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.regex.Matcher;
  40 import java.util.regex.Pattern;
  41 import java.util.regex.PatternSyntaxException;
  42 import java.util.stream.IntStream;
  43 import java.util.stream.StreamSupport;
  44 import jdk.internal.HotSpotIntrinsicCandidate;
  45 
  46 /**
  47  * The {@code String} class represents character strings. All
  48  * string literals in Java programs, such as {@code "abc"}, are
  49  * implemented as instances of this class.
  50  * <p>
  51  * Strings are constant; their values cannot be changed after they
  52  * are created. String buffers support mutable strings.
  53  * Because String objects are immutable they can be shared. For example:
  54  * <blockquote><pre>
  55  *     String str = "abc";
  56  * </pre></blockquote><p>
  57  * is equivalent to:
  58  * <blockquote><pre>
  59  *     char data[] = {'a', 'b', 'c'};
  60  *     String str = new String(data);
  61  * </pre></blockquote><p>
  62  * Here are some more examples of how strings can be used:
  63  * <blockquote><pre>
  64  *     System.out.println("abc");
  65  *     String cde = "cde";
  66  *     System.out.println("abc" + cde);
  67  *     String c = "abc".substring(2,3);
  68  *     String d = cde.substring(1, 2);
  69  * </pre></blockquote>
  70  * <p>
  71  * The class {@code String} includes methods for examining
  72  * individual characters of the sequence, for comparing strings, for
  73  * searching strings, for extracting substrings, and for creating a
  74  * copy of a string with all characters translated to uppercase or to
  75  * lowercase. Case mapping is based on the Unicode Standard version
  76  * specified by the {@link java.lang.Character Character} class.
  77  * <p>
  78  * The Java language provides special support for the string
  79  * concatenation operator (&nbsp;+&nbsp;), and for conversion of
  80  * other objects to strings. String concatenation is implemented
  81  * through the {@code StringBuilder}(or {@code StringBuffer})
  82  * class and its {@code append} method.
  83  * String conversions are implemented through the method
  84  * {@code toString}, defined by {@code Object} and
  85  * inherited by all classes in Java. For additional information on
  86  * string concatenation and conversion, see Gosling, Joy, and Steele,
  87  * <i>The Java Language Specification</i>.
  88  *
  89  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  90  * or method in this class will cause a {@link NullPointerException} to be
  91  * thrown.
  92  *
  93  * <p>A {@code String} represents a string in the UTF-16 format
  94  * in which <em>supplementary characters</em> are represented by <em>surrogate
  95  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  96  * Character Representations</a> in the {@code Character} class for
  97  * more information).
  98  * Index values refer to {@code char} code units, so a supplementary
  99  * character uses two positions in a {@code String}.
 100  * <p>The {@code String} class provides methods for dealing with
 101  * Unicode code points (i.e., characters), in addition to those for
 102  * dealing with Unicode code units (i.e., {@code char} values).
 103  *
 104  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 105  * into account.  The {@link java.text.Collator} class provides methods for
 106  * finer-grain, locale-sensitive String comparison.
 107  *
 108  * @author  Lee Boynton
 109  * @author  Arthur van Hoff
 110  * @author  Martin Buchholz
 111  * @author  Ulf Zibis
 112  * @see     java.lang.Object#toString()
 113  * @see     java.lang.StringBuffer
 114  * @see     java.lang.StringBuilder
 115  * @see     java.nio.charset.Charset
 116  * @since   1.0
 117  */
 118 
 119 public final class String
 120     implements java.io.Serializable, Comparable<String>, CharSequence {
 121 
 122     /** The value is used for character storage. */
 123     private final byte[] value;
 124 
 125     /**
 126      * The identifier of the encoding used to encode the bytes in
 127      * {@code value}. The supported values in this implementation are
 128      *
 129      * LATIN1
 130      * UTF16
 131      *
 132      */
 133     private final byte coder;
 134 
 135     /** Cache the hash code for the string */
 136     private int hash; // Default to 0
 137 
 138     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 139     private static final long serialVersionUID = -6849794470754667710L;
 140 
 141     /**
 142      * If String compaction is disabled, the bytes in {@code value} are
 143      * always encoded in UTF16.
 144      *
 145      * For methods with several possible implementation paths, when String
 146      * compaction is disabled, only one code path is taken.
 147      *
 148      * The instance field value is generally opaque to optimizing JIT
 149      * compilers. Therefore, in performance-sensitive place, an explicit
 150      * check of the static boolean {@code COMPACT_STRINGS} is done first
 151      * before checking the {@code coder} field since the static boolean
 152      * {@code COMPACT_STRINGS} would be constant folded away by an
 153      * optimizing JIT compiler. The idioms for these cases are as follows.
 154      *
 155      * For code such as:
 156      *
 157      *    if (coder == LATIN1) { ... }
 158      *
 159      * can be written more optimally as
 160      *
 161      *    if (coder() == LATIN1) { ... }
 162      *
 163      * or:
 164      *
 165      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 166      *
 167      * An optimizing JIT compiler can fold the above conditional as:
 168      *
 169      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 170      *    COMPACT_STRINGS == false => if (false)           { ... }
 171      *
 172      * @implNote
 173      * The actual value for this field is injected by JVM. The static
 174      * initialization block is used to set the value here to communicate
 175      * that this static final field is not statically foldable, and to
 176      * avoid any possible circular dependency during vm initialization.
 177      */
 178     static final boolean COMPACT_STRINGS;
 179 
 180     static {
 181         COMPACT_STRINGS = true;
 182     }
 183 
 184     /**
 185      * Class String is special cased within the Serialization Stream Protocol.
 186      *
 187      * A String instance is written into an ObjectOutputStream according to
 188      * <a href="{@docRoot}/../platform/serialization/spec/output.html">
 189      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 190      */
 191     private static final ObjectStreamField[] serialPersistentFields =
 192         new ObjectStreamField[0];
 193 
 194     /**
 195      * Initializes a newly created {@code String} object so that it represents
 196      * an empty character sequence.  Note that use of this constructor is
 197      * unnecessary since Strings are immutable.
 198      */
 199     public String() {
 200         this.value = "".value;
 201         this.coder = "".coder;
 202     }
 203 
 204     /**
 205      * Initializes a newly created {@code String} object so that it represents
 206      * the same sequence of characters as the argument; in other words, the
 207      * newly created string is a copy of the argument string. Unless an
 208      * explicit copy of {@code original} is needed, use of this constructor is
 209      * unnecessary since Strings are immutable.
 210      *
 211      * @param  original
 212      *         A {@code String}
 213      */
 214     @HotSpotIntrinsicCandidate
 215     public String(String original) {
 216         this.value = original.value;
 217         this.coder = original.coder;
 218         this.hash = original.hash;
 219     }
 220 
 221     /**
 222      * Allocates a new {@code String} so that it represents the sequence of
 223      * characters currently contained in the character array argument. The
 224      * contents of the character array are copied; subsequent modification of
 225      * the character array does not affect the newly created string.
 226      *
 227      * @param  value
 228      *         The initial value of the string
 229      */
 230     public String(char value[]) {
 231         this(value, 0, value.length, null);
 232     }
 233 
 234     /**
 235      * Allocates a new {@code String} that contains characters from a subarray
 236      * of the character array argument. The {@code offset} argument is the
 237      * index of the first character of the subarray and the {@code count}
 238      * argument specifies the length of the subarray. The contents of the
 239      * subarray are copied; subsequent modification of the character array does
 240      * not affect the newly created string.
 241      *
 242      * @param  value
 243      *         Array that is the source of characters
 244      *
 245      * @param  offset
 246      *         The initial offset
 247      *
 248      * @param  count
 249      *         The length
 250      *
 251      * @throws  IndexOutOfBoundsException
 252      *          If {@code offset} is negative, {@code count} is negative, or
 253      *          {@code offset} is greater than {@code value.length - count}
 254      */
 255     public String(char value[], int offset, int count) {
 256         this(value, offset, count, rangeCheck(value, offset, count));
 257     }
 258 
 259     private static Void rangeCheck(char[] value, int offset, int count) {
 260         checkBoundsOffCount(offset, count, value.length);
 261         return null;
 262     }
 263 
 264     /**
 265      * Allocates a new {@code String} that contains characters from a subarray
 266      * of the <a href="Character.html#unicode">Unicode code point</a> array
 267      * argument.  The {@code offset} argument is the index of the first code
 268      * point of the subarray and the {@code count} argument specifies the
 269      * length of the subarray.  The contents of the subarray are converted to
 270      * {@code char}s; subsequent modification of the {@code int} array does not
 271      * affect the newly created string.
 272      *
 273      * @param  codePoints
 274      *         Array that is the source of Unicode code points
 275      *
 276      * @param  offset
 277      *         The initial offset
 278      *
 279      * @param  count
 280      *         The length
 281      *
 282      * @throws  IllegalArgumentException
 283      *          If any invalid Unicode code point is found in {@code
 284      *          codePoints}
 285      *
 286      * @throws  IndexOutOfBoundsException
 287      *          If {@code offset} is negative, {@code count} is negative, or
 288      *          {@code offset} is greater than {@code codePoints.length - count}
 289      *
 290      * @since  1.5
 291      */
 292     public String(int[] codePoints, int offset, int count) {
 293         checkBoundsOffCount(offset, count, codePoints.length);
 294         if (count == 0) {
 295             this.value = "".value;
 296             this.coder = "".coder;
 297             return;
 298         }
 299         if (COMPACT_STRINGS) {
 300             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 301             if (val != null) {
 302                 this.coder = LATIN1;
 303                 this.value = val;
 304                 return;
 305             }
 306         }
 307         this.coder = UTF16;
 308         this.value = StringUTF16.toBytes(codePoints, offset, count);
 309     }
 310 
 311     /**
 312      * Allocates a new {@code String} constructed from a subarray of an array
 313      * of 8-bit integer values.
 314      *
 315      * <p> The {@code offset} argument is the index of the first byte of the
 316      * subarray, and the {@code count} argument specifies the length of the
 317      * subarray.
 318      *
 319      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 320      * specified in the method above.
 321      *
 322      * @deprecated This method does not properly convert bytes into characters.
 323      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 324      * {@code String} constructors that take a {@link
 325      * java.nio.charset.Charset}, charset name, or that use the platform's
 326      * default charset.
 327      *
 328      * @param  ascii
 329      *         The bytes to be converted to characters
 330      *
 331      * @param  hibyte
 332      *         The top 8 bits of each 16-bit Unicode code unit
 333      *
 334      * @param  offset
 335      *         The initial offset
 336      * @param  count
 337      *         The length
 338      *
 339      * @throws  IndexOutOfBoundsException
 340      *          If {@code offset} is negative, {@code count} is negative, or
 341      *          {@code offset} is greater than {@code ascii.length - count}
 342      *
 343      * @see  #String(byte[], int)
 344      * @see  #String(byte[], int, int, java.lang.String)
 345      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 346      * @see  #String(byte[], int, int)
 347      * @see  #String(byte[], java.lang.String)
 348      * @see  #String(byte[], java.nio.charset.Charset)
 349      * @see  #String(byte[])
 350      */
 351     @Deprecated
 352     public String(byte ascii[], int hibyte, int offset, int count) {
 353         checkBoundsOffCount(offset, count, ascii.length);
 354         if (count == 0) {
 355             this.value = "".value;
 356             this.coder = "".coder;
 357             return;
 358         }
 359         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 360             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 361             this.coder = LATIN1;
 362         } else {
 363             hibyte <<= 8;
 364             byte[] val = StringUTF16.newBytesFor(count);
 365             for (int i = 0; i < count; i++) {
 366                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 367             }
 368             this.value = val;
 369             this.coder = UTF16;
 370         }
 371     }
 372 
 373     /**
 374      * Allocates a new {@code String} containing characters constructed from
 375      * an array of 8-bit integer values. Each character <i>c</i>in the
 376      * resulting string is constructed from the corresponding component
 377      * <i>b</i> in the byte array such that:
 378      *
 379      * <blockquote><pre>
 380      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 381      *                         | (<b><i>b</i></b> &amp; 0xff))
 382      * </pre></blockquote>
 383      *
 384      * @deprecated  This method does not properly convert bytes into
 385      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 386      * {@code String} constructors that take a {@link
 387      * java.nio.charset.Charset}, charset name, or that use the platform's
 388      * default charset.
 389      *
 390      * @param  ascii
 391      *         The bytes to be converted to characters
 392      *
 393      * @param  hibyte
 394      *         The top 8 bits of each 16-bit Unicode code unit
 395      *
 396      * @see  #String(byte[], int, int, java.lang.String)
 397      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 398      * @see  #String(byte[], int, int)
 399      * @see  #String(byte[], java.lang.String)
 400      * @see  #String(byte[], java.nio.charset.Charset)
 401      * @see  #String(byte[])
 402      */
 403     @Deprecated
 404     public String(byte ascii[], int hibyte) {
 405         this(ascii, hibyte, 0, ascii.length);
 406     }
 407 
 408     /**
 409      * Constructs a new {@code String} by decoding the specified subarray of
 410      * bytes using the specified charset.  The length of the new {@code String}
 411      * is a function of the charset, and hence may not be equal to the length
 412      * of the subarray.
 413      *
 414      * <p> The behavior of this constructor when the given bytes are not valid
 415      * in the given charset is unspecified.  The {@link
 416      * java.nio.charset.CharsetDecoder} class should be used when more control
 417      * over the decoding process is required.
