1 /*
   2  * Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.ObjectStreamField;
  29 import java.io.UnsupportedEncodingException;
  30 import java.lang.annotation.Native;
  31 import java.nio.charset.Charset;
  32 import java.util.ArrayList;
  33 import java.util.Arrays;
  34 import java.util.Comparator;
  35 import java.util.Formatter;
  36 import java.util.Locale;
  37 import java.util.Objects;
  38 import java.util.Spliterator;
  39 import java.util.StringJoiner;
  40 import java.util.function.Function;
  41 import java.util.regex.Matcher;
  42 import java.util.regex.Pattern;
  43 import java.util.regex.PatternSyntaxException;
  44 import java.util.stream.Collectors;
  45 import java.util.stream.IntStream;
  46 import java.util.stream.Stream;
  47 import java.util.stream.StreamSupport;
  48 import jdk.internal.HotSpotIntrinsicCandidate;
  49 import jdk.internal.vm.annotation.Stable;
  50 
  51 import static java.util.function.Predicate.not;
  52 
  53 /**
  54  * The {@code String} class represents character strings. All
  55  * string literals in Java programs, such as {@code "abc"}, are
  56  * implemented as instances of this class.
  57  * <p>
  58  * Strings are constant; their values cannot be changed after they
  59  * are created. String buffers support mutable strings.
  60  * Because String objects are immutable they can be shared. For example:
  61  * <blockquote><pre>
  62  *     String str = "abc";
  63  * </pre></blockquote><p>
  64  * is equivalent to:
  65  * <blockquote><pre>
  66  *     char data[] = {'a', 'b', 'c'};
  67  *     String str = new String(data);
  68  * </pre></blockquote><p>
  69  * Here are some more examples of how strings can be used:
  70  * <blockquote><pre>
  71  *     System.out.println("abc");
  72  *     String cde = "cde";
  73  *     System.out.println("abc" + cde);
  74  *     String c = "abc".substring(2,3);
  75  *     String d = cde.substring(1, 2);
  76  * </pre></blockquote>
  77  * <p>
  78  * The class {@code String} includes methods for examining
  79  * individual characters of the sequence, for comparing strings, for
  80  * searching strings, for extracting substrings, and for creating a
  81  * copy of a string with all characters translated to uppercase or to
  82  * lowercase. Case mapping is based on the Unicode Standard version
  83  * specified by the {@link java.lang.Character Character} class.
  84  * <p>
  85  * The Java language provides special support for the string
  86  * concatenation operator (&nbsp;+&nbsp;), and for conversion of
  87  * other objects to strings. For additional information on string
  88  * concatenation and conversion, see <i>The Java&trade; Language Specification</i>.
  89  *
  90  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  91  * or method in this class will cause a {@link NullPointerException} to be
  92  * thrown.
  93  *
  94  * <p>A {@code String} represents a string in the UTF-16 format
  95  * in which <em>supplementary characters</em> are represented by <em>surrogate
  96  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  97  * Character Representations</a> in the {@code Character} class for
  98  * more information).
  99  * Index values refer to {@code char} code units, so a supplementary
 100  * character uses two positions in a {@code String}.
 101  * <p>The {@code String} class provides methods for dealing with
 102  * Unicode code points (i.e., characters), in addition to those for
 103  * dealing with Unicode code units (i.e., {@code char} values).
 104  *
 105  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 106  * into account.  The {@link java.text.Collator} class provides methods for
 107  * finer-grain, locale-sensitive String comparison.
 108  *
 109  * @implNote The implementation of the string concatenation operator is left to
 110  * the discretion of a Java compiler, as long as the compiler ultimately conforms
 111  * to <i>The Java&trade; Language Specification</i>. For example, the {@code javac} compiler
 112  * may implement the operator with {@code StringBuffer}, {@code StringBuilder},
 113  * or {@code java.lang.invoke.StringConcatFactory} depending on the JDK version. The
 114  * implementation of string conversion is typically through the method {@code toString},
 115  * defined by {@code Object} and inherited by all classes in Java.
 116  *
 117  * @author  Lee Boynton
 118  * @author  Arthur van Hoff
 119  * @author  Martin Buchholz
 120  * @author  Ulf Zibis
 121  * @see     java.lang.Object#toString()
 122  * @see     java.lang.StringBuffer
 123  * @see     java.lang.StringBuilder
 124  * @see     java.nio.charset.Charset
 125  * @since   1.0
 126  * @jls     15.18.1 String Concatenation Operator +
 127  */
 128 
 129 public final class String
 130     implements java.io.Serializable, Comparable<String>, CharSequence {
 131 
 132     /**
 133      * The value is used for character storage.
 134      *
 135      * @implNote This field is trusted by the VM, and is a subject to
 136      * constant folding if String instance is constant. Overwriting this
 137      * field after construction will cause problems.
 138      *
 139      * Additionally, it is marked with {@link Stable} to trust the contents
 140      * of the array. No other facility in JDK provides this functionality (yet).
 141      * {@link Stable} is safe here, because value is never null.
 142      */
 143     @Stable
 144     private final byte[] value;
 145 
 146     /**
 147      * The identifier of the encoding used to encode the bytes in
 148      * {@code value}. The supported values in this implementation are
 149      *
 150      * LATIN1
 151      * UTF16
 152      *
 153      * @implNote This field is trusted by the VM, and is a subject to
 154      * constant folding if String instance is constant. Overwriting this
 155      * field after construction will cause problems.
 156      */
 157     private final byte coder;
 158 
 159     /** Cache the hash code for the string */
 160     private int hash; // Default to 0
 161 
 162     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 163     private static final long serialVersionUID = -6849794470754667710L;
 164 
 165     /**
 166      * If String compaction is disabled, the bytes in {@code value} are
 167      * always encoded in UTF16.
 168      *
 169      * For methods with several possible implementation paths, when String
 170      * compaction is disabled, only one code path is taken.
 171      *
 172      * The instance field value is generally opaque to optimizing JIT
 173      * compilers. Therefore, in performance-sensitive place, an explicit
 174      * check of the static boolean {@code COMPACT_STRINGS} is done first
 175      * before checking the {@code coder} field since the static boolean
 176      * {@code COMPACT_STRINGS} would be constant folded away by an
 177      * optimizing JIT compiler. The idioms for these cases are as follows.
 178      *
 179      * For code such as:
 180      *
 181      *    if (coder == LATIN1) { ... }
 182      *
 183      * can be written more optimally as
 184      *
 185      *    if (coder() == LATIN1) { ... }
 186      *
 187      * or:
 188      *
 189      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 190      *
 191      * An optimizing JIT compiler can fold the above conditional as:
 192      *
 193      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 194      *    COMPACT_STRINGS == false => if (false)           { ... }
 195      *
 196      * @implNote
 197      * The actual value for this field is injected by JVM. The static
 198      * initialization block is used to set the value here to communicate
 199      * that this static final field is not statically foldable, and to
 200      * avoid any possible circular dependency during vm initialization.
 201      */
 202     static final boolean COMPACT_STRINGS;
 203 
 204     static {
 205         COMPACT_STRINGS = true;
 206     }
 207 
 208     /**
 209      * Class String is special cased within the Serialization Stream Protocol.
 210      *
 211      * A String instance is written into an ObjectOutputStream according to
 212      * <a href="{@docRoot}/../specs/serialization/protocol.html#stream-elements">
 213      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 214      */
 215     private static final ObjectStreamField[] serialPersistentFields =
 216         new ObjectStreamField[0];
 217 
 218     /**
 219      * Initializes a newly created {@code String} object so that it represents
 220      * an empty character sequence.  Note that use of this constructor is
 221      * unnecessary since Strings are immutable.
 222      */
 223     public String() {
 224         this.value = "".value;
 225         this.coder = "".coder;
 226     }
 227 
 228     /**
 229      * Initializes a newly created {@code String} object so that it represents
 230      * the same sequence of characters as the argument; in other words, the
 231      * newly created string is a copy of the argument string. Unless an
 232      * explicit copy of {@code original} is needed, use of this constructor is
 233      * unnecessary since Strings are immutable.
 234      *
 235      * @param  original
 236      *         A {@code String}
 237      */
 238     @HotSpotIntrinsicCandidate
 239     public String(String original) {
 240         this.value = original.value;
 241         this.coder = original.coder;
 242         this.hash = original.hash;
 243     }
 244 
 245     /**
 246      * Allocates a new {@code String} so that it represents the sequence of
 247      * characters currently contained in the character array argument. The
 248      * contents of the character array are copied; subsequent modification of
 249      * the character array does not affect the newly created string.
 250      *
 251      * @param  value
 252      *         The initial value of the string
 253      */
 254     public String(char value[]) {
 255         this(value, 0, value.length, null);
 256     }
 257 
 258     /**
 259      * Allocates a new {@code String} that contains characters from a subarray
 260      * of the character array argument. The {@code offset} argument is the
 261      * index of the first character of the subarray and the {@code count}
 262      * argument specifies the length of the subarray. The contents of the
 263      * subarray are copied; subsequent modification of the character array does
 264      * not affect the newly created string.
 265      *
 266      * @param  value
 267      *         Array that is the source of characters
 268      *
 269      * @param  offset
 270      *         The initial offset
 271      *
 272      * @param  count
 273      *         The length
 274      *
 275      * @throws  IndexOutOfBoundsException
 276      *          If {@code offset} is negative, {@code count} is negative, or
 277      *          {@code offset} is greater than {@code value.length - count}
 278      */
 279     public String(char value[], int offset, int count) {
 280         this(value, offset, count, rangeCheck(value, offset, count));
 281     }
 282 
 283     private static Void rangeCheck(char[] value, int offset, int count) {
 284         checkBoundsOffCount(offset, count, value.length);
 285         return null;
 286     }
 287 
 288     /**
 289      * Allocates a new {@code String} that contains characters from a subarray
 290      * of the <a href="Character.html#unicode">Unicode code point</a> array
 291      * argument.  The {@code offset} argument is the index of the first code
 292      * point of the subarray and the {@code count} argument specifies the
 293      * length of the subarray.  The contents of the subarray are converted to
 294      * {@code char}s; subsequent modification of the {@code int} array does not
 295      * affect the newly created string.
 296      *
 297      * @param  codePoints
 298      *         Array that is the source of Unicode code points
 299      *
 300      * @param  offset
 301      *         The initial offset
 302      *
 303      * @param  count
 304      *         The length
 305      *
 306      * @throws  IllegalArgumentException
 307      *          If any invalid Unicode code point is found in {@code
 308      *          codePoints}
 309      *
 310      * @throws  IndexOutOfBoundsException
 311      *          If {@code offset} is negative, {@code count} is negative, or
 312      *          {@code offset} is greater than {@code codePoints.length - count}
 313      *
 314      * @since  1.5
 315      */
 316     public String(int[] codePoints, int offset, int count) {
 317         checkBoundsOffCount(offset, count, codePoints.length);
 318         if (count == 0) {
 319             this.value = "".value;
 320             this.coder = "".coder;
 321             return;
 322         }
 323         if (COMPACT_STRINGS) {
 324             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 325             if (val != null) {
 326                 this.coder = LATIN1;
 327                 this.value = val;
 328                 return;
 329             }
 330         }
 331         this.coder = UTF16;
 332         this.value = StringUTF16.toBytes(codePoints, offset, count);
 333     }
 334 
 335     /**
 336      * Allocates a new {@code String} constructed from a subarray of an array
 337      * of 8-bit integer values.
 338      *
 339      * <p> The {@code offset} argument is the index of the first byte of the
 340      * subarray, and the {@code count} argument specifies the length of the
 341      * subarray.
 342      *
 343      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 344      * specified in the {@link #String(byte[],int) String(byte[],int)} constructor.
 345      *
 346      * @deprecated This method does not properly convert bytes into characters.
 347      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 348      * {@code String} constructors that take a {@link
 349      * java.nio.charset.Charset}, charset name, or that use the platform's
 350      * default charset.
 351      *
 352      * @param  ascii
 353      *         The bytes to be converted to characters
 354      *
 355      * @param  hibyte
 356      *         The top 8 bits of each 16-bit Unicode code unit
 357      *
 358      * @param  offset
 359      *         The initial offset
 360      * @param  count
 361      *         The length
 362      *
 363      * @throws  IndexOutOfBoundsException
 364      *          If {@code offset} is negative, {@code count} is negative, or
 365      *          {@code offset} is greater than {@code ascii.length - count}
 366      *
 367      * @see  #String(byte[], int)
 368      * @see  #String(byte[], int, int, java.lang.String)
 369      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 370      * @see  #String(byte[], int, int)
 371      * @see  #String(byte[], java.lang.String)
 372      * @see  #String(byte[], java.nio.charset.Charset)
 373      * @see  #String(byte[])
 374      */
 375     @Deprecated(since="1.1")
 376     public String(byte ascii[], int hibyte, int offset, int count) {
 377         checkBoundsOffCount(offset, count, ascii.length);
 378         if (count == 0) {
 379             this.value = "".value;
 380             this.coder = "".coder;
 381             return;
 382         }
 383         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 384             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 385             this.coder = LATIN1;
 386         } else {
 387             hibyte <<= 8;
 388             byte[] val = StringUTF16.newBytesFor(count);
 389             for (int i = 0; i < count; i++) {
 390                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 391             }
 392             this.value = val;
 393             this.coder = UTF16;
 394         }
 395     }
 396 
 397     /**
 398      * Allocates a new {@code String} containing characters constructed from
 399      * an array of 8-bit integer values. Each character <i>c</i> in the
 400      * resulting string is constructed from the corresponding component
 401      * <i>b</i> in the byte array such that:
 402      *
 403      * <blockquote><pre>
 404      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 405      *                         | (<b><i>b</i></b> &amp; 0xff))
 406      * </pre></blockquote>
 407      *
 408      * @deprecated  This method does not properly convert bytes into
 409      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 410      * {@code String} constructors that take a {@link
 411      * java.nio.charset.Charset}, charset name, or that use the platform's
 412      * default charset.
 413      *
 414      * @param  ascii
 415      *         The bytes to be converted to characters
 416      *
 417      * @param  hibyte
 418      *         The top 8 bits of each 16-bit Unicode code unit
 419      *
 420      * @see  #String(byte[], int, int, java.lang.String)
 421      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 422      * @see  #String(byte[], int, int)
 423      * @see  #String(byte[], java.lang.String)
 424      * @see  #String(byte[], java.nio.charset.Charset)
 425      * @see  #String(byte[])
 426      */
 427     @Deprecated(since="1.1")
 428     public String(byte ascii[], int hibyte) {
 429         this(ascii, hibyte, 0, ascii.length);
 430     }
 431 
 432     /**
 433      * Constructs a new {@code String} by decoding the specified subarray of
 434      * bytes using the specified charset.  The length of the new {@code String}
 435      * is a function of the charset, and hence may not be equal to the length
 436      * of the subarray.
 437      *
 438      * <p> The behavior of this constructor when the given bytes are not valid
 439      * in the given charset is unspecified.  The {@link
 440      * java.nio.charset.CharsetDecoder} class should be used when more control
 441      * over the decoding process is required.
