1 /*
   2  * Copyright (c) 1994, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.ObjectStreamField;
  29 import java.io.UnsupportedEncodingException;
  30 import java.nio.charset.Charset;
  31 import java.util.ArrayList;
  32 import java.util.Arrays;
  33 import java.util.Comparator;
  34 import java.util.Formatter;
  35 import java.util.Locale;
  36 import java.util.Objects;
  37 import java.util.Spliterator;
  38 import java.util.StringJoiner;
  39 import java.util.regex.Matcher;
  40 import java.util.regex.Pattern;
  41 import java.util.regex.PatternSyntaxException;
  42 import java.util.stream.IntStream;
  43 import java.util.stream.StreamSupport;
  44 import jdk.internal.HotSpotIntrinsicCandidate;
  45 import jdk.internal.vm.annotation.Stable;
  46 
  47 /**
  48  * The {@code String} class represents character strings. All
  49  * string literals in Java programs, such as {@code "abc"}, are
  50  * implemented as instances of this class.
  51  * <p>
  52  * Strings are constant; their values cannot be changed after they
  53  * are created. String buffers support mutable strings.
  54  * Because String objects are immutable they can be shared. For example:
  55  * <blockquote><pre>
  56  *     String str = "abc";
  57  * </pre></blockquote><p>
  58  * is equivalent to:
  59  * <blockquote><pre>
  60  *     char data[] = {'a', 'b', 'c'};
  61  *     String str = new String(data);
  62  * </pre></blockquote><p>
  63  * Here are some more examples of how strings can be used:
  64  * <blockquote><pre>
  65  *     System.out.println("abc");
  66  *     String cde = "cde";
  67  *     System.out.println("abc" + cde);
  68  *     String c = "abc".substring(2,3);
  69  *     String d = cde.substring(1, 2);
  70  * </pre></blockquote>
  71  * <p>
  72  * The class {@code String} includes methods for examining
  73  * individual characters of the sequence, for comparing strings, for
  74  * searching strings, for extracting substrings, and for creating a
  75  * copy of a string with all characters translated to uppercase or to
  76  * lowercase. Case mapping is based on the Unicode Standard version
  77  * specified by the {@link java.lang.Character Character} class.
  78  * <p>
  79  * The Java language provides special support for the string
  80  * concatenation operator (&nbsp;+&nbsp;), and for conversion of
  81  * other objects to strings. For additional information on string
  82  * concatenation and conversion, see <i>The Java&trade; Language Specification</i>.
  83  *
  84  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  85  * or method in this class will cause a {@link NullPointerException} to be
  86  * thrown.
  87  *
  88  * <p>A {@code String} represents a string in the UTF-16 format
  89  * in which <em>supplementary characters</em> are represented by <em>surrogate
  90  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  91  * Character Representations</a> in the {@code Character} class for
  92  * more information).
  93  * Index values refer to {@code char} code units, so a supplementary
  94  * character uses two positions in a {@code String}.
  95  * <p>The {@code String} class provides methods for dealing with
  96  * Unicode code points (i.e., characters), in addition to those for
  97  * dealing with Unicode code units (i.e., {@code char} values).
  98  *
  99  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 100  * into account.  The {@link java.text.Collator} class provides methods for
 101  * finer-grain, locale-sensitive String comparison.
 102  *
 103  * @implNote The implementation of the string concatenation operator is left to
 104  * the discretion of a Java compiler, as long as the compiler ultimately conforms
 105  * to <i>The Java&trade; Language Specification</i>. For example, the {@code javac} compiler
 106  * may implement the operator with {@code StringBuffer}, {@code StringBuilder},
 107  * or {@code java.lang.invoke.StringConcatFactory} depending on the JDK version. The
 108  * implementation of string conversion is typically through the method {@code toString},
 109  * defined by {@code Object} and inherited by all classes in Java.
 110  *
 111  * @author  Lee Boynton
 112  * @author  Arthur van Hoff
 113  * @author  Martin Buchholz
 114  * @author  Ulf Zibis
 115  * @see     java.lang.Object#toString()
 116  * @see     java.lang.StringBuffer
 117  * @see     java.lang.StringBuilder
 118  * @see     java.nio.charset.Charset
 119  * @since   1.0
 120  * @jls     15.18.1 String Concatenation Operator +
 121  */
 122 
 123 public final class String
 124     implements java.io.Serializable, Comparable<String>, CharSequence {
 125 
 126     /**
 127      * The value is used for character storage.
 128      *
 129      * @implNote This field is trusted by the VM, and is a subject to
 130      * constant folding if String instance is constant. Overwriting this
 131      * field after construction will cause problems.
 132      *
 133      * Additionally, it is marked with {@link Stable} to trust the contents
 134      * of the array. No other facility in JDK provides this functionality (yet).
 135      * {@link Stable} is safe here, because value is never null.
 136      */
 137     @Stable
 138     private final byte[] value;
 139 
 140     /**
 141      * The identifier of the encoding used to encode the bytes in
 142      * {@code value}. The supported values in this implementation are
 143      *
 144      * LATIN1
 145      * UTF16
 146      *
 147      * @implNote This field is trusted by the VM, and is a subject to
 148      * constant folding if String instance is constant. Overwriting this
 149      * field after construction will cause problems.
 150      */
 151     private final byte coder;
 152 
 153     /** Cache the hash code for the string */
 154     private int hash; // Default to 0
 155 
 156     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 157     private static final long serialVersionUID = -6849794470754667710L;
 158 
 159     /**
 160      * If String compaction is disabled, the bytes in {@code value} are
 161      * always encoded in UTF16.
 162      *
 163      * For methods with several possible implementation paths, when String
 164      * compaction is disabled, only one code path is taken.
 165      *
 166      * The instance field value is generally opaque to optimizing JIT
 167      * compilers. Therefore, in performance-sensitive place, an explicit
 168      * check of the static boolean {@code COMPACT_STRINGS} is done first
 169      * before checking the {@code coder} field since the static boolean
 170      * {@code COMPACT_STRINGS} would be constant folded away by an
 171      * optimizing JIT compiler. The idioms for these cases are as follows.
 172      *
 173      * For code such as:
 174      *
 175      *    if (coder == LATIN1) { ... }
 176      *
 177      * can be written more optimally as
 178      *
 179      *    if (coder() == LATIN1) { ... }
 180      *
 181      * or:
 182      *
 183      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 184      *
 185      * An optimizing JIT compiler can fold the above conditional as:
 186      *
 187      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 188      *    COMPACT_STRINGS == false => if (false)           { ... }
 189      *
 190      * @implNote
 191      * The actual value for this field is injected by JVM. The static
 192      * initialization block is used to set the value here to communicate
 193      * that this static final field is not statically foldable, and to
 194      * avoid any possible circular dependency during vm initialization.
 195      */
 196     static final boolean COMPACT_STRINGS;
 197 
 198     static {
 199         COMPACT_STRINGS = true;
 200     }
 201 
 202     /**
 203      * Class String is special cased within the Serialization Stream Protocol.
 204      *
 205      * A String instance is written into an ObjectOutputStream according to
 206      * <a href="{@docRoot}/../platform/serialization/spec/output.html">
 207      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 208      */
 209     private static final ObjectStreamField[] serialPersistentFields =
 210         new ObjectStreamField[0];
 211 
 212     /**
 213      * Initializes a newly created {@code String} object so that it represents
 214      * an empty character sequence.  Note that use of this constructor is
 215      * unnecessary since Strings are immutable.