 418      *
 419      * @param  bytes
 420      *         The bytes to be decoded into characters
 421      *
 422      * @param  offset
 423      *         The index of the first byte to decode
 424      *
 425      * @param  length
 426      *         The number of bytes to decode
 427 
 428      * @param  charsetName
 429      *         The name of a supported {@linkplain java.nio.charset.Charset
 430      *         charset}
 431      *
 432      * @throws  UnsupportedEncodingException
 433      *          If the named charset is not supported
 434      *
 435      * @throws  IndexOutOfBoundsException
 436      *          If {@code offset} is negative, {@code length} is negative, or
 437      *          {@code offset} is greater than {@code bytes.length - length}
 438      *
 439      * @since  1.1
 440      */
 441     public String(byte bytes[], int offset, int length, String charsetName)
 442             throws UnsupportedEncodingException {
 443         if (charsetName == null)
 444             throw new NullPointerException("charsetName");
 445         checkBoundsOffCount(offset, length, bytes.length);
 446         StringCoding.Result ret =
 447             StringCoding.decode(charsetName, bytes, offset, length);
 448         this.value = ret.value;
 449         this.coder = ret.coder;
 450     }
 451 
 452     /**
 453      * Constructs a new {@code String} by decoding the specified subarray of
 454      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 455      * The length of the new {@code String} is a function of the charset, and
 456      * hence may not be equal to the length of the subarray.
 457      *
 458      * <p> This method always replaces malformed-input and unmappable-character
 459      * sequences with this charset's default replacement string.  The {@link
 460      * java.nio.charset.CharsetDecoder} class should be used when more control
 461      * over the decoding process is required.
 462      *
 463      * @param  bytes
 464      *         The bytes to be decoded into characters
 465      *
 466      * @param  offset
 467      *         The index of the first byte to decode
 468      *
 469      * @param  length
 470      *         The number of bytes to decode
 471      *
 472      * @param  charset
 473      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 474      *         decode the {@code bytes}
 475      *
 476      * @throws  IndexOutOfBoundsException
 477      *          If {@code offset} is negative, {@code length} is negative, or
 478      *          {@code offset} is greater than {@code bytes.length - length}
 479      *
 480      * @since  1.6
 481      */
 482     public String(byte bytes[], int offset, int length, Charset charset) {
 483         if (charset == null)
 484             throw new NullPointerException("charset");
 485         checkBoundsOffCount(offset, length, bytes.length);
 486         StringCoding.Result ret =
 487             StringCoding.decode(charset, bytes, offset, length);
 488         this.value = ret.value;
 489         this.coder = ret.coder;
 490     }
 491 
 492     /**
 493      * Constructs a new {@code String} by decoding the specified array of bytes
 494      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 495      * length of the new {@code String} is a function of the charset, and hence
 496      * may not be equal to the length of the byte array.
 497      *
 498      * <p> The behavior of this constructor when the given bytes are not valid
 499      * in the given charset is unspecified.  The {@link
 500      * java.nio.charset.CharsetDecoder} class should be used when more control
 501      * over the decoding process is required.
 502      *
 503      * @param  bytes
 504      *         The bytes to be decoded into characters
 505      *
 506      * @param  charsetName
 507      *         The name of a supported {@linkplain java.nio.charset.Charset
 508      *         charset}
 509      *
 510      * @throws  UnsupportedEncodingException
 511      *          If the named charset is not supported
 512      *
 513      * @since  1.1
 514      */
 515     public String(byte bytes[], String charsetName)
 516             throws UnsupportedEncodingException {
 517         this(bytes, 0, bytes.length, charsetName);
 518     }
 519 
 520     /**
 521      * Constructs a new {@code String} by decoding the specified array of
 522      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 523      * The length of the new {@code String} is a function of the charset, and
 524      * hence may not be equal to the length of the byte array.
 525      *
 526      * <p> This method always replaces malformed-input and unmappable-character
 527      * sequences with this charset's default replacement string.  The {@link
 528      * java.nio.charset.CharsetDecoder} class should be used when more control
 529      * over the decoding process is required.
 530      *
 531      * @param  bytes
 532      *         The bytes to be decoded into characters
 533      *
 534      * @param  charset
 535      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 536      *         decode the {@code bytes}
 537      *
 538      * @since  1.6
 539      */
 540     public String(byte bytes[], Charset charset) {
 541         this(bytes, 0, bytes.length, charset);
 542     }
 543 
 544     /**
 545      * Constructs a new {@code String} by decoding the specified subarray of
 546      * bytes using the platform's default charset.  The length of the new
 547      * {@code String} is a function of the charset, and hence may not be equal
 548      * to the length of the subarray.
 549      *
 550      * <p> The behavior of this constructor when the given bytes are not valid
 551      * in the default charset is unspecified.  The {@link
 552      * java.nio.charset.CharsetDecoder} class should be used when more control
 553      * over the decoding process is required.
 554      *
 555      * @param  bytes
 556      *         The bytes to be decoded into characters
 557      *
 558      * @param  offset
 559      *         The index of the first byte to decode
 560      *
 561      * @param  length
 562      *         The number of bytes to decode
 563      *
 564      * @throws  IndexOutOfBoundsException
 565      *          If {@code offset} is negative, {@code length} is negative, or
 566      *          {@code offset} is greater than {@code bytes.length - length}
 567      *
 568      * @since  1.1
 569      */
 570     public String(byte bytes[], int offset, int length) {
 571         checkBoundsOffCount(offset, length, bytes.length);
 572         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 573         this.value = ret.value;
 574         this.coder = ret.coder;
 575     }
 576 
 577     /**
 578      * Constructs a new {@code String} by decoding the specified array of bytes
 579      * using the platform's default charset.  The length of the new {@code
 580      * String} is a function of the charset, and hence may not be equal to the
 581      * length of the byte array.
 582      *
 583      * <p> The behavior of this constructor when the given bytes are not valid
 584      * in the default charset is unspecified.  The {@link
 585      * java.nio.charset.CharsetDecoder} class should be used when more control
 586      * over the decoding process is required.
 587      *
 588      * @param  bytes
 589      *         The bytes to be decoded into characters
 590      *
 591      * @since  1.1
 592      */
 593     public String(byte[] bytes) {
 594         this(bytes, 0, bytes.length);
 595     }
 596 
 597     /**
 598      * Allocates a new string that contains the sequence of characters
 599      * currently contained in the string buffer argument. The contents of the
 600      * string buffer are copied; subsequent modification of the string buffer
 601      * does not affect the newly created string.
 602      *
 603      * @param  buffer
 604      *         A {@code StringBuffer}
 605      */
 606     public String(StringBuffer buffer) {
 607         this(buffer.toString());
 608     }
 609 
 610     /**
 611      * Allocates a new string that contains the sequence of characters
 612      * currently contained in the string builder argument. The contents of the
 613      * string builder are copied; subsequent modification of the string builder
 614      * does not affect the newly created string.
 615      *
 616      * <p> This constructor is provided to ease migration to {@code
 617      * StringBuilder}. Obtaining a string from a string builder via the {@code
 618      * toString} method is likely to run faster and is generally preferred.
 619      *
 620      * @param   builder
 621      *          A {@code StringBuilder}
 622      *
 623      * @since  1.5
 624      */
 625     public String(StringBuilder builder) {
 626         this(builder, null);
 627     }
 628 
 629    /*
 630     * Package private constructor which shares value array for speed.
 631     * this constructor is always expected to be called with share==true.
 632     * a separate constructor is needed because we already have a public
 633     * String(char[]) constructor that makes a copy of the given char[].
 634     */
 635     // TBD: this is kept for package internal use (Thread/System),
 636     // should be removed if they all have a byte[] version
 637     String(char[] val, boolean share) {
 638         // assert share : "unshared not supported";
 639         this(val, 0, val.length, null);
 640     }
 641 
 642     /**
 643      * Returns the length of this string.
 644      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 645      * code units</a> in the string.
 646      *
 647      * @return  the length of the sequence of characters represented by this
 648      *          object.
 649      */
 650     public int length() {
 651         return value.length >> coder();
 652     }
 653 
 654     /**
 655      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 656      *
 657      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 658      * {@code false}
 659      *
 660      * @since 1.6
 661      */
 662     public boolean isEmpty() {
 663         return value.length == 0;
 664     }
 665 
 666     /**
 667      * Returns the {@code char} value at the
 668      * specified index. An index ranges from {@code 0} to
 669      * {@code length() - 1}. The first {@code char} value of the sequence
 670      * is at index {@code 0}, the next at index {@code 1},
 671      * and so on, as for array indexing.
 672      *
 673      * <p>If the {@code char} value specified by the index is a
 674      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 675      * value is returned.
 676      *
 677      * @param      index   the index of the {@code char} value.
 678      * @return     the {@code char} value at the specified index of this string.
 679      *             The first {@code char} value is at index {@code 0}.
 680      * @exception  IndexOutOfBoundsException  if the {@code index}
 681      *             argument is negative or not less than the length of this
 682      *             string.
 683      */
 684     public char charAt(int index) {
 685         if (isLatin1()) {
 686             return StringLatin1.charAt(value, index);
 687         } else {
 688             return StringUTF16.charAt(value, index);
 689         }
 690     }
 691 
 692     /**
 693      * Returns the character (Unicode code point) at the specified
 694      * index. The index refers to {@code char} values
 695      * (Unicode code units) and ranges from {@code 0} to
 696      * {@link #length()}{@code  - 1}.
 697      *
 698      * <p> If the {@code char} value specified at the given index
 699      * is in the high-surrogate range, the following index is less
 700      * than the length of this {@code String}, and the
 701      * {@code char} value at the following index is in the
 702      * low-surrogate range, then the supplementary code point
 703      * corresponding to this surrogate pair is returned. Otherwise,
 704      * the {@code char} value at the given index is returned.
 705      *
 706      * @param      index the index to the {@code char} values
 707      * @return     the code point value of the character at the
 708      *             {@code index}
 709      * @exception  IndexOutOfBoundsException  if the {@code index}
 710      *             argument is negative or not less than the length of this
 711      *             string.
 712      * @since      1.5
 713      */
 714     public int codePointAt(int index) {
 715         if (isLatin1()) {
 716             checkIndex(index, value.length);
 717             return value[index] & 0xff;
 718         }
 719         int length = value.length >> 1;
 720         checkIndex(index, length);
 721         return StringUTF16.codePointAt(value, index, length);
 722     }
 723 
 724     /**
 725      * Returns the character (Unicode code point) before the specified
 726      * index. The index refers to {@code char} values
 727      * (Unicode code units) and ranges from {@code 1} to {@link
 728      * CharSequence#length() length}.
 729      *
 730      * <p> If the {@code char} value at {@code (index - 1)}
 731      * is in the low-surrogate range, {@code (index - 2)} is not
 732      * negative, and the {@code char} value at {@code (index -
 733      * 2)} is in the high-surrogate range, then the
 734      * supplementary code point value of the surrogate pair is
 735      * returned. If the {@code char} value at {@code index -
 736      * 1} is an unpaired low-surrogate or a high-surrogate, the
 737      * surrogate value is returned.
 738      *
 739      * @param     index the index following the code point that should be returned
 740      * @return    the Unicode code point value before the given index.
 741      * @exception IndexOutOfBoundsException if the {@code index}
 742      *            argument is less than 1 or greater than the length
 743      *            of this string.
 744      * @since     1.5
 745      */
 746     public int codePointBefore(int index) {
 747         int i = index - 1;
 748         if (i < 0 || i >= length()) {
 749             throw new StringIndexOutOfBoundsException(index);
 750         }
 751         if (isLatin1()) {
 752             return (value[i] & 0xff);
 753         }
 754         return StringUTF16.codePointBefore(value, index);
 755     }
 756 
 757     /**
 758      * Returns the number of Unicode code points in the specified text
 759      * range of this {@code String}. The text range begins at the
 760      * specified {@code beginIndex} and extends to the
 761      * {@code char} at index {@code endIndex - 1}. Thus the
 762      * length (in {@code char}s) of the text range is
 763      * {@code endIndex-beginIndex}. Unpaired surrogates within
 764      * the text range count as one code point each.
 765      *
 766      * @param beginIndex the index to the first {@code char} of
 767      * the text range.
 768      * @param endIndex the index after the last {@code char} of
 769      * the text range.
 770      * @return the number of Unicode code points in the specified text
 771      * range
 772      * @exception IndexOutOfBoundsException if the
 773      * {@code beginIndex} is negative, or {@code endIndex}
 774      * is larger than the length of this {@code String}, or
 775      * {@code beginIndex} is larger than {@code endIndex}.
 776      * @since  1.5
 777      */
 778     public int codePointCount(int beginIndex, int endIndex) {
 779         if (beginIndex < 0 || beginIndex > endIndex ||
 780             endIndex > length()) {
 781             throw new IndexOutOfBoundsException();
 782         }
 783         if (isLatin1()) {
 784             return endIndex - beginIndex;
 785         }
 786         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 787     }
 788 
 789     /**
 790      * Returns the index within this {@code String} that is
 791      * offset from the given {@code index} by
 792      * {@code codePointOffset} code points. Unpaired surrogates
 793      * within the text range given by {@code index} and
 794      * {@code codePointOffset} count as one code point each.