 442      *
 443      * @param  bytes
 444      *         The bytes to be decoded into characters
 445      *
 446      * @param  offset
 447      *         The index of the first byte to decode
 448      *
 449      * @param  length
 450      *         The number of bytes to decode
 451 
 452      * @param  charsetName
 453      *         The name of a supported {@linkplain java.nio.charset.Charset
 454      *         charset}
 455      *
 456      * @throws  UnsupportedEncodingException
 457      *          If the named charset is not supported
 458      *
 459      * @throws  IndexOutOfBoundsException
 460      *          If {@code offset} is negative, {@code length} is negative, or
 461      *          {@code offset} is greater than {@code bytes.length - length}
 462      *
 463      * @since  1.1
 464      */
 465     public String(byte bytes[], int offset, int length, String charsetName)
 466             throws UnsupportedEncodingException {
 467         if (charsetName == null)
 468             throw new NullPointerException("charsetName");
 469         checkBoundsOffCount(offset, length, bytes.length);
 470         StringCoding.Result ret =
 471             StringCoding.decode(charsetName, bytes, offset, length);
 472         this.value = ret.value;
 473         this.coder = ret.coder;
 474     }
 475 
 476     /**
 477      * Constructs a new {@code String} by decoding the specified subarray of
 478      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 479      * The length of the new {@code String} is a function of the charset, and
 480      * hence may not be equal to the length of the subarray.
 481      *
 482      * <p> This method always replaces malformed-input and unmappable-character
 483      * sequences with this charset's default replacement string.  The {@link
 484      * java.nio.charset.CharsetDecoder} class should be used when more control
 485      * over the decoding process is required.
 486      *
 487      * @param  bytes
 488      *         The bytes to be decoded into characters
 489      *
 490      * @param  offset
 491      *         The index of the first byte to decode
 492      *
 493      * @param  length
 494      *         The number of bytes to decode
 495      *
 496      * @param  charset
 497      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 498      *         decode the {@code bytes}
 499      *
 500      * @throws  IndexOutOfBoundsException
 501      *          If {@code offset} is negative, {@code length} is negative, or
 502      *          {@code offset} is greater than {@code bytes.length - length}
 503      *
 504      * @since  1.6
 505      */
 506     public String(byte bytes[], int offset, int length, Charset charset) {
 507         if (charset == null)
 508             throw new NullPointerException("charset");
 509         checkBoundsOffCount(offset, length, bytes.length);
 510         StringCoding.Result ret =
 511             StringCoding.decode(charset, bytes, offset, length);
 512         this.value = ret.value;
 513         this.coder = ret.coder;
 514     }
 515 
 516     /**
 517      * Constructs a new {@code String} by decoding the specified array of bytes
 518      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 519      * length of the new {@code String} is a function of the charset, and hence
 520      * may not be equal to the length of the byte array.
 521      *
 522      * <p> The behavior of this constructor when the given bytes are not valid
 523      * in the given charset is unspecified.  The {@link
 524      * java.nio.charset.CharsetDecoder} class should be used when more control
 525      * over the decoding process is required.
 526      *
 527      * @param  bytes
 528      *         The bytes to be decoded into characters
 529      *
 530      * @param  charsetName
 531      *         The name of a supported {@linkplain java.nio.charset.Charset
 532      *         charset}
 533      *
 534      * @throws  UnsupportedEncodingException
 535      *          If the named charset is not supported
 536      *
 537      * @since  1.1
 538      */
 539     public String(byte bytes[], String charsetName)
 540             throws UnsupportedEncodingException {
 541         this(bytes, 0, bytes.length, charsetName);
 542     }
 543 
 544     /**
 545      * Constructs a new {@code String} by decoding the specified array of
 546      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 547      * The length of the new {@code String} is a function of the charset, and
 548      * hence may not be equal to the length of the byte array.
 549      *
 550      * <p> This method always replaces malformed-input and unmappable-character
 551      * sequences with this charset's default replacement string.  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  charset
 559      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 560      *         decode the {@code bytes}
 561      *
 562      * @since  1.6
 563      */
 564     public String(byte bytes[], Charset charset) {
 565         this(bytes, 0, bytes.length, charset);
 566     }
 567 
 568     /**
 569      * Constructs a new {@code String} by decoding the specified subarray of
 570      * bytes using the platform's default charset.  The length of the new
 571      * {@code String} is a function of the charset, and hence may not be equal
 572      * to the length of the subarray.
 573      *
 574      * <p> The behavior of this constructor when the given bytes are not valid
 575      * in the default charset is unspecified.  The {@link
 576      * java.nio.charset.CharsetDecoder} class should be used when more control
 577      * over the decoding process is required.
 578      *
 579      * @param  bytes
 580      *         The bytes to be decoded into characters
 581      *
 582      * @param  offset
 583      *         The index of the first byte to decode
 584      *
 585      * @param  length
 586      *         The number of bytes to decode
 587      *
 588      * @throws  IndexOutOfBoundsException
 589      *          If {@code offset} is negative, {@code length} is negative, or
 590      *          {@code offset} is greater than {@code bytes.length - length}
 591      *
 592      * @since  1.1
 593      */
 594     public String(byte bytes[], int offset, int length) {
 595         checkBoundsOffCount(offset, length, bytes.length);
 596         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 597         this.value = ret.value;
 598         this.coder = ret.coder;
 599     }
 600 
 601     /**
 602      * Constructs a new {@code String} by decoding the specified array of bytes
 603      * using the platform's default charset.  The length of the new {@code
 604      * String} is a function of the charset, and hence may not be equal to the
 605      * length of the byte array.
 606      *
 607      * <p> The behavior of this constructor when the given bytes are not valid
 608      * in the default charset is unspecified.  The {@link
 609      * java.nio.charset.CharsetDecoder} class should be used when more control
 610      * over the decoding process is required.
 611      *
 612      * @param  bytes
 613      *         The bytes to be decoded into characters
 614      *
 615      * @since  1.1
 616      */
 617     public String(byte[] bytes) {
 618         this(bytes, 0, bytes.length);
 619     }
 620 
 621     /**
 622      * Allocates a new string that contains the sequence of characters
 623      * currently contained in the string buffer argument. The contents of the
 624      * string buffer are copied; subsequent modification of the string buffer
 625      * does not affect the newly created string.
 626      *
 627      * @param  buffer
 628      *         A {@code StringBuffer}
 629      */
 630     public String(StringBuffer buffer) {
 631         this(buffer.toString());
 632     }
 633 
 634     /**
 635      * Allocates a new string that contains the sequence of characters
 636      * currently contained in the string builder argument. The contents of the
 637      * string builder are copied; subsequent modification of the string builder
 638      * does not affect the newly created string.
 639      *
 640      * <p> This constructor is provided to ease migration to {@code
 641      * StringBuilder}. Obtaining a string from a string builder via the {@code
 642      * toString} method is likely to run faster and is generally preferred.
 643      *
 644      * @param   builder
 645      *          A {@code StringBuilder}
 646      *
 647      * @since  1.5
 648      */
 649     public String(StringBuilder builder) {
 650         this(builder, null);
 651     }
 652 
 653     /**
 654      * Returns the length of this string.
 655      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 656      * code units</a> in the string.
 657      *
 658      * @return  the length of the sequence of characters represented by this
 659      *          object.
 660      */
 661     public int length() {
 662         return value.length >> coder();
 663     }
 664 
 665     /**
 666      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 667      *
 668      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 669      * {@code false}
 670      *
 671      * @since 1.6
 672      */
 673     public boolean isEmpty() {
 674         return value.length == 0;
 675     }
 676 
 677     /**
 678      * Returns the {@code char} value at the
 679      * specified index. An index ranges from {@code 0} to
 680      * {@code length() - 1}. The first {@code char} value of the sequence
 681      * is at index {@code 0}, the next at index {@code 1},
 682      * and so on, as for array indexing.
 683      *
 684      * <p>If the {@code char} value specified by the index is a
 685      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 686      * value is returned.
 687      *
 688      * @param      index   the index of the {@code char} value.
 689      * @return     the {@code char} value at the specified index of this string.
 690      *             The first {@code char} value is at index {@code 0}.
 691      * @exception  IndexOutOfBoundsException  if the {@code index}
 692      *             argument is negative or not less than the length of this
 693      *             string.
 694      */
 695     public char charAt(int index) {
 696         if (isLatin1()) {
 697             return StringLatin1.charAt(value, index);
 698         } else {
 699             return StringUTF16.charAt(value, index);
 700         }
 701     }
 702 
 703     /**
 704      * Returns the character (Unicode code point) at the specified
 705      * index. The index refers to {@code char} values
 706      * (Unicode code units) and ranges from {@code 0} to
 707      * {@link #length()}{@code  - 1}.
 708      *
 709      * <p> If the {@code char} value specified at the given index
 710      * is in the high-surrogate range, the following index is less
 711      * than the length of this {@code String}, and the
 712      * {@code char} value at the following index is in the
 713      * low-surrogate range, then the supplementary code point
 714      * corresponding to this surrogate pair is returned. Otherwise,
 715      * the {@code char} value at the given index is returned.
 716      *
 717      * @param      index the index to the {@code char} values
 718      * @return     the code point value of the character at the
 719      *             {@code index}
 720      * @exception  IndexOutOfBoundsException  if the {@code index}
 721      *             argument is negative or not less than the length of this
 722      *             string.
 723      * @since      1.5
 724      */
 725     public int codePointAt(int index) {
 726         if (isLatin1()) {
 727             checkIndex(index, value.length);
 728             return value[index] & 0xff;
 729         }
 730         int length = value.length >> 1;
 731         checkIndex(index, length);
 732         return StringUTF16.codePointAt(value, index, length);
 733     }
 734 
 735     /**
 736      * Returns the character (Unicode code point) before the specified
 737      * index. The index refers to {@code char} values
 738      * (Unicode code units) and ranges from {@code 1} to {@link
 739      * CharSequence#length() length}.
 740      *
 741      * <p> If the {@code char} value at {@code (index - 1)}
 742      * is in the low-surrogate range, {@code (index - 2)} is not
 743      * negative, and the {@code char} value at {@code (index -
 744      * 2)} is in the high-surrogate range, then the
 745      * supplementary code point value of the surrogate pair is
 746      * returned. If the {@code char} value at {@code index -
 747      * 1} is an unpaired low-surrogate or a high-surrogate, the
 748      * surrogate value is returned.
 749      *
 750      * @param     index the index following the code point that should be returned
 751      * @return    the Unicode code point value before the given index.
 752      * @exception IndexOutOfBoundsException if the {@code index}
 753      *            argument is less than 1 or greater than the length
 754      *            of this string.
 755      * @since     1.5
 756      */
 757     public int codePointBefore(int index) {
 758         int i = index - 1;
 759         if (i < 0 || i >= length()) {
 760             throw new StringIndexOutOfBoundsException(index);
 761         }
 762         if (isLatin1()) {
 763             return (value[i] & 0xff);
 764         }
 765         return StringUTF16.codePointBefore(value, index);
 766     }
 767 
 768     /**
 769      * Returns the number of Unicode code points in the specified text
 770      * range of this {@code String}. The text range begins at the
 771      * specified {@code beginIndex} and extends to the
 772      * {@code char} at index {@code endIndex - 1}. Thus the
 773      * length (in {@code char}s) of the text range is
 774      * {@code endIndex-beginIndex}. Unpaired surrogates within
 775      * the text range count as one code point each.
 776      *
 777      * @param beginIndex the index to the first {@code char} of
 778      * the text range.
 779      * @param endIndex the index after the last {@code char} of
 780      * the text range.
 781      * @return the number of Unicode code points in the specified text
 782      * range
 783      * @exception IndexOutOfBoundsException if the
 784      * {@code beginIndex} is negative, or {@code endIndex}
 785      * is larger than the length of this {@code String}, or
 786      * {@code beginIndex} is larger than {@code endIndex}.
 787      * @since  1.5
 788      */
 789     public int codePointCount(int beginIndex, int endIndex) {
 790         if (beginIndex < 0 || beginIndex > endIndex ||
 791             endIndex > length()) {
 792             throw new IndexOutOfBoundsException();
 793         }
 794         if (isLatin1()) {
 795             return endIndex - beginIndex;
 796         }
 797         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 798     }
 799 
 800     /**
 801      * Returns the index within this {@code String} that is
 802      * offset from the given {@code index} by
 803      * {@code codePointOffset} code points. Unpaired surrogates
 804      * within the text range given by {@code index} and
 805      * {@code codePointOffset} count as one code point each.
 806      *
 807      * @param index the index to be offset
 808      * @param codePointOffset the offset in code points
 809      * @return the index within this {@code String}
 810      * @exception IndexOutOfBoundsException if {@code index}
 811      *   is negative or larger then the length of this
 812      *   {@code String}, or if {@code codePointOffset} is positive
 813      *   and the substring starting with {@code index} has fewer
 814      *   than {@code codePointOffset} code points,
 815      *   or if {@code codePointOffset} is negative and the substring
 816      *   before {@code index} has fewer than the absolute value
 817      *   of {@code codePointOffset} code points.
 818      * @since 1.5
 819      */
 820     public int offsetByCodePoints(int index, int codePointOffset) {
 821         if (index < 0 || index > length()) {
 822             throw new IndexOutOfBoundsException();
 823         }
 824         return Character.offsetByCodePoints(this, index, codePointOffset);
 825     }
 826 
 827     /**
 828      * Copies characters from this string into the destination character
 829      * array.
 830      * <p>
 831      * The first character to be copied is at index {@code srcBegin};
 832      * the last character to be copied is at index {@code srcEnd-1}
 833      * (thus the total number of characters to be copied is
 834      * {@code srcEnd-srcBegin}). The characters are copied into the
 835      * subarray of {@code dst} starting at index {@code dstBegin}
 836      * and ending at index:
 837      * <blockquote><pre>
 838      *     dstBegin + (srcEnd-srcBegin) - 1
 839      * </pre></blockquote>
 840      *
 841      * @param      srcBegin   index of the first character in the string
 842      *                        to copy.
 843      * @param      srcEnd     index after the last character in the string
 844      *                        to copy.
 845      * @param      dst        the destination array.
 846      * @param      dstBegin   the start offset in the destination array.
 847      * @exception IndexOutOfBoundsException If any of the following
 848      *            is true:
 849      *            <ul><li>{@code srcBegin} is negative.
 850      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 851      *            <li>{@code srcEnd} is greater than the length of this
 852      *                string
 853      *            <li>{@code dstBegin} is negative
 854      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 855      *                {@code dst.length}</ul>
 856      */
 857     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 858         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 859         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 860         if (isLatin1()) {
 861             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 862         } else {
 863             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 864         }
 865     }
 866 
 867     /**
 868      * Copies characters from this string into the destination byte array. Each
 869      * byte receives the 8 low-order bits of the corresponding character. The
 870      * eight high-order bits of each character are not copied and do not
 871      * participate in the transfer in any way.
 872      *
 873      * <p> The first character to be copied is at index {@code srcBegin}; the
 874      * last character to be copied is at index {@code srcEnd-1}.  The total
 875      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 876      * characters, converted to bytes, are copied into the subarray of {@code
 877      * dst} starting at index {@code dstBegin} and ending at index:
 878      *
 879      * <blockquote><pre>
 880      *     dstBegin + (srcEnd-srcBegin) - 1
 881      * </pre></blockquote>
 882      *
 883      * @deprecated  This method does not properly convert characters into
 884      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 885      * {@link #getBytes()} method, which uses the platform's default charset.
