * yields exactly the same result as the expression
2103      *
2104      * <blockquote>
2105      * <code>
2106      * {@link java.util.regex.Pattern}.{@link
2107      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2108      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2109      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2110      * </code>
2111      * </blockquote>
2112      *
2113      *<p>
2114      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2115      * replacement string may cause the results to be different than if it were
2116      * being treated as a literal replacement string; see
2117      * {@link java.util.regex.Matcher#replaceFirst}.
2118      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2119      * meaning of these characters, if desired.
2120      *
2121      * @param   regex
2122      *          the regular expression to which this string is to be matched
2123      * @param   replacement
2124      *          the string to be substituted for the first match
2125      *
2126      * @return  The resulting {@code String}
2127      *
2128      * @throws  PatternSyntaxException
2129      *          if the regular expression's syntax is invalid
2130      *
2131      * @see java.util.regex.Pattern
2132      *
2133      * @since 1.4
2134      * @spec JSR-51
2135      */
2136     public String replaceFirst(String regex, String replacement) {
2137         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2138     }
2139 
2140     /**
2141      * Replaces each substring of this string that matches the given <a
2142      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2143      * given replacement.
2144      *
2145      * <p> An invocation of this method of the form
2146      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2147      * yields exactly the same result as the expression
2148      *
2149      * <blockquote>
2150      * <code>
2151      * {@link java.util.regex.Pattern}.{@link
2152      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2153      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2154      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2155      * </code>
2156      * </blockquote>
2157      *
2158      *<p>
2159      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2160      * replacement string may cause the results to be different than if it were
2161      * being treated as a literal replacement string; see
2162      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2163      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2164      * meaning of these characters, if desired.
2165      *
2166      * @param   regex
2167      *          the regular expression to which this string is to be matched
2168      * @param   replacement
2169      *          the string to be substituted for each match
2170      *
2171      * @return  The resulting {@code String}
2172      *
2173      * @throws  PatternSyntaxException
2174      *          if the regular expression's syntax is invalid
2175      *
2176      * @see java.util.regex.Pattern
2177      *
2178      * @since 1.4
2179      * @spec JSR-51
2180      */
2181     public String replaceAll(String regex, String replacement) {
2182         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2183     }
2184 
2185     /**
2186      * Replaces each substring of this string that matches the literal target
2187      * sequence with the specified literal replacement sequence. The
2188      * replacement proceeds from the beginning of the string to the end, for
2189      * example, replacing "aa" with "b" in the string "aaa" will result in
2190      * "ba" rather than "ab".
2191      *
2192      * @param  target The sequence of char values to be replaced
2193      * @param  replacement The replacement sequence of char values
2194      * @return  The resulting string
2195      * @since 1.5
2196      */
2197     public String replace(CharSequence target, CharSequence replacement) {
2198         String tgtStr = target.toString();
2199         String replStr = replacement.toString();
2200         int j = indexOf(tgtStr);
2201         if (j < 0) {
2202             return this;
2203         }
2204         int tgtLen = tgtStr.length();
2205         int tgtLen1 = Math.max(tgtLen, 1);
2206         int thisLen = length();
2207 
2208         int newLenHint = thisLen - tgtLen + replStr.length();
2209         if (newLenHint < 0) {
2210             throw new OutOfMemoryError();
2211         }
2212         StringBuilder sb = new StringBuilder(newLenHint);
2213         int i = 0;
2214         do {
2215             sb.append(this, i, j).append(replStr);
2216             i = j + tgtLen;
2217         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2218         return sb.append(this, i, thisLen).toString();
2219     }
2220 
2221     /**
2222      * Splits this string around matches of the given
2223      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2224      *
2225      * <p> The array returned by this method contains each substring of this
2226      * string that is terminated by another substring that matches the given
2227      * expression or is terminated by the end of the string.  The substrings in
2228      * the array are in the order in which they occur in this string.  If the
2229      * expression does not match any part of the input then the resulting array
2230      * has just one element, namely this string.
2231      *
2232      * <p> When there is a positive-width match at the beginning of this
2233      * string then an empty leading substring is included at the beginning
2234      * of the resulting array. A zero-width match at the beginning however
2235      * never produces such empty leading substring.