 795      *
 796      * @param index the index to be offset
 797      * @param codePointOffset the offset in code points
 798      * @return the index within this {@code String}
 799      * @exception IndexOutOfBoundsException if {@code index}
 800      *   is negative or larger then the length of this
 801      *   {@code String}, or if {@code codePointOffset} is positive
 802      *   and the substring starting with {@code index} has fewer
 803      *   than {@code codePointOffset} code points,
 804      *   or if {@code codePointOffset} is negative and the substring
 805      *   before {@code index} has fewer than the absolute value
 806      *   of {@code codePointOffset} code points.
 807      * @since 1.5
 808      */
 809     public int offsetByCodePoints(int index, int codePointOffset) {
 810         if (index < 0 || index > length()) {
 811             throw new IndexOutOfBoundsException();
 812         }
 813         return Character.offsetByCodePoints(this, index, codePointOffset);
 814     }
 815 
 816     /**
 817      * Copies characters from this string into the destination character
 818      * array.
 819      * <p>
 820      * The first character to be copied is at index {@code srcBegin};
 821      * the last character to be copied is at index {@code srcEnd-1}
 822      * (thus the total number of characters to be copied is
 823      * {@code srcEnd-srcBegin}). The characters are copied into the
 824      * subarray of {@code dst} starting at index {@code dstBegin}
 825      * and ending at index:
 826      * <blockquote><pre>
 827      *     dstBegin + (srcEnd-srcBegin) - 1
 828      * </pre></blockquote>
 829      *
 830      * @param      srcBegin   index of the first character in the string
 831      *                        to copy.
 832      * @param      srcEnd     index after the last character in the string
 833      *                        to copy.
 834      * @param      dst        the destination array.
 835      * @param      dstBegin   the start offset in the destination array.
 836      * @exception IndexOutOfBoundsException If any of the following
 837      *            is true:
 838      *            <ul><li>{@code srcBegin} is negative.
 839      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 840      *            <li>{@code srcEnd} is greater than the length of this
 841      *                string
 842      *            <li>{@code dstBegin} is negative
 843      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 844      *                {@code dst.length}</ul>
 845      */
 846     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 847         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 848         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 849         if (isLatin1()) {
 850             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 851         } else {
 852             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 853         }
 854     }
 855 
 856     /**
 857      * Copies characters from this string into the destination byte array. Each
 858      * byte receives the 8 low-order bits of the corresponding character. The
 859      * eight high-order bits of each character are not copied and do not
 860      * participate in the transfer in any way.
 861      *
 862      * <p> The first character to be copied is at index {@code srcBegin}; the
 863      * last character to be copied is at index {@code srcEnd-1}.  The total
 864      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 865      * characters, converted to bytes, are copied into the subarray of {@code
 866      * dst} starting at index {@code dstBegin} and ending at index:
 867      *
 868      * <blockquote><pre>
 869      *     dstBegin + (srcEnd-srcBegin) - 1
 870      * </pre></blockquote>
 871      *
 872      * @deprecated  This method does not properly convert characters into
 873      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 874      * {@link #getBytes()} method, which uses the platform's default charset.
 875      *
 876      * @param  srcBegin
 877      *         Index of the first character in the string to copy
 878      *
 879      * @param  srcEnd
 880      *         Index after the last character in the string to copy
 881      *
 882      * @param  dst
 883      *         The destination array
 884      *
 885      * @param  dstBegin
 886      *         The start offset in the destination array
 887      *
 888      * @throws  IndexOutOfBoundsException
 889      *          If any of the following is true:
 890      *          <ul>
 891      *            <li> {@code srcBegin} is negative
 892      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 893      *            <li> {@code srcEnd} is greater than the length of this String
 894      *            <li> {@code dstBegin} is negative
 895      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 896      *                 dst.length}
 897      *          </ul>
 898      */
 899     @Deprecated
 900     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 901         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 902         Objects.requireNonNull(dst);
 903         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 904         if (isLatin1()) {
 905             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 906         } else {
 907             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 908         }
 909     }
 910 
 911     /**
 912      * Encodes this {@code String} into a sequence of bytes using the named
 913      * charset, storing the result into a new byte array.
 914      *
 915      * <p> The behavior of this method when this string cannot be encoded in
 916      * the given charset is unspecified.  The {@link
 917      * java.nio.charset.CharsetEncoder} class should be used when more control
 918      * over the encoding process is required.
 919      *
 920      * @param  charsetName
 921      *         The name of a supported {@linkplain java.nio.charset.Charset
 922      *         charset}
 923      *
 924      * @return  The resultant byte array
 925      *
 926      * @throws  UnsupportedEncodingException
 927      *          If the named charset is not supported
 928      *
 929      * @since  1.1
 930      */
 931     public byte[] getBytes(String charsetName)
 932             throws UnsupportedEncodingException {
 933         if (charsetName == null) throw new NullPointerException();
 934         return StringCoding.encode(charsetName, coder(), value);
 935     }
 936 
 937     /**
 938      * Encodes this {@code String} into a sequence of bytes using the given
 939      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 940      * new byte array.
 941      *
 942      * <p> This method always replaces malformed-input and unmappable-character
 943      * sequences with this charset's default replacement byte array.  The
 944      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 945      * control over the encoding process is required.
 946      *
 947      * @param  charset
 948      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 949      *         the {@code String}
 950      *
 951      * @return  The resultant byte array
 952      *
 953      * @since  1.6
 954      */
 955     public byte[] getBytes(Charset charset) {
 956         if (charset == null) throw new NullPointerException();
 957         return StringCoding.encode(charset, coder(), value);
 958      }
 959 
 960     /**
 961      * Encodes this {@code String} into a sequence of bytes using the
 962      * platform's default charset, storing the result into a new byte array.
 963      *
 964      * <p> The behavior of this method when this string cannot be encoded in
 965      * the default charset is unspecified.  The {@link
 966      * java.nio.charset.CharsetEncoder} class should be used when more control
 967      * over the encoding process is required.
 968      *
 969      * @return  The resultant byte array
 970      *
 971      * @since      1.1
 972      */
 973     public byte[] getBytes() {
 974         return StringCoding.encode(coder(), value);
 975     }
 976 
 977     /**
 978      * Compares this string to the specified object.  The result is {@code
 979      * true} if and only if the argument is not {@code null} and is a {@code
 980      * String} object that represents the same sequence of characters as this
 981      * object.
 982      *
 983      * <p>For finer-grained String comparison, refer to
 984      * {@link java.text.Collator}.
 985      *
 986      * @param  anObject
 987      *         The object to compare this {@code String} against
 988      *
 989      * @return  {@code true} if the given object represents a {@code String}
 990      *          equivalent to this string, {@code false} otherwise
 991      *
 992      * @see  #compareTo(String)
 993      * @see  #equalsIgnoreCase(String)
 994      */
 995     public boolean equals(Object anObject) {
 996         if (this == anObject) {
 997             return true;
 998         }
 999         if (anObject instanceof String) {
1000             String aString = (String)anObject;
1001             if (coder() == aString.coder()) {
1002                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1003                                   : StringUTF16.equals(value, aString.value);
1004             }
1005         }
1006         return false;
1007     }
1008 
1009     /**
1010      * Compares this string to the specified {@code StringBuffer}.  The result
1011      * is {@code true} if and only if this {@code String} represents the same
1012      * sequence of characters as the specified {@code StringBuffer}. This method
1013      * synchronizes on the {@code StringBuffer}.
1014      *
1015      * <p>For finer-grained String comparison, refer to
1016      * {@link java.text.Collator}.
1017      *
1018      * @param  sb
1019      *         The {@code StringBuffer} to compare this {@code String} against
1020      *
1021      * @return  {@code true} if this {@code String} represents the same
1022      *          sequence of characters as the specified {@code StringBuffer},
1023      *          {@code false} otherwise
1024      *
1025      * @since  1.4
1026      */
1027     public boolean contentEquals(StringBuffer sb) {
1028         return contentEquals((CharSequence)sb);
1029     }
1030 
1031     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1032         int len = length();
1033         if (len != sb.length()) {
1034             return false;
1035         }
1036         byte v1[] = value;
1037         byte v2[] = sb.getValue();
1038         if (coder() == sb.getCoder()) {
1039             int n = v1.length;
1040             for (int i = 0; i < n; i++) {
1041                 if (v1[i] != v2[i]) {
1042                     return false;
1043                 }
1044             }
1045         } else {
1046             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1047                 return false;
1048             }
1049             for (int i = 0; i < len; i++) {
1050                 if ((char)(v1[i] & 0xff) != StringUTF16.getChar(v2, i)) {
1051                     return false;
1052                 }
1053             }
1054         }
1055         return true;
1056     }
1057 
1058     /**
1059      * Compares this string to the specified {@code CharSequence}.  The
1060      * result is {@code true} if and only if this {@code String} represents the
1061      * same sequence of char values as the specified sequence. Note that if the
1062      * {@code CharSequence} is a {@code StringBuffer} then the method
1063      * synchronizes on it.
1064      *
1065      * <p>For finer-grained String comparison, refer to
1066      * {@link java.text.Collator}.
1067      *
1068      * @param  cs
1069      *         The sequence to compare this {@code String} against
1070      *
1071      * @return  {@code true} if this {@code String} represents the same
1072      *          sequence of char values as the specified sequence, {@code
1073      *          false} otherwise
1074      *
1075      * @since  1.5
1076      */
1077     public boolean contentEquals(CharSequence cs) {
1078         // Argument is a StringBuffer, StringBuilder
1079         if (cs instanceof AbstractStringBuilder) {
1080             if (cs instanceof StringBuffer) {
1081                 synchronized(cs) {
1082                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1083                 }
1084             } else {
1085                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1086             }
1087         }
1088         // Argument is a String
1089         if (cs instanceof String) {
1090             return equals(cs);
1091         }
1092         // Argument is a generic CharSequence
1093         int n = cs.length();
1094         if (n != length()) {
1095             return false;
1096         }
1097         byte[] val = this.value;
1098         if (isLatin1()) {
1099             for (int i = 0; i < n; i++) {
1100                 if ((val[i] & 0xff) != cs.charAt(i)) {
1101                     return false;
1102                 }
1103             }
1104         } else {
1105             for (int i = 0; i < n; i++) {
1106                 if (StringUTF16.getChar(val, i) != cs.charAt(i)) {
1107                     return false;
1108                 }
1109             }
1110         }
1111         return true;
1112     }
1113 
1114     /**
1115      * Compares this {@code String} to another {@code String}, ignoring case
1116      * considerations.  Two strings are considered equal ignoring case if they
1117      * are of the same length and corresponding characters in the two strings
1118      * are equal ignoring case.
1119      *
1120      * <p> Two characters {@code c1} and {@code c2} are considered the same
1121      * ignoring case if at least one of the following is true:
1122      * <ul>
1123      *   <li> The two characters are the same (as compared by the
1124      *        {@code ==} operator)
1125      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1126      *        on each character produces the same result
1127      * </ul>
1128      *
1129      * <p>Note that this method does <em>not</em> take locale into account, and
1130      * will result in unsatisfactory results for certain locales.  The
1131      * {@link java.text.Collator} class provides locale-sensitive comparison.
1132      *
1133      * @param  anotherString
1134      *         The {@code String} to compare this {@code String} against
1135      *
1136      * @return  {@code true} if the argument is not {@code null} and it
1137      *          represents an equivalent {@code String} ignoring case; {@code
1138      *          false} otherwise
1139      *
1140      * @see  #equals(Object)
1141      */
1142     public boolean equalsIgnoreCase(String anotherString) {
1143         return (this == anotherString) ? true
1144                 : (anotherString != null)
1145                 && (anotherString.length() == length())
1146                 && regionMatches(true, 0, anotherString, 0, length());
1147     }
1148 
1149     /**
1150      * Compares two strings lexicographically.
1151      * The comparison is based on the Unicode value of each character in
1152      * the strings. The character sequence represented by this
1153      * {@code String} object is compared lexicographically to the
1154      * character sequence represented by the argument string. The result is
1155      * a negative integer if this {@code String} object
1156      * lexicographically precedes the argument string. The result is a
1157      * positive integer if this {@code String} object lexicographically
1158      * follows the argument string. The result is zero if the strings
1159      * are equal; {@code compareTo} returns {@code 0} exactly when
1160      * the {@link #equals(Object)} method would return {@code true}.
1161      * <p>
1162      * This is the definition of lexicographic ordering. If two strings are
1163      * different, then either they have different characters at some index
1164      * that is a valid index for both strings, or their lengths are different,
1165      * or both. If they have different characters at one or more index
1166      * positions, let <i>k</i> be the smallest such index; then the string
1167      * whose character at position <i>k</i> has the smaller value, as
1168      * determined by using the {@code <} operator, lexicographically precedes the
1169      * other string. In this case, {@code compareTo} returns the
1170      * difference of the two character values at position {@code k} in
1171      * the two string -- that is, the value:
1172      * <blockquote><pre>
1173      * this.charAt(k)-anotherString.charAt(k)
1174      * </pre></blockquote>
1175      * If there is no index position at which they differ, then the shorter
1176      * string lexicographically precedes the longer string. In this case,
1177      * {@code compareTo} returns the difference of the lengths of the
1178      * strings -- that is, the value:
1179      * <blockquote><pre>
1180      * this.length()-anotherString.length()
1181      * </pre></blockquote>
1182      *
1183      * <p>For finer-grained String comparison, refer to
1184      * {@link java.text.Collator}.
1185      *
1186      * @param   anotherString   the {@code String} to be compared.
1187      * @return  the value {@code 0} if the argument string is equal to
1188      *          this string; a value less than {@code 0} if this string
1189      *          is lexicographically less than the string argument; and a
1190      *          value greater than {@code 0} if this string is
1191      *          lexicographically greater than the string argument.