 886      *
 887      * @param  srcBegin
 888      *         Index of the first character in the string to copy
 889      *
 890      * @param  srcEnd
 891      *         Index after the last character in the string to copy
 892      *
 893      * @param  dst
 894      *         The destination array
 895      *
 896      * @param  dstBegin
 897      *         The start offset in the destination array
 898      *
 899      * @throws  IndexOutOfBoundsException
 900      *          If any of the following is true:
 901      *          <ul>
 902      *            <li> {@code srcBegin} is negative
 903      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 904      *            <li> {@code srcEnd} is greater than the length of this String
 905      *            <li> {@code dstBegin} is negative
 906      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 907      *                 dst.length}
 908      *          </ul>
 909      */
 910     @Deprecated(since="1.1")
 911     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 912         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 913         Objects.requireNonNull(dst);
 914         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 915         if (isLatin1()) {
 916             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 917         } else {
 918             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 919         }
 920     }
 921 
 922     /**
 923      * Encodes this {@code String} into a sequence of bytes using the named
 924      * charset, storing the result into a new byte array.
 925      *
 926      * <p> The behavior of this method when this string cannot be encoded in
 927      * the given charset is unspecified.  The {@link
 928      * java.nio.charset.CharsetEncoder} class should be used when more control
 929      * over the encoding process is required.
 930      *
 931      * @param  charsetName
 932      *         The name of a supported {@linkplain java.nio.charset.Charset
 933      *         charset}
 934      *
 935      * @return  The resultant byte array
 936      *
 937      * @throws  UnsupportedEncodingException
 938      *          If the named charset is not supported
 939      *
 940      * @since  1.1
 941      */
 942     public byte[] getBytes(String charsetName)
 943             throws UnsupportedEncodingException {
 944         if (charsetName == null) throw new NullPointerException();
 945         return StringCoding.encode(charsetName, coder(), value);
 946     }
 947 
 948     /**
 949      * Encodes this {@code String} into a sequence of bytes using the given
 950      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 951      * new byte array.
 952      *
 953      * <p> This method always replaces malformed-input and unmappable-character
 954      * sequences with this charset's default replacement byte array.  The
 955      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 956      * control over the encoding process is required.
 957      *
 958      * @param  charset
 959      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 960      *         the {@code String}
 961      *
 962      * @return  The resultant byte array
 963      *
 964      * @since  1.6
 965      */
 966     public byte[] getBytes(Charset charset) {
 967         if (charset == null) throw new NullPointerException();
 968         return StringCoding.encode(charset, coder(), value);
 969      }
 970 
 971     /**
 972      * Encodes this {@code String} into a sequence of bytes using the
 973      * platform's default charset, storing the result into a new byte array.
 974      *
 975      * <p> The behavior of this method when this string cannot be encoded in
 976      * the default charset is unspecified.  The {@link
 977      * java.nio.charset.CharsetEncoder} class should be used when more control
 978      * over the encoding process is required.
 979      *
 980      * @return  The resultant byte array
 981      *
 982      * @since      1.1
 983      */
 984     public byte[] getBytes() {
 985         return StringCoding.encode(coder(), value);
 986     }
 987 
 988     /**
 989      * Compares this string to the specified object.  The result is {@code
 990      * true} if and only if the argument is not {@code null} and is a {@code
 991      * String} object that represents the same sequence of characters as this
 992      * object.
 993      *
 994      * <p>For finer-grained String comparison, refer to
 995      * {@link java.text.Collator}.
 996      *
 997      * @param  anObject
 998      *         The object to compare this {@code String} against
 999      *
1000      * @return  {@code true} if the given object represents a {@code String}
1001      *          equivalent to this string, {@code false} otherwise
1002      *
1003      * @see  #compareTo(String)
1004      * @see  #equalsIgnoreCase(String)
1005      */
1006     public boolean equals(Object anObject) {
1007         if (this == anObject) {
1008             return true;
1009         }
1010         if (anObject instanceof String) {
1011             String aString = (String)anObject;
1012             if (coder() == aString.coder()) {
1013                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1014                                   : StringUTF16.equals(value, aString.value);
1015             }
1016         }
1017         return false;
1018     }
1019 
1020     /**
1021      * Compares this string to the specified {@code StringBuffer}.  The result
1022      * is {@code true} if and only if this {@code String} represents the same
1023      * sequence of characters as the specified {@code StringBuffer}. This method
1024      * synchronizes on the {@code StringBuffer}.
1025      *
1026      * <p>For finer-grained String comparison, refer to
1027      * {@link java.text.Collator}.
1028      *
1029      * @param  sb
1030      *         The {@code StringBuffer} to compare this {@code String} against
1031      *
1032      * @return  {@code true} if this {@code String} represents the same
1033      *          sequence of characters as the specified {@code StringBuffer},
1034      *          {@code false} otherwise
1035      *
1036      * @since  1.4
1037      */
1038     public boolean contentEquals(StringBuffer sb) {
1039         return contentEquals((CharSequence)sb);
1040     }
1041 
1042     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1043         int len = length();
1044         if (len != sb.length()) {
1045             return false;
1046         }
1047         byte v1[] = value;
1048         byte v2[] = sb.getValue();
1049         if (coder() == sb.getCoder()) {
1050             int n = v1.length;
1051             for (int i = 0; i < n; i++) {
1052                 if (v1[i] != v2[i]) {
1053                     return false;
1054                 }
1055             }
1056         } else {
1057             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1058                 return false;
1059             }
1060             return StringUTF16.contentEquals(v1, v2, len);
1061         }
1062         return true;
1063     }
1064 
1065     /**
1066      * Compares this string to the specified {@code CharSequence}.  The
1067      * result is {@code true} if and only if this {@code String} represents the
1068      * same sequence of char values as the specified sequence. Note that if the
1069      * {@code CharSequence} is a {@code StringBuffer} then the method
1070      * synchronizes on it.
1071      *
1072      * <p>For finer-grained String comparison, refer to
1073      * {@link java.text.Collator}.
1074      *
1075      * @param  cs
1076      *         The sequence to compare this {@code String} against
1077      *
1078      * @return  {@code true} if this {@code String} represents the same
1079      *          sequence of char values as the specified sequence, {@code
1080      *          false} otherwise
1081      *
1082      * @since  1.5
1083      */
1084     public boolean contentEquals(CharSequence cs) {
1085         // Argument is a StringBuffer, StringBuilder
1086         if (cs instanceof AbstractStringBuilder) {
1087             if (cs instanceof StringBuffer) {
1088                 synchronized(cs) {
1089                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1090                 }
1091             } else {
1092                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1093             }
1094         }
1095         // Argument is a String
1096         if (cs instanceof String) {
1097             return equals(cs);
1098         }
1099         // Argument is a generic CharSequence
1100         int n = cs.length();
1101         if (n != length()) {
1102             return false;
1103         }
1104         byte[] val = this.value;
1105         if (isLatin1()) {
1106             for (int i = 0; i < n; i++) {
1107                 if ((val[i] & 0xff) != cs.charAt(i)) {
1108                     return false;
1109                 }
1110             }
1111         } else {
1112             if (!StringUTF16.contentEquals(val, cs, n)) {
1113                 return false;
1114             }
1115         }
1116         return true;
1117     }
1118 
1119     /**
1120      * Compares this {@code String} to another {@code String}, ignoring case
1121      * considerations.  Two strings are considered equal ignoring case if they
1122      * are of the same length and corresponding characters in the two strings
1123      * are equal ignoring case.
1124      *
1125      * <p> Two characters {@code c1} and {@code c2} are considered the same
1126      * ignoring case if at least one of the following is true:
1127      * <ul>
1128      *   <li> The two characters are the same (as compared by the
1129      *        {@code ==} operator)
1130      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1131      *        on each character produces the same result
1132      * </ul>
1133      *
1134      * <p>Note that this method does <em>not</em> take locale into account, and
1135      * will result in unsatisfactory results for certain locales.  The
1136      * {@link java.text.Collator} class provides locale-sensitive comparison.
1137      *
1138      * @param  anotherString
1139      *         The {@code String} to compare this {@code String} against
1140      *
1141      * @return  {@code true} if the argument is not {@code null} and it
1142      *          represents an equivalent {@code String} ignoring case; {@code
1143      *          false} otherwise
1144      *
1145      * @see  #equals(Object)
1146      */
1147     public boolean equalsIgnoreCase(String anotherString) {
1148         return (this == anotherString) ? true
1149                 : (anotherString != null)
1150                 && (anotherString.length() == length())
1151                 && regionMatches(true, 0, anotherString, 0, length());
1152     }
1153 
1154     /**
1155      * Compares two strings lexicographically.
1156      * The comparison is based on the Unicode value of each character in
1157      * the strings. The character sequence represented by this
1158      * {@code String} object is compared lexicographically to the
1159      * character sequence represented by the argument string. The result is
1160      * a negative integer if this {@code String} object
1161      * lexicographically precedes the argument string. The result is a
1162      * positive integer if this {@code String} object lexicographically
1163      * follows the argument string. The result is zero if the strings
1164      * are equal; {@code compareTo} returns {@code 0} exactly when
1165      * the {@link #equals(Object)} method would return {@code true}.
1166      * <p>
1167      * This is the definition of lexicographic ordering. If two strings are
1168      * different, then either they have different characters at some index
1169      * that is a valid index for both strings, or their lengths are different,
1170      * or both. If they have different characters at one or more index
1171      * positions, let <i>k</i> be the smallest such index; then the string
1172      * whose character at position <i>k</i> has the smaller value, as
1173      * determined by using the {@code <} operator, lexicographically precedes the
1174      * other string. In this case, {@code compareTo} returns the
1175      * difference of the two character values at position {@code k} in
1176      * the two string -- that is, the value:
1177      * <blockquote><pre>
1178      * this.charAt(k)-anotherString.charAt(k)
1179      * </pre></blockquote>
1180      * If there is no index position at which they differ, then the shorter
1181      * string lexicographically precedes the longer string. In this case,
1182      * {@code compareTo} returns the difference of the lengths of the
1183      * strings -- that is, the value:
1184      * <blockquote><pre>
1185      * this.length()-anotherString.length()
1186      * </pre></blockquote>
1187      *
1188      * <p>For finer-grained String comparison, refer to
1189      * {@link java.text.Collator}.
1190      *
1191      * @param   anotherString   the {@code String} to be compared.
1192      * @return  the value {@code 0} if the argument string is equal to
1193      *          this string; a value less than {@code 0} if this string
1194      *          is lexicographically less than the string argument; and a
1195      *          value greater than {@code 0} if this string is
1196      *          lexicographically greater than the string argument.
1197      */
1198     public int compareTo(String anotherString) {
1199         byte v1[] = value;
1200         byte v2[] = anotherString.value;
1201         if (coder() == anotherString.coder()) {
1202             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1203                               : StringUTF16.compareTo(v1, v2);
1204         }
1205         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1206                           : StringUTF16.compareToLatin1(v1, v2);
1207      }
1208 
1209     /**
1210      * A Comparator that orders {@code String} objects as by
1211      * {@code compareToIgnoreCase}. This comparator is serializable.
1212      * <p>
1213      * Note that this Comparator does <em>not</em> take locale into account,
1214      * and will result in an unsatisfactory ordering for certain locales.
1215      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1216      *
1217      * @see     java.text.Collator
1218      * @since   1.2
1219      */
1220     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1221                                          = new CaseInsensitiveComparator();
1222     private static class CaseInsensitiveComparator
1223             implements Comparator<String>, java.io.Serializable {
1224         // use serialVersionUID from JDK 1.2.2 for interoperability
1225         private static final long serialVersionUID = 8575799808933029326L;
1226 
1227         public int compare(String s1, String s2) {
1228             byte v1[] = s1.value;
1229             byte v2[] = s2.value;
1230             if (s1.coder() == s2.coder()) {
1231                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1232                                      : StringUTF16.compareToCI(v1, v2);
1233             }
1234             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1235                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1236         }
1237 
1238         /** Replaces the de-serialized object. */
1239         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1240     }
1241 
1242     /**
1243      * Compares two strings lexicographically, ignoring case
1244      * differences. This method returns an integer whose sign is that of
1245      * calling {@code compareTo} with normalized versions of the strings
1246      * where case differences have been eliminated by calling
1247      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1248      * each character.
1249      * <p>
1250      * Note that this method does <em>not</em> take locale into account,
1251      * and will result in an unsatisfactory ordering for certain locales.
1252      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1253      *
1254      * @param   str   the {@code String} to be compared.
1255      * @return  a negative integer, zero, or a positive integer as the
1256      *          specified String is greater than, equal to, or less
1257      *          than this String, ignoring case considerations.
1258      * @see     java.text.Collator
1259      * @since   1.2
1260      */
1261     public int compareToIgnoreCase(String str) {
1262         return CASE_INSENSITIVE_ORDER.compare(this, str);
1263     }
1264 
1265     /**
1266      * Tests if two string regions are equal.
1267      * <p>
1268      * A substring of this {@code String} object is compared to a substring
1269      * of the argument other. The result is true if these substrings
1270      * represent identical character sequences. The substring of this
1271      * {@code String} object to be compared begins at index {@code toffset}
1272      * and has length {@code len}. The substring of other to be compared
1273      * begins at index {@code ooffset} and has length {@code len}. The
1274      * result is {@code false} if and only if at least one of the following
1275      * is true:
1276      * <ul><li>{@code toffset} is negative.
1277      * <li>{@code ooffset} is negative.
1278      * <li>{@code toffset+len} is greater than the length of this
1279      * {@code String} object.
1280      * <li>{@code ooffset+len} is greater than the length of the other
1281      * argument.
1282      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1283      * such that:
1284      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1285      * <i>k</i>{@code )}
1286      * </ul>
1287      *
1288      * <p>Note that this method does <em>not</em> take locale into account.  The
1289      * {@link java.text.Collator} class provides locale-sensitive comparison.
1290      *
1291      * @param   toffset   the starting offset of the subregion in this string.
1292      * @param   other     the string argument.
1293      * @param   ooffset   the starting offset of the subregion in the string
1294      *                    argument.
1295      * @param   len       the number of characters to compare.
1296      * @return  {@code true} if the specified subregion of this string
1297      *          exactly matches the specified subregion of the string argument;
1298      *          {@code false} otherwise.
1299      */
1300     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1301         byte tv[] = value;
1302         byte ov[] = other.value;
1303         // Note: toffset, ooffset, or len might be near -1>>>1.