 216      */
 217     public String() {
 218         this.value = "".value;
 219         this.coder = "".coder;
 220     }
 221 
 222     /**
 223      * Initializes a newly created {@code String} object so that it represents
 224      * the same sequence of characters as the argument; in other words, the
 225      * newly created string is a copy of the argument string. Unless an
 226      * explicit copy of {@code original} is needed, use of this constructor is
 227      * unnecessary since Strings are immutable.
 228      *
 229      * @param  original
 230      *         A {@code String}
 231      */
 232     @HotSpotIntrinsicCandidate
 233     public String(String original) {
 234         this.value = original.value;
 235         this.coder = original.coder;
 236         this.hash = original.hash;
 237     }
 238 
 239     /**
 240      * Allocates a new {@code String} so that it represents the sequence of
 241      * characters currently contained in the character array argument. The
 242      * contents of the character array are copied; subsequent modification of
 243      * the character array does not affect the newly created string.
 244      *
 245      * @param  value
 246      *         The initial value of the string
 247      */
 248     public String(char value[]) {
 249         this(value, 0, value.length, null);
 250     }
 251 
 252     /**
 253      * Allocates a new {@code String} that contains characters from a subarray
 254      * of the character array argument. The {@code offset} argument is the
 255      * index of the first character of the subarray and the {@code count}
 256      * argument specifies the length of the subarray. The contents of the
 257      * subarray are copied; subsequent modification of the character array does
 258      * not affect the newly created string.
 259      *
 260      * @param  value
 261      *         Array that is the source of characters
 262      *
 263      * @param  offset
 264      *         The initial offset
 265      *
 266      * @param  count
 267      *         The length
 268      *
 269      * @throws  IndexOutOfBoundsException
 270      *          If {@code offset} is negative, {@code count} is negative, or
 271      *          {@code offset} is greater than {@code value.length - count}
 272      */
 273     public String(char value[], int offset, int count) {
 274         this(value, offset, count, rangeCheck(value, offset, count));
 275     }
 276 
 277     private static Void rangeCheck(char[] value, int offset, int count) {
 278         checkBoundsOffCount(offset, count, value.length);
 279         return null;
 280     }
 281 
 282     /**
 283      * Allocates a new {@code String} that contains characters from a subarray
 284      * of the <a href="Character.html#unicode">Unicode code point</a> array
 285      * argument.  The {@code offset} argument is the index of the first code
 286      * point of the subarray and the {@code count} argument specifies the
 287      * length of the subarray.  The contents of the subarray are converted to
 288      * {@code char}s; subsequent modification of the {@code int} array does not
 289      * affect the newly created string.
 290      *
 291      * @param  codePoints
 292      *         Array that is the source of Unicode code points
 293      *
 294      * @param  offset
 295      *         The initial offset
 296      *
 297      * @param  count
 298      *         The length
 299      *
 300      * @throws  IllegalArgumentException
 301      *          If any invalid Unicode code point is found in {@code
 302      *          codePoints}
 303      *
 304      * @throws  IndexOutOfBoundsException
 305      *          If {@code offset} is negative, {@code count} is negative, or
 306      *          {@code offset} is greater than {@code codePoints.length - count}
 307      *
 308      * @since  1.5
 309      */
 310     public String(int[] codePoints, int offset, int count) {
 311         checkBoundsOffCount(offset, count, codePoints.length);
 312         if (count == 0) {
 313             this.value = "".value;
 314             this.coder = "".coder;
 315             return;
 316         }
 317         if (COMPACT_STRINGS) {
 318             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 319             if (val != null) {
 320                 this.coder = LATIN1;
 321                 this.value = val;
 322                 return;
 323             }
 324         }
 325         this.coder = UTF16;
 326         this.value = StringUTF16.toBytes(codePoints, offset, count);
 327     }
 328 
 329     /**
 330      * Allocates a new {@code String} constructed from a subarray of an array
 331      * of 8-bit integer values.
 332      *
 333      * <p> The {@code offset} argument is the index of the first byte of the
 334      * subarray, and the {@code count} argument specifies the length of the
 335      * subarray.
 336      *
 337      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 338      * specified in the method above.
 339      *
 340      * @deprecated This method does not properly convert bytes into characters.
 341      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 342      * {@code String} constructors that take a {@link
 343      * java.nio.charset.Charset}, charset name, or that use the platform's
 344      * default charset.
 345      *
 346      * @param  ascii
 347      *         The bytes to be converted to characters
 348      *
 349      * @param  hibyte
 350      *         The top 8 bits of each 16-bit Unicode code unit
 351      *
 352      * @param  offset
 353      *         The initial offset
 354      * @param  count
 355      *         The length
 356      *
 357      * @throws  IndexOutOfBoundsException
 358      *          If {@code offset} is negative, {@code count} is negative, or
 359      *          {@code offset} is greater than {@code ascii.length - count}
 360      *
 361      * @see  #String(byte[], int)
 362      * @see  #String(byte[], int, int, java.lang.String)
 363      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 364      * @see  #String(byte[], int, int)
 365      * @see  #String(byte[], java.lang.String)
 366      * @see  #String(byte[], java.nio.charset.Charset)
 367      * @see  #String(byte[])
 368      */
 369     @Deprecated(since="1.1")
 370     public String(byte ascii[], int hibyte, int offset, int count) {
 371         checkBoundsOffCount(offset, count, ascii.length);
 372         if (count == 0) {
 373             this.value = "".value;
 374             this.coder = "".coder;
 375             return;
 376         }
 377         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 378             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 379             this.coder = LATIN1;
 380         } else {
 381             hibyte <<= 8;
 382             byte[] val = StringUTF16.newBytesFor(count);
 383             for (int i = 0; i < count; i++) {
 384                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 385             }
 386             this.value = val;
 387             this.coder = UTF16;
 388         }
 389     }
 390 
 391     /**
 392      * Allocates a new {@code String} containing characters constructed from
 393      * an array of 8-bit integer values. Each character <i>c</i>in the
 394      * resulting string is constructed from the corresponding component
 395      * <i>b</i> in the byte array such that:
 396      *
 397      * <blockquote><pre>
 398      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 399      *                         | (<b><i>b</i></b> &amp; 0xff))
 400      * </pre></blockquote>
 401      *
 402      * @deprecated  This method does not properly convert bytes into
 403      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 404      * {@code String} constructors that take a {@link
 405      * java.nio.charset.Charset}, charset name, or that use the platform's
 406      * default charset.
 407      *
 408      * @param  ascii
 409      *         The bytes to be converted to characters
 410      *
 411      * @param  hibyte
 412      *         The top 8 bits of each 16-bit Unicode code unit
 413      *
 414      * @see  #String(byte[], int, int, java.lang.String)
 415      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 416      * @see  #String(byte[], int, int)
 417      * @see  #String(byte[], java.lang.String)
 418      * @see  #String(byte[], java.nio.charset.Charset)
 419      * @see  #String(byte[])
 420      */
 421     @Deprecated(since="1.1")
 422     public String(byte ascii[], int hibyte) {
 423         this(ascii, hibyte, 0, ascii.length);
 424     }
 425 
 426     /**
 427      * Constructs a new {@code String} by decoding the specified subarray of
 428      * bytes using the specified charset.  The length of the new {@code String}
 429      * is a function of the charset, and hence may not be equal to the length
 430      * of the subarray.