1192      */
1193     public int compareTo(String anotherString) {
1194         byte v1[] = value;
1195         byte v2[] = anotherString.value;
1196         if (coder() == anotherString.coder()) {
1197             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1198                               : StringUTF16.compareTo(v1, v2);
1199         }
1200         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1201                           : StringUTF16.compareToLatin1(v1, v2);
1202      }
1203 
1204     /**
1205      * A Comparator that orders {@code String} objects as by
1206      * {@code compareToIgnoreCase}. This comparator is serializable.
1207      * <p>
1208      * Note that this Comparator does <em>not</em> take locale into account,
1209      * and will result in an unsatisfactory ordering for certain locales.
1210      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1211      *
1212      * @see     java.text.Collator
1213      * @since   1.2
1214      */
1215     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1216                                          = new CaseInsensitiveComparator();
1217     private static class CaseInsensitiveComparator
1218             implements Comparator<String>, java.io.Serializable {
1219         // use serialVersionUID from JDK 1.2.2 for interoperability
1220         private static final long serialVersionUID = 8575799808933029326L;
1221 
1222         public int compare(String s1, String s2) {
1223             byte v1[] = s1.value;
1224             byte v2[] = s2.value;
1225             if (s1.coder() == s2.coder()) {
1226                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1227                                      : StringUTF16.compareToCI(v1, v2);
1228             }
1229             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1230                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1231         }
1232 
1233         /** Replaces the de-serialized object. */
1234         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1235     }
1236 
1237     /**
1238      * Compares two strings lexicographically, ignoring case
1239      * differences. This method returns an integer whose sign is that of
1240      * calling {@code compareTo} with normalized versions of the strings
1241      * where case differences have been eliminated by calling
1242      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1243      * each character.
1244      * <p>
1245      * Note that this method does <em>not</em> take locale into account,
1246      * and will result in an unsatisfactory ordering for certain locales.
1247      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1248      *
1249      * @param   str   the {@code String} to be compared.
1250      * @return  a negative integer, zero, or a positive integer as the
1251      *          specified String is greater than, equal to, or less
1252      *          than this String, ignoring case considerations.
1253      * @see     java.text.Collator
1254      * @since   1.2
1255      */
1256     public int compareToIgnoreCase(String str) {
1257         return CASE_INSENSITIVE_ORDER.compare(this, str);
1258     }
1259 
1260     /**
1261      * Tests if two string regions are equal.
1262      * <p>
1263      * A substring of this {@code String} object is compared to a substring
1264      * of the argument other. The result is true if these substrings
1265      * represent identical character sequences. The substring of this
1266      * {@code String} object to be compared begins at index {@code toffset}
1267      * and has length {@code len}. The substring of other to be compared
1268      * begins at index {@code ooffset} and has length {@code len}. The
1269      * result is {@code false} if and only if at least one of the following
1270      * is true:
1271      * <ul><li>{@code toffset} is negative.
1272      * <li>{@code ooffset} is negative.
1273      * <li>{@code toffset+len} is greater than the length of this
1274      * {@code String} object.
1275      * <li>{@code ooffset+len} is greater than the length of the other
1276      * argument.
1277      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1278      * such that:
1279      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1280      * <i>k</i>{@code )}
1281      * </ul>
1282      *
1283      * <p>Note that this method does <em>not</em> take locale into account.  The
1284      * {@link java.text.Collator} class provides locale-sensitive comparison.
1285      *
1286      * @param   toffset   the starting offset of the subregion in this string.
1287      * @param   other     the string argument.
1288      * @param   ooffset   the starting offset of the subregion in the string
1289      *                    argument.
1290      * @param   len       the number of characters to compare.
1291      * @return  {@code true} if the specified subregion of this string
1292      *          exactly matches the specified subregion of the string argument;
1293      *          {@code false} otherwise.
1294      */
1295     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1296         byte tv[] = value;
1297         byte ov[] = other.value;
1298         // Note: toffset, ooffset, or len might be near -1>>>1.
1299         if ((ooffset < 0) || (toffset < 0) ||
1300              (toffset > (long)length() - len) ||
1301              (ooffset > (long)other.length() - len)) {
1302             return false;
1303         }
1304         if (coder() == other.coder()) {
1305             if (!isLatin1() && (len > 0)) {
1306                 toffset = toffset << 1;
1307                 ooffset = ooffset << 1;
1308                 len = len << 1;
1309             }
1310             while (len-- > 0) {
1311                 if (tv[toffset++] != ov[ooffset++]) {
1312                     return false;
1313                 }
1314             }
1315         } else {
1316             if (coder() == LATIN1) {
1317                 while (len-- > 0) {
1318                     if (StringLatin1.getChar(tv, toffset++) !=
1319                         StringUTF16.getChar(ov, ooffset++)) {
1320                         return false;
1321                     }
1322                 }
1323             } else {
1324                 while (len-- > 0) {
1325                     if (StringUTF16.getChar(tv, toffset++) !=
1326                         StringLatin1.getChar(ov, ooffset++)) {
1327                         return false;
1328                     }
1329                 }
1330             }
1331         }
1332         return true;
1333     }
1334 
1335     /**
1336      * Tests if two string regions are equal.
1337      * <p>
1338      * A substring of this {@code String} object is compared to a substring
1339      * of the argument {@code other}. The result is {@code true} if these
1340      * substrings represent character sequences that are the same, ignoring
1341      * case if and only if {@code ignoreCase} is true. The substring of
1342      * this {@code String} object to be compared begins at index
1343      * {@code toffset} and has length {@code len}. The substring of
1344      * {@code other} to be compared begins at index {@code ooffset} and
1345      * has length {@code len}. The result is {@code false} if and only if
1346      * at least one of the following is true:
1347      * <ul><li>{@code toffset} is negative.
1348      * <li>{@code ooffset} is negative.
1349      * <li>{@code toffset+len} is greater than the length of this
1350      * {@code String} object.
1351      * <li>{@code ooffset+len} is greater than the length of the other
1352      * argument.
1353      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1354      * integer <i>k</i> less than {@code len} such that:
1355      * <blockquote><pre>
1356      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1357      * </pre></blockquote>
1358      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1359      * integer <i>k</i> less than {@code len} such that:
1360      * <blockquote><pre>
1361      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1362      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1363      * </pre></blockquote>
1364      * </ul>
1365      *
1366      * <p>Note that this method does <em>not</em> take locale into account,
1367      * and will result in unsatisfactory results for certain locales when
1368      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1369      * provides locale-sensitive comparison.
1370      *
1371      * @param   ignoreCase   if {@code true}, ignore case when comparing
1372      *                       characters.
1373      * @param   toffset      the starting offset of the subregion in this
1374      *                       string.
1375      * @param   other        the string argument.
1376      * @param   ooffset      the starting offset of the subregion in the string
1377      *                       argument.
1378      * @param   len          the number of characters to compare.
1379      * @return  {@code true} if the specified subregion of this string
1380      *          matches the specified subregion of the string argument;
1381      *          {@code false} otherwise. Whether the matching is exact
1382      *          or case insensitive depends on the {@code ignoreCase}
1383      *          argument.
1384      */
1385     public boolean regionMatches(boolean ignoreCase, int toffset,
1386             String other, int ooffset, int len) {
1387         if (!ignoreCase) {
1388             return regionMatches(toffset, other, ooffset, len);
1389         }
1390         // Note: toffset, ooffset, or len might be near -1>>>1.
1391         if ((ooffset < 0) || (toffset < 0)
1392                 || (toffset > (long)length() - len)
1393                 || (ooffset > (long)other.length() - len)) {
1394             return false;
1395         }
1396         byte tv[] = value;
1397         byte ov[] = other.value;
1398         if (coder() == other.coder()) {
1399             return isLatin1()
1400               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1401               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1402         }
1403         return isLatin1()
1404               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1405               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1406     }
1407 
1408     /**
1409      * Tests if the substring of this string beginning at the
1410      * specified index starts with the specified prefix.
1411      *
1412      * @param   prefix    the prefix.
1413      * @param   toffset   where to begin looking in this string.
1414      * @return  {@code true} if the character sequence represented by the
1415      *          argument is a prefix of the substring of this object starting
1416      *          at index {@code toffset}; {@code false} otherwise.
1417      *          The result is {@code false} if {@code toffset} is
1418      *          negative or greater than the length of this
1419      *          {@code String} object; otherwise the result is the same
1420      *          as the result of the expression
1421      *          <pre>
1422      *          this.substring(toffset).startsWith(prefix)
1423      *          </pre>
1424      */
1425     public boolean startsWith(String prefix, int toffset) {
1426         // Note: toffset might be near -1>>>1.
1427         if (toffset < 0 || toffset > length() - prefix.length()) {
1428             return false;
1429         }
1430         byte ta[] = value;
1431         byte pa[] = prefix.value;
1432         int po = 0;
1433         int pc = pa.length;
1434         if (coder() == prefix.coder()) {
1435             int to = isLatin1() ? toffset : toffset << 1;
1436             while (po < pc) {
1437                 if (ta[to++] != pa[po++]) {
1438                     return false;
1439                 }
1440             }
1441         } else {
1442             if (isLatin1()) {  // && pcoder == UTF16
1443                 return false;
1444             }
1445             // coder == UTF16 && pcoder == LATIN1)
1446             while (po < pc) {
1447                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1448                     return false;
1449                }
1450             }
1451         }
1452         return true;
1453     }
1454 
1455     /**
1456      * Tests if this string starts with the specified prefix.
1457      *
1458      * @param   prefix   the prefix.
1459      * @return  {@code true} if the character sequence represented by the
1460      *          argument is a prefix of the character sequence represented by
1461      *          this string; {@code false} otherwise.
1462      *          Note also that {@code true} will be returned if the
1463      *          argument is an empty string or is equal to this
1464      *          {@code String} object as determined by the
1465      *          {@link #equals(Object)} method.
1466      * @since   1.0
1467      */
1468     public boolean startsWith(String prefix) {
1469         return startsWith(prefix, 0);
1470     }
1471 
1472     /**
1473      * Tests if this string ends with the specified suffix.
1474      *
1475      * @param   suffix   the suffix.
1476      * @return  {@code true} if the character sequence represented by the
1477      *          argument is a suffix of the character sequence represented by
1478      *          this object; {@code false} otherwise. Note that the
1479      *          result will be {@code true} if the argument is the
1480      *          empty string or is equal to this {@code String} object
1481      *          as determined by the {@link #equals(Object)} method.
1482      */
1483     public boolean endsWith(String suffix) {
1484         return startsWith(suffix, length() - suffix.length());
1485     }
1486 
1487     /**
1488      * Returns a hash code for this string. The hash code for a
1489      * {@code String} object is computed as
1490      * <blockquote><pre>
1491      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1492      * </pre></blockquote>
1493      * using {@code int} arithmetic, where {@code s[i]} is the
1494      * <i>i</i>th character of the string, {@code n} is the length of
1495      * the string, and {@code ^} indicates exponentiation.
1496      * (The hash value of the empty string is zero.)
1497      *
1498      * @return  a hash code value for this object.
1499      */
1500     public int hashCode() {
1501         if (hash == 0 && value.length > 0) {
1502             hash = isLatin1() ? StringLatin1.hashCode(value)
1503                               : StringUTF16.hashCode(value);
1504         }
1505         return hash;
1506     }
1507 
1508     /**
1509      * Returns the index within this string of the first occurrence of
1510      * the specified character. If a character with value
1511      * {@code ch} occurs in the character sequence represented by
1512      * this {@code String} object, then the index (in Unicode
1513      * code units) of the first such occurrence is returned. For
1514      * values of {@code ch} in the range from 0 to 0xFFFF
1515      * (inclusive), this is the smallest value <i>k</i> such that:
1516      * <blockquote><pre>
1517      * this.charAt(<i>k</i>) == ch
1518      * </pre></blockquote>
1519      * is true. For other values of {@code ch}, it is the
1520      * smallest value <i>k</i> such that:
1521      * <blockquote><pre>
1522      * this.codePointAt(<i>k</i>) == ch
1523      * </pre></blockquote>
1524      * is true. In either case, if no such character occurs in this
1525      * string, then {@code -1} is returned.
1526      *
1527      * @param   ch   a character (Unicode code point).
1528      * @return  the index of the first occurrence of the character in the
1529      *          character sequence represented by this object, or
1530      *          {@code -1} if the character does not occur.
1531      */
1532     public int indexOf(int ch) {
1533         return indexOf(ch, 0);
1534     }
1535 
1536     /**
1537      * Returns the index within this string of the first occurrence of the
1538      * specified character, starting the search at the specified index.
1539      * <p>
1540      * If a character with value {@code ch} occurs in the
1541      * character sequence represented by this {@code String}
1542      * object at an index no smaller than {@code fromIndex}, then
1543      * the index of the first such occurrence is returned. For values
1544      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1545      * this is the smallest value <i>k</i> such that:
1546      * <blockquote><pre>
1547      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1548      * </pre></blockquote>
1549      * is true. For other values of {@code ch}, it is the
1550      * smallest value <i>k</i> such that:
1551      * <blockquote><pre>
1552      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1553      * </pre></blockquote>
1554      * is true. In either case, if no such character occurs in this
1555      * string at or after position {@code fromIndex}, then
1556      * {@code -1} is returned.