2236      *
2237      * <p> The {@code limit} parameter controls the number of times the
2238      * pattern is applied and therefore affects the length of the resulting
2239      * array.  If the limit <i>n</i> is greater than zero then the pattern
2240      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2241      * length will be no greater than <i>n</i>, and the array's last entry
2242      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2243      * is non-positive then the pattern will be applied as many times as
2244      * possible and the array can have any length.  If <i>n</i> is zero then
2245      * the pattern will be applied as many times as possible, the array can
2246      * have any length, and trailing empty strings will be discarded.
2247      *
2248      * <p> The string {@code "boo:and:foo"}, for example, yields the
2249      * following results with these parameters:
2250      *
2251      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and result">
2252      * <tr>
2253      *     <th>Regex</th>
2254      *     <th>Limit</th>
2255      *     <th>Result</th>
2256      * </tr>
2257      * <tr><td align=center>:</td>
2258      *     <td align=center>2</td>
2259      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2260      * <tr><td align=center>:</td>
2261      *     <td align=center>5</td>
2262      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2263      * <tr><td align=center>:</td>
2264      *     <td align=center>-2</td>
2265      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2266      * <tr><td align=center>o</td>
2267      *     <td align=center>5</td>
2268      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2269      * <tr><td align=center>o</td>
2270      *     <td align=center>-2</td>
2271      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2272      * <tr><td align=center>o</td>
2273      *     <td align=center>0</td>
2274      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2275      * </table></blockquote>
2276      *
2277      * <p> An invocation of this method of the form
2278      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2279      * yields the same result as the expression
2280      *
2281      * <blockquote>
2282      * <code>
2283      * {@link java.util.regex.Pattern}.{@link
2284      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2285      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2286      * </code>
2287      * </blockquote>
2288      *
2289      *
2290      * @param  regex
2291      *         the delimiting regular expression
2292      *
2293      * @param  limit
2294      *         the result threshold, as described above
2295      *
2296      * @return  the array of strings computed by splitting this string
2297      *          around matches of the given regular expression
2298      *
2299      * @throws  PatternSyntaxException
2300      *          if the regular expression's syntax is invalid
2301      *
2302      * @see java.util.regex.Pattern
2303      *
2304      * @since 1.4
2305      * @spec JSR-51
2306      */
2307     public String[] split(String regex, int limit) {
2308         /* fastpath if the regex is a
2309          (1)one-char String and this character is not one of the
2310             RegEx's meta characters ".$|()[{^?*+\\", or
2311          (2)two-char String and the first char is the backslash and
2312             the second is not the ascii digit or ascii letter.
2313          */
2314         char ch = 0;
2315         if (((regex.length() == 1 &&
2316              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2317              (regex.length() == 2 &&
2318               regex.charAt(0) == '\\' &&
2319               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2320               ((ch-'a')|('z'-ch)) < 0 &&
2321               ((ch-'A')|('Z'-ch)) < 0)) &&
2322             (ch < Character.MIN_HIGH_SURROGATE ||
2323              ch > Character.MAX_LOW_SURROGATE))
2324         {
2325             int off = 0;
2326             int next = 0;
2327             boolean limited = limit > 0;
2328             ArrayList<String> list = new ArrayList<>();
2329             while ((next = indexOf(ch, off)) != -1) {
2330                 if (!limited || list.size() < limit - 1) {
2331                     list.add(substring(off, next));
2332                     off = next + 1;
2333                 } else {    // last one
2334                     //assert (list.size() == limit - 1);
2335                     int last = length();
2336                     list.add(substring(off, last));
2337                     off = last;
2338                     break;
2339                 }
2340             }
2341             // If no match was found, return this
2342             if (off == 0)
2343                 return new String[]{this};
2344 
2345             // Add remaining segment
2346             if (!limited || list.size() < limit)
2347                 list.add(substring(off, length()));
2348 
2349             // Construct result
2350             int resultSize = list.size();
2351             if (limit == 0) {
2352                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2353                     resultSize--;
2354                 }
2355             }
2356             String[] result = new String[resultSize];
2357             return list.subList(0, resultSize).toArray(result);
2358         }
2359         return Pattern.compile(regex).split(this, limit);
2360     }
2361 
2362     /**
2363      * Splits this string around matches of the given <a
2364      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2365      *
2366      * <p> This method works as if by invoking the two-argument {@link
2367      * #split(String, int) split} method with the given expression and a limit
2368      * argument of zero.  Trailing empty strings are therefore not included in
2369      * the resulting array.