 431      *
 432      * <p> The behavior of this constructor when the given bytes are not valid
 433      * in the given charset is unspecified.  The {@link
 434      * java.nio.charset.CharsetDecoder} class should be used when more control
 435      * over the decoding process is required.
 436      *
 437      * @param  bytes
 438      *         The bytes to be decoded into characters
 439      *
 440      * @param  offset
 441      *         The index of the first byte to decode
 442      *
 443      * @param  length
 444      *         The number of bytes to decode
 445 
 446      * @param  charsetName
 447      *         The name of a supported {@linkplain java.nio.charset.Charset
 448      *         charset}
 449      *
 450      * @throws  UnsupportedEncodingException
 451      *          If the named charset is not supported
 452      *
 453      * @throws  IndexOutOfBoundsException
 454      *          If {@code offset} is negative, {@code length} is negative, or
 455      *          {@code offset} is greater than {@code bytes.length - length}
 456      *
 457      * @since  1.1
 458      */
 459     public String(byte bytes[], int offset, int length, String charsetName)
 460             throws UnsupportedEncodingException {
 461         if (charsetName == null)
 462             throw new NullPointerException("charsetName");
 463         checkBoundsOffCount(offset, length, bytes.length);
 464         StringCoding.Result ret =
 465             StringCoding.decode(charsetName, bytes, offset, length);
 466         this.value = ret.value;
 467         this.coder = ret.coder;
 468     }
 469 
 470     /**
 471      * Constructs a new {@code String} by decoding the specified subarray of
 472      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 473      * The length of the new {@code String} is a function of the charset, and
 474      * hence may not be equal to the length of the subarray.
 475      *
 476      * <p> This method always replaces malformed-input and unmappable-character
 477      * sequences with this charset's default replacement string.  The {@link
 478      * java.nio.charset.CharsetDecoder} class should be used when more control
 479      * over the decoding process is required.
 480      *
 481      * @param  bytes
 482      *         The bytes to be decoded into characters
 483      *
 484      * @param  offset
 485      *         The index of the first byte to decode
 486      *
 487      * @param  length
 488      *         The number of bytes to decode
 489      *
 490      * @param  charset
 491      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 492      *         decode the {@code bytes}
 493      *
 494      * @throws  IndexOutOfBoundsException
 495      *          If {@code offset} is negative, {@code length} is negative, or
 496      *          {@code offset} is greater than {@code bytes.length - length}
 497      *
 498      * @since  1.6
 499      */
 500     public String(byte bytes[], int offset, int length, Charset charset) {
 501         if (charset == null)
 502             throw new NullPointerException("charset");
 503         checkBoundsOffCount(offset, length, bytes.length);
 504         StringCoding.Result ret =
 505             StringCoding.decode(charset, bytes, offset, length);
 506         this.value = ret.value;
 507         this.coder = ret.coder;
 508     }
 509 
 510     /**
 511      * Constructs a new {@code String} by decoding the specified array of bytes
 512      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 513      * length of the new {@code String} is a function of the charset, and hence
 514      * may not be equal to the length of the byte array.
 515      *
 516      * <p> The behavior of this constructor when the given bytes are not valid
 517      * in the given charset is unspecified.  The {@link
 518      * java.nio.charset.CharsetDecoder} class should be used when more control
 519      * over the decoding process is required.
 520      *
 521      * @param  bytes
 522      *         The bytes to be decoded into characters
 523      *
 524      * @param  charsetName
 525      *         The name of a supported {@linkplain java.nio.charset.Charset
 526      *         charset}
 527      *
 528      * @throws  UnsupportedEncodingException
 529      *          If the named charset is not supported
 530      *
 531      * @since  1.1
 532      */
 533     public String(byte bytes[], String charsetName)
 534             throws UnsupportedEncodingException {
 535         this(bytes, 0, bytes.length, charsetName);
 536     }
 537 
 538     /**
 539      * Constructs a new {@code String} by decoding the specified array of
 540      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 541      * The length of the new {@code String} is a function of the charset, and
 542      * hence may not be equal to the length of the byte array.
 543      *
 544      * <p> This method always replaces malformed-input and unmappable-character
 545      * sequences with this charset's default replacement string.  The {@link
 546      * java.nio.charset.CharsetDecoder} class should be used when more control
 547      * over the decoding process is required.
 548      *
 549      * @param  bytes
 550      *         The bytes to be decoded into characters
 551      *
 552      * @param  charset
 553      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 554      *         decode the {@code bytes}
 555      *
 556      * @since  1.6
 557      */
 558     public String(byte bytes[], Charset charset) {
 559         this(bytes, 0, bytes.length, charset);
 560     }
 561 
 562     /**
 563      * Constructs a new {@code String} by decoding the specified subarray of
 564      * bytes using the platform's default charset.  The length of the new
 565      * {@code String} is a function of the charset, and hence may not be equal
 566      * to the length of the subarray.
 567      *
 568      * <p> The behavior of this constructor when the given bytes are not valid
 569      * in the default charset is unspecified.  The {@link
 570      * java.nio.charset.CharsetDecoder} class should be used when more control
 571      * over the decoding process is required.
 572      *
 573      * @param  bytes
 574      *         The bytes to be decoded into characters
 575      *
 576      * @param  offset
 577      *         The index of the first byte to decode
 578      *
 579      * @param  length
 580      *         The number of bytes to decode
 581      *
 582      * @throws  IndexOutOfBoundsException
 583      *          If {@code offset} is negative, {@code length} is negative, or
 584      *          {@code offset} is greater than {@code bytes.length - length}
 585      *
 586      * @since  1.1
 587      */
 588     public String(byte bytes[], int offset, int length) {
 589         checkBoundsOffCount(offset, length, bytes.length);
 590         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 591         this.value = ret.value;
 592         this.coder = ret.coder;
 593     }
 594 
 595     /**
 596      * Constructs a new {@code String} by decoding the specified array of bytes
 597      * using the platform's default charset.  The length of the new {@code
 598      * String} is a function of the charset, and hence may not be equal to the
 599      * length of the byte array.
 600      *
 601      * <p> The behavior of this constructor when the given bytes are not valid
 602      * in the default charset is unspecified.  The {@link
 603      * java.nio.charset.CharsetDecoder} class should be used when more control
 604      * over the decoding process is required.
 605      *
 606      * @param  bytes
 607      *         The bytes to be decoded into characters
 608      *
 609      * @since  1.1
 610      */
 611     public String(byte[] bytes) {
 612         this(bytes, 0, bytes.length);
 613     }
 614 
 615     /**
 616      * Allocates a new string that contains the sequence of characters
 617      * currently contained in the string buffer argument. The contents of the
 618      * string buffer are copied; subsequent modification of the string buffer
 619      * does not affect the newly created string.
 620      *
 621      * @param  buffer
 622      *         A {@code StringBuffer}
 623      */
 624     public String(StringBuffer buffer) {
 625         this(buffer.toString());
 626     }
 627 
 628     /**
 629      * Allocates a new string that contains the sequence of characters
 630      * currently contained in the string builder argument. The contents of the
 631      * string builder are copied; subsequent modification of the string builder
 632      * does not affect the newly created string.