1557      *
1558      * <p>
1559      * There is no restriction on the value of {@code fromIndex}. If it
1560      * is negative, it has the same effect as if it were zero: this entire
1561      * string may be searched. If it is greater than the length of this
1562      * string, it has the same effect as if it were equal to the length of
1563      * this string: {@code -1} is returned.
1564      *
1565      * <p>All indices are specified in {@code char} values
1566      * (Unicode code units).
1567      *
1568      * @param   ch          a character (Unicode code point).
1569      * @param   fromIndex   the index to start the search from.
1570      * @return  the index of the first occurrence of the character in the
1571      *          character sequence represented by this object that is greater
1572      *          than or equal to {@code fromIndex}, or {@code -1}
1573      *          if the character does not occur.
1574      */
1575     public int indexOf(int ch, int fromIndex) {
1576         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1577                           : StringUTF16.indexOf(value, ch, fromIndex);
1578     }
1579 
1580     /**
1581      * Returns the index within this string of the last occurrence of
1582      * the specified character. For values of {@code ch} in the
1583      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1584      * units) returned is the largest value <i>k</i> such that:
1585      * <blockquote><pre>
1586      * this.charAt(<i>k</i>) == ch
1587      * </pre></blockquote>
1588      * is true. For other values of {@code ch}, it is the
1589      * largest value <i>k</i> such that:
1590      * <blockquote><pre>
1591      * this.codePointAt(<i>k</i>) == ch
1592      * </pre></blockquote>
1593      * is true.  In either case, if no such character occurs in this
1594      * string, then {@code -1} is returned.  The
1595      * {@code String} is searched backwards starting at the last
1596      * character.
1597      *
1598      * @param   ch   a character (Unicode code point).
1599      * @return  the index of the last occurrence of the character in the
1600      *          character sequence represented by this object, or
1601      *          {@code -1} if the character does not occur.
1602      */
1603     public int lastIndexOf(int ch) {
1604         return lastIndexOf(ch, length() - 1);
1605     }
1606 
1607     /**
1608      * Returns the index within this string of the last occurrence of
1609      * the specified character, searching backward starting at the
1610      * specified index. For values of {@code ch} in the range
1611      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1612      * value <i>k</i> such that:
1613      * <blockquote><pre>
1614      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1615      * </pre></blockquote>
1616      * is true. For other values of {@code ch}, it is the
1617      * largest value <i>k</i> such that:
1618      * <blockquote><pre>
1619      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1620      * </pre></blockquote>
1621      * is true. In either case, if no such character occurs in this
1622      * string at or before position {@code fromIndex}, then
1623      * {@code -1} is returned.
1624      *
1625      * <p>All indices are specified in {@code char} values
1626      * (Unicode code units).
1627      *
1628      * @param   ch          a character (Unicode code point).
1629      * @param   fromIndex   the index to start the search from. There is no
1630      *          restriction on the value of {@code fromIndex}. If it is
1631      *          greater than or equal to the length of this string, it has
1632      *          the same effect as if it were equal to one less than the
1633      *          length of this string: this entire string may be searched.
1634      *          If it is negative, it has the same effect as if it were -1:
1635      *          -1 is returned.
1636      * @return  the index of the last occurrence of the character in the
1637      *          character sequence represented by this object that is less
1638      *          than or equal to {@code fromIndex}, or {@code -1}
1639      *          if the character does not occur before that point.
1640      */
1641     public int lastIndexOf(int ch, int fromIndex) {
1642         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1643                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1644     }
1645 
1646     /**
1647      * Returns the index within this string of the first occurrence of the
1648      * specified substring.
1649      *
1650      * <p>The returned index is the smallest value {@code k} for which:
1651      * <pre>{@code
1652      * this.startsWith(str, k)
1653      * }</pre>
1654      * If no such value of {@code k} exists, then {@code -1} is returned.
1655      *
1656      * @param   str   the substring to search for.
1657      * @return  the index of the first occurrence of the specified substring,
1658      *          or {@code -1} if there is no such occurrence.
1659      */
1660     public int indexOf(String str) {
1661         if (coder() == str.coder()) {
1662             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1663                               : StringUTF16.indexOf(value, str.value);
1664         }
1665         if (coder() == LATIN1) {  // str.coder == UTF16
1666             return -1;
1667         }
1668         return StringUTF16.indexOfLatin1(value, str.value);
1669     }
1670 
1671     /**
1672      * Returns the index within this string of the first occurrence of the
1673      * specified substring, starting at the specified index.
1674      *
1675      * <p>The returned index is the smallest value {@code k} for which:
1676      * <pre>{@code
1677      *     k >= Math.min(fromIndex, this.length()) &&
1678      *                   this.startsWith(str, k)
1679      * }</pre>
1680      * If no such value of {@code k} exists, then {@code -1} is returned.
1681      *
1682      * @param   str         the substring to search for.
1683      * @param   fromIndex   the index from which to start the search.
1684      * @return  the index of the first occurrence of the specified substring,
1685      *          starting at the specified index,
1686      *          or {@code -1} if there is no such occurrence.
1687      */
1688     public int indexOf(String str, int fromIndex) {
1689         return indexOf(value, coder(), length(), str, fromIndex);
1690     }
1691 
1692     /**
1693      * Code shared by String and AbstractStringBuilder to do searches. The
1694      * source is the character array being searched, and the target
1695      * is the string being searched for.
1696      *
1697      * @param   src       the characters being searched.
1698      * @param   srcCoder  the coder of the source string.
1699      * @param   srcCount  length of the source string.
1700      * @param   tgtStr    the characters being searched for.
1701      * @param   fromIndex the index to begin searching from.
1702      */
1703     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1704                        String tgtStr, int fromIndex) {
1705         byte[] tgt    = tgtStr.value;
1706         byte tgtCoder = tgtStr.coder();
1707         int tgtCount  = tgtStr.length();
1708 
1709         if (fromIndex >= srcCount) {
1710             return (tgtCount == 0 ? srcCount : -1);
1711         }
1712         if (fromIndex < 0) {
1713             fromIndex = 0;
1714         }
1715         if (tgtCount == 0) {
1716             return fromIndex;
1717         }
1718         if (srcCoder == tgtCoder) {
1719             return srcCoder == LATIN1
1720                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1721                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1722         }
1723         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1724             return -1;
1725         }
1726         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1727         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1728     }
1729 
1730     /**
1731      * Returns the index within this string of the last occurrence of the
1732      * specified substring.  The last occurrence of the empty string ""
1733      * is considered to occur at the index value {@code this.length()}.
1734      *
1735      * <p>The returned index is the largest value {@code k} for which:
1736      * <pre>{@code
1737      * this.startsWith(str, k)
1738      * }</pre>
1739      * If no such value of {@code k} exists, then {@code -1} is returned.
1740      *
1741      * @param   str   the substring to search for.
1742      * @return  the index of the last occurrence of the specified substring,
1743      *          or {@code -1} if there is no such occurrence.
1744      */
1745     public int lastIndexOf(String str) {
1746         return lastIndexOf(str, length());
1747     }
1748 
1749     /**
1750      * Returns the index within this string of the last occurrence of the
1751      * specified substring, searching backward starting at the specified index.
1752      *
1753      * <p>The returned index is the largest value {@code k} for which:
1754      * <pre>{@code
1755      *     k <= Math.min(fromIndex, this.length()) &&
1756      *                   this.startsWith(str, k)
1757      * }</pre>
1758      * If no such value of {@code k} exists, then {@code -1} is returned.
1759      *
1760      * @param   str         the substring to search for.
1761      * @param   fromIndex   the index to start the search from.
1762      * @return  the index of the last occurrence of the specified substring,
1763      *          searching backward from the specified index,
1764      *          or {@code -1} if there is no such occurrence.
1765      */
1766     public int lastIndexOf(String str, int fromIndex) {
1767         return lastIndexOf(value, coder(), length(), str, fromIndex);
1768     }
1769 
1770     /**
1771      * Code shared by String and AbstractStringBuilder to do searches. The
1772      * source is the character array being searched, and the target
1773      * is the string being searched for.
1774      *
1775      * @param   src         the characters being searched.
1776      * @param   srcCoder  coder handles the mapping between bytes/chars
1777      * @param   srcCount    count of the source string.
1778      * @param   tgt         the characters being searched for.
1779      * @param   fromIndex   the index to begin searching from.
1780      */
1781     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1782                            String tgtStr, int fromIndex) {
1783         byte[] tgt = tgtStr.value;
1784         byte tgtCoder = tgtStr.coder();
1785         int tgtCount = tgtStr.length();
1786         /*
1787          * Check arguments; return immediately where possible. For
1788          * consistency, don't check for null str.
1789          */
1790         int rightIndex = srcCount - tgtCount;
1791         if (fromIndex < 0) {
1792             return -1;
1793         }
1794         if (fromIndex > rightIndex) {
1795             fromIndex = rightIndex;
1796         }
1797         /* Empty string always matches. */
1798         if (tgtCount == 0) {
1799             return fromIndex;
1800         }
1801         if (srcCoder == tgtCoder) {
1802             return srcCoder == LATIN1
1803                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1804                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1805         }
1806         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1807             return -1;
1808         }
1809                                      // srcCoder == UTF16 && tgtCoder == LATIN1
1810         int min = tgtCount - 1;
1811         int i = min + fromIndex;
1812         int strLastIndex = tgtCount - 1;
1813 
1814         char strLastChar = (char)(tgt[strLastIndex] & 0xff);
1815     startSearchForLastChar:
1816         while (true) {
1817             while (i >= min && StringUTF16.getChar(src, i) != strLastChar) {
1818                 i--;
1819             }
1820             if (i < min) {
1821                 return -1;
1822             }
1823             int j = i - 1;
1824             int start = j - strLastIndex;
1825             int k = strLastIndex - 1;
1826             while (j > start) {
1827                 if (StringUTF16.getChar(src, j--) != (tgt[k--] & 0xff)) {
1828                     i--;
1829                     continue startSearchForLastChar;
1830                 }
1831             }
1832             return start + 1;
1833         }
1834     }
1835 
1836     /**
1837      * Returns a string that is a substring of this string. The
1838      * substring begins with the character at the specified index and
1839      * extends to the end of this string. <p>
1840      * Examples:
1841      * <blockquote><pre>
1842      * "unhappy".substring(2) returns "happy"
1843      * "Harbison".substring(3) returns "bison"
1844      * "emptiness".substring(9) returns "" (an empty string)
1845      * </pre></blockquote>
1846      *
1847      * @param      beginIndex   the beginning index, inclusive.
1848      * @return     the specified substring.
1849      * @exception  IndexOutOfBoundsException  if
1850      *             {@code beginIndex} is negative or larger than the
1851      *             length of this {@code String} object.
1852      */
1853     public String substring(int beginIndex) {
1854         if (beginIndex < 0) {
1855             throw new StringIndexOutOfBoundsException(beginIndex);
1856         }
1857         int subLen = length() - beginIndex;
1858         if (subLen < 0) {
1859             throw new StringIndexOutOfBoundsException(subLen);
1860         }
1861         if (beginIndex == 0) {
1862             return this;
1863         }
1864         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1865                           : StringUTF16.newString(value, beginIndex, subLen);
1866     }
1867 
1868     /**
1869      * Returns a string that is a substring of this string. The
1870      * substring begins at the specified {@code beginIndex} and
1871      * extends to the character at index {@code endIndex - 1}.
1872      * Thus the length of the substring is {@code endIndex-beginIndex}.
1873      * <p>
1874      * Examples:
1875      * <blockquote><pre>
1876      * "hamburger".substring(4, 8) returns "urge"
1877      * "smiles".substring(1, 5) returns "mile"
1878      * </pre></blockquote>
1879      *
1880      * @param      beginIndex   the beginning index, inclusive.
1881      * @param      endIndex     the ending index, exclusive.
1882      * @return     the specified substring.
1883      * @exception  IndexOutOfBoundsException  if the
1884      *             {@code beginIndex} is negative, or
1885      *             {@code endIndex} is larger than the length of
1886      *             this {@code String} object, or
1887      *             {@code beginIndex} is larger than
1888      *             {@code endIndex}.
1889      */
1890     public String substring(int beginIndex, int endIndex) {
1891         int length = length();
1892         checkBoundsBeginEnd(beginIndex, endIndex, length);
1893         int subLen = endIndex - beginIndex;
1894         if (beginIndex == 0 && endIndex == length) {
1895             return this;
1896         }
1897         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1898                           : StringUTF16.newString(value, beginIndex, subLen);
1899     }
1900 
1901     /**
1902      * Returns a character sequence that is a subsequence of this sequence.
1903      *
1904      * <p> An invocation of this method of the form
1905      *
1906      * <blockquote><pre>
1907      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1908      *
1909      * behaves in exactly the same way as the invocation
1910      *
1911      * <blockquote><pre>
1912      * str.substring(begin,&nbsp;end)</pre></blockquote>
1913      *
1914      * @apiNote
1915      * This method is defined so that the {@code String} class can implement
1916      * the {@link CharSequence} interface.
1917      *
1918      * @param   beginIndex   the begin index, inclusive.
1919      * @param   endIndex     the end index, exclusive.
1920      * @return  the specified subsequence.
1921      *
1922      * @throws  IndexOutOfBoundsException
1923      *          if {@code beginIndex} or {@code endIndex} is negative,
1924      *          if {@code endIndex} is greater than {@code length()},
1925      *          or if {@code beginIndex} is greater than {@code endIndex}
1926      *
1927      * @since 1.4
1928      * @spec JSR-51
1929      */
1930     public CharSequence subSequence(int beginIndex, int endIndex) {
1931         return this.substring(beginIndex, endIndex);
1932     }
1933 
1934     /**
1935      * Concatenates the specified string to the end of this string.