1304         if ((ooffset < 0) || (toffset < 0) ||
1305              (toffset > (long)length() - len) ||
1306              (ooffset > (long)other.length() - len)) {
1307             return false;
1308         }
1309         if (coder() == other.coder()) {
1310             if (!isLatin1() && (len > 0)) {
1311                 toffset = toffset << 1;
1312                 ooffset = ooffset << 1;
1313                 len = len << 1;
1314             }
1315             while (len-- > 0) {
1316                 if (tv[toffset++] != ov[ooffset++]) {
1317                     return false;
1318                 }
1319             }
1320         } else {
1321             if (coder() == LATIN1) {
1322                 while (len-- > 0) {
1323                     if (StringLatin1.getChar(tv, toffset++) !=
1324                         StringUTF16.getChar(ov, ooffset++)) {
1325                         return false;
1326                     }
1327                 }
1328             } else {
1329                 while (len-- > 0) {
1330                     if (StringUTF16.getChar(tv, toffset++) !=
1331                         StringLatin1.getChar(ov, ooffset++)) {
1332                         return false;
1333                     }
1334                 }
1335             }
1336         }
1337         return true;
1338     }
1339 
1340     /**
1341      * Tests if two string regions are equal.
1342      * <p>
1343      * A substring of this {@code String} object is compared to a substring
1344      * of the argument {@code other}. The result is {@code true} if these
1345      * substrings represent character sequences that are the same, ignoring
1346      * case if and only if {@code ignoreCase} is true. The substring of
1347      * this {@code String} object to be compared begins at index
1348      * {@code toffset} and has length {@code len}. The substring of
1349      * {@code other} to be compared begins at index {@code ooffset} and
1350      * has length {@code len}. The result is {@code false} if and only if
1351      * at least one of the following is true:
1352      * <ul><li>{@code toffset} is negative.
1353      * <li>{@code ooffset} is negative.
1354      * <li>{@code toffset+len} is greater than the length of this
1355      * {@code String} object.
1356      * <li>{@code ooffset+len} is greater than the length of the other
1357      * argument.
1358      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1359      * integer <i>k</i> less than {@code len} such that:
1360      * <blockquote><pre>
1361      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1362      * </pre></blockquote>
1363      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1364      * integer <i>k</i> less than {@code len} such that:
1365      * <blockquote><pre>
1366      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1367      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1368      * </pre></blockquote>
1369      * </ul>
1370      *
1371      * <p>Note that this method does <em>not</em> take locale into account,
1372      * and will result in unsatisfactory results for certain locales when
1373      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1374      * provides locale-sensitive comparison.
1375      *
1376      * @param   ignoreCase   if {@code true}, ignore case when comparing
1377      *                       characters.
1378      * @param   toffset      the starting offset of the subregion in this
1379      *                       string.
1380      * @param   other        the string argument.
1381      * @param   ooffset      the starting offset of the subregion in the string
1382      *                       argument.
1383      * @param   len          the number of characters to compare.
1384      * @return  {@code true} if the specified subregion of this string
1385      *          matches the specified subregion of the string argument;
1386      *          {@code false} otherwise. Whether the matching is exact
1387      *          or case insensitive depends on the {@code ignoreCase}
1388      *          argument.
1389      */
1390     public boolean regionMatches(boolean ignoreCase, int toffset,
1391             String other, int ooffset, int len) {
1392         if (!ignoreCase) {
1393             return regionMatches(toffset, other, ooffset, len);
1394         }
1395         // Note: toffset, ooffset, or len might be near -1>>>1.
1396         if ((ooffset < 0) || (toffset < 0)
1397                 || (toffset > (long)length() - len)
1398                 || (ooffset > (long)other.length() - len)) {
1399             return false;
1400         }
1401         byte tv[] = value;
1402         byte ov[] = other.value;
1403         if (coder() == other.coder()) {
1404             return isLatin1()
1405               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1406               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1407         }
1408         return isLatin1()
1409               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1410               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1411     }
1412 
1413     /**
1414      * Tests if the substring of this string beginning at the
1415      * specified index starts with the specified prefix.
1416      *
1417      * @param   prefix    the prefix.
1418      * @param   toffset   where to begin looking in this string.
1419      * @return  {@code true} if the character sequence represented by the
1420      *          argument is a prefix of the substring of this object starting
1421      *          at index {@code toffset}; {@code false} otherwise.
1422      *          The result is {@code false} if {@code toffset} is
1423      *          negative or greater than the length of this
1424      *          {@code String} object; otherwise the result is the same
1425      *          as the result of the expression
1426      *          <pre>
1427      *          this.substring(toffset).startsWith(prefix)
1428      *          </pre>
1429      */
1430     public boolean startsWith(String prefix, int toffset) {
1431         // Note: toffset might be near -1>>>1.
1432         if (toffset < 0 || toffset > length() - prefix.length()) {
1433             return false;
1434         }
1435         byte ta[] = value;
1436         byte pa[] = prefix.value;
1437         int po = 0;
1438         int pc = pa.length;
1439         if (coder() == prefix.coder()) {
1440             int to = isLatin1() ? toffset : toffset << 1;
1441             while (po < pc) {
1442                 if (ta[to++] != pa[po++]) {
1443                     return false;
1444                 }
1445             }
1446         } else {
1447             if (isLatin1()) {  // && pcoder == UTF16
1448                 return false;
1449             }
1450             // coder == UTF16 && pcoder == LATIN1)
1451             while (po < pc) {
1452                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1453                     return false;
1454                }
1455             }
1456         }
1457         return true;
1458     }
1459 
1460     /**
1461      * Tests if this string starts with the specified prefix.
1462      *
1463      * @param   prefix   the prefix.
1464      * @return  {@code true} if the character sequence represented by the
1465      *          argument is a prefix of the character sequence represented by
1466      *          this string; {@code false} otherwise.
1467      *          Note also that {@code true} will be returned if the
1468      *          argument is an empty string or is equal to this
1469      *          {@code String} object as determined by the
1470      *          {@link #equals(Object)} method.
1471      * @since   1.0
1472      */
1473     public boolean startsWith(String prefix) {
1474         return startsWith(prefix, 0);
1475     }
1476 
1477     /**
1478      * Tests if this string ends with the specified suffix.
1479      *
1480      * @param   suffix   the suffix.
1481      * @return  {@code true} if the character sequence represented by the
1482      *          argument is a suffix of the character sequence represented by
1483      *          this object; {@code false} otherwise. Note that the
1484      *          result will be {@code true} if the argument is the
1485      *          empty string or is equal to this {@code String} object
1486      *          as determined by the {@link #equals(Object)} method.
1487      */
1488     public boolean endsWith(String suffix) {
1489         return startsWith(suffix, length() - suffix.length());
1490     }
1491 
1492     /**
1493      * Returns a hash code for this string. The hash code for a
1494      * {@code String} object is computed as
1495      * <blockquote><pre>
1496      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1497      * </pre></blockquote>
1498      * using {@code int} arithmetic, where {@code s[i]} is the
1499      * <i>i</i>th character of the string, {@code n} is the length of
1500      * the string, and {@code ^} indicates exponentiation.
1501      * (The hash value of the empty string is zero.)
1502      *
1503      * @return  a hash code value for this object.
1504      */
1505     public int hashCode() {
1506         int h = hash;
1507         if (h == 0 && value.length > 0) {
1508             hash = h = isLatin1() ? StringLatin1.hashCode(value)
1509                                   : StringUTF16.hashCode(value);
1510         }
1511         return h;
1512     }
1513 
1514     /**
1515      * Returns the index within this string of the first occurrence of
1516      * the specified character. If a character with value
1517      * {@code ch} occurs in the character sequence represented by
1518      * this {@code String} object, then the index (in Unicode
1519      * code units) of the first such occurrence is returned. For
1520      * values of {@code ch} in the range from 0 to 0xFFFF
1521      * (inclusive), this is the smallest value <i>k</i> such that:
1522      * <blockquote><pre>
1523      * this.charAt(<i>k</i>) == ch
1524      * </pre></blockquote>
1525      * is true. For other values of {@code ch}, it is the
1526      * smallest value <i>k</i> such that:
1527      * <blockquote><pre>
1528      * this.codePointAt(<i>k</i>) == ch
1529      * </pre></blockquote>
1530      * is true. In either case, if no such character occurs in this
1531      * string, then {@code -1} is returned.
1532      *
1533      * @param   ch   a character (Unicode code point).
1534      * @return  the index of the first occurrence of the character in the
1535      *          character sequence represented by this object, or
1536      *          {@code -1} if the character does not occur.
1537      */
1538     public int indexOf(int ch) {
1539         return indexOf(ch, 0);
1540     }
1541 
1542     /**
1543      * Returns the index within this string of the first occurrence of the
1544      * specified character, starting the search at the specified index.
1545      * <p>
1546      * If a character with value {@code ch} occurs in the
1547      * character sequence represented by this {@code String}
1548      * object at an index no smaller than {@code fromIndex}, then
1549      * the index of the first such occurrence is returned. For values
1550      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1551      * this is the smallest value <i>k</i> such that:
1552      * <blockquote><pre>
1553      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1554      * </pre></blockquote>
1555      * is true. For other values of {@code ch}, it is the
1556      * smallest value <i>k</i> such that:
1557      * <blockquote><pre>
1558      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1559      * </pre></blockquote>
1560      * is true. In either case, if no such character occurs in this
1561      * string at or after position {@code fromIndex}, then
1562      * {@code -1} is returned.
1563      *
1564      * <p>
1565      * There is no restriction on the value of {@code fromIndex}. If it
1566      * is negative, it has the same effect as if it were zero: this entire
1567      * string may be searched. If it is greater than the length of this
1568      * string, it has the same effect as if it were equal to the length of
1569      * this string: {@code -1} is returned.
1570      *
1571      * <p>All indices are specified in {@code char} values
1572      * (Unicode code units).
1573      *
1574      * @param   ch          a character (Unicode code point).
1575      * @param   fromIndex   the index to start the search from.
1576      * @return  the index of the first occurrence of the character in the
1577      *          character sequence represented by this object that is greater
1578      *          than or equal to {@code fromIndex}, or {@code -1}
1579      *          if the character does not occur.
1580      */
1581     public int indexOf(int ch, int fromIndex) {
1582         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1583                           : StringUTF16.indexOf(value, ch, fromIndex);
1584     }
1585 
1586     /**
1587      * Returns the index within this string of the last occurrence of
1588      * the specified character. For values of {@code ch} in the
1589      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1590      * units) returned is the largest value <i>k</i> such that:
1591      * <blockquote><pre>
1592      * this.charAt(<i>k</i>) == ch
1593      * </pre></blockquote>
1594      * is true. For other values of {@code ch}, it is the
1595      * largest value <i>k</i> such that:
1596      * <blockquote><pre>
1597      * this.codePointAt(<i>k</i>) == ch
1598      * </pre></blockquote>
1599      * is true.  In either case, if no such character occurs in this
1600      * string, then {@code -1} is returned.  The
1601      * {@code String} is searched backwards starting at the last
1602      * character.
1603      *
1604      * @param   ch   a character (Unicode code point).
1605      * @return  the index of the last occurrence of the character in the
1606      *          character sequence represented by this object, or
1607      *          {@code -1} if the character does not occur.
1608      */
1609     public int lastIndexOf(int ch) {
1610         return lastIndexOf(ch, length() - 1);
1611     }
1612 
1613     /**
1614      * Returns the index within this string of the last occurrence of
1615      * the specified character, searching backward starting at the
1616      * specified index. For values of {@code ch} in the range
1617      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1618      * value <i>k</i> such that:
1619      * <blockquote><pre>
1620      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1621      * </pre></blockquote>
1622      * is true. For other values of {@code ch}, it is the
1623      * largest value <i>k</i> such that:
1624      * <blockquote><pre>
1625      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1626      * </pre></blockquote>
1627      * is true. In either case, if no such character occurs in this
1628      * string at or before position {@code fromIndex}, then
1629      * {@code -1} is returned.
1630      *
1631      * <p>All indices are specified in {@code char} values
1632      * (Unicode code units).
1633      *
1634      * @param   ch          a character (Unicode code point).
1635      * @param   fromIndex   the index to start the search from. There is no
1636      *          restriction on the value of {@code fromIndex}. If it is
1637      *          greater than or equal to the length of this string, it has
1638      *          the same effect as if it were equal to one less than the
1639      *          length of this string: this entire string may be searched.
1640      *          If it is negative, it has the same effect as if it were -1:
1641      *          -1 is returned.
1642      * @return  the index of the last occurrence of the character in the
1643      *          character sequence represented by this object that is less
1644      *          than or equal to {@code fromIndex}, or {@code -1}
1645      *          if the character does not occur before that point.
1646      */
1647     public int lastIndexOf(int ch, int fromIndex) {
1648         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1649                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1650     }
1651 
1652     /**
1653      * Returns the index within this string of the first occurrence of the
1654      * specified substring.
1655      *
1656      * <p>The returned index is the smallest value {@code k} for which:
1657      * <pre>{@code
1658      * this.startsWith(str, k)
1659      * }</pre>
1660      * If no such value of {@code k} exists, then {@code -1} is returned.
1661      *
1662      * @param   str   the substring to search for.
1663      * @return  the index of the first occurrence of the specified substring,
1664      *          or {@code -1} if there is no such occurrence.
1665      */
1666     public int indexOf(String str) {
1667         if (coder() == str.coder()) {
1668             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1669                               : StringUTF16.indexOf(value, str.value);
1670         }
1671         if (coder() == LATIN1) {  // str.coder == UTF16
1672             return -1;
1673         }
1674         return StringUTF16.indexOfLatin1(value, str.value);
1675     }
1676 
1677     /**
1678      * Returns the index within this string of the first occurrence of the
1679      * specified substring, starting at the specified index.
1680      *
1681      * <p>The returned index is the smallest value {@code k} for which:
1682      * <pre>{@code
1683      *     k >= Math.min(fromIndex, this.length()) &&
1684      *                   this.startsWith(str, k)
1685      * }</pre>
1686      * If no such value of {@code k} exists, then {@code -1} is returned.
1687      *
1688      * @param   str         the substring to search for.
1689      * @param   fromIndex   the index from which to start the search.
1690      * @return  the index of the first occurrence of the specified substring,
1691      *          starting at the specified index,
1692      *          or {@code -1} if there is no such occurrence.
1693      */
1694     public int indexOf(String str, int fromIndex) {
1695         return indexOf(value, coder(), length(), str, fromIndex);
1696     }
1697 
1698     /**
1699      * Code shared by String and AbstractStringBuilder to do searches. The
1700      * source is the character array being searched, and the target
1701      * is the string being searched for.
1702      *
1703      * @param   src       the characters being searched.
1704      * @param   srcCoder  the coder of the source string.
1705      * @param   srcCount  length of the source string.
1706      * @param   tgtStr    the characters being searched for.
1707      * @param   fromIndex the index to begin searching from.
1708      */
1709     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1710                        String tgtStr, int fromIndex) {
1711         byte[] tgt    = tgtStr.value;
1712         byte tgtCoder = tgtStr.coder();
1713         int tgtCount  = tgtStr.length();
1714 
1715         if (fromIndex >= srcCount) {
1716             return (tgtCount == 0 ? srcCount : -1);
1717         }
1718         if (fromIndex < 0) {
1719             fromIndex = 0;
1720         }
1721         if (tgtCount == 0) {
1722             return fromIndex;
1723         }
1724         if (tgtCount > srcCount) {
1725             return -1;
1726         }
1727         if (srcCoder == tgtCoder) {
1728             return srcCoder == LATIN1
1729                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1730                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1731         }
1732         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1733             return -1;
1734         }
1735         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1736         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1737     }
1738 
1739     /**
1740      * Returns the index within this string of the last occurrence of the
1741      * specified substring.  The last occurrence of the empty string ""
1742      * is considered to occur at the index value {@code this.length()}.