 633      *
 634      * <p> This constructor is provided to ease migration to {@code
 635      * StringBuilder}. Obtaining a string from a string builder via the {@code
 636      * toString} method is likely to run faster and is generally preferred.
 637      *
 638      * @param   builder
 639      *          A {@code StringBuilder}
 640      *
 641      * @since  1.5
 642      */
 643     public String(StringBuilder builder) {
 644         this(builder, null);
 645     }
 646 
 647    /*
 648     * Package private constructor which shares value array for speed.
 649     * this constructor is always expected to be called with share==true.
 650     * a separate constructor is needed because we already have a public
 651     * String(char[]) constructor that makes a copy of the given char[].
 652     */
 653     // TBD: this is kept for package internal use (Thread/System),
 654     // should be removed if they all have a byte[] version
 655     String(char[] val, boolean share) {
 656         // assert share : "unshared not supported";
 657         this(val, 0, val.length, null);
 658     }
 659 
 660     /**
 661      * Returns the length of this string.
 662      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 663      * code units</a> in the string.
 664      *
 665      * @return  the length of the sequence of characters represented by this
 666      *          object.
 667      */
 668     public int length() {
 669         return value.length >> coder();
 670     }
 671 
 672     /**
 673      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 674      *
 675      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 676      * {@code false}
 677      *
 678      * @since 1.6
 679      */
 680     public boolean isEmpty() {
 681         return value.length == 0;
 682     }
 683 
 684     /**
 685      * Returns the {@code char} value at the
 686      * specified index. An index ranges from {@code 0} to
 687      * {@code length() - 1}. The first {@code char} value of the sequence
 688      * is at index {@code 0}, the next at index {@code 1},
 689      * and so on, as for array indexing.
 690      *
 691      * <p>If the {@code char} value specified by the index is a
 692      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 693      * value is returned.
 694      *
 695      * @param      index   the index of the {@code char} value.
 696      * @return     the {@code char} value at the specified index of this string.
 697      *             The first {@code char} value is at index {@code 0}.
 698      * @exception  IndexOutOfBoundsException  if the {@code index}
 699      *             argument is negative or not less than the length of this
 700      *             string.
 701      */
 702     public char charAt(int index) {
 703         if (isLatin1()) {
 704             return StringLatin1.charAt(value, index);
 705         } else {
 706             return StringUTF16.charAt(value, index);
 707         }
 708     }
 709 
 710     /**
 711      * Returns the character (Unicode code point) at the specified
 712      * index. The index refers to {@code char} values
 713      * (Unicode code units) and ranges from {@code 0} to
 714      * {@link #length()}{@code  - 1}.
 715      *
 716      * <p> If the {@code char} value specified at the given index
 717      * is in the high-surrogate range, the following index is less
 718      * than the length of this {@code String}, and the
 719      * {@code char} value at the following index is in the
 720      * low-surrogate range, then the supplementary code point
 721      * corresponding to this surrogate pair is returned. Otherwise,
 722      * the {@code char} value at the given index is returned.
 723      *
 724      * @param      index the index to the {@code char} values
 725      * @return     the code point value of the character at the
 726      *             {@code index}
 727      * @exception  IndexOutOfBoundsException  if the {@code index}
 728      *             argument is negative or not less than the length of this
 729      *             string.
 730      * @since      1.5
 731      */
 732     public int codePointAt(int index) {
 733         if (isLatin1()) {
 734             checkIndex(index, value.length);
 735             return value[index] & 0xff;
 736         }
 737         int length = value.length >> 1;
 738         checkIndex(index, length);
 739         return StringUTF16.codePointAt(value, index, length);
 740     }
 741 
 742     /**
 743      * Returns the character (Unicode code point) before the specified
 744      * index. The index refers to {@code char} values
 745      * (Unicode code units) and ranges from {@code 1} to {@link
 746      * CharSequence#length() length}.
 747      *
 748      * <p> If the {@code char} value at {@code (index - 1)}
 749      * is in the low-surrogate range, {@code (index - 2)} is not
 750      * negative, and the {@code char} value at {@code (index -
 751      * 2)} is in the high-surrogate range, then the
 752      * supplementary code point value of the surrogate pair is
 753      * returned. If the {@code char} value at {@code index -
 754      * 1} is an unpaired low-surrogate or a high-surrogate, the
 755      * surrogate value is returned.
 756      *
 757      * @param     index the index following the code point that should be returned
 758      * @return    the Unicode code point value before the given index.
 759      * @exception IndexOutOfBoundsException if the {@code index}
 760      *            argument is less than 1 or greater than the length
 761      *            of this string.
 762      * @since     1.5
 763      */
 764     public int codePointBefore(int index) {
 765         int i = index - 1;
 766         if (i < 0 || i >= length()) {
 767             throw new StringIndexOutOfBoundsException(index);
 768         }
 769         if (isLatin1()) {
 770             return (value[i] & 0xff);
 771         }
 772         return StringUTF16.codePointBefore(value, index);
 773     }
 774 
 775     /**
 776      * Returns the number of Unicode code points in the specified text
 777      * range of this {@code String}. The text range begins at the
 778      * specified {@code beginIndex} and extends to the
 779      * {@code char} at index {@code endIndex - 1}. Thus the
 780      * length (in {@code char}s) of the text range is
 781      * {@code endIndex-beginIndex}. Unpaired surrogates within
 782      * the text range count as one code point each.
 783      *
 784      * @param beginIndex the index to the first {@code char} of
 785      * the text range.
 786      * @param endIndex the index after the last {@code char} of
 787      * the text range.
 788      * @return the number of Unicode code points in the specified text
 789      * range
 790      * @exception IndexOutOfBoundsException if the
 791      * {@code beginIndex} is negative, or {@code endIndex}
 792      * is larger than the length of this {@code String}, or
 793      * {@code beginIndex} is larger than {@code endIndex}.
 794      * @since  1.5
 795      */
 796     public int codePointCount(int beginIndex, int endIndex) {
 797         if (beginIndex < 0 || beginIndex > endIndex ||
 798             endIndex > length()) {
 799             throw new IndexOutOfBoundsException();
 800         }
 801         if (isLatin1()) {
 802             return endIndex - beginIndex;
 803         }
 804         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 805     }
 806 
 807     /**
 808      * Returns the index within this {@code String} that is
 809      * offset from the given {@code index} by
 810      * {@code codePointOffset} code points. Unpaired surrogates
 811      * within the text range given by {@code index} and
 812      * {@code codePointOffset} count as one code point each.
 813      *
 814      * @param index the index to be offset
 815      * @param codePointOffset the offset in code points
 816      * @return the index within this {@code String}
 817      * @exception IndexOutOfBoundsException if {@code index}
 818      *   is negative or larger then the length of this
 819      *   {@code String}, or if {@code codePointOffset} is positive
 820      *   and the substring starting with {@code index} has fewer
 821      *   than {@code codePointOffset} code points,
 822      *   or if {@code codePointOffset} is negative and the substring
 823      *   before {@code index} has fewer than the absolute value
 824      *   of {@code codePointOffset} code points.
 825      * @since 1.5
 826      */
 827     public int offsetByCodePoints(int index, int codePointOffset) {
 828         if (index < 0 || index > length()) {
 829             throw new IndexOutOfBoundsException();
 830         }
 831         return Character.offsetByCodePoints(this, index, codePointOffset);
 832     }
 833 
 834     /**
 835      * Copies characters from this string into the destination character
 836      * array.