1936      * <p>
1937      * If the length of the argument string is {@code 0}, then this
1938      * {@code String} object is returned. Otherwise, a
1939      * {@code String} object is returned that represents a character
1940      * sequence that is the concatenation of the character sequence
1941      * represented by this {@code String} object and the character
1942      * sequence represented by the argument string.<p>
1943      * Examples:
1944      * <blockquote><pre>
1945      * "cares".concat("s") returns "caress"
1946      * "to".concat("get").concat("her") returns "together"
1947      * </pre></blockquote>
1948      *
1949      * @param   str   the {@code String} that is concatenated to the end
1950      *                of this {@code String}.
1951      * @return  a string that represents the concatenation of this object's
1952      *          characters followed by the string argument's characters.
1953      */
1954     public String concat(String str) {
1955         int olen = str.length();
1956         if (olen == 0) {
1957             return this;
1958         }
1959         if (coder() == str.coder()) {
1960             byte[] val = this.value;
1961             byte[] oval = str.value;
1962             int len = val.length + oval.length;
1963             byte[] buf = Arrays.copyOf(val, len);
1964             System.arraycopy(oval, 0, buf, val.length, oval.length);
1965             return new String(buf, coder);
1966         }
1967         int len = length();
1968         byte[] buf = StringUTF16.newBytesFor(len + olen);
1969         getBytes(buf, 0, UTF16);
1970         str.getBytes(buf, len, UTF16);
1971         return new String(buf, UTF16);
1972     }
1973 
1974     /**
1975      * Returns a string resulting from replacing all occurrences of
1976      * {@code oldChar} in this string with {@code newChar}.
1977      * <p>
1978      * If the character {@code oldChar} does not occur in the
1979      * character sequence represented by this {@code String} object,
1980      * then a reference to this {@code String} object is returned.
1981      * Otherwise, a {@code String} object is returned that
1982      * represents a character sequence identical to the character sequence
1983      * represented by this {@code String} object, except that every
1984      * occurrence of {@code oldChar} is replaced by an occurrence
1985      * of {@code newChar}.
1986      * <p>
1987      * Examples:
1988      * <blockquote><pre>
1989      * "mesquite in your cellar".replace('e', 'o')
1990      *         returns "mosquito in your collar"
1991      * "the war of baronets".replace('r', 'y')
1992      *         returns "the way of bayonets"
1993      * "sparring with a purple porpoise".replace('p', 't')
1994      *         returns "starring with a turtle tortoise"
1995      * "JonL".replace('q', 'x') returns "JonL" (no change)
1996      * </pre></blockquote>
1997      *
1998      * @param   oldChar   the old character.
1999      * @param   newChar   the new character.
2000      * @return  a string derived from this string by replacing every
2001      *          occurrence of {@code oldChar} with {@code newChar}.
2002      */
2003     public String replace(char oldChar, char newChar) {
2004         if (oldChar != newChar) {
2005             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
2006                                     : StringUTF16.replace(value, oldChar, newChar);
2007             if (ret != null) {
2008                 return ret;
2009             }
2010         }
2011         return this;
2012     }
2013 
2014     /**
2015      * Tells whether or not this string matches the given <a
2016      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2017      *
2018      * <p> An invocation of this method of the form
2019      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2020      * same result as the expression
2021      *
2022      * <blockquote>
2023      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2024      * matches(<i>regex</i>, <i>str</i>)}
2025      * </blockquote>
2026      *
2027      * @param   regex
2028      *          the regular expression to which this string is to be matched
2029      *
2030      * @return  {@code true} if, and only if, this string matches the
2031      *          given regular expression
2032      *
2033      * @throws  PatternSyntaxException
2034      *          if the regular expression's syntax is invalid
2035      *
2036      * @see java.util.regex.Pattern
2037      *
2038      * @since 1.4
2039      * @spec JSR-51
2040      */
2041     public boolean matches(String regex) {
2042         return Pattern.matches(regex, this);
2043     }
2044 
2045     /**
2046      * Returns true if and only if this string contains the specified
2047      * sequence of char values.
2048      *
2049      * @param s the sequence to search for
2050      * @return true if this string contains {@code s}, false otherwise
2051      * @since 1.5
2052      */
2053     public boolean contains(CharSequence s) {
2054         return indexOf(s.toString()) >= 0;
2055     }
2056 
2057     /**
2058      * Replaces the first substring of this string that matches the given <a
2059      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2060      * given replacement.
2061      *
2062      * <p> An invocation of this method of the form
2063      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2064      * yields exactly the same result as the expression
2065      *
2066      * <blockquote>
2067      * <code>
2068      * {@link java.util.regex.Pattern}.{@link
2069      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2070      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2071      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2072      * </code>
2073      * </blockquote>
2074      *
2075      *<p>
2076      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2077      * replacement string may cause the results to be different than if it were
2078      * being treated as a literal replacement string; see
2079      * {@link java.util.regex.Matcher#replaceFirst}.
2080      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2081      * meaning of these characters, if desired.
2082      *
2083      * @param   regex
2084      *          the regular expression to which this string is to be matched
2085      * @param   replacement
2086      *          the string to be substituted for the first match
2087      *
2088      * @return  The resulting {@code String}
2089      *
2090      * @throws  PatternSyntaxException
2091      *          if the regular expression's syntax is invalid
2092      *
2093      * @see java.util.regex.Pattern
2094      *
2095      * @since 1.4
2096      * @spec JSR-51
2097      */
2098     public String replaceFirst(String regex, String replacement) {
2099         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2100     }
2101 
2102     /**
2103      * Replaces each substring of this string that matches the given <a
2104      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2105      * given replacement.
2106      *
2107      * <p> An invocation of this method of the form
2108      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2109      * yields exactly the same result as the expression
2110      *
2111      * <blockquote>
2112      * <code>
2113      * {@link java.util.regex.Pattern}.{@link
2114      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2115      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2116      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2117      * </code>
2118      * </blockquote>
2119      *
2120      *<p>
2121      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2122      * replacement string may cause the results to be different than if it were
2123      * being treated as a literal replacement string; see
2124      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2125      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2126      * meaning of these characters, if desired.
2127      *
2128      * @param   regex
2129      *          the regular expression to which this string is to be matched
2130      * @param   replacement
2131      *          the string to be substituted for each match
2132      *
2133      * @return  The resulting {@code String}
2134      *
2135      * @throws  PatternSyntaxException
2136      *          if the regular expression's syntax is invalid
2137      *
2138      * @see java.util.regex.Pattern
2139      *
2140      * @since 1.4
2141      * @spec JSR-51
2142      */
2143     public String replaceAll(String regex, String replacement) {
2144         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2145     }
2146 
2147     /**
2148      * Replaces each substring of this string that matches the literal target
2149      * sequence with the specified literal replacement sequence. The
2150      * replacement proceeds from the beginning of the string to the end, for
2151      * example, replacing "aa" with "b" in the string "aaa" will result in
2152      * "ba" rather than "ab".
2153      *
2154      * @param  target The sequence of char values to be replaced
2155      * @param  replacement The replacement sequence of char values
2156      * @return  The resulting string
2157      * @since 1.5
2158      */
2159     public String replace(CharSequence target, CharSequence replacement) {
2160         String tgtStr = target.toString();
2161         String replStr = replacement.toString();
2162         int j = indexOf(tgtStr);
2163         if (j < 0) {
2164             return this;
2165         }
2166         int tgtLen = tgtStr.length();
2167         int tgtLen1 = Math.max(tgtLen, 1);
2168         int thisLen = length();
2169 
2170         int newLenHint = thisLen - tgtLen + replStr.length();
2171         if (newLenHint < 0) {
2172             throw new OutOfMemoryError();
2173         }
2174         StringBuilder sb = new StringBuilder(newLenHint);
2175         int i = 0;
2176         do {
2177             sb.append(this, i, j).append(replStr);
2178             i = j + tgtLen;
2179         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2180         return sb.append(this, i, thisLen).toString();
2181     }
2182 
2183     /**
2184      * Splits this string around matches of the given
2185      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2186      *
2187      * <p> The array returned by this method contains each substring of this
2188      * string that is terminated by another substring that matches the given
2189      * expression or is terminated by the end of the string.  The substrings in
2190      * the array are in the order in which they occur in this string.  If the
2191      * expression does not match any part of the input then the resulting array
2192      * has just one element, namely this string.
2193      *
2194      * <p> When there is a positive-width match at the beginning of this
2195      * string then an empty leading substring is included at the beginning
2196      * of the resulting array. A zero-width match at the beginning however
2197      * never produces such empty leading substring.
2198      *
2199      * <p> The {@code limit} parameter controls the number of times the
2200      * pattern is applied and therefore affects the length of the resulting
2201      * array.  If the limit <i>n</i> is greater than zero then the pattern
2202      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2203      * length will be no greater than <i>n</i>, and the array's last entry
2204      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2205      * is non-positive then the pattern will be applied as many times as
2206      * possible and the array can have any length.  If <i>n</i> is zero then
2207      * the pattern will be applied as many times as possible, the array can
2208      * have any length, and trailing empty strings will be discarded.
2209      *
2210      * <p> The string {@code "boo:and:foo"}, for example, yields the
2211      * following results with these parameters:
2212      *
2213      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and result">
2214      * <tr>
2215      *     <th>Regex</th>
2216      *     <th>Limit</th>
2217      *     <th>Result</th>
2218      * </tr>
2219      * <tr><td align=center>:</td>
2220      *     <td align=center>2</td>
2221      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2222      * <tr><td align=center>:</td>
2223      *     <td align=center>5</td>
2224      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2225      * <tr><td align=center>:</td>
2226      *     <td align=center>-2</td>
2227      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2228      * <tr><td align=center>o</td>
2229      *     <td align=center>5</td>
2230      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2231      * <tr><td align=center>o</td>
2232      *     <td align=center>-2</td>
2233      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2234      * <tr><td align=center>o</td>
2235      *     <td align=center>0</td>
2236      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2237      * </table></blockquote>
2238      *
2239      * <p> An invocation of this method of the form
2240      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2241      * yields the same result as the expression
2242      *
2243      * <blockquote>
2244      * <code>
2245      * {@link java.util.regex.Pattern}.{@link
2246      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2247      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2248      * </code>
2249      * </blockquote>
2250      *
2251      *
2252      * @param  regex
2253      *         the delimiting regular expression
2254      *
2255      * @param  limit
2256      *         the result threshold, as described above
2257      *
2258      * @return  the array of strings computed by splitting this string
2259      *          around matches of the given regular expression
2260      *
2261      * @throws  PatternSyntaxException
2262      *          if the regular expression's syntax is invalid
2263      *
2264      * @see java.util.regex.Pattern
2265      *
2266      * @since 1.4
2267      * @spec JSR-51
2268      */
2269     public String[] split(String regex, int limit) {
2270         /* fastpath if the regex is a
2271          (1)one-char String and this character is not one of the
2272             RegEx's meta characters ".$|()[{^?*+\\", or
2273          (2)two-char String and the first char is the backslash and
2274             the second is not the ascii digit or ascii letter.
2275          */
2276         char ch = 0;
2277         if (((regex.length() == 1 &&
2278              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2279              (regex.length() == 2 &&
2280               regex.charAt(0) == '\\' &&
2281               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2282               ((ch-'a')|('z'-ch)) < 0 &&
2283               ((ch-'A')|('Z'-ch)) < 0)) &&
2284             (ch < Character.MIN_HIGH_SURROGATE ||
2285              ch > Character.MAX_LOW_SURROGATE))
2286         {
2287             int off = 0;
2288             int next = 0;
2289             boolean limited = limit > 0;
2290             ArrayList<String> list = new ArrayList<>();
2291             while ((next = indexOf(ch, off)) != -1) {
2292                 if (!limited || list.size() < limit - 1) {
2293                     list.add(substring(off, next));
2294                     off = next + 1;
2295                 } else {    // last one
2296                     //assert (list.size() == limit - 1);
2297                     int last = length();
2298                     list.add(substring(off, last));
2299                     off = last;
2300                     break;
2301                 }
2302             }
2303             // If no match was found, return this
2304             if (off == 0)
2305                 return new String[]{this};
2306 
2307             // Add remaining segment
2308             if (!limited || list.size() < limit)
2309                 list.add(substring(off, length()));
2310 
2311             // Construct result
2312             int resultSize = list.size();
2313             if (limit == 0) {
2314                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2315                     resultSize--;
2316                 }
2317             }
2318             String[] result = new String[resultSize];
2319             return list.subList(0, resultSize).toArray(result);
2320         }
2321         return Pattern.compile(regex).split(this, limit);
2322     }
2323 
2324     /**
2325      * Splits this string around matches of the given <a
2326      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2327      *
2328      * <p> This method works as if by invoking the two-argument {@link
2329      * #split(String, int) split} method with the given expression and a limit
2330      * argument of zero.  Trailing empty strings are therefore not included in
2331      * the resulting array.