2370      *
2371      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2372      * results with these expressions:
2373      *
2374      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and result">
2375      * <tr>
2376      *  <th>Regex</th>
2377      *  <th>Result</th>
2378      * </tr>
2379      * <tr><td align=center>:</td>
2380      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2381      * <tr><td align=center>o</td>
2382      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2383      * </table></blockquote>
2384      *
2385      *
2386      * @param  regex
2387      *         the delimiting regular expression
2388      *
2389      * @return  the array of strings computed by splitting this string
2390      *          around matches of the given regular expression
2391      *
2392      * @throws  PatternSyntaxException
2393      *          if the regular expression's syntax is invalid
2394      *
2395      * @see java.util.regex.Pattern
2396      *
2397      * @since 1.4
2398      * @spec JSR-51
2399      */
2400     public String[] split(String regex) {
2401         return split(regex, 0);
2402     }
2403 
2404     /**
2405      * Returns a new String composed of copies of the
2406      * {@code CharSequence elements} joined together with a copy of
2407      * the specified {@code delimiter}.
2408      *
2409      * <blockquote>For example,
2410      * <pre>{@code
2411      *     String message = String.join("-", "Java", "is", "cool");
2412      *     // message returned is: "Java-is-cool"
2413      * }</pre></blockquote>
2414      *
2415      * Note that if an element is null, then {@code "null"} is added.
2416      *
2417      * @param  delimiter the delimiter that separates each element
2418      * @param  elements the elements to join together.
2419      *
2420      * @return a new {@code String} that is composed of the {@code elements}
2421      *         separated by the {@code delimiter}
2422      *
2423      * @throws NullPointerException If {@code delimiter} or {@code elements}
2424      *         is {@code null}
2425      *
2426      * @see java.util.StringJoiner
2427      * @since 1.8
2428      */
2429     public static String join(CharSequence delimiter, CharSequence... elements) {
2430         Objects.requireNonNull(delimiter);
2431         Objects.requireNonNull(elements);
2432         // Number of elements not likely worth Arrays.stream overhead.
2433         StringJoiner joiner = new StringJoiner(delimiter);
2434         for (CharSequence cs: elements) {
2435             joiner.add(cs);
2436         }
2437         return joiner.toString();
2438     }
2439 
2440     /**
2441      * Returns a new {@code String} composed of copies of the
2442      * {@code CharSequence elements} joined together with a copy of the
2443      * specified {@code delimiter}.
2444      *
2445      * <blockquote>For example,
2446      * <pre>{@code
2447      *     List<String> strings = new LinkedList<>();
2448      *     strings.add("Java");strings.add("is");
2449      *     strings.add("cool");
2450      *     String message = String.join(" ", strings);
2451      *     //message returned is: "Java is cool"
2452      *
2453      *     Set<String> strings = new LinkedHashSet<>();
2454      *     strings.add("Java"); strings.add("is");
2455      *     strings.add("very"); strings.add("cool");
2456      *     String message = String.join("-", strings);
2457      *     //message returned is: "Java-is-very-cool"
2458      * }</pre></blockquote>
2459      *
2460      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2461      *
2462      * @param  delimiter a sequence of characters that is used to separate each
2463      *         of the {@code elements} in the resulting {@code String}
2464      * @param  elements an {@code Iterable} that will have its {@code elements}
2465      *         joined together.
2466      *
2467      * @return a new {@code String} that is composed from the {@code elements}
2468      *         argument
2469      *
2470      * @throws NullPointerException If {@code delimiter} or {@code elements}
2471      *         is {@code null}
2472      *
2473      * @see    #join(CharSequence,CharSequence...)
2474      * @see    java.util.StringJoiner
2475      * @since 1.8
2476      */
2477     public static String join(CharSequence delimiter,
2478             Iterable<? extends CharSequence> elements) {
2479         Objects.requireNonNull(delimiter);
2480         Objects.requireNonNull(elements);
2481         StringJoiner joiner = new StringJoiner(delimiter);
2482         for (CharSequence cs: elements) {
2483             joiner.add(cs);
2484         }
2485         return joiner.toString();
2486     }
2487 
2488     /**
2489      * Converts all of the characters in this {@code String} to lower
2490      * case using the rules of the given {@code Locale}.  Case mapping is based
2491      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2492      * class. Since case mappings are not always 1:1 char mappings, the resulting
2493      * {@code String} may be a different length than the original {@code String}.