 837      * <p>
 838      * The first character to be copied is at index {@code srcBegin};
 839      * the last character to be copied is at index {@code srcEnd-1}
 840      * (thus the total number of characters to be copied is
 841      * {@code srcEnd-srcBegin}). The characters are copied into the
 842      * subarray of {@code dst} starting at index {@code dstBegin}
 843      * and ending at index:
 844      * <blockquote><pre>
 845      *     dstBegin + (srcEnd-srcBegin) - 1
 846      * </pre></blockquote>
 847      *
 848      * @param      srcBegin   index of the first character in the string
 849      *                        to copy.
 850      * @param      srcEnd     index after the last character in the string
 851      *                        to copy.
 852      * @param      dst        the destination array.
 853      * @param      dstBegin   the start offset in the destination array.
 854      * @exception IndexOutOfBoundsException If any of the following
 855      *            is true:
 856      *            <ul><li>{@code srcBegin} is negative.
 857      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 858      *            <li>{@code srcEnd} is greater than the length of this
 859      *                string
 860      *            <li>{@code dstBegin} is negative
 861      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 862      *                {@code dst.length}</ul>
 863      */
 864     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 865         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 866         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 867         if (isLatin1()) {
 868             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 869         } else {
 870             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 871         }
 872     }
 873 
 874     /**
 875      * Copies characters from this string into the destination byte array. Each
 876      * byte receives the 8 low-order bits of the corresponding character. The
 877      * eight high-order bits of each character are not copied and do not
 878      * participate in the transfer in any way.
 879      *
 880      * <p> The first character to be copied is at index {@code srcBegin}; the
 881      * last character to be copied is at index {@code srcEnd-1}.  The total
 882      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 883      * characters, converted to bytes, are copied into the subarray of {@code
 884      * dst} starting at index {@code dstBegin} and ending at index:
 885      *
 886      * <blockquote><pre>
 887      *     dstBegin + (srcEnd-srcBegin) - 1
 888      * </pre></blockquote>
 889      *
 890      * @deprecated  This method does not properly convert characters into
 891      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 892      * {@link #getBytes()} method, which uses the platform's default charset.
 893      *
 894      * @param  srcBegin
 895      *         Index of the first character in the string to copy
 896      *
 897      * @param  srcEnd
 898      *         Index after the last character in the string to copy
 899      *
 900      * @param  dst
 901      *         The destination array
 902      *
 903      * @param  dstBegin
 904      *         The start offset in the destination array
 905      *
 906      * @throws  IndexOutOfBoundsException
 907      *          If any of the following is true:
 908      *          <ul>
 909      *            <li> {@code srcBegin} is negative
 910      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 911      *            <li> {@code srcEnd} is greater than the length of this String
 912      *            <li> {@code dstBegin} is negative
 913      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 914      *                 dst.length}
 915      *          </ul>
 916      */
 917     @Deprecated(since="1.1")
 918     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 919         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 920         Objects.requireNonNull(dst);
 921         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 922         if (isLatin1()) {
 923             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 924         } else {
 925             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 926         }
 927     }
 928 
 929     /**
 930      * Encodes this {@code String} into a sequence of bytes using the named
 931      * charset, storing the result into a new byte array.
 932      *
 933      * <p> The behavior of this method when this string cannot be encoded in
 934      * the given charset is unspecified.  The {@link
 935      * java.nio.charset.CharsetEncoder} class should be used when more control
 936      * over the encoding process is required.
 937      *
 938      * @param  charsetName
 939      *         The name of a supported {@linkplain java.nio.charset.Charset
 940      *         charset}
 941      *
 942      * @return  The resultant byte array
 943      *
 944      * @throws  UnsupportedEncodingException
 945      *          If the named charset is not supported
 946      *
 947      * @since  1.1
 948      */
 949     public byte[] getBytes(String charsetName)
 950             throws UnsupportedEncodingException {
 951         if (charsetName == null) throw new NullPointerException();
 952         return StringCoding.encode(charsetName, coder(), value);
 953     }
 954 
 955     /**
 956      * Encodes this {@code String} into a sequence of bytes using the given
 957      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 958      * new byte array.
 959      *
 960      * <p> This method always replaces malformed-input and unmappable-character
 961      * sequences with this charset's default replacement byte array.  The
 962      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 963      * control over the encoding process is required.
 964      *
 965      * @param  charset
 966      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 967      *         the {@code String}
 968      *
 969      * @return  The resultant byte array
 970      *
 971      * @since  1.6
 972      */
 973     public byte[] getBytes(Charset charset) {
 974         if (charset == null) throw new NullPointerException();
 975         return StringCoding.encode(charset, coder(), value);
 976      }
 977 
 978     /**
 979      * Encodes this {@code String} into a sequence of bytes using the
 980      * platform's default charset, storing the result into a new byte array.
 981      *
 982      * <p> The behavior of this method when this string cannot be encoded in
 983      * the default charset is unspecified.  The {@link
 984      * java.nio.charset.CharsetEncoder} class should be used when more control
 985      * over the encoding process is required.
 986      *
 987      * @return  The resultant byte array
 988      *
 989      * @since      1.1
 990      */
 991     public byte[] getBytes() {
 992         return StringCoding.encode(coder(), value);
 993     }
 994 
 995     /**
 996      * Compares this string to the specified object.  The result is {@code
 997      * true} if and only if the argument is not {@code null} and is a {@code
 998      * String} object that represents the same sequence of characters as this
 999      * object.
1000      *
1001      * <p>For finer-grained String comparison, refer to
1002      * {@link java.text.Collator}.
1003      *
1004      * @param  anObject
1005      *         The object to compare this {@code String} against
1006      *
1007      * @return  {@code true} if the given object represents a {@code String}
1008      *          equivalent to this string, {@code false} otherwise
1009      *
1010      * @see  #compareTo(String)
1011      * @see  #equalsIgnoreCase(String)
1012      */
1013     public boolean equals(Object anObject) {
1014         if (this == anObject) {
1015             return true;
1016         }
1017         if (anObject instanceof String) {
1018             String aString = (String)anObject;
1019             if (coder() == aString.coder()) {
1020                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1021                                   : StringUTF16.equals(value, aString.value);
1022             }
1023         }
1024         return false;
1025     }
1026 
1027     /**
1028      * Compares this string to the specified {@code StringBuffer}.  The result
1029      * is {@code true} if and only if this {@code String} represents the same
1030      * sequence of characters as the specified {@code StringBuffer}. This method
1031      * synchronizes on the {@code StringBuffer}.
1032      *
1033      * <p>For finer-grained String comparison, refer to
1034      * {@link java.text.Collator}.