2332      *
2333      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2334      * results with these expressions:
2335      *
2336      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and result">
2337      * <tr>
2338      *  <th>Regex</th>
2339      *  <th>Result</th>
2340      * </tr>
2341      * <tr><td align=center>:</td>
2342      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2343      * <tr><td align=center>o</td>
2344      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2345      * </table></blockquote>
2346      *
2347      *
2348      * @param  regex
2349      *         the delimiting regular expression
2350      *
2351      * @return  the array of strings computed by splitting this string
2352      *          around matches of the given regular expression
2353      *
2354      * @throws  PatternSyntaxException
2355      *          if the regular expression's syntax is invalid
2356      *
2357      * @see java.util.regex.Pattern
2358      *
2359      * @since 1.4
2360      * @spec JSR-51
2361      */
2362     public String[] split(String regex) {
2363         return split(regex, 0);
2364     }
2365 
2366     /**
2367      * Returns a new String composed of copies of the
2368      * {@code CharSequence elements} joined together with a copy of
2369      * the specified {@code delimiter}.
2370      *
2371      * <blockquote>For example,
2372      * <pre>{@code
2373      *     String message = String.join("-", "Java", "is", "cool");
2374      *     // message returned is: "Java-is-cool"
2375      * }</pre></blockquote>
2376      *
2377      * Note that if an element is null, then {@code "null"} is added.
2378      *
2379      * @param  delimiter the delimiter that separates each element
2380      * @param  elements the elements to join together.
2381      *
2382      * @return a new {@code String} that is composed of the {@code elements}
2383      *         separated by the {@code delimiter}
2384      *
2385      * @throws NullPointerException If {@code delimiter} or {@code elements}
2386      *         is {@code null}
2387      *
2388      * @see java.util.StringJoiner
2389      * @since 1.8
2390      */
2391     public static String join(CharSequence delimiter, CharSequence... elements) {
2392         Objects.requireNonNull(delimiter);
2393         Objects.requireNonNull(elements);
2394         // Number of elements not likely worth Arrays.stream overhead.
2395         StringJoiner joiner = new StringJoiner(delimiter);
2396         for (CharSequence cs: elements) {
2397             joiner.add(cs);
2398         }
2399         return joiner.toString();
2400     }
2401 
2402     /**
2403      * Returns a new {@code String} composed of copies of the
2404      * {@code CharSequence elements} joined together with a copy of the
2405      * specified {@code delimiter}.
2406      *
2407      * <blockquote>For example,
2408      * <pre>{@code
2409      *     List<String> strings = new LinkedList<>();
2410      *     strings.add("Java");strings.add("is");
2411      *     strings.add("cool");
2412      *     String message = String.join(" ", strings);
2413      *     //message returned is: "Java is cool"
2414      *
2415      *     Set<String> strings = new LinkedHashSet<>();
2416      *     strings.add("Java"); strings.add("is");
2417      *     strings.add("very"); strings.add("cool");
2418      *     String message = String.join("-", strings);
2419      *     //message returned is: "Java-is-very-cool"
2420      * }</pre></blockquote>
2421      *
2422      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2423      *
2424      * @param  delimiter a sequence of characters that is used to separate each
2425      *         of the {@code elements} in the resulting {@code String}
2426      * @param  elements an {@code Iterable} that will have its {@code elements}
2427      *         joined together.
2428      *
2429      * @return a new {@code String} that is composed from the {@code elements}
2430      *         argument
2431      *
2432      * @throws NullPointerException If {@code delimiter} or {@code elements}
2433      *         is {@code null}
2434      *
2435      * @see    #join(CharSequence,CharSequence...)
2436      * @see    java.util.StringJoiner
2437      * @since 1.8
2438      */
2439     public static String join(CharSequence delimiter,
2440             Iterable<? extends CharSequence> elements) {
2441         Objects.requireNonNull(delimiter);
2442         Objects.requireNonNull(elements);
2443         StringJoiner joiner = new StringJoiner(delimiter);
2444         for (CharSequence cs: elements) {
2445             joiner.add(cs);
2446         }
2447         return joiner.toString();
2448     }
2449 
2450     /**
2451      * Converts all of the characters in this {@code String} to lower
2452      * case using the rules of the given {@code Locale}.  Case mapping is based
2453      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2454      * class. Since case mappings are not always 1:1 char mappings, the resulting
2455      * {@code String} may be a different length than the original {@code String}.
2456      * <p>
2457      * Examples of lowercase  mappings are in the following table:
2458      * <table border="1" summary="Lowercase mapping examples showing language code of locale, upper case, lower case, and description">
2459      * <tr>
2460      *   <th>Language Code of Locale</th>
2461      *   <th>Upper Case</th>
2462      *   <th>Lower Case</th>
2463      *   <th>Description</th>
2464      * </tr>
2465      * <tr>
2466      *   <td>tr (Turkish)</td>
2467      *   <td>\u0130</td>
2468      *   <td>\u0069</td>
2469      *   <td>capital letter I with dot above -&gt; small letter i</td>
2470      * </tr>
2471      * <tr>
2472      *   <td>tr (Turkish)</td>
2473      *   <td>\u0049</td>
2474      *   <td>\u0131</td>
2475      *   <td>capital letter I -&gt; small letter dotless i </td>
2476      * </tr>
2477      * <tr>
2478      *   <td>(all)</td>
2479      *   <td>French Fries</td>
2480      *   <td>french fries</td>
2481      *   <td>lowercased all chars in String</td>
2482      * </tr>
2483      * <tr>
2484      *   <td>(all)</td>
2485      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2486      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2487      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2488      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2489      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2490      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2491      *   <td>lowercased all chars in String</td>
2492      * </tr>
2493      * </table>
2494      *
2495      * @param locale use the case transformation rules for this locale
2496      * @return the {@code String}, converted to lowercase.
2497      * @see     java.lang.String#toLowerCase()
2498      * @see     java.lang.String#toUpperCase()
2499      * @see     java.lang.String#toUpperCase(Locale)
2500      * @since   1.1
2501      */
2502     public String toLowerCase(Locale locale) {
2503         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2504                           : StringUTF16.toLowerCase(this, value, locale);
2505     }
2506 
2507     /**
2508      * Converts all of the characters in this {@code String} to lower
2509      * case using the rules of the default locale. This is equivalent to calling
2510      * {@code toLowerCase(Locale.getDefault())}.
2511      * <p>
2512      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2513      * results if used for strings that are intended to be interpreted locale
2514      * independently.
2515      * Examples are programming language identifiers, protocol keys, and HTML
2516      * tags.
2517      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2518      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2519      * LATIN SMALL LETTER DOTLESS I character.
2520      * To obtain correct results for locale insensitive strings, use
2521      * {@code toLowerCase(Locale.ROOT)}.
2522      *
2523      * @return  the {@code String}, converted to lowercase.
2524      * @see     java.lang.String#toLowerCase(Locale)
2525      */
2526     public String toLowerCase() {
2527         return toLowerCase(Locale.getDefault());
2528     }
2529 
2530     /**
2531      * Converts all of the characters in this {@code String} to upper
2532      * case using the rules of the given {@code Locale}. Case mapping is based
2533      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2534      * class. Since case mappings are not always 1:1 char mappings, the resulting
2535      * {@code String} may be a different length than the original {@code String}.
2536      * <p>
2537      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2538      *
2539      * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.">
2540      * <tr>
2541      *   <th>Language Code of Locale</th>
2542      *   <th>Lower Case</th>
2543      *   <th>Upper Case</th>
2544      *   <th>Description</th>
2545      * </tr>
2546      * <tr>
2547      *   <td>tr (Turkish)</td>
2548      *   <td>\u0069</td>
2549      *   <td>\u0130</td>
2550      *   <td>small letter i -&gt; capital letter I with dot above</td>
2551      * </tr>
2552      * <tr>
2553      *   <td>tr (Turkish)</td>
2554      *   <td>\u0131</td>
2555      *   <td>\u0049</td>
2556      *   <td>small letter dotless i -&gt; capital letter I</td>
2557      * </tr>
2558      * <tr>
2559      *   <td>(all)</td>
2560      *   <td>\u00df</td>
2561      *   <td>\u0053 \u0053</td>
2562      *   <td>small letter sharp s -&gt; two letters: SS</td>
2563      * </tr>
2564      * <tr>
2565      *   <td>(all)</td>
2566      *   <td>Fahrvergn&uuml;gen</td>
2567      *   <td>FAHRVERGN&Uuml;GEN</td>
2568      *   <td></td>
2569      * </tr>
2570      * </table>
2571      * @param locale use the case transformation rules for this locale
2572      * @return the {@code String}, converted to uppercase.
2573      * @see     java.lang.String#toUpperCase()
2574      * @see     java.lang.String#toLowerCase()
2575      * @see     java.lang.String#toLowerCase(Locale)
2576      * @since   1.1
2577      */
2578     public String toUpperCase(Locale locale) {
2579         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2580                           : StringUTF16.toUpperCase(this, value, locale);
2581     }
2582 
2583     /**
2584      * Converts all of the characters in this {@code String} to upper
2585      * case using the rules of the default locale. This method is equivalent to
2586      * {@code toUpperCase(Locale.getDefault())}.
2587      * <p>
2588      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2589      * results if used for strings that are intended to be interpreted locale
2590      * independently.
2591      * Examples are programming language identifiers, protocol keys, and HTML
2592      * tags.
2593      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2594      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2595      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2596      * To obtain correct results for locale insensitive strings, use
2597      * {@code toUpperCase(Locale.ROOT)}.
2598      *
2599      * @return  the {@code String}, converted to uppercase.
2600      * @see     java.lang.String#toUpperCase(Locale)
2601      */
2602     public String toUpperCase() {
2603         return toUpperCase(Locale.getDefault());
2604     }
2605 
2606     /**
2607      * Returns a string whose value is this string, with any leading and trailing
2608      * whitespace removed.
2609      * <p>
2610      * If this {@code String} object represents an empty character
2611      * sequence, or the first and last characters of character sequence
2612      * represented by this {@code String} object both have codes
2613      * greater than {@code '\u005Cu0020'} (the space character), then a
2614      * reference to this {@code String} object is returned.
2615      * <p>
2616      * Otherwise, if there is no character with a code greater than
2617      * {@code '\u005Cu0020'} in the string, then a
2618      * {@code String} object representing an empty string is
2619      * returned.
2620      * <p>
2621      * Otherwise, let <i>k</i> be the index of the first character in the
2622      * string whose code is greater than {@code '\u005Cu0020'}, and let
2623      * <i>m</i> be the index of the last character in the string whose code
2624      * is greater than {@code '\u005Cu0020'}. A {@code String}
2625      * object is returned, representing the substring of this string that
2626      * begins with the character at index <i>k</i> and ends with the
2627      * character at index <i>m</i>-that is, the result of
2628      * {@code this.substring(k, m + 1)}.
2629      * <p>
2630      * This method may be used to trim whitespace (as defined above) from
2631      * the beginning and end of a string.
2632      *
2633      * @return  A string whose value is this string, with any leading and trailing white
2634      *          space removed, or this string if it has no leading or
2635      *          trailing white space.
2636      */
2637     public String trim() {
2638         String ret = isLatin1() ? StringLatin1.trim(value)
2639                                 : StringUTF16.trim(value);
2640         return ret == null ? this : ret;
2641     }
2642 
2643     /**
2644      * This object (which is already a string!) is itself returned.
2645      *
2646      * @return  the string itself.
2647      */
2648     public String toString() {
2649         return this;
2650     }
2651 
2652     /**
2653      * Returns a stream of {@code int} zero-extending the {@code char} values
2654      * from this sequence.  Any char which maps to a <a
2655      * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
2656      * point</a> is passed through uninterpreted.
2657      *
2658      * @return an IntStream of char values from this sequence
2659      * @since 9
2660      */
2661     @Override
2662     public IntStream chars() {
2663         return StreamSupport.intStream(
2664             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2665                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
2666             false);
2667     }
2668 
2669 
2670     /**
2671      * Returns a stream of code point values from this sequence.  Any surrogate
2672      * pairs encountered in the sequence are combined as if by {@linkplain
2673      * Character#toCodePoint Character.toCodePoint} and the result is passed
2674      * to the stream. Any other code units, including ordinary BMP characters,
2675      * unpaired surrogates, and undefined code units, are zero-extended to
2676      * {@code int} values which are then passed to the stream.
2677      *
2678      * @return an IntStream of Unicode code points from this sequence
2679      * @since 9
2680      */
2681     @Override
2682     public IntStream codePoints() {
2683         return StreamSupport.intStream(
2684             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2685                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
2686             false);
2687     }
2688 
2689     /**
2690      * Converts this string to a new character array.
2691      *
2692      * @return  a newly allocated character array whose length is the length
2693      *          of this string and whose contents are initialized to contain
2694      *          the character sequence represented by this string.
2695      */
2696     public char[] toCharArray() {
2697         return isLatin1() ? StringLatin1.toChars(value)
2698                           : StringUTF16.toChars(value);
2699     }
2700 
2701     /**
2702      * Returns a formatted string using the specified format string and
2703      * arguments.
2704      *
2705      * <p> The locale always used is the one returned by {@link
2706      * java.util.Locale#getDefault() Locale.getDefault()}.
2707      *
2708      * @param  format
2709      *         A <a href="../util/Formatter.html#syntax">format string</a>
2710      *
2711      * @param  args
2712      *         Arguments referenced by the format specifiers in the format
2713      *         string.  If there are more arguments than format specifiers, the
2714      *         extra arguments are ignored.  The number of arguments is
2715      *         variable and may be zero.  The maximum number of arguments is
2716      *         limited by the maximum dimension of a Java array as defined by
2717      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2718      *         The behaviour on a
2719      *         {@code null} argument depends on the <a
2720      *         href="../util/Formatter.html#syntax">conversion</a>.