2494      * <p>
2495      * Examples of lowercase  mappings are in the following table:
2496      * <table border="1" summary="Lowercase mapping examples showing language code of locale, upper case, lower case, and description">
2497      * <tr>
2498      *   <th>Language Code of Locale</th>
2499      *   <th>Upper Case</th>
2500      *   <th>Lower Case</th>
2501      *   <th>Description</th>
2502      * </tr>
2503      * <tr>
2504      *   <td>tr (Turkish)</td>
2505      *   <td>\u0130</td>
2506      *   <td>\u0069</td>
2507      *   <td>capital letter I with dot above -&gt; small letter i</td>
2508      * </tr>
2509      * <tr>
2510      *   <td>tr (Turkish)</td>
2511      *   <td>\u0049</td>
2512      *   <td>\u0131</td>
2513      *   <td>capital letter I -&gt; small letter dotless i </td>
2514      * </tr>
2515      * <tr>
2516      *   <td>(all)</td>
2517      *   <td>French Fries</td>
2518      *   <td>french fries</td>
2519      *   <td>lowercased all chars in String</td>
2520      * </tr>
2521      * <tr>
2522      *   <td>(all)</td>
2523      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2524      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2525      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2526      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2527      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2528      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2529      *   <td>lowercased all chars in String</td>
2530      * </tr>
2531      * </table>
2532      *
2533      * @param locale use the case transformation rules for this locale
2534      * @return the {@code String}, converted to lowercase.
2535      * @see     java.lang.String#toLowerCase()
2536      * @see     java.lang.String#toUpperCase()
2537      * @see     java.lang.String#toUpperCase(Locale)
2538      * @since   1.1
2539      */
2540     public String toLowerCase(Locale locale) {
2541         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2542                           : StringUTF16.toLowerCase(this, value, locale);
2543     }
2544 
2545     /**
2546      * Converts all of the characters in this {@code String} to lower
2547      * case using the rules of the default locale. This is equivalent to calling
2548      * {@code toLowerCase(Locale.getDefault())}.
2549      * <p>
2550      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2551      * results if used for strings that are intended to be interpreted locale
2552      * independently.
2553      * Examples are programming language identifiers, protocol keys, and HTML
2554      * tags.
2555      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2556      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2557      * LATIN SMALL LETTER DOTLESS I character.
2558      * To obtain correct results for locale insensitive strings, use
2559      * {@code toLowerCase(Locale.ROOT)}.
2560      *
2561      * @return  the {@code String}, converted to lowercase.
2562      * @see     java.lang.String#toLowerCase(Locale)
2563      */
2564     public String toLowerCase() {
2565         return toLowerCase(Locale.getDefault());
2566     }
2567 
2568     /**
2569      * Converts all of the characters in this {@code String} to upper
2570      * case using the rules of the given {@code Locale}. Case mapping is based
2571      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2572      * class. Since case mappings are not always 1:1 char mappings, the resulting
2573      * {@code String} may be a different length than the original {@code String}.
2574      * <p>
2575      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2576      *
2577      * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.">
2578      * <tr>
2579      *   <th>Language Code of Locale</th>
2580      *   <th>Lower Case</th>
2581      *   <th>Upper Case</th>
2582      *   <th>Description</th>
2583      * </tr>
2584      * <tr>
2585      *   <td>tr (Turkish)</td>
2586      *   <td>\u0069</td>
2587      *   <td>\u0130</td>
2588      *   <td>small letter i -&gt; capital letter I with dot above</td>
2589      * </tr>
2590      * <tr>
2591      *   <td>tr (Turkish)</td>
2592      *   <td>\u0131</td>
2593      *   <td>\u0049</td>
2594      *   <td>small letter dotless i -&gt; capital letter I</td>
2595      * </tr>
2596      * <tr>
2597      *   <td>(all)</td>
2598      *   <td>\u00df</td>
2599      *   <td>\u0053 \u0053</td>
2600      *   <td>small letter sharp s -&gt; two letters: SS</td>
2601      * </tr>
2602      * <tr>
2603      *   <td>(all)</td>
2604      *   <td>Fahrvergn&uuml;gen</td>
2605      *   <td>FAHRVERGN&Uuml;GEN</td>
2606      *   <td></td>
2607      * </tr>
2608      * </table>
2609      * @param locale use the case transformation rules for this locale
2610      * @return the {@code String}, converted to uppercase.