1743      *
1744      * <p>The returned index is the largest value {@code k} for which:
1745      * <pre>{@code
1746      * this.startsWith(str, k)
1747      * }</pre>
1748      * If no such value of {@code k} exists, then {@code -1} is returned.
1749      *
1750      * @param   str   the substring to search for.
1751      * @return  the index of the last occurrence of the specified substring,
1752      *          or {@code -1} if there is no such occurrence.
1753      */
1754     public int lastIndexOf(String str) {
1755         return lastIndexOf(str, length());
1756     }
1757 
1758     /**
1759      * Returns the index within this string of the last occurrence of the
1760      * specified substring, searching backward starting at the specified index.
1761      *
1762      * <p>The returned index is the largest value {@code k} for which:
1763      * <pre>{@code
1764      *     k <= Math.min(fromIndex, this.length()) &&
1765      *                   this.startsWith(str, k)
1766      * }</pre>
1767      * If no such value of {@code k} exists, then {@code -1} is returned.
1768      *
1769      * @param   str         the substring to search for.
1770      * @param   fromIndex   the index to start the search from.
1771      * @return  the index of the last occurrence of the specified substring,
1772      *          searching backward from the specified index,
1773      *          or {@code -1} if there is no such occurrence.
1774      */
1775     public int lastIndexOf(String str, int fromIndex) {
1776         return lastIndexOf(value, coder(), length(), str, fromIndex);
1777     }
1778 
1779     /**
1780      * Code shared by String and AbstractStringBuilder to do searches. The
1781      * source is the character array being searched, and the target
1782      * is the string being searched for.
1783      *
1784      * @param   src         the characters being searched.
1785      * @param   srcCoder    coder handles the mapping between bytes/chars
1786      * @param   srcCount    count of the source string.
1787      * @param   tgt         the characters being searched for.
1788      * @param   fromIndex   the index to begin searching from.
1789      */
1790     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1791                            String tgtStr, int fromIndex) {
1792         byte[] tgt = tgtStr.value;
1793         byte tgtCoder = tgtStr.coder();
1794         int tgtCount = tgtStr.length();
1795         /*
1796          * Check arguments; return immediately where possible. For
1797          * consistency, don't check for null str.
1798          */
1799         int rightIndex = srcCount - tgtCount;
1800         if (fromIndex > rightIndex) {
1801             fromIndex = rightIndex;
1802         }
1803         if (fromIndex < 0) {
1804             return -1;
1805         }
1806         /* Empty string always matches. */
1807         if (tgtCount == 0) {
1808             return fromIndex;
1809         }
1810         if (srcCoder == tgtCoder) {
1811             return srcCoder == LATIN1
1812                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1813                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1814         }
1815         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1816             return -1;
1817         }
1818         // srcCoder == UTF16 && tgtCoder == LATIN1
1819         return StringUTF16.lastIndexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1820     }
1821 
1822     /**
1823      * Returns a string that is a substring of this string. The
1824      * substring begins with the character at the specified index and
1825      * extends to the end of this string. <p>
1826      * Examples:
1827      * <blockquote><pre>
1828      * "unhappy".substring(2) returns "happy"
1829      * "Harbison".substring(3) returns "bison"
1830      * "emptiness".substring(9) returns "" (an empty string)
1831      * </pre></blockquote>
1832      *
1833      * @param      beginIndex   the beginning index, inclusive.
1834      * @return     the specified substring.
1835      * @exception  IndexOutOfBoundsException  if
1836      *             {@code beginIndex} is negative or larger than the
1837      *             length of this {@code String} object.
1838      */
1839     public String substring(int beginIndex) {
1840         if (beginIndex < 0) {
1841             throw new StringIndexOutOfBoundsException(beginIndex);
1842         }
1843         int subLen = length() - beginIndex;
1844         if (subLen < 0) {
1845             throw new StringIndexOutOfBoundsException(subLen);
1846         }
1847         if (beginIndex == 0) {
1848             return this;
1849         }
1850         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1851                           : StringUTF16.newString(value, beginIndex, subLen);
1852     }
1853 
1854     /**
1855      * Returns a string that is a substring of this string. The
1856      * substring begins at the specified {@code beginIndex} and
1857      * extends to the character at index {@code endIndex - 1}.
1858      * Thus the length of the substring is {@code endIndex-beginIndex}.
1859      * <p>
1860      * Examples:
1861      * <blockquote><pre>
1862      * "hamburger".substring(4, 8) returns "urge"
1863      * "smiles".substring(1, 5) returns "mile"
1864      * </pre></blockquote>
1865      *
1866      * @param      beginIndex   the beginning index, inclusive.
1867      * @param      endIndex     the ending index, exclusive.
1868      * @return     the specified substring.
1869      * @exception  IndexOutOfBoundsException  if the
1870      *             {@code beginIndex} is negative, or
1871      *             {@code endIndex} is larger than the length of
1872      *             this {@code String} object, or
1873      *             {@code beginIndex} is larger than
1874      *             {@code endIndex}.
1875      */
1876     public String substring(int beginIndex, int endIndex) {
1877         int length = length();
1878         checkBoundsBeginEnd(beginIndex, endIndex, length);
1879         int subLen = endIndex - beginIndex;
1880         if (beginIndex == 0 && endIndex == length) {
1881             return this;
1882         }
1883         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1884                           : StringUTF16.newString(value, beginIndex, subLen);
1885     }
1886 
1887     /**
1888      * Returns a character sequence that is a subsequence of this sequence.
1889      *
1890      * <p> An invocation of this method of the form
1891      *
1892      * <blockquote><pre>
1893      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1894      *
1895      * behaves in exactly the same way as the invocation
1896      *
1897      * <blockquote><pre>
1898      * str.substring(begin,&nbsp;end)</pre></blockquote>
1899      *
1900      * @apiNote
1901      * This method is defined so that the {@code String} class can implement
1902      * the {@link CharSequence} interface.
1903      *
1904      * @param   beginIndex   the begin index, inclusive.
1905      * @param   endIndex     the end index, exclusive.
1906      * @return  the specified subsequence.
1907      *
1908      * @throws  IndexOutOfBoundsException
1909      *          if {@code beginIndex} or {@code endIndex} is negative,
1910      *          if {@code endIndex} is greater than {@code length()},
1911      *          or if {@code beginIndex} is greater than {@code endIndex}
1912      *
1913      * @since 1.4
1914      * @spec JSR-51
1915      */
1916     public CharSequence subSequence(int beginIndex, int endIndex) {
1917         return this.substring(beginIndex, endIndex);
1918     }
1919 
1920     /**
1921      * Concatenates the specified string to the end of this string.
1922      * <p>
1923      * If the length of the argument string is {@code 0}, then this
1924      * {@code String} object is returned. Otherwise, a
1925      * {@code String} object is returned that represents a character
1926      * sequence that is the concatenation of the character sequence
1927      * represented by this {@code String} object and the character
1928      * sequence represented by the argument string.<p>
1929      * Examples:
1930      * <blockquote><pre>
1931      * "cares".concat("s") returns "caress"
1932      * "to".concat("get").concat("her") returns "together"
1933      * </pre></blockquote>
1934      *
1935      * @param   str   the {@code String} that is concatenated to the end
1936      *                of this {@code String}.
1937      * @return  a string that represents the concatenation of this object's
1938      *          characters followed by the string argument's characters.
1939      */
1940     public String concat(String str) {
1941         int olen = str.length();
1942         if (olen == 0) {
1943             return this;
1944         }
1945         if (coder() == str.coder()) {
1946             byte[] val = this.value;
1947             byte[] oval = str.value;
1948             int len = val.length + oval.length;
1949             byte[] buf = Arrays.copyOf(val, len);
1950             System.arraycopy(oval, 0, buf, val.length, oval.length);
1951             return new String(buf, coder);
1952         }
1953         int len = length();
1954         byte[] buf = StringUTF16.newBytesFor(len + olen);
1955         getBytes(buf, 0, UTF16);
1956         str.getBytes(buf, len, UTF16);
1957         return new String(buf, UTF16);
1958     }
1959 
1960     /**
1961      * Returns a string resulting from replacing all occurrences of
1962      * {@code oldChar} in this string with {@code newChar}.
1963      * <p>
1964      * If the character {@code oldChar} does not occur in the
1965      * character sequence represented by this {@code String} object,
1966      * then a reference to this {@code String} object is returned.
1967      * Otherwise, a {@code String} object is returned that
1968      * represents a character sequence identical to the character sequence
1969      * represented by this {@code String} object, except that every
1970      * occurrence of {@code oldChar} is replaced by an occurrence
1971      * of {@code newChar}.
1972      * <p>
1973      * Examples:
1974      * <blockquote><pre>
1975      * "mesquite in your cellar".replace('e', 'o')
1976      *         returns "mosquito in your collar"
1977      * "the war of baronets".replace('r', 'y')
1978      *         returns "the way of bayonets"
1979      * "sparring with a purple porpoise".replace('p', 't')
1980      *         returns "starring with a turtle tortoise"
1981      * "JonL".replace('q', 'x') returns "JonL" (no change)
1982      * </pre></blockquote>
1983      *
1984      * @param   oldChar   the old character.
1985      * @param   newChar   the new character.
1986      * @return  a string derived from this string by replacing every
1987      *          occurrence of {@code oldChar} with {@code newChar}.
1988      */
1989     public String replace(char oldChar, char newChar) {
1990         if (oldChar != newChar) {
1991             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
1992                                     : StringUTF16.replace(value, oldChar, newChar);
1993             if (ret != null) {
1994                 return ret;
1995             }
1996         }
1997         return this;
1998     }
1999 
2000     /**
2001      * Tells whether or not this string matches the given <a
2002      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2003      *
2004      * <p> An invocation of this method of the form
2005      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2006      * same result as the expression
2007      *
2008      * <blockquote>
2009      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2010      * matches(<i>regex</i>, <i>str</i>)}
2011      * </blockquote>
2012      *
2013      * @param   regex
2014      *          the regular expression to which this string is to be matched
2015      *
2016      * @return  {@code true} if, and only if, this string matches the
2017      *          given regular expression
2018      *
2019      * @throws  PatternSyntaxException
2020      *          if the regular expression's syntax is invalid
2021      *
2022      * @see java.util.regex.Pattern
2023      *
2024      * @since 1.4
2025      * @spec JSR-51
2026      */
2027     public boolean matches(String regex) {
2028         return Pattern.matches(regex, this);
2029     }
2030 
2031     /**
2032      * Returns true if and only if this string contains the specified
2033      * sequence of char values.
2034      *
2035      * @param s the sequence to search for
2036      * @return true if this string contains {@code s}, false otherwise
2037      * @since 1.5
2038      */
2039     public boolean contains(CharSequence s) {
2040         return indexOf(s.toString()) >= 0;
2041     }
2042 
2043     /**
2044      * Replaces the first substring of this string that matches the given <a
2045      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2046      * given replacement.
2047      *
2048      * <p> An invocation of this method of the form
2049      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2050      * yields exactly the same result as the expression
2051      *
2052      * <blockquote>
2053      * <code>
2054      * {@link java.util.regex.Pattern}.{@link
2055      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2056      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2057      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2058      * </code>
2059      * </blockquote>
2060      *
2061      *<p>
2062      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2063      * replacement string may cause the results to be different than if it were
2064      * being treated as a literal replacement string; see
2065      * {@link java.util.regex.Matcher#replaceFirst}.
2066      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2067      * meaning of these characters, if desired.
2068      *
2069      * @param   regex
2070      *          the regular expression to which this string is to be matched
2071      * @param   replacement
2072      *          the string to be substituted for the first match
2073      *
2074      * @return  The resulting {@code String}
2075      *
2076      * @throws  PatternSyntaxException
2077      *          if the regular expression's syntax is invalid
2078      *
2079      * @see java.util.regex.Pattern
2080      *
2081      * @since 1.4
2082      * @spec JSR-51
2083      */
2084     public String replaceFirst(String regex, String replacement) {
2085         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2086     }
2087 
2088     /**
2089      * Replaces each substring of this string that matches the given <a
2090      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2091      * given replacement.
2092      *
2093      * <p> An invocation of this method of the form
2094      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2095      * yields exactly the same result as the expression
2096      *
2097      * <blockquote>
2098      * <code>
2099      * {@link java.util.regex.Pattern}.{@link
2100      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2101      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2102      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2103      * </code>
2104      * </blockquote>
2105      *
2106      *<p>
2107      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2108      * replacement string may cause the results to be different than if it were
2109      * being treated as a literal replacement string; see
2110      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2111      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2112      * meaning of these characters, if desired.
2113      *
2114      * @param   regex
2115      *          the regular expression to which this string is to be matched
2116      * @param   replacement
2117      *          the string to be substituted for each match
2118      *
2119      * @return  The resulting {@code String}
2120      *
2121      * @throws  PatternSyntaxException
2122      *          if the regular expression's syntax is invalid
2123      *
2124      * @see java.util.regex.Pattern
2125      *
2126      * @since 1.4
2127      * @spec JSR-51
2128      */
2129     public String replaceAll(String regex, String replacement) {
2130         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2131     }
2132 
2133     /**
2134      * Replaces each substring of this string that matches the literal target
2135      * sequence with the specified literal replacement sequence. The
2136      * replacement proceeds from the beginning of the string to the end, for
2137      * example, replacing "aa" with "b" in the string "aaa" will result in
2138      * "ba" rather than "ab".
2139      *
2140      * @param  target The sequence of char values to be replaced
2141      * @param  replacement The replacement sequence of char values
2142      * @return  The resulting string
2143      * @since 1.5
2144      */
2145     public String replace(CharSequence target, CharSequence replacement) {
2146         String tgtStr = target.toString();
2147         String replStr = replacement.toString();
2148         int j = indexOf(tgtStr);
2149         if (j < 0) {
2150             return this;
2151         }
2152         int tgtLen = tgtStr.length();
2153         int tgtLen1 = Math.max(tgtLen, 1);
2154         int thisLen = length();
2155 
2156         int newLenHint = thisLen - tgtLen + replStr.length();
2157         if (newLenHint < 0) {
2158             throw new OutOfMemoryError();
2159         }
2160         StringBuilder sb = new StringBuilder(newLenHint);
2161         int i = 0;
2162         do {
2163             sb.append(this, i, j).append(replStr);
2164             i = j + tgtLen;
2165         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2166         return sb.append(this, i, thisLen).toString();
2167     }
2168 
2169     /**
2170      * Splits this string around matches of the given
2171      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2172      *
2173      * <p> The array returned by this method contains each substring of this
2174      * string that is terminated by another substring that matches the given
2175      * expression or is terminated by the end of the string.  The substrings in
2176      * the array are in the order in which they occur in this string.  If the
2177      * expression does not match any part of the input then the resulting array
2178      * has just one element, namely this string.
2179      *
2180      * <p> When there is a positive-width match at the beginning of this
2181      * string then an empty leading substring is included at the beginning
2182      * of the resulting array. A zero-width match at the beginning however
2183      * never produces such empty leading substring.