2721      *
2722      * @throws  java.util.IllegalFormatException
2723      *          If a format string contains an illegal syntax, a format
2724      *          specifier that is incompatible with the given arguments,
2725      *          insufficient arguments given the format string, or other
2726      *          illegal conditions.  For specification of all possible
2727      *          formatting errors, see the <a
2728      *          href="../util/Formatter.html#detail">Details</a> section of the
2729      *          formatter class specification.
2730      *
2731      * @return  A formatted string
2732      *
2733      * @see  java.util.Formatter
2734      * @since  1.5
2735      */
2736     public static String format(String format, Object... args) {
2737         return new Formatter().format(format, args).toString();
2738     }
2739 
2740     /**
2741      * Returns a formatted string using the specified locale, format string,
2742      * and arguments.
2743      *
2744      * @param  l
2745      *         The {@linkplain java.util.Locale locale} to apply during
2746      *         formatting.  If {@code l} is {@code null} then no localization
2747      *         is applied.
2748      *
2749      * @param  format
2750      *         A <a href="../util/Formatter.html#syntax">format string</a>
2751      *
2752      * @param  args
2753      *         Arguments referenced by the format specifiers in the format
2754      *         string.  If there are more arguments than format specifiers, the
2755      *         extra arguments are ignored.  The number of arguments is
2756      *         variable and may be zero.  The maximum number of arguments is
2757      *         limited by the maximum dimension of a Java array as defined by
2758      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2759      *         The behaviour on a
2760      *         {@code null} argument depends on the
2761      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2762      *
2763      * @throws  java.util.IllegalFormatException
2764      *          If a format string contains an illegal syntax, a format
2765      *          specifier that is incompatible with the given arguments,
2766      *          insufficient arguments given the format string, or other
2767      *          illegal conditions.  For specification of all possible
2768      *          formatting errors, see the <a
2769      *          href="../util/Formatter.html#detail">Details</a> section of the
2770      *          formatter class specification
2771      *
2772      * @return  A formatted string
2773      *
2774      * @see  java.util.Formatter
2775      * @since  1.5
2776      */
2777     public static String format(Locale l, String format, Object... args) {
2778         return new Formatter(l).format(format, args).toString();
2779     }
2780 
2781     /**
2782      * Returns the string representation of the {@code Object} argument.
2783      *
2784      * @param   obj   an {@code Object}.
2785      * @return  if the argument is {@code null}, then a string equal to
2786      *          {@code "null"}; otherwise, the value of
2787      *          {@code obj.toString()} is returned.
2788      * @see     java.lang.Object#toString()
2789      */
2790     public static String valueOf(Object obj) {
2791         return (obj == null) ? "null" : obj.toString();
2792     }
2793 
2794     /**
2795      * Returns the string representation of the {@code char} array
2796      * argument. The contents of the character array are copied; subsequent
2797      * modification of the character array does not affect the returned
2798      * string.
2799      *
2800      * @param   data     the character array.
2801      * @return  a {@code String} that contains the characters of the
2802      *          character array.
2803      */
2804     public static String valueOf(char data[]) {
2805         return new String(data);
2806     }
2807 
2808     /**
2809      * Returns the string representation of a specific subarray of the
2810      * {@code char} array argument.
2811      * <p>
2812      * The {@code offset} argument is the index of the first
2813      * character of the subarray. The {@code count} argument
2814      * specifies the length of the subarray. The contents of the subarray
2815      * are copied; subsequent modification of the character array does not
2816      * affect the returned string.
2817      *
2818      * @param   data     the character array.
2819      * @param   offset   initial offset of the subarray.
2820      * @param   count    length of the subarray.
2821      * @return  a {@code String} that contains the characters of the
2822      *          specified subarray of the character array.
2823      * @exception IndexOutOfBoundsException if {@code offset} is
2824      *          negative, or {@code count} is negative, or
2825      *          {@code offset+count} is larger than
2826      *          {@code data.length}.
2827      */
2828     public static String valueOf(char data[], int offset, int count) {
2829         return new String(data, offset, count);
2830     }
2831 
2832     /**
2833      * Equivalent to {@link #valueOf(char[], int, int)}.
2834      *
2835      * @param   data     the character array.
2836      * @param   offset   initial offset of the subarray.
2837      * @param   count    length of the subarray.
2838      * @return  a {@code String} that contains the characters of the
2839      *          specified subarray of the character array.
2840      * @exception IndexOutOfBoundsException if {@code offset} is
2841      *          negative, or {@code count} is negative, or
2842      *          {@code offset+count} is larger than
2843      *          {@code data.length}.
2844      */
2845     public static String copyValueOf(char data[], int offset, int count) {
2846         return new String(data, offset, count);
2847     }
2848 
2849     /**
2850      * Equivalent to {@link #valueOf(char[])}.
2851      *
2852      * @param   data   the character array.
2853      * @return  a {@code String} that contains the characters of the
2854      *          character array.
2855      */
2856     public static String copyValueOf(char data[]) {
2857         return new String(data);
2858     }
2859 
2860     /**
2861      * Returns the string representation of the {@code boolean} argument.
2862      *
2863      * @param   b   a {@code boolean}.
2864      * @return  if the argument is {@code true}, a string equal to
2865      *          {@code "true"} is returned; otherwise, a string equal to
2866      *          {@code "false"} is returned.
2867      */
2868     public static String valueOf(boolean b) {
2869         return b ? "true" : "false";
2870     }
2871 
2872     /**
2873      * Returns the string representation of the {@code char}
2874      * argument.
2875      *
2876      * @param   c   a {@code char}.
2877      * @return  a string of length {@code 1} containing
2878      *          as its single character the argument {@code c}.
2879      */
2880     public static String valueOf(char c) {
2881         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
2882             return new String(StringLatin1.toBytes(c), LATIN1);
2883         }
2884         return new String(StringUTF16.toBytes(c), UTF16);
2885     }
2886 
2887     /**
2888      * Returns the string representation of the {@code int} argument.
2889      * <p>
2890      * The representation is exactly the one returned by the
2891      * {@code Integer.toString} method of one argument.
2892      *
2893      * @param   i   an {@code int}.
2894      * @return  a string representation of the {@code int} argument.
2895      * @see     java.lang.Integer#toString(int, int)
2896      */
2897     public static String valueOf(int i) {
2898         return Integer.toString(i);
2899     }
2900 
2901     /**
2902      * Returns the string representation of the {@code long} argument.
2903      * <p>
2904      * The representation is exactly the one returned by the
2905      * {@code Long.toString} method of one argument.
2906      *
2907      * @param   l   a {@code long}.
2908      * @return  a string representation of the {@code long} argument.
2909      * @see     java.lang.Long#toString(long)
2910      */
2911     public static String valueOf(long l) {
2912         return Long.toString(l);
2913     }
2914 
2915     /**
2916      * Returns the string representation of the {@code float} argument.
2917      * <p>
2918      * The representation is exactly the one returned by the
2919      * {@code Float.toString} method of one argument.
2920      *
2921      * @param   f   a {@code float}.
2922      * @return  a string representation of the {@code float} argument.
2923      * @see     java.lang.Float#toString(float)
2924      */
2925     public static String valueOf(float f) {
2926         return Float.toString(f);
2927     }
2928 
2929     /**
2930      * Returns the string representation of the {@code double} argument.
2931      * <p>
2932      * The representation is exactly the one returned by the
2933      * {@code Double.toString} method of one argument.
2934      *
2935      * @param   d   a {@code double}.
2936      * @return  a  string representation of the {@code double} argument.
2937      * @see     java.lang.Double#toString(double)
2938      */
2939     public static String valueOf(double d) {
2940         return Double.toString(d);
2941     }
2942 
2943     /**
2944      * Returns a canonical representation for the string object.
2945      * <p>
2946      * A pool of strings, initially empty, is maintained privately by the
2947      * class {@code String}.
2948      * <p>
2949      * When the intern method is invoked, if the pool already contains a
2950      * string equal to this {@code String} object as determined by
2951      * the {@link #equals(Object)} method, then the string from the pool is
2952      * returned. Otherwise, this {@code String} object is added to the
2953      * pool and a reference to this {@code String} object is returned.
2954      * <p>
2955      * It follows that for any two strings {@code s} and {@code t},
2956      * {@code s.intern() == t.intern()} is {@code true}
2957      * if and only if {@code s.equals(t)} is {@code true}.
2958      * <p>
2959      * All literal strings and string-valued constant expressions are
2960      * interned. String literals are defined in section 3.10.5 of the
2961      * <cite>The Java&trade; Language Specification</cite>.
2962      *
2963      * @return  a string that has the same contents as this string, but is
2964      *          guaranteed to be from a pool of unique strings.
2965      */
2966     public native String intern();
2967 
2968     ////////////////////////////////////////////////////////////////
2969 
2970     /**
2971      * Copy character bytes from this string into dst starting at dstBegin.
2972      * This method doesn't perform any range checking.
2973      *
2974      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
2975      * coders are different, and dst is big enough (range check)
2976      *
2977      * @param dstBegin  the char index, not offset of byte[]
2978      * @param coder     the coder of dst[]
2979      */
2980     void getBytes(byte dst[], int dstBegin, byte coder) {
2981         if (coder() == coder) {
2982             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
2983         } else {    // this.coder == LATIN && coder == UTF16
2984             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
2985         }
2986     }
2987 
2988     /*
2989      * Package private constructor. Trailing Void argument is there for
2990      * disambiguating it against other (public) constructors.
2991      *
2992      * Stores the char[] value into a byte[] that each byte represents
2993      * the8 low-order bits of the corresponding character, if the char[]
2994      * contains only latin1 character. Or a byte[] that stores all
2995      * characters in their byte sequences defined by the {@code StringUTF16}.
2996      */
2997     String(char[] value, int off, int len, Void sig) {
2998         if (len == 0) {
2999             this.value = "".value;
3000             this.coder = "".coder;
3001             return;
3002         }
3003         if (COMPACT_STRINGS) {
3004             byte[] val = StringUTF16.compress(value, off, len);
3005             if (val != null) {
3006                 this.value = val;
3007                 this.coder = LATIN1;
3008                 return;
3009             }
3010         }
3011         this.coder = UTF16;
3012         this.value = StringUTF16.toBytes(value, off, len);
3013     }
3014 
3015     /*
3016      * Package private constructor. Trailing Void argument is there for
3017      * disambiguating it against other (public) constructors.
3018      */
3019     String(AbstractStringBuilder asb, Void sig) {
3020         byte[] val = asb.getValue();
3021         int length = asb.length();
3022         if (asb.isLatin1()) {
3023             this.coder = LATIN1;
3024             this.value = Arrays.copyOfRange(val, 0, length);
3025         } else {
3026             if (COMPACT_STRINGS) {
3027                 byte[] buf = StringUTF16.compress(val, 0, length);
3028                 if (buf != null) {
3029                     this.coder = LATIN1;
3030                     this.value = buf;
3031                     return;
3032                 }
3033             }
3034             this.coder = UTF16;
3035             this.value = Arrays.copyOfRange(val, 0, length << 1);
3036         }
3037     }
3038 
3039    /*
3040     * Package private constructor which shares value array for speed.
3041     */
3042     String(byte[] value, byte coder) {
3043         this.value = value;
3044         this.coder = coder;
3045     }
3046 
3047     byte coder() {
3048         return COMPACT_STRINGS ? coder : UTF16;
3049     }
3050 
3051     private boolean isLatin1() {
3052         return COMPACT_STRINGS && coder == LATIN1;
3053     }
3054 
3055     static final byte LATIN1 = 0;
3056     static final byte UTF16  = 1;
3057 
3058     /*
3059      * StringIndexOutOfBoundsException  if {@code index} is
3060      * negative or greater than or equal to {@code length}.
3061      */
3062     static void checkIndex(int index, int length) {
3063         if (index < 0 || index >= length) {
3064             throw new StringIndexOutOfBoundsException("index " + index);
3065         }
3066     }
3067 
3068     /*
3069      * StringIndexOutOfBoundsException  if {@code offset}
3070      * is negative or greater than {@code length}.
3071      */
3072     static void checkOffset(int offset, int length) {
3073         if (offset < 0 || offset > length) {
3074             throw new StringIndexOutOfBoundsException("offset " + offset +
3075                                                       ",length " + length);
3076         }
3077     }
3078 
3079     /*
3080      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3081      * bounds.
3082      *
3083      * @throws  StringIndexOutOfBoundsException
3084      *          If {@code offset} is negative, {@code count} is negative,
3085      *          or {@code offset} is greater than {@code length - count}
3086      */
3087     static void checkBoundsOffCount(int offset, int count, int length) {
3088         if (offset < 0 || count < 0 || offset > length - count) {
3089             throw new StringIndexOutOfBoundsException(
3090                 "offset " + offset + ", count " + count + ", length " + length);
3091         }
3092     }
3093 
3094     /*
3095      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3096      * bounds.
3097      *
3098      * @throws  StringIndexOutOfBoundsException
3099      *          If {@code begin} is negative, {@code begin} is greater than
3100      *          {@code end}, or {@code end} is greater than {@code length}.
3101      */
3102     private static void checkBoundsBeginEnd(int begin, int end, int length) {
3103         if (begin < 0 || begin > end || end > length) {
3104             throw new StringIndexOutOfBoundsException(
3105                 "begin " + begin + ", end " + end + ", length " + length);
3106         }
3107     }
3108 }