2611      * @see     java.lang.String#toUpperCase()
2612      * @see     java.lang.String#toLowerCase()
2613      * @see     java.lang.String#toLowerCase(Locale)
2614      * @since   1.1
2615      */
2616     public String toUpperCase(Locale locale) {
2617         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2618                           : StringUTF16.toUpperCase(this, value, locale);
2619     }
2620 
2621     /**
2622      * Converts all of the characters in this {@code String} to upper
2623      * case using the rules of the default locale. This method is equivalent to
2624      * {@code toUpperCase(Locale.getDefault())}.
2625      * <p>
2626      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2627      * results if used for strings that are intended to be interpreted locale
2628      * independently.
2629      * Examples are programming language identifiers, protocol keys, and HTML
2630      * tags.
2631      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2632      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2633      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2634      * To obtain correct results for locale insensitive strings, use
2635      * {@code toUpperCase(Locale.ROOT)}.
2636      *
2637      * @return  the {@code String}, converted to uppercase.
2638      * @see     java.lang.String#toUpperCase(Locale)
2639      */
2640     public String toUpperCase() {
2641         return toUpperCase(Locale.getDefault());
2642     }
2643 
2644     /**
2645      * Returns a string whose value is this string, with any leading and trailing
2646      * whitespace removed.
2647      * <p>
2648      * If this {@code String} object represents an empty character
2649      * sequence, or the first and last characters of character sequence
2650      * represented by this {@code String} object both have codes
2651      * greater than {@code '\u005Cu0020'} (the space character), then a
2652      * reference to this {@code String} object is returned.
2653      * <p>
2654      * Otherwise, if there is no character with a code greater than
2655      * {@code '\u005Cu0020'} in the string, then a
2656      * {@code String} object representing an empty string is
2657      * returned.
2658      * <p>
2659      * Otherwise, let <i>k</i> be the index of the first character in the
2660      * string whose code is greater than {@code '\u005Cu0020'}, and let
2661      * <i>m</i> be the index of the last character in the string whose code
2662      * is greater than {@code '\u005Cu0020'}. A {@code String}
2663      * object is returned, representing the substring of this string that
2664      * begins with the character at index <i>k</i> and ends with the
2665      * character at index <i>m</i>-that is, the result of
2666      * {@code this.substring(k, m + 1)}.
2667      * <p>
2668      * This method may be used to trim whitespace (as defined above) from
2669      * the beginning and end of a string.
2670      *
2671      * @return  A string whose value is this string, with any leading and trailing white
2672      *          space removed, or this string if it has no leading or
2673      *          trailing white space.
2674      */
2675     public String trim() {
2676         String ret = isLatin1() ? StringLatin1.trim(value)
2677                                 : StringUTF16.trim(value);
2678         return ret == null ? this : ret;
2679     }
2680 
2681     /**
2682      * This object (which is already a string!) is itself returned.
2683      *
2684      * @return  the string itself.
2685      */
2686     public String toString() {
2687         return this;
2688     }
2689 
2690     /**
2691      * Returns a stream of {@code int} zero-extending the {@code char} values
2692      * from this sequence.  Any char which maps to a <a
2693      * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
2694      * point</a> is passed through uninterpreted.
2695      *
2696      * @return an IntStream of char values from this sequence
2697      * @since 9
2698      */
2699     @Override
2700     public IntStream chars() {
2701         return StreamSupport.intStream(
2702             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2703                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
2704             false);
2705     }
2706 
2707 
2708     /**
2709      * Returns a stream of code point values from this sequence.  Any surrogate
2710      * pairs encountered in the sequence are combined as if by {@linkplain
2711      * Character#toCodePoint Character.toCodePoint} and the result is passed
2712      * to the stream. Any other code units, including ordinary BMP characters,
2713      * unpaired surrogates, and undefined code units, are zero-extended to
2714      * {@code int} values which are then passed to the stream.
2715      *
2716      * @return an IntStream of Unicode code points from this sequence
2717      * @since 9
2718      */
2719     @Override
2720     public IntStream codePoints() {
2721         return StreamSupport.intStream(
2722             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2723                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
2724             false);
2725     }
2726 
2727     /**
2728      * Converts this string to a new character array.
2729      *
2730      * @return  a newly allocated character array whose length is the length
2731      *          of this string and whose contents are initialized to contain
2732      *          the character sequence represented by this string.
2733      */
2734     public char[] toCharArray() {
2735         return isLatin1() ? StringLatin1.toChars(value)
2736                           : StringUTF16.toChars(value);
2737     }
2738 
2739     /**
2740      * Returns a formatted string using the specified format string and
2741      * arguments.