2184      *
2185      * <p> The {@code limit} parameter controls the number of times the
2186      * pattern is applied and therefore affects the length of the resulting
2187      * array.
2188      * <ul>
2189      *    <li><p>
2190      *    If the <i>limit</i> is positive then the pattern will be applied
2191      *    at most <i>limit</i>&nbsp;-&nbsp;1 times, the array's length will be
2192      *    no greater than <i>limit</i>, and the array's last entry will contain
2193      *    all input beyond the last matched delimiter.</p></li>
2194      *
2195      *    <li><p>
2196      *    If the <i>limit</i> is zero then the pattern will be applied as
2197      *    many times as possible, the array can have any length, and trailing
2198      *    empty strings will be discarded.</p></li>
2199      *
2200      *    <li><p>
2201      *    If the <i>limit</i> is negative then the pattern will be applied
2202      *    as many times as possible and the array can have any length.</p></li>
2203      * </ul>
2204      *
2205      * <p> The string {@code "boo:and:foo"}, for example, yields the
2206      * following results with these parameters:
2207      *
2208      * <blockquote><table class="plain">
2209      * <caption style="display:none">Split example showing regex, limit, and result</caption>
2210      * <thead>
2211      * <tr>
2212      *     <th scope="col">Regex</th>
2213      *     <th scope="col">Limit</th>
2214      *     <th scope="col">Result</th>
2215      * </tr>
2216      * </thead>
2217      * <tbody>
2218      * <tr><th scope="row" rowspan="3" style="font-weight:normal">:</th>
2219      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">2</th>
2220      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2221      * <tr><!-- : -->
2222      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">5</th>
2223      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2224      * <tr><!-- : -->
2225      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">-2</th>
2226      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2227      * <tr><th scope="row" rowspan="3" style="font-weight:normal">o</th>
2228      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">5</th>
2229      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2230      * <tr><!-- o -->
2231      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">-2</th>
2232      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2233      * <tr><!-- o -->
2234      *     <th scope="row" style="font-weight:normal; text-align:right; padding-right:1em">0</th>
2235      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2236      * </tbody>
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 class="plain">
2337      * <caption style="display:none">Split examples showing regex and result</caption>
2338      * <thead>
2339      * <tr>
2340      *  <th scope="col">Regex</th>
2341      *  <th scope="col">Result</th>
2342      * </tr>
2343      * </thead>
2344      * <tbody>
2345      * <tr><th scope="row" style="text-weight:normal">:</th>
2346      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2347      * <tr><th scope="row" style="text-weight:normal">o</th>
2348      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2349      * </tbody>
2350      * </table></blockquote>
2351      *
2352      *
2353      * @param  regex
2354      *         the delimiting regular expression
2355      *
2356      * @return  the array of strings computed by splitting this string
2357      *          around matches of the given regular expression
2358      *
2359      * @throws  PatternSyntaxException
2360      *          if the regular expression's syntax is invalid
2361      *
2362      * @see java.util.regex.Pattern
2363      *
2364      * @since 1.4
2365      * @spec JSR-51
2366      */
2367     public String[] split(String regex) {
2368         return split(regex, 0);
2369     }
2370 
2371     /**
2372      * Returns a new String composed of copies of the
2373      * {@code CharSequence elements} joined together with a copy of
2374      * the specified {@code delimiter}.
2375      *
2376      * <blockquote>For example,
2377      * <pre>{@code
2378      *     String message = String.join("-", "Java", "is", "cool");
2379      *     // message returned is: "Java-is-cool"
2380      * }</pre></blockquote>
2381      *
2382      * Note that if an element is null, then {@code "null"} is added.
2383      *
2384      * @param  delimiter the delimiter that separates each element
2385      * @param  elements the elements to join together.
2386      *
2387      * @return a new {@code String} that is composed of the {@code elements}
2388      *         separated by the {@code delimiter}
2389      *
2390      * @throws NullPointerException If {@code delimiter} or {@code elements}
2391      *         is {@code null}
2392      *
2393      * @see java.util.StringJoiner
2394      * @since 1.8
2395      */
2396     public static String join(CharSequence delimiter, CharSequence... elements) {
2397         Objects.requireNonNull(delimiter);
2398         Objects.requireNonNull(elements);
2399         // Number of elements not likely worth Arrays.stream overhead.
2400         StringJoiner joiner = new StringJoiner(delimiter);
2401         for (CharSequence cs: elements) {
2402             joiner.add(cs);
2403         }
2404         return joiner.toString();
2405     }
2406 
2407     /**
2408      * Returns a new {@code String} composed of copies of the
2409      * {@code CharSequence elements} joined together with a copy of the
2410      * specified {@code delimiter}.
2411      *
2412      * <blockquote>For example,
2413      * <pre>{@code
2414      *     List<String> strings = List.of("Java", "is", "cool");
2415      *     String message = String.join(" ", strings);
2416      *     //message returned is: "Java is cool"
2417      *
2418      *     Set<String> strings =
2419      *         new LinkedHashSet<>(List.of("Java", "is", "very", "cool"));
2420      *     String message = String.join("-", strings);
2421      *     //message returned is: "Java-is-very-cool"
2422      * }</pre></blockquote>
2423      *
2424      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2425      *
2426      * @param  delimiter a sequence of characters that is used to separate each
2427      *         of the {@code elements} in the resulting {@code String}
2428      * @param  elements an {@code Iterable} that will have its {@code elements}
2429      *         joined together.
2430      *
2431      * @return a new {@code String} that is composed from the {@code elements}
2432      *         argument
2433      *
2434      * @throws NullPointerException If {@code delimiter} or {@code elements}
2435      *         is {@code null}
2436      *
2437      * @see    #join(CharSequence,CharSequence...)
2438      * @see    java.util.StringJoiner
2439      * @since 1.8
2440      */
2441     public static String join(CharSequence delimiter,
2442             Iterable<? extends CharSequence> elements) {
2443         Objects.requireNonNull(delimiter);
2444         Objects.requireNonNull(elements);
2445         StringJoiner joiner = new StringJoiner(delimiter);
2446         for (CharSequence cs: elements) {
2447             joiner.add(cs);
2448         }
2449         return joiner.toString();
2450     }
2451 
2452     /**
2453      * Converts all of the characters in this {@code String} to lower
2454      * case using the rules of the given {@code Locale}.  Case mapping is based
2455      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2456      * class. Since case mappings are not always 1:1 char mappings, the resulting
2457      * {@code String} may be a different length than the original {@code String}.
2458      * <p>
2459      * Examples of lowercase  mappings are in the following table:
2460      * <table class="plain">
2461      * <caption style="display:none">Lowercase mapping examples showing language code of locale, upper case, lower case, and description</caption>
2462      * <thead>
2463      * <tr>
2464      *   <th scope="col">Language Code of Locale</th>
2465      *   <th scope="col">Upper Case</th>
2466      *   <th scope="col">Lower Case</th>
2467      *   <th scope="col">Description</th>
2468      * </tr>
2469      * </thead>
2470      * <tbody>
2471      * <tr>
2472      *   <td>tr (Turkish)</td>
2473      *   <th scope="row" style="font-weight:normal; text-align:left">\u0130</th>
2474      *   <td>\u0069</td>
2475      *   <td>capital letter I with dot above -&gt; small letter i</td>
2476      * </tr>
2477      * <tr>
2478      *   <td>tr (Turkish)</td>
2479      *   <th scope="row" style="font-weight:normal; text-align:left">\u0049</th>
2480      *   <td>\u0131</td>
2481      *   <td>capital letter I -&gt; small letter dotless i </td>
2482      * </tr>
2483      * <tr>
2484      *   <td>(all)</td>
2485      *   <th scope="row" style="font-weight:normal; text-align:left">French Fries</th>
2486      *   <td>french fries</td>
2487      *   <td>lowercased all chars in String</td>
2488      * </tr>
2489      * <tr>
2490      *   <td>(all)</td>
2491      *   <th scope="row" style="font-weight:normal; text-align:left">
2492      *       &Iota;&Chi;&Theta;&Upsilon;&Sigma;</th>
2493      *   <td>&iota;&chi;&theta;&upsilon;&sigma;</td>
2494      *   <td>lowercased all chars in String</td>
2495      * </tr>
2496      * </tbody>
2497      * </table>
2498      *
2499      * @param locale use the case transformation rules for this locale
2500      * @return the {@code String}, converted to lowercase.
2501      * @see     java.lang.String#toLowerCase()
2502      * @see     java.lang.String#toUpperCase()
2503      * @see     java.lang.String#toUpperCase(Locale)
2504      * @since   1.1
2505      */
2506     public String toLowerCase(Locale locale) {
2507         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2508                           : StringUTF16.toLowerCase(this, value, locale);
2509     }
2510 
2511     /**
2512      * Converts all of the characters in this {@code String} to lower
2513      * case using the rules of the default locale. This is equivalent to calling
2514      * {@code toLowerCase(Locale.getDefault())}.
2515      * <p>
2516      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2517      * results if used for strings that are intended to be interpreted locale
2518      * independently.
2519      * Examples are programming language identifiers, protocol keys, and HTML
2520      * tags.
2521      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2522      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2523      * LATIN SMALL LETTER DOTLESS I character.
2524      * To obtain correct results for locale insensitive strings, use
2525      * {@code toLowerCase(Locale.ROOT)}.
2526      *
2527      * @return  the {@code String}, converted to lowercase.
2528      * @see     java.lang.String#toLowerCase(Locale)
2529      */
2530     public String toLowerCase() {
2531         return toLowerCase(Locale.getDefault());
2532     }
2533 
2534     /**
2535      * Converts all of the characters in this {@code String} to upper
2536      * case using the rules of the given {@code Locale}. Case mapping is based
2537      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2538      * class. Since case mappings are not always 1:1 char mappings, the resulting
2539      * {@code String} may be a different length than the original {@code String}.
2540      * <p>
2541      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2542      *
2543      * <table class="plain">
2544      * <caption style="display:none">Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.</caption>
2545      * <thead>
2546      * <tr>
2547      *   <th scope="col">Language Code of Locale</th>
2548      *   <th scope="col">Lower Case</th>
2549      *   <th scope="col">Upper Case</th>
2550      *   <th scope="col">Description</th>
2551      * </tr>
2552      * </thead>
2553      * <tbody>
2554      * <tr>
2555      *   <td>tr (Turkish)</td>
2556      *   <th scope="row" style="font-weight:normal; text-align:left">\u0069</th>
2557      *   <td>\u0130</td>
2558      *   <td>small letter i -&gt; capital letter I with dot above</td>
2559      * </tr>
2560      * <tr>
2561      *   <td>tr (Turkish)</td>
2562      *   <th scope="row" style="font-weight:normal; text-align:left">\u0131</th>
2563      *   <td>\u0049</td>
2564      *   <td>small letter dotless i -&gt; capital letter I</td>
2565      * </tr>
2566      * <tr>
2567      *   <td>(all)</td>
2568      *   <th scope="row" style="font-weight:normal; text-align:left">\u00df</th>
2569      *   <td>\u0053 \u0053</td>
2570      *   <td>small letter sharp s -&gt; two letters: SS</td>
2571      * </tr>
2572      * <tr>
2573      *   <td>(all)</td>
2574      *   <th scope="row" style="font-weight:normal; text-align:left">Fahrvergn&uuml;gen</th>
2575      *   <td>FAHRVERGN&Uuml;GEN</td>
2576      *   <td></td>
2577      * </tr>
2578      * </tbody>
2579      * </table>
2580      * @param locale use the case transformation rules for this locale
2581      * @return the {@code String}, converted to uppercase.
2582      * @see     java.lang.String#toUpperCase()
2583      * @see     java.lang.String#toLowerCase()
2584      * @see     java.lang.String#toLowerCase(Locale)
2585      * @since   1.1
2586      */
2587     public String toUpperCase(Locale locale) {
2588         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2589                           : StringUTF16.toUpperCase(this, value, locale);
2590     }
2591 
2592     /**
2593      * Converts all of the characters in this {@code String} to upper
2594      * case using the rules of the default locale. This method is equivalent to
2595      * {@code toUpperCase(Locale.getDefault())}.
2596      * <p>
2597      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2598      * results if used for strings that are intended to be interpreted locale
2599      * independently.
2600      * Examples are programming language identifiers, protocol keys, and HTML
2601      * tags.
2602      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2603      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2604      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2605      * To obtain correct results for locale insensitive strings, use
2606      * {@code toUpperCase(Locale.ROOT)}.
2607      *
2608      * @return  the {@code String}, converted to uppercase.
2609      * @see     java.lang.String#toUpperCase(Locale)
2610      */
2611     public String toUpperCase() {
2612         return toUpperCase(Locale.getDefault());
2613     }
2614 
2615     /**
2616      * Returns a string whose value is this string, with all leading
2617      * and trailing space removed, where space is defined
2618      * as any character whose codepoint is less than or equal to
2619      * {@code 'U+0020'} (the space character).
2620      * <p>
2621      * If this {@code String} object represents an empty character
2622      * sequence, or the first and last characters of character sequence
2623      * represented by this {@code String} object both have codes
2624      * that are not space (as defined above), then a
2625      * reference to this {@code String} object is returned.
2626      * <p>
2627      * Otherwise, if all characters in this string are space (as
2628      * defined above), then a  {@code String} object representing an
2629      * empty string is returned.
2630      * <p>
2631      * Otherwise, let <i>k</i> be the index of the first character in the
2632      * string whose code is not a space (as defined above) and let
2633      * <i>m</i> be the index of the last character in the string whose code
2634      * is not a space (as defined above). A {@code String}
2635      * object is returned, representing the substring of this string that
2636      * begins with the character at index <i>k</i> and ends with the
2637      * character at index <i>m</i>-that is, the result of
2638      * {@code this.substring(k, m + 1)}.
2639      * <p>
2640      * This method may be used to trim space (as defined above) from
2641      * the beginning and end of a string.
2642      *
2643      * @return  a string whose value is this string, with all leading
2644      *          and trailing space removed, or this string if it
2645      *          has no leading or trailing space.
2646      */
2647     public String trim() {
2648         String ret = isLatin1() ? StringLatin1.trim(value)
2649                                 : StringUTF16.trim(value);
2650         return ret == null ? this : ret;
2651     }
2652 
2653     /**
2654      * Returns a string whose value is this string, with all leading
2655      * and trailing {@link Character#isWhitespace(int) white space}
2656      * removed.
2657      * <p>
2658      * If this {@code String} object represents an empty string,
2659      * or if all code points in this string are
2660      * {@link Character#isWhitespace(int) white space}, then an empty string
2661      * is returned.
2662      * <p>
2663      * Otherwise, returns a substring of this string beginning with the first
2664      * code point that is not a {@link Character#isWhitespace(int) white space}
2665      * up to and including the last code point that is not a
2666      * {@link Character#isWhitespace(int) white space}.
2667      * <p>
2668      * This method may be used to strip
2669      * {@link Character#isWhitespace(int) white space} from
2670      * the beginning and end of a string.