1035      *
1036      * @param  sb
1037      *         The {@code StringBuffer} to compare this {@code String} against
1038      *
1039      * @return  {@code true} if this {@code String} represents the same
1040      *          sequence of characters as the specified {@code StringBuffer},
1041      *          {@code false} otherwise
1042      *
1043      * @since  1.4
1044      */
1045     public boolean contentEquals(StringBuffer sb) {
1046         return contentEquals((CharSequence)sb);
1047     }
1048 
1049     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1050         int len = length();
1051         if (len != sb.length()) {
1052             return false;
1053         }
1054         byte v1[] = value;
1055         byte v2[] = sb.getValue();
1056         if (coder() == sb.getCoder()) {
1057             int n = v1.length;
1058             for (int i = 0; i < n; i++) {
1059                 if (v1[i] != v2[i]) {
1060                     return false;
1061                 }
1062             }
1063         } else {
1064             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1065                 return false;
1066             }
1067             return StringUTF16.contentEquals(v1, v2, len);
1068         }
1069         return true;
1070     }
1071 
1072     /**
1073      * Compares this string to the specified {@code CharSequence}.  The
1074      * result is {@code true} if and only if this {@code String} represents the
1075      * same sequence of char values as the specified sequence. Note that if the
1076      * {@code CharSequence} is a {@code StringBuffer} then the method
1077      * synchronizes on it.
1078      *
1079      * <p>For finer-grained String comparison, refer to
1080      * {@link java.text.Collator}.
1081      *
1082      * @param  cs
1083      *         The sequence to compare this {@code String} against
1084      *
1085      * @return  {@code true} if this {@code String} represents the same
1086      *          sequence of char values as the specified sequence, {@code
1087      *          false} otherwise
1088      *
1089      * @since  1.5
1090      */
1091     public boolean contentEquals(CharSequence cs) {
1092         // Argument is a StringBuffer, StringBuilder
1093         if (cs instanceof AbstractStringBuilder) {
1094             if (cs instanceof StringBuffer) {
1095                 synchronized(cs) {
1096                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1097                 }
1098             } else {
1099                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1100             }
1101         }
1102         // Argument is a String
1103         if (cs instanceof String) {
1104             return equals(cs);
1105         }
1106         // Argument is a generic CharSequence
1107         int n = cs.length();
1108         if (n != length()) {
1109             return false;
1110         }
1111         byte[] val = this.value;
1112         if (isLatin1()) {
1113             for (int i = 0; i < n; i++) {
1114                 if ((val[i] & 0xff) != cs.charAt(i)) {
1115                     return false;
1116                 }
1117             }
1118         } else {
1119             if (!StringUTF16.contentEquals(val, cs, n)) {
1120                 return false;
1121             }
1122         }
1123         return true;
1124     }
1125 
1126     /**
1127      * Compares this {@code String} to another {@code String}, ignoring case
1128      * considerations.  Two strings are considered equal ignoring case if they
1129      * are of the same length and corresponding characters in the two strings
1130      * are equal ignoring case.
1131      *
1132      * <p> Two characters {@code c1} and {@code c2} are considered the same
1133      * ignoring case if at least one of the following is true:
1134      * <ul>
1135      *   <li> The two characters are the same (as compared by the
1136      *        {@code ==} operator)
1137      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1138      *        on each character produces the same result
1139      * </ul>
1140      *
1141      * <p>Note that this method does <em>not</em> take locale into account, and
1142      * will result in unsatisfactory results for certain locales.  The
1143      * {@link java.text.Collator} class provides locale-sensitive comparison.
1144      *
1145      * @param  anotherString
1146      *         The {@code String} to compare this {@code String} against
1147      *
1148      * @return  {@code true} if the argument is not {@code null} and it
1149      *          represents an equivalent {@code String} ignoring case; {@code
1150      *          false} otherwise
1151      *
1152      * @see  #equals(Object)
1153      */
1154     public boolean equalsIgnoreCase(String anotherString) {
1155         return (this == anotherString) ? true
1156                 : (anotherString != null)
1157                 && (anotherString.length() == length())
1158                 && regionMatches(true, 0, anotherString, 0, length());
1159     }
1160 
1161     /**
1162      * Compares two strings lexicographically.
1163      * The comparison is based on the Unicode value of each character in
1164      * the strings. The character sequence represented by this
1165      * {@code String} object is compared lexicographically to the
1166      * character sequence represented by the argument string. The result is
1167      * a negative integer if this {@code String} object
1168      * lexicographically precedes the argument string. The result is a
1169      * positive integer if this {@code String} object lexicographically
1170      * follows the argument string. The result is zero if the strings
1171      * are equal; {@code compareTo} returns {@code 0} exactly when
1172      * the {@link #equals(Object)} method would return {@code true}.
1173      * <p>
1174      * This is the definition of lexicographic ordering. If two strings are
1175      * different, then either they have different characters at some index
1176      * that is a valid index for both strings, or their lengths are different,
1177      * or both. If they have different characters at one or more index
1178      * positions, let <i>k</i> be the smallest such index; then the string
1179      * whose character at position <i>k</i> has the smaller value, as
1180      * determined by using the {@code <} operator, lexicographically precedes the
1181      * other string. In this case, {@code compareTo} returns the
1182      * difference of the two character values at position {@code k} in
1183      * the two string -- that is, the value:
1184      * <blockquote><pre>
1185      * this.charAt(k)-anotherString.charAt(k)
1186      * </pre></blockquote>
1187      * If there is no index position at which they differ, then the shorter
1188      * string lexicographically precedes the longer string. In this case,
1189      * {@code compareTo} returns the difference of the lengths of the
1190      * strings -- that is, the value:
1191      * <blockquote><pre>
1192      * this.length()-anotherString.length()
1193      * </pre></blockquote>
1194      *
1195      * <p>For finer-grained String comparison, refer to
1196      * {@link java.text.Collator}.
1197      *
1198      * @param   anotherString   the {@code String} to be compared.
1199      * @return  the value {@code 0} if the argument string is equal to
1200      *          this string; a value less than {@code 0} if this string
1201      *          is lexicographically less than the string argument; and a
1202      *          value greater than {@code 0} if this string is
1203      *          lexicographically greater than the string argument.
1204      */
1205     public int compareTo(String anotherString) {
1206         byte v1[] = value;
1207         byte v2[] = anotherString.value;
1208         if (coder() == anotherString.coder()) {
1209             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1210                               : StringUTF16.compareTo(v1, v2);
1211         }
1212         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1213                           : StringUTF16.compareToLatin1(v1, v2);
1214      }
1215 
1216     /**
1217      * A Comparator that orders {@code String} objects as by
1218      * {@code compareToIgnoreCase}. This comparator is serializable.
1219      * <p>
1220      * Note that this Comparator does <em>not</em> take locale into account,
1221      * and will result in an unsatisfactory ordering for certain locales.
1222      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1223      *
1224      * @see     java.text.Collator
1225      * @since   1.2
1226      */
1227     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1228                                          = new CaseInsensitiveComparator();
1229     private static class CaseInsensitiveComparator
1230             implements Comparator<String>, java.io.Serializable {
1231         // use serialVersionUID from JDK 1.2.2 for interoperability
1232         private static final long serialVersionUID = 8575799808933029326L;
1233 
1234         public int compare(String s1, String s2) {
1235             byte v1[] = s1.value;
1236             byte v2[] = s2.value;
1237             if (s1.coder() == s2.coder()) {
1238                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1239                                      : StringUTF16.compareToCI(v1, v2);
1240             }
1241             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1242                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1243         }
1244 
1245         /** Replaces the de-serialized object. */
1246         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1247     }
1248 
1249     /**
1250      * Compares two strings lexicographically, ignoring case
1251      * differences. This method returns an integer whose sign is that of
1252      * calling {@code compareTo} with normalized versions of the strings
1253      * where case differences have been eliminated by calling
1254      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1255      * each character.