2742      *
2743      * <p> The locale always used is the one returned by {@link
2744      * java.util.Locale#getDefault() Locale.getDefault()}.
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 <a
2758      *         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(String format, Object... args) {
2775         return new Formatter().format(format, args).toString();
2776     }
2777 
2778     /**
2779      * Returns a formatted string using the specified locale, format string,
2780      * and arguments.
2781      *
2782      * @param  l
2783      *         The {@linkplain java.util.Locale locale} to apply during
2784      *         formatting.  If {@code l} is {@code null} then no localization
2785      *         is applied.
2786      *
2787      * @param  format
2788      *         A <a href="../util/Formatter.html#syntax">format string</a>
2789      *
2790      * @param  args
2791      *         Arguments referenced by the format specifiers in the format
2792      *         string.  If there are more arguments than format specifiers, the
2793      *         extra arguments are ignored.  The number of arguments is
2794      *         variable and may be zero.  The maximum number of arguments is
2795      *         limited by the maximum dimension of a Java array as defined by
2796      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2797      *         The behaviour on a
2798      *         {@code null} argument depends on the
2799      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2800      *
2801      * @throws  java.util.IllegalFormatException
2802      *          If a format string contains an illegal syntax, a format
2803      *          specifier that is incompatible with the given arguments,
2804      *          insufficient arguments given the format string, or other
2805      *          illegal conditions.  For specification of all possible
2806      *          formatting errors, see the <a
2807      *          href="../util/Formatter.html#detail">Details</a> section of the
2808      *          formatter class specification
2809      *
2810      * @return  A formatted string
2811      *
2812      * @see  java.util.Formatter
2813      * @since  1.5
2814      */
2815     public static String format(Locale l, String format, Object... args) {
2816         return new Formatter(l).format(format, args).toString();
2817     }
2818 
2819     /**
2820      * Returns the string representation of the {@code Object} argument.
2821      *
2822      * @param   obj   an {@code Object}.
2823      * @return  if the argument is {@code null}, then a string equal to
2824      *          {@code "null"}; otherwise, the value of
2825      *          {@code obj.toString()} is returned.
2826      * @see     java.lang.Object#toString()
2827      */
2828     public static String valueOf(Object obj) {
2829         return (obj == null) ? "null" : obj.toString();
2830     }
2831 
2832     /**
2833      * Returns the string representation of the {@code char} array
2834      * argument. The contents of the character array are copied; subsequent
2835      * modification of the character array does not affect the returned
2836      * string.
2837      *
2838      * @param   data     the character array.
2839      * @return  a {@code String} that contains the characters of the
2840      *          character array.
2841      */
2842     public static String valueOf(char data[]) {
2843         return new String(data);
2844     }
2845 
2846     /**
2847      * Returns the string representation of a specific subarray of the
2848      * {@code char} array argument.
2849      * <p>
2850      * The {@code offset} argument is the index of the first
2851      * character of the subarray. The {@code count} argument
2852      * specifies the length of the subarray. The contents of the subarray
2853      * are copied; subsequent modification of the character array does not
2854      * affect the returned string.
2855      *
2856      * @param   data     the character array.
2857      * @param   offset   initial offset of the subarray.
2858      * @param   count    length of the subarray.
2859      * @return  a {@code String} that contains the characters of the
2860      *          specified subarray of the character array.
2861      * @exception IndexOutOfBoundsException if {@code offset} is
2862      *          negative, or {@code count} is negative, or
2863      *          {@code offset+count} is larger than
2864      *          {@code data.length}.
2865      */
2866     public static String valueOf(char data[], int offset, int count) {
2867         return new String(data, offset, count);
2868     }
2869 
2870     /**
2871      * Equivalent to {@link #valueOf(char[], int, int)}.
2872      *
2873      * @param   data     the character array.
2874      * @param   offset   initial offset of the subarray.
2875      * @param   count    length of the subarray.
2876      * @return  a {@code String} that contains the characters of the
2877      *          specified subarray of the character array.
2878      * @exception IndexOutOfBoundsException if {@code offset} is
2879      *          negative, or {@code count} is negative, or
2880      *          {@code offset+count} is larger than
2881      *          {@code data.length}.
2882      */
2883     public static String copyValueOf(char data[], int offset, int count) {
2884         return new String(data, offset, count);
2885     }
2886 
2887     /**
2888      * Equivalent to {@link #valueOf(char[])}.
2889      *
2890      * @param   data   the character array.