2671      *
2672      * @return  a string whose value is this string, with all leading
2673      *          and trailing white space removed
2674      *
2675      * @see Character#isWhitespace(int)
2676      *
2677      * @since 11
2678      */
2679     public String strip() {
2680         String ret = isLatin1() ? StringLatin1.strip(value)
2681                                 : StringUTF16.strip(value);
2682         return ret == null ? this : ret;
2683     }
2684 
2685     /**
2686      * Returns a string whose value is this string, with all leading
2687      * {@link Character#isWhitespace(int) white space} removed.
2688      * <p>
2689      * If this {@code String} object represents an empty string,
2690      * or if all code points in this string are
2691      * {@link Character#isWhitespace(int) white space}, then an empty string
2692      * is returned.
2693      * <p>
2694      * Otherwise, returns a substring of this string beginning with the first
2695      * code point that is not a {@link Character#isWhitespace(int) white space}
2696      * up to to and including the last code point of this string.
2697      * <p>
2698      * This method may be used to trim
2699      * {@link Character#isWhitespace(int) white space} from
2700      * the beginning of a string.
2701      *
2702      * @return  a string whose value is this string, with all leading white
2703      *          space removed
2704      *
2705      * @see Character#isWhitespace(int)
2706      *
2707      * @since 11
2708      */
2709     public String stripLeading() {
2710         String ret = isLatin1() ? StringLatin1.stripLeading(value)
2711                                 : StringUTF16.stripLeading(value);
2712         return ret == null ? this : ret;
2713     }
2714 
2715     /**
2716      * Returns a string whose value is this string, with all trailing
2717      * {@link Character#isWhitespace(int) white space} removed.
2718      * <p>
2719      * If this {@code String} object represents an empty string,
2720      * or if all characters in this string are
2721      * {@link Character#isWhitespace(int) white space}, then an empty string
2722      * is returned.
2723      * <p>
2724      * Otherwise, returns a substring of this string beginning with the first
2725      * code point of this string up to and including the last code point
2726      * that is not a {@link Character#isWhitespace(int) white space}.
2727      * <p>
2728      * This method may be used to trim
2729      * {@link Character#isWhitespace(int) white space} from
2730      * the end of a string.
2731      *
2732      * @return  a string whose value is this string, with all trailing white
2733      *          space removed
2734      *
2735      * @see Character#isWhitespace(int)
2736      *
2737      * @since 11
2738      */
2739     public String stripTrailing() {
2740         String ret = isLatin1() ? StringLatin1.stripTrailing(value)
2741                                 : StringUTF16.stripTrailing(value);
2742         return ret == null ? this : ret;
2743     }
2744 
2745     /**
2746      * Returns {@code true} if the string is empty or contains only
2747      * {@link Character#isWhitespace(int) white space} codepoints,
2748      * otherwise {@code false}.
2749      *
2750      * @return {@code true} if the string is empty or contains only
2751      *         {@link Character#isWhitespace(int) white space} codepoints,
2752      *         otherwise {@code false}
2753      *
2754      * @see Character#isWhitespace(int)
2755      *
2756      * @since 11
2757      */
2758     public boolean isBlank() {
2759         return indexOfNonWhitespace() == length();
2760     }
2761 
2762     private Stream<String> lines(int maxLeading, int maxTrailing) {
2763         return isLatin1() ? StringLatin1.lines(value, maxLeading, maxTrailing)
2764                           : StringUTF16.lines(value, maxLeading, maxTrailing);
2765     }
2766 
2767     /**
2768      * Returns a stream of lines extracted from this string,
2769      * separated by line terminators.
2770      * <p>
2771      * A <i>line terminator</i> is one of the following:
2772      * a line feed character {@code "\n"} (U+000A),
2773      * a carriage return character {@code "\r"} (U+000D),
2774      * or a carriage return followed immediately by a line feed
2775      * {@code "\r\n"} (U+000D U+000A).
2776      * <p>
2777      * A <i>line</i> is either a sequence of zero or more characters
2778      * followed by a line terminator, or it is a sequence of one or
2779      * more characters followed by the end of the string. A
2780      * line does not include the line terminator.
2781      * <p>
2782      * The stream returned by this method contains the lines from
2783      * this string in the order in which they occur.
2784      *
2785      * @apiNote This definition of <i>line</i> implies that an empty
2786      *          string has zero lines and that there is no empty line
2787      *          following a line terminator at the end of a string.
2788      *
2789      * @implNote This method provides better performance than
2790      *           split("\R") by supplying elements lazily and
2791      *           by faster search of new line terminators.
2792      *
2793      * @return  the stream of lines extracted from this string
2794      *
2795      * @since 11
2796      */
2797     public Stream<String> lines() {
2798         return lines(0, 0);
2799     }
2800 
2801     /**
2802      * Adjusts the indentation of each line of this string based on the value of
2803      * {@code n}, and normalizes line termination characters.
2804      * <p>
2805      * This string is conceptually separated into lines using
2806      * {@link String#lines()}. Each line is then adjusted as described below
2807      * and then suffixed with a line feed {@code "\n"} (U+000A). The resulting
2808      * lines are then concatenated and returned.
2809      * <p>
2810      * If {@code n > 0} then {@code n} spaces (U+0020) are inserted at the
2811      * beginning of each line. {@link String#isBlank() Blank lines} are
2812      * unaffected.
2813      * <p>
2814      * If {@code n < 0} then up to {@code n}
2815      * {@link Character#isWhitespace(int) white space characters} are removed
2816      * from the beginning of each line. If a given line does not contain
2817      * sufficient white space then all leading
2818      * {@link Character#isWhitespace(int) white space characters} are removed.
2819      * Each white space character is treated as a single character. In
2820      * particular, the tab character {@code "\t"} (U+0009) is considered a
2821      * single character; it is not expanded.
2822      * <p>
2823      * If {@code n == 0} then the line remains unchanged. However, line
2824      * terminators are still normalized.
2825      *
2826      * @param n  number of leading
2827      *           {@link Character#isWhitespace(int) white space characters}
2828      *           to add or remove
2829      *
2830      * @return string with indentation adjusted and line endings normalized
2831      *
2832      * @see String#lines()
2833      * @see String#isBlank()
2834      * @see Character#isWhitespace(int)
2835      *
2836      * @since 12
2837      */
2838     public String indent(int n) {
2839         return isEmpty() ? "" :  indent(n, false);
2840     }
2841 
2842     private String indent(int n, boolean removeBlanks) {
2843         Stream<String> stream = removeBlanks ? lines(Integer.MAX_VALUE, Integer.MAX_VALUE)
2844                                              : lines();
2845         if (n > 0) {
2846             final String spaces = " ".repeat(n);
2847             stream = stream.map(s -> s.isBlank() ? s : spaces + s);
2848         } else if (n == Integer.MIN_VALUE) {
2849             stream = stream.map(s -> s.stripLeading());
2850         } else if (n < 0) {
2851             stream = stream.map(s -> s.substring(Math.min(-n, s.indexOfNonWhitespace())));
2852         }
2853         return stream.collect(Collectors.joining("\n", "", "\n"));
2854     }
2855 
2856     private int indexOfNonWhitespace() {
2857         return isLatin1() ? StringLatin1.indexOfNonWhitespace(value)
2858                           : StringUTF16.indexOfNonWhitespace(value);
2859     }
2860 
2861     private int lastIndexOfNonWhitespace() {
2862         return isLatin1() ? StringLatin1.lastIndexOfNonWhitespace(value)
2863                           : StringUTF16.lastIndexOfNonWhitespace(value);
2864     }
2865 
2866     /**
2867      * Removes vertical and horizontal white space margins from around the
2868      * essential body of a multi-line string, while preserving relative
2869      * indentation.
2870      * <p>
2871      * This string is first conceptually separated into lines as if by
2872      * {@link String#lines()}.
2873      * <p>
2874      * Then, the <i>minimum indentation</i> (min) is determined as follows. For
2875      * each non-blank line (as defined by {@link String#isBlank()}), the
2876      * leading {@link Character#isWhitespace(int) white space} characters are
2877      * counted. The <i>min</i> value is the smallest of these counts.
2878      * <p>
2879      * For each non-blank line, <i>min</i> leading white space characters are
2880      * removed. Each white space character is treated as a single character. In
2881      * particular, the tab character {@code "\t"} (U+0009) is considered a
2882      * single character; it is not expanded.
2883      * <p>
2884      * Leading and trailing blank lines, if any, are removed. Trailing spaces are
2885      * preserved.
2886      * <p>
2887      * Each line is suffixed with a line feed character {@code "\n"} (U+000A).
2888      * <p>
2889      * Finally, the lines are concatenated into a single string and returned.
2890      *
2891      * @apiNote
2892      * This method's primary purpose is to shift a block of lines as far as
2893      * possible to the left, while preserving relative indentation. Lines
2894      * that were indented the least will thus have no leading white space.
2895      *
2896      * Example:
2897      * <blockquote><pre>
2898      * `
2899      *      This is the first line
2900      *          This is the second line
2901      * `.align();
2902      *
2903      * returns
2904      * This is the first line
2905      *     This is the second line
2906      * </pre></blockquote>
2907      *
2908      * @return string with margins removed and line terminators normalized
2909      *
2910      * @see String#lines()
2911      * @see String#isBlank()
2912      * @see String#indent(int)
2913      * @see Character#isWhitespace(int)
2914      *
2915      * @since 12
2916      */
2917     public String align() {
2918         return align(0);
2919     }
2920 
2921     /**
2922      * Removes vertical and horizontal white space margins from around the
2923      * essential body of a multi-line string, while preserving relative
2924      * indentation and with optional indentation adjustment.
2925      * <p>
2926      * Invoking this method is equivalent to:
2927      * <blockquote>
2928      *  {@code this.align().indent(n)}
2929      * </blockquote>
2930      *
2931      * @apiNote
2932      * Examples:
2933      * <blockquote><pre>
2934      * `
2935      *      This is the first line
2936      *          This is the second line
2937      * `.align(0);
2938      *
2939      * returns
2940      * This is the first line
2941      *     This is the second line
2942      *
2943      *
2944      * `
2945      *    This is the first line
2946      *       This is the second line
2947      * `.align(4);
2948      * returns
2949      *     This is the first line
2950      *         This is the second line
2951      * </pre></blockquote>
2952      *
2953      * @param n  number of leading white space characters
2954      *           to add or remove
2955      *
2956      * @return string with margins removed, indentation adjusted and
2957      *         line terminators normalized
2958      *
2959      * @see String#align()
2960      *
2961      * @since 12
2962      */
2963     public String align(int n) {
2964         if (isEmpty()) {
2965             return "";
2966         }
2967         int outdent = lines().filter(not(String::isBlank))
2968                              .mapToInt(String::indexOfNonWhitespace)
2969                              .min()
2970                              .orElse(0);
2971         // overflow-conscious code
2972         int indent = n - outdent;
2973         return indent(indent > n ? Integer.MIN_VALUE : indent, true);
2974     }
2975 
2976     /**
2977      * This method allows the application of a function to {@code this}
2978      * string. The function should expect a single String argument
2979      * and produce an {@code R} result.
2980      *
2981      * @param f    functional interface to a apply
2982      *
2983      * @param <R>  class of the result
2984      *
2985      * @return     the result of applying the function to this string
2986      *
2987      * @see java.util.function.Function
2988      *
2989      * @since 12
2990      */
2991     public <R> R transform(Function<? super String, ? extends R> f) {
2992         return f.apply(this);
2993     }
2994 
2995     /**
2996      * This object (which is already a string!) is itself returned.
2997      *
2998      * @return  the string itself.
2999      */
3000     public String toString() {
3001         return this;
3002     }
3003 
3004     /**
3005      * Returns a stream of {@code int} zero-extending the {@code char} values
3006      * from this sequence.  Any char which maps to a <a
3007      * href="{@docRoot}/java.base/java/lang/Character.html#unicode">surrogate code
3008      * point</a> is passed through uninterpreted.
3009      *
3010      * @return an IntStream of char values from this sequence
3011      * @since 9
3012      */
3013     @Override
3014     public IntStream chars() {
3015         return StreamSupport.intStream(
3016             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
3017                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
3018             false);
3019     }
3020 
3021 
3022     /**
3023      * Returns a stream of code point values from this sequence.  Any surrogate
3024      * pairs encountered in the sequence are combined as if by {@linkplain
3025      * Character#toCodePoint Character.toCodePoint} and the result is passed
3026      * to the stream. Any other code units, including ordinary BMP characters,
3027      * unpaired surrogates, and undefined code units, are zero-extended to
3028      * {@code int} values which are then passed to the stream.
3029      *
3030      * @return an IntStream of Unicode code points from this sequence
3031      * @since 9
3032      */
3033     @Override
3034     public IntStream codePoints() {
3035         return StreamSupport.intStream(
3036             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
3037                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
3038             false);
3039     }
3040 
3041     /**
3042      * Converts this string to a new character array.
3043      *
3044      * @return  a newly allocated character array whose length is the length
3045      *          of this string and whose contents are initialized to contain
3046      *          the character sequence represented by this string.
3047      */
3048     public char[] toCharArray() {
3049         return isLatin1() ? StringLatin1.toChars(value)
3050                           : StringUTF16.toChars(value);
3051     }
3052 
3053     /**
3054      * Returns a formatted string using the specified format string and
3055      * arguments.
3056      *
3057      * <p> The locale always used is the one returned by {@link
3058      * java.util.Locale#getDefault(java.util.Locale.Category)
3059      * Locale.getDefault(Locale.Category)} with
3060      * {@link java.util.Locale.Category#FORMAT FORMAT} category specified.
3061      *
3062      * @param  format
3063      *         A <a href="../util/Formatter.html#syntax">format string</a>
3064      *
3065      * @param  args
3066      *         Arguments referenced by the format specifiers in the format
3067      *         string.  If there are more arguments than format specifiers, the
3068      *         extra arguments are ignored.  The number of arguments is
3069      *         variable and may be zero.  The maximum number of arguments is
3070      *         limited by the maximum dimension of a Java array as defined by
3071      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
3072      *         The behaviour on a
3073      *         {@code null} argument depends on the <a
3074      *         href="../util/Formatter.html#syntax">conversion</a>.
3075      *
3076      * @throws  java.util.IllegalFormatException
3077      *          If a format string contains an illegal syntax, a format
3078      *          specifier that is incompatible with the given arguments,
3079      *          insufficient arguments given the format string, or other
3080      *          illegal conditions.  For specification of all possible
3081      *          formatting errors, see the <a
3082      *          href="../util/Formatter.html#detail">Details</a> section of the
3083      *          formatter class specification.
3084      *
3085      * @return  A formatted string
3086      *
3087      * @see  java.util.Formatter
3088      * @since  1.5
3089      */
3090     public static String format(String format, Object... args) {
3091         return new Formatter().format(format, args).toString();
3092     }
3093 
3094     /**
3095      * Returns a formatted string using the specified locale, format string,
3096      * and arguments.
3097      *
3098      * @param  l
3099      *         The {@linkplain java.util.Locale locale} to apply during
3100      *         formatting.  If {@code l} is {@code null} then no localization
3101      *         is applied.