1256      * <p>
1257      * Note that this method does <em>not</em> take locale into account,
1258      * and will result in an unsatisfactory ordering for certain locales.
1259      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1260      *
1261      * @param   str   the {@code String} to be compared.
1262      * @return  a negative integer, zero, or a positive integer as the
1263      *          specified String is greater than, equal to, or less
1264      *          than this String, ignoring case considerations.
1265      * @see     java.text.Collator
1266      * @since   1.2
1267      */
1268     public int compareToIgnoreCase(String str) {
1269         return CASE_INSENSITIVE_ORDER.compare(this, str);
1270     }
1271 
1272     /**
1273      * Tests if two string regions are equal.
1274      * <p>
1275      * A substring of this {@code String} object is compared to a substring
1276      * of the argument other. The result is true if these substrings
1277      * represent identical character sequences. The substring of this
1278      * {@code String} object to be compared begins at index {@code toffset}
1279      * and has length {@code len}. The substring of other to be compared
1280      * begins at index {@code ooffset} and has length {@code len}. The
1281      * result is {@code false} if and only if at least one of the following
1282      * is true:
1283      * <ul><li>{@code toffset} is negative.
1284      * <li>{@code ooffset} is negative.
1285      * <li>{@code toffset+len} is greater than the length of this
1286      * {@code String} object.
1287      * <li>{@code ooffset+len} is greater than the length of the other
1288      * argument.
1289      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1290      * such that:
1291      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1292      * <i>k</i>{@code )}
1293      * </ul>
1294      *
1295      * <p>Note that this method does <em>not</em> take locale into account.  The
1296      * {@link java.text.Collator} class provides locale-sensitive comparison.
1297      *
1298      * @param   toffset   the starting offset of the subregion in this string.
1299      * @param   other     the string argument.
1300      * @param   ooffset   the starting offset of the subregion in the string
1301      *                    argument.
1302      * @param   len       the number of characters to compare.
1303      * @return  {@code true} if the specified subregion of this string
1304      *          exactly matches the specified subregion of the string argument;
1305      *          {@code false} otherwise.
1306      */
1307     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1308         byte tv[] = value;
1309         byte ov[] = other.value;
1310         // Note: toffset, ooffset, or len might be near -1>>>1.
1311         if ((ooffset < 0) || (toffset < 0) ||
1312              (toffset > (long)length() - len) ||
1313              (ooffset > (long)other.length() - len)) {
1314             return false;
1315         }
1316         if (coder() == other.coder()) {
1317             if (!isLatin1() && (len > 0)) {
1318                 toffset = toffset << 1;
1319                 ooffset = ooffset << 1;
1320                 len = len << 1;
1321             }
1322             while (len-- > 0) {
1323                 if (tv[toffset++] != ov[ooffset++]) {
1324                     return false;
1325                 }
1326             }
1327         } else {
1328             if (coder() == LATIN1) {
1329                 while (len-- > 0) {
1330                     if (StringLatin1.getChar(tv, toffset++) !=
1331                         StringUTF16.getChar(ov, ooffset++)) {
1332                         return false;
1333                     }
1334                 }
1335             } else {
1336                 while (len-- > 0) {
1337                     if (StringUTF16.getChar(tv, toffset++) !=
1338                         StringLatin1.getChar(ov, ooffset++)) {
1339                         return false;
1340                     }
1341                 }
1342             }
1343         }
1344         return true;
1345     }
1346 
1347     /**
1348      * Tests if two string regions are equal.
1349      * <p>
1350      * A substring of this {@code String} object is compared to a substring
1351      * of the argument {@code other}. The result is {@code true} if these
1352      * substrings represent character sequences that are the same, ignoring
1353      * case if and only if {@code ignoreCase} is true. The substring of
1354      * this {@code String} object to be compared begins at index
1355      * {@code toffset} and has length {@code len}. The substring of
1356      * {@code other} to be compared begins at index {@code ooffset} and
1357      * has length {@code len}. The result is {@code false} if and only if
1358      * at least one of the following is true:
1359      * <ul><li>{@code toffset} is negative.
1360      * <li>{@code ooffset} is negative.
1361      * <li>{@code toffset+len} is greater than the length of this
1362      * {@code String} object.
1363      * <li>{@code ooffset+len} is greater than the length of the other
1364      * argument.
1365      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1366      * integer <i>k</i> less than {@code len} such that:
1367      * <blockquote><pre>
1368      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1369      * </pre></blockquote>
1370      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1371      * integer <i>k</i> less than {@code len} such that:
1372      * <blockquote><pre>
1373      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1374      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1375      * </pre></blockquote>
1376      * </ul>
1377      *
1378      * <p>Note that this method does <em>not</em> take locale into account,
1379      * and will result in unsatisfactory results for certain locales when
1380      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1381      * provides locale-sensitive comparison.
1382      *
1383      * @param   ignoreCase   if {@code true}, ignore case when comparing
1384      *                       characters.
1385      * @param   toffset      the starting offset of the subregion in this
1386      *                       string.
1387      * @param   other        the string argument.
1388      * @param   ooffset      the starting offset of the subregion in the string
1389      *                       argument.
1390      * @param   len          the number of characters to compare.
1391      * @return  {@code true} if the specified subregion of this string
1392      *          matches the specified subregion of the string argument;
1393      *          {@code false} otherwise. Whether the matching is exact
1394      *          or case insensitive depends on the {@code ignoreCase}
1395      *          argument.
1396      */
1397     public boolean regionMatches(boolean ignoreCase, int toffset,
1398             String other, int ooffset, int len) {
1399         if (!ignoreCase) {
1400             return regionMatches(toffset, other, ooffset, len);
1401         }
1402         // Note: toffset, ooffset, or len might be near -1>>>1.
1403         if ((ooffset < 0) || (toffset < 0)
1404                 || (toffset > (long)length() - len)
1405                 || (ooffset > (long)other.length() - len)) {
1406             return false;
1407         }
1408         byte tv[] = value;
1409         byte ov[] = other.value;
1410         if (coder() == other.coder()) {
1411             return isLatin1()
1412               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1413               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1414         }
1415         return isLatin1()
1416               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1417               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1418     }
1419 
1420     /**
1421      * Tests if the substring of this string beginning at the
1422      * specified index starts with the specified prefix.
1423      *
1424      * @param   prefix    the prefix.
1425      * @param   toffset   where to begin looking in this string.
1426      * @return  {@code true} if the character sequence represented by the
1427      *          argument is a prefix of the substring of this object starting
1428      *          at index {@code toffset}; {@code false} otherwise.
1429      *          The result is {@code false} if {@code toffset} is
1430      *          negative or greater than the length of this
1431      *          {@code String} object; otherwise the result is the same
1432      *          as the result of the expression
1433      *          <pre>
1434      *          this.substring(toffset).startsWith(prefix)
1435      *          </pre>
1436      */
1437     public boolean startsWith(String prefix, int toffset) {
1438         // Note: toffset might be near -1>>>1.