2891      * @return  a {@code String} that contains the characters of the
2892      *          character array.
2893      */
2894     public static String copyValueOf(char data[]) {
2895         return new String(data);
2896     }
2897 
2898     /**
2899      * Returns the string representation of the {@code boolean} argument.
2900      *
2901      * @param   b   a {@code boolean}.
2902      * @return  if the argument is {@code true}, a string equal to
2903      *          {@code "true"} is returned; otherwise, a string equal to
2904      *          {@code "false"} is returned.
2905      */
2906     public static String valueOf(boolean b) {
2907         return b ? "true" : "false";
2908     }
2909 
2910     /**
2911      * Returns the string representation of the {@code char}
2912      * argument.
2913      *
2914      * @param   c   a {@code char}.
2915      * @return  a string of length {@code 1} containing
2916      *          as its single character the argument {@code c}.
2917      */
2918     public static String valueOf(char c) {
2919         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
2920             return new String(StringLatin1.toBytes(c), LATIN1);
2921         }
2922         return new String(StringUTF16.toBytes(c), UTF16);
2923     }
2924 
2925     /**
2926      * Returns the string representation of the {@code int} argument.
2927      * <p>
2928      * The representation is exactly the one returned by the
2929      * {@code Integer.toString} method of one argument.
2930      *
2931      * @param   i   an {@code int}.
2932      * @return  a string representation of the {@code int} argument.
2933      * @see     java.lang.Integer#toString(int, int)
2934      */
2935     public static String valueOf(int i) {
2936         return Integer.toString(i);
2937     }
2938 
2939     /**
2940      * Returns the string representation of the {@code long} argument.
2941      * <p>
2942      * The representation is exactly the one returned by the
2943      * {@code Long.toString} method of one argument.
2944      *
2945      * @param   l   a {@code long}.
2946      * @return  a string representation of the {@code long} argument.
2947      * @see     java.lang.Long#toString(long)
2948      */
2949     public static String valueOf(long l) {
2950         return Long.toString(l);
2951     }
2952 
2953     /**
2954      * Returns the string representation of the {@code float} argument.
2955      * <p>
2956      * The representation is exactly the one returned by the
2957      * {@code Float.toString} method of one argument.
2958      *
2959      * @param   f   a {@code float}.
2960      * @return  a string representation of the {@code float} argument.
2961      * @see     java.lang.Float#toString(float)
2962      */
2963     public static String valueOf(float f) {
2964         return Float.toString(f);
2965     }
2966 
2967     /**
2968      * Returns the string representation of the {@code double} argument.
2969      * <p>
2970      * The representation is exactly the one returned by the
2971      * {@code Double.toString} method of one argument.
2972      *
2973      * @param   d   a {@code double}.
2974      * @return  a  string representation of the {@code double} argument.
2975      * @see     java.lang.Double#toString(double)
2976      */
2977     public static String valueOf(double d) {
2978         return Double.toString(d);
2979     }
2980 
2981     /**
2982      * Returns a canonical representation for the string object.
2983      * <p>
2984      * A pool of strings, initially empty, is maintained privately by the
2985      * class {@code String}.
2986      * <p>
2987      * When the intern method is invoked, if the pool already contains a
2988      * string equal to this {@code String} object as determined by
2989      * the {@link #equals(Object)} method, then the string from the pool is
2990      * returned. Otherwise, this {@code String} object is added to the
2991      * pool and a reference to this {@code String} object is returned.
2992      * <p>
2993      * It follows that for any two strings {@code s} and {@code t},
2994      * {@code s.intern() == t.intern()} is {@code true}
2995      * if and only if {@code s.equals(t)} is {@code true}.
2996      * <p>
2997      * All literal strings and string-valued constant expressions are
2998      * interned. String literals are defined in section 3.10.5 of the
2999      * <cite>The Java&trade; Language Specification</cite>.
3000      *
3001      * @return  a string that has the same contents as this string, but is
3002      *          guaranteed to be from a pool of unique strings.
3003      */
3004     public native String intern();
3005 
3006     ////////////////////////////////////////////////////////////////
3007 
3008     /**
3009      * Copy character bytes from this string into dst starting at dstBegin.
3010      * This method doesn't perform any range checking.