3102      *
3103      * @param  format
3104      *         A <a href="../util/Formatter.html#syntax">format string</a>
3105      *
3106      * @param  args
3107      *         Arguments referenced by the format specifiers in the format
3108      *         string.  If there are more arguments than format specifiers, the
3109      *         extra arguments are ignored.  The number of arguments is
3110      *         variable and may be zero.  The maximum number of arguments is
3111      *         limited by the maximum dimension of a Java array as defined by
3112      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
3113      *         The behaviour on a
3114      *         {@code null} argument depends on the
3115      *         <a href="../util/Formatter.html#syntax">conversion</a>.
3116      *
3117      * @throws  java.util.IllegalFormatException
3118      *          If a format string contains an illegal syntax, a format
3119      *          specifier that is incompatible with the given arguments,
3120      *          insufficient arguments given the format string, or other
3121      *          illegal conditions.  For specification of all possible
3122      *          formatting errors, see the <a
3123      *          href="../util/Formatter.html#detail">Details</a> section of the
3124      *          formatter class specification
3125      *
3126      * @return  A formatted string
3127      *
3128      * @see  java.util.Formatter
3129      * @since  1.5
3130      */
3131     public static String format(Locale l, String format, Object... args) {
3132         return new Formatter(l).format(format, args).toString();
3133     }
3134 
3135     /**
3136      * Returns the string representation of the {@code Object} argument.
3137      *
3138      * @param   obj   an {@code Object}.
3139      * @return  if the argument is {@code null}, then a string equal to
3140      *          {@code "null"}; otherwise, the value of
3141      *          {@code obj.toString()} is returned.
3142      * @see     java.lang.Object#toString()
3143      */
3144     public static String valueOf(Object obj) {
3145         return (obj == null) ? "null" : obj.toString();
3146     }
3147 
3148     /**
3149      * Returns the string representation of the {@code char} array
3150      * argument. The contents of the character array are copied; subsequent
3151      * modification of the character array does not affect the returned
3152      * string.
3153      *
3154      * @param   data     the character array.
3155      * @return  a {@code String} that contains the characters of the
3156      *          character array.
3157      */
3158     public static String valueOf(char data[]) {
3159         return new String(data);
3160     }
3161 
3162     /**
3163      * Returns the string representation of a specific subarray of the
3164      * {@code char} array argument.
3165      * <p>
3166      * The {@code offset} argument is the index of the first
3167      * character of the subarray. The {@code count} argument
3168      * specifies the length of the subarray. The contents of the subarray
3169      * are copied; subsequent modification of the character array does not
3170      * affect the returned string.
3171      *
3172      * @param   data     the character array.
3173      * @param   offset   initial offset of the subarray.
3174      * @param   count    length of the subarray.
3175      * @return  a {@code String} that contains the characters of the
3176      *          specified subarray of the character array.
3177      * @exception IndexOutOfBoundsException if {@code offset} is
3178      *          negative, or {@code count} is negative, or
3179      *          {@code offset+count} is larger than
3180      *          {@code data.length}.
3181      */
3182     public static String valueOf(char data[], int offset, int count) {
3183         return new String(data, offset, count);
3184     }
3185 
3186     /**
3187      * Equivalent to {@link #valueOf(char[], int, int)}.
3188      *
3189      * @param   data     the character array.
3190      * @param   offset   initial offset of the subarray.
3191      * @param   count    length of the subarray.
3192      * @return  a {@code String} that contains the characters of the
3193      *          specified subarray of the character array.
3194      * @exception IndexOutOfBoundsException if {@code offset} is
3195      *          negative, or {@code count} is negative, or
3196      *          {@code offset+count} is larger than
3197      *          {@code data.length}.
3198      */
3199     public static String copyValueOf(char data[], int offset, int count) {
3200         return new String(data, offset, count);
3201     }
3202 
3203     /**
3204      * Equivalent to {@link #valueOf(char[])}.
3205      *
3206      * @param   data   the character array.
3207      * @return  a {@code String} that contains the characters of the
3208      *          character array.
3209      */
3210     public static String copyValueOf(char data[]) {
3211         return new String(data);
3212     }
3213 
3214     /**
3215      * Returns the string representation of the {@code boolean} argument.
3216      *
3217      * @param   b   a {@code boolean}.
3218      * @return  if the argument is {@code true}, a string equal to
3219      *          {@code "true"} is returned; otherwise, a string equal to
3220      *          {@code "false"} is returned.
3221      */
3222     public static String valueOf(boolean b) {
3223         return b ? "true" : "false";
3224     }
3225 
3226     /**
3227      * Returns the string representation of the {@code char}
3228      * argument.
3229      *
3230      * @param   c   a {@code char}.
3231      * @return  a string of length {@code 1} containing
3232      *          as its single character the argument {@code c}.
3233      */
3234     public static String valueOf(char c) {
3235         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
3236             return new String(StringLatin1.toBytes(c), LATIN1);
3237         }
3238         return new String(StringUTF16.toBytes(c), UTF16);
3239     }
3240 
3241     /**
3242      * Returns the string representation of the {@code int} argument.
3243      * <p>
3244      * The representation is exactly the one returned by the
3245      * {@code Integer.toString} method of one argument.
3246      *
3247      * @param   i   an {@code int}.
3248      * @return  a string representation of the {@code int} argument.
3249      * @see     java.lang.Integer#toString(int, int)
3250      */
3251     public static String valueOf(int i) {
3252         return Integer.toString(i);
3253     }
3254 
3255     /**
3256      * Returns the string representation of the {@code long} argument.
3257      * <p>
3258      * The representation is exactly the one returned by the
3259      * {@code Long.toString} method of one argument.
3260      *
3261      * @param   l   a {@code long}.
3262      * @return  a string representation of the {@code long} argument.
3263      * @see     java.lang.Long#toString(long)
3264      */
3265     public static String valueOf(long l) {
3266         return Long.toString(l);
3267     }
3268 
3269     /**
3270      * Returns the string representation of the {@code float} argument.
3271      * <p>
3272      * The representation is exactly the one returned by the
3273      * {@code Float.toString} method of one argument.
3274      *
3275      * @param   f   a {@code float}.
3276      * @return  a string representation of the {@code float} argument.
3277      * @see     java.lang.Float#toString(float)
3278      */
3279     public static String valueOf(float f) {
3280         return Float.toString(f);
3281     }
3282 
3283     /**
3284      * Returns the string representation of the {@code double} argument.
3285      * <p>
3286      * The representation is exactly the one returned by the
3287      * {@code Double.toString} method of one argument.
3288      *
3289      * @param   d   a {@code double}.
3290      * @return  a  string representation of the {@code double} argument.
3291      * @see     java.lang.Double#toString(double)
3292      */
3293     public static String valueOf(double d) {
3294         return Double.toString(d);
3295     }
3296 
3297     /**
3298      * Returns a canonical representation for the string object.
3299      * <p>
3300      * A pool of strings, initially empty, is maintained privately by the
3301      * class {@code String}.
3302      * <p>
3303      * When the intern method is invoked, if the pool already contains a
3304      * string equal to this {@code String} object as determined by
3305      * the {@link #equals(Object)} method, then the string from the pool is
3306      * returned. Otherwise, this {@code String} object is added to the
3307      * pool and a reference to this {@code String} object is returned.
3308      * <p>
3309      * It follows that for any two strings {@code s} and {@code t},
3310      * {@code s.intern() == t.intern()} is {@code true}
3311      * if and only if {@code s.equals(t)} is {@code true}.
3312      * <p>
3313      * All literal strings and string-valued constant expressions are
3314      * interned. String literals are defined in section 3.10.5 of the
3315      * <cite>The Java&trade; Language Specification</cite>.
3316      *
3317      * @return  a string that has the same contents as this string, but is
3318      *          guaranteed to be from a pool of unique strings.
3319      * @jls 3.10.5 String Literals
3320      */
3321     public native String intern();
3322 
3323     /**
3324      * Returns a string whose value is the concatenation of this
3325      * string repeated {@code count} times.
3326      * <p>
3327      * If this string is empty or count is zero then the empty
3328      * string is returned.
3329      *
3330      * @param   count number of times to repeat
3331      *
3332      * @return  A string composed of this string repeated
3333      *          {@code count} times or the empty string if this
3334      *          string is empty or count is zero
3335      *
3336      * @throws  IllegalArgumentException if the {@code count} is
3337      *          negative.
3338      *
3339      * @since 11
3340      */
3341     public String repeat(int count) {
3342         if (count < 0) {
3343             throw new IllegalArgumentException("count is negative: " + count);
3344         }
3345         if (count == 1) {
3346             return this;
3347         }
3348         final int len = value.length;
3349         if (len == 0 || count == 0) {
3350             return "";
3351         }
3352         if (len == 1) {
3353             final byte[] single = new byte[count];
3354             Arrays.fill(single, value[0]);
3355             return new String(single, coder);
3356         }
3357         if (Integer.MAX_VALUE / count < len) {
3358             throw new OutOfMemoryError("Repeating " + len + " bytes String " + count +
3359                     " times will produce a String exceeding maximum size.");
3360         }
3361         final int limit = len * count;
3362         final byte[] multiple = new byte[limit];
3363         System.arraycopy(value, 0, multiple, 0, len);
3364         int copied = len;
3365         for (; copied < limit - copied; copied <<= 1) {
3366             System.arraycopy(multiple, 0, multiple, copied, copied);
3367         }
3368         System.arraycopy(multiple, 0, multiple, copied, limit - copied);
3369         return new String(multiple, coder);
3370     }
3371 
3372     ////////////////////////////////////////////////////////////////
3373 
3374     /**
3375      * Copy character bytes from this string into dst starting at dstBegin.
3376      * This method doesn't perform any range checking.
3377      *
3378      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
3379      * coders are different, and dst is big enough (range check)
3380      *
3381      * @param dstBegin  the char index, not offset of byte[]
3382      * @param coder     the coder of dst[]
3383      */
3384     void getBytes(byte dst[], int dstBegin, byte coder) {
3385         if (coder() == coder) {
3386             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
3387         } else {    // this.coder == LATIN && coder == UTF16
3388             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
3389         }
3390     }
3391 
3392     /*
3393      * Package private constructor. Trailing Void argument is there for
3394      * disambiguating it against other (public) constructors.
3395      *
3396      * Stores the char[] value into a byte[] that each byte represents
3397      * the8 low-order bits of the corresponding character, if the char[]
3398      * contains only latin1 character. Or a byte[] that stores all
3399      * characters in their byte sequences defined by the {@code StringUTF16}.
3400      */
3401     String(char[] value, int off, int len, Void sig) {
3402         if (len == 0) {
3403             this.value = "".value;
3404             this.coder = "".coder;
3405             return;
3406         }
3407         if (COMPACT_STRINGS) {
3408             byte[] val = StringUTF16.compress(value, off, len);
3409             if (val != null) {
3410                 this.value = val;
3411                 this.coder = LATIN1;
3412                 return;
3413             }
3414         }
3415         this.coder = UTF16;
3416         this.value = StringUTF16.toBytes(value, off, len);
3417     }
3418 
3419     /*
3420      * Package private constructor. Trailing Void argument is there for
3421      * disambiguating it against other (public) constructors.
3422      */
3423     String(AbstractStringBuilder asb, Void sig) {
3424         byte[] val = asb.getValue();
3425         int length = asb.length();
3426         if (asb.isLatin1()) {
3427             this.coder = LATIN1;
3428             this.value = Arrays.copyOfRange(val, 0, length);
3429         } else {
3430             if (COMPACT_STRINGS) {
3431                 byte[] buf = StringUTF16.compress(val, 0, length);
3432                 if (buf != null) {
3433                     this.coder = LATIN1;
3434                     this.value = buf;
3435                     return;
3436                 }
3437             }
3438             this.coder = UTF16;
3439             this.value = Arrays.copyOfRange(val, 0, length << 1);
3440         }
3441     }
3442 
3443    /*
3444     * Package private constructor which shares value array for speed.
3445     */
3446     String(byte[] value, byte coder) {
3447         this.value = value;
3448         this.coder = coder;
3449     }
3450 
3451     byte coder() {
3452         return COMPACT_STRINGS ? coder : UTF16;
3453     }
3454 
3455     byte[] value() {
3456         return value;
3457     }
3458 
3459     private boolean isLatin1() {
3460         return COMPACT_STRINGS && coder == LATIN1;
3461     }
3462 
3463     @Native static final byte LATIN1 = 0;
3464     @Native static final byte UTF16  = 1;
3465 
3466     /*
3467      * StringIndexOutOfBoundsException  if {@code index} is
3468      * negative or greater than or equal to {@code length}.
3469      */
3470     static void checkIndex(int index, int length) {
3471         if (index < 0 || index >= length) {
3472             throw new StringIndexOutOfBoundsException("index " + index +
3473                                                       ",length " + length);
3474         }
3475     }
3476 
3477     /*
3478      * StringIndexOutOfBoundsException  if {@code offset}
3479      * is negative or greater than {@code length}.
3480      */
3481     static void checkOffset(int offset, int length) {
3482         if (offset < 0 || offset > length) {
3483             throw new StringIndexOutOfBoundsException("offset " + offset +
3484                                                       ",length " + length);
3485         }
3486     }
3487 
3488     /*
3489      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3490      * bounds.
3491      *
3492      * @throws  StringIndexOutOfBoundsException
3493      *          If {@code offset} is negative, {@code count} is negative,
3494      *          or {@code offset} is greater than {@code length - count}
3495      */
3496     static void checkBoundsOffCount(int offset, int count, int length) {
3497         if (offset < 0 || count < 0 || offset > length - count) {
3498             throw new StringIndexOutOfBoundsException(
3499                 "offset " + offset + ", count " + count + ", length " + length);
3500         }
3501     }
3502 
3503     /*
3504      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3505      * bounds.
3506      *
3507      * @throws  StringIndexOutOfBoundsException
3508      *          If {@code begin} is negative, {@code begin} is greater than
3509      *          {@code end}, or {@code end} is greater than {@code length}.
3510      */
3511     static void checkBoundsBeginEnd(int begin, int end, int length) {
3512         if (begin < 0 || begin > end || end > length) {
3513             throw new StringIndexOutOfBoundsException(
3514                 "begin " + begin + ", end " + end + ", length " + length);
3515         }
3516     }
3517 
3518     /**
3519      * Returns the string representation of the {@code codePoint}
3520      * argument.
3521      *
3522      * @param   codePoint a {@code codePoint}.
3523      * @return  a string of length {@code 1} or {@code 2} containing
3524      *          as its single character the argument {@code codePoint}.
3525      * @throws IllegalArgumentException if the specified
3526      *          {@code codePoint} is not a {@linkplain Character#isValidCodePoint
3527      *          valid Unicode code point}.
3528      */
3529     static String valueOfCodePoint(int codePoint) {
3530         if (COMPACT_STRINGS && StringLatin1.canEncode(codePoint)) {
3531             return new String(StringLatin1.toBytes((char)codePoint), LATIN1);
3532         } else if (Character.isBmpCodePoint(codePoint)) {
3533             return new String(StringUTF16.toBytes((char)codePoint), UTF16);
3534         } else if (Character.isSupplementaryCodePoint(codePoint)) {
3535             return new String(StringUTF16.toBytesSupplementary(codePoint), UTF16);
3536         }
3537 
3538         throw new IllegalArgumentException(
3539             format("Not a valid Unicode code point: 0x%X", codePoint));
3540     }
3541 }