3011      *
3012      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
3013      * coders are different, and dst is big enough (range check)
3014      *
3015      * @param dstBegin  the char index, not offset of byte[]
3016      * @param coder     the coder of dst[]
3017      */
3018     void getBytes(byte dst[], int dstBegin, byte coder) {
3019         if (coder() == coder) {
3020             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
3021         } else {    // this.coder == LATIN && coder == UTF16
3022             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
3023         }
3024     }
3025 
3026     /*
3027      * Package private constructor. Trailing Void argument is there for
3028      * disambiguating it against other (public) constructors.
3029      *
3030      * Stores the char[] value into a byte[] that each byte represents
3031      * the8 low-order bits of the corresponding character, if the char[]
3032      * contains only latin1 character. Or a byte[] that stores all
3033      * characters in their byte sequences defined by the {@code StringUTF16}.
3034      */
3035     String(char[] value, int off, int len, Void sig) {
3036         if (len == 0) {
3037             this.value = "".value;
3038             this.coder = "".coder;
3039             return;
3040         }
3041         if (COMPACT_STRINGS) {
3042             byte[] val = StringUTF16.compress(value, off, len);
3043             if (val != null) {
3044                 this.value = val;
3045                 this.coder = LATIN1;
3046                 return;
3047             }
3048         }
3049         this.coder = UTF16;
3050         this.value = StringUTF16.toBytes(value, off, len);
3051     }
3052 
3053     /*
3054      * Package private constructor. Trailing Void argument is there for
3055      * disambiguating it against other (public) constructors.
3056      */
3057     String(AbstractStringBuilder asb, Void sig) {
3058         byte[] val = asb.getValue();
3059         int length = asb.length();
3060         if (asb.isLatin1()) {
3061             this.coder = LATIN1;
3062             this.value = Arrays.copyOfRange(val, 0, length);
3063         } else {
3064             if (COMPACT_STRINGS) {
3065                 byte[] buf = StringUTF16.compress(val, 0, length);
3066                 if (buf != null) {
3067                     this.coder = LATIN1;
3068                     this.value = buf;
3069                     return;
3070                 }
3071             }
3072             this.coder = UTF16;
3073             this.value = Arrays.copyOfRange(val, 0, length << 1);
3074         }
3075     }
3076 
3077    /*
3078     * Package private constructor which shares value array for speed.
3079     */
3080     String(byte[] value, byte coder) {
3081         this.value = value;
3082         this.coder = coder;
3083     }
3084 
3085     byte coder() {
3086         return COMPACT_STRINGS ? coder : UTF16;
3087     }
3088 
3089     private boolean isLatin1() {
3090         return COMPACT_STRINGS && coder == LATIN1;
3091     }
3092 
3093     static final byte LATIN1 = 0;
3094     static final byte UTF16  = 1;
3095 
3096     /*
3097      * StringIndexOutOfBoundsException  if {@code index} is
3098      * negative or greater than or equal to {@code length}.
3099      */
3100     static void checkIndex(int index, int length) {
3101         if (index < 0 || index >= length) {
3102             throw new StringIndexOutOfBoundsException("index " + index);
3103         }
3104     }
3105 
3106     /*
3107      * StringIndexOutOfBoundsException  if {@code offset}
3108      * is negative or greater than {@code length}.
3109      */
3110     static void checkOffset(int offset, int length) {
3111         if (offset < 0 || offset > length) {
3112             throw new StringIndexOutOfBoundsException("offset " + offset +
3113                                                       ",length " + length);
3114         }
3115     }
3116 
3117     /*
3118      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3119      * bounds.
3120      *
3121      * @throws  StringIndexOutOfBoundsException
3122      *          If {@code offset} is negative, {@code count} is negative,
3123      *          or {@code offset} is greater than {@code length - count}
3124      */
3125     static void checkBoundsOffCount(int offset, int count, int length) {
3126         if (offset < 0 || count < 0 || offset > length - count) {
3127             throw new StringIndexOutOfBoundsException(
3128                 "offset " + offset + ", count " + count + ", length " + length);
3129         }
3130     }
3131 
3132     /*
3133      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3134      * bounds.
3135      *
3136      * @throws  StringIndexOutOfBoundsException
3137      *          If {@code begin} is negative, {@code begin} is greater than
3138      *          {@code end}, or {@code end} is greater than {@code length}.
3139      */
3140     private static void checkBoundsBeginEnd(int begin, int end, int length) {
3141         if (begin < 0 || begin > end || end > length) {
3142             throw new StringIndexOutOfBoundsException(
3143                 "begin " + begin + ", end " + end + ", length " + length);
3144         }
3145     }
3146 }