1439         if (toffset < 0 || toffset > length() - prefix.length()) {
1440             return false;
1441         }
1442         byte ta[] = value;
1443         byte pa[] = prefix.value;
1444         int po = 0;
1445         int pc = pa.length;
1446         if (coder() == prefix.coder()) {
1447             int to = isLatin1() ? toffset : toffset << 1;
1448             while (po < pc) {
1449                 if (ta[to++] != pa[po++]) {
1450                     return false;
1451                 }
1452             }
1453         } else {
1454             if (isLatin1()) {  // && pcoder == UTF16
1455                 return false;
1456             }
1457             // coder == UTF16 && pcoder == LATIN1)
1458             while (po < pc) {
1459                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1460                     return false;
1461                }
1462             }
1463         }
1464         return true;
1465     }
1466 
1467     /**
1468      * Tests if this string starts with the specified prefix.
1469      *
1470      * @param   prefix   the prefix.
1471      * @return  {@code true} if the character sequence represented by the
1472      *          argument is a prefix of the character sequence represented by
1473      *          this string; {@code false} otherwise.
1474      *          Note also that {@code true} will be returned if the
1475      *          argument is an empty string or is equal to this
1476      *          {@code String} object as determined by the
1477      *          {@link #equals(Object)} method.
1478      * @since   1.0
1479      */
1480     public boolean startsWith(String prefix) {
1481         return startsWith(prefix, 0);
1482     }
1483 
1484     /**
1485      * Tests if this string ends with the specified suffix.
1486      *
1487      * @param   suffix   the suffix.
1488      * @return  {@code true} if the character sequence represented by the
1489      *          argument is a suffix of the character sequence represented by
1490      *          this object; {@code false} otherwise. Note that the
1491      *          result will be {@code true} if the argument is the
1492      *          empty string or is equal to this {@code String} object
1493      *          as determined by the {@link #equals(Object)} method.
1494      */
1495     public boolean endsWith(String suffix) {
1496         return startsWith(suffix, length() - suffix.length());
1497     }
1498 
1499     /**
1500      * Returns a hash code for this string. The hash code for a
1501      * {@code String} object is computed as
1502      * <blockquote><pre>
1503      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1504      * </pre></blockquote>
1505      * using {@code int} arithmetic, where {@code s[i]} is the
1506      * <i>i</i>th character of the string, {@code n} is the length of
1507      * the string, and {@code ^} indicates exponentiation.
1508      * (The hash value of the empty string is zero.)
1509      *
1510      * @return  a hash code value for this object.
1511      */
1512     public int hashCode() {
1513         int h = hash;
1514         if (h == 0 && value.length > 0) {
1515             hash = h = isLatin1() ? StringLatin1.hashCode(value)
1516                                   : StringUTF16.hashCode(value);
1517         }
1518         return h;
1519     }
1520 
1521     /**
1522      * Returns the index within this string of the first occurrence of
1523      * the specified character. If a character with value
1524      * {@code ch} occurs in the character sequence represented by
1525      * this {@code String} object, then the index (in Unicode
1526      * code units) of the first such occurrence is returned. For
1527      * values of {@code ch} in the range from 0 to 0xFFFF
1528      * (inclusive), this is the smallest value <i>k</i> such that:
1529      * <blockquote><pre>
1530      * this.charAt(<i>k</i>) == ch
1531      * </pre></blockquote>
1532      * is true. For other values of {@code ch}, it is the
1533      * smallest value <i>k</i> such that:
1534      * <blockquote><pre>
1535      * this.codePointAt(<i>k</i>) == ch
1536      * </pre></blockquote>
1537      * is true. In either case, if no such character occurs in this
1538      * string, then {@code -1} is returned.
1539      *
1540      * @param   ch   a character (Unicode code point).
1541      * @return  the index of the first occurrence of the character in the
1542      *          character sequence represented by this object, or
1543      *          {@code -1} if the character does not occur.
1544      */
1545     public int indexOf(int ch) {
1546         return indexOf(ch, 0);
1547     }
1548 
1549     /**
1550      * Returns the index within this string of the first occurrence of the
1551      * specified character, starting the search at the specified index.
1552      * <p>
1553      * If a character with value {@code ch} occurs in the
1554      * character sequence represented by this {@code String}
1555      * object at an index no smaller than {@code fromIndex}, then
1556      * the index of the first such occurrence is returned. For values
1557      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1558      * this is the smallest value <i>k</i> such that:
1559      * <blockquote><pre>
1560      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1561      * </pre></blockquote>
1562      * is true. For other values of {@code ch}, it is the
1563      * smallest value <i>k</i> such that:
1564      * <blockquote><pre>
1565      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1566      * </pre></blockquote>
1567      * is true. In either case, if no such character occurs in this
1568      * string at or after position {@code fromIndex}, then
1569      * {@code -1} is returned.
1570      *
1571      * <p>
1572      * There is no restriction on the value of {@code fromIndex}. If it
1573      * is negative, it has the same effect as if it were zero: this entire
1574      * string may be searched. If it is greater than the length of this
1575      * string, it has the same effect as if it were equal to the length of
1576      * this string: {@code -1} is returned.
1577      *
1578      * <p>All indices are specified in {@code char} values
1579      * (Unicode code units).
1580      *
1581      * @param   ch          a character (Unicode code point).
1582      * @param   fromIndex   the index to start the search from.
1583      * @return  the index of the first occurrence of the character in the
1584      *          character sequence represented by this object that is greater
1585      *          than or equal to {@code fromIndex}, or {@code -1}
1586      *          if the character does not occur.
1587      */
1588     public int indexOf(int ch, int fromIndex) {
1589         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1590                           : StringUTF16.indexOf(value, ch, fromIndex);
1591     }
1592 
1593     /**
1594      * Returns the index within this string of the last occurrence of
1595      * the specified character. For values of {@code ch} in the
1596      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1597      * units) returned is the largest value <i>k</i> such that:
1598      * <blockquote><pre>
1599      * this.charAt(<i>k</i>) == ch
1600      * </pre></blockquote>
1601      * is true. For other values of {@code ch}, it is the
1602      * largest value <i>k</i> such that:
1603      * <blockquote><pre>
1604      * this.codePointAt(<i>k</i>) == ch
1605      * </pre></blockquote>
1606      * is true.  In either case, if no such character occurs in this
1607      * string, then {@code -1} is returned.  The
1608      * {@code String} is searched backwards starting at the last
1609      * character.
1610      *
1611      * @param   ch   a character (Unicode code point).
1612      * @return  the index of the last occurrence of the character in the
1613      *          character sequence represented by this object, or
1614      *          {@code -1} if the character does not occur.
1615      */
1616     public int lastIndexOf(int ch) {
1617         return lastIndexOf(ch, length() - 1);
1618     }
1619 
1620     /**
1621      * Returns the index within this string of the last occurrence of
1622      * the specified character, searching backward starting at the
1623      * specified index. For values of {@code ch} in the range
1624      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1625      * value <i>k</i> such that:
1626      * <blockquote><pre>
1627      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1628      * </pre></blockquote>
1629      * is true. For other values of {@code ch}, it is the
1630      * largest value <i>k</i> such that:
1631      * <blockquote><pre>
1632      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1633      * </pre></blockquote>
1634      * is true. In either case, if no such character occurs in this
1635      * string at or before position {@code fromIndex}, then
1636      * {@code -1} is returned.
1637      *
1638      * <p>All indices are specified in {@code char} values
1639      * (Unicode code units).
1640      *
1641      * @param   ch          a character (Unicode code point).
1642      * @param   fromIndex   the index to start the search from. There is no
1643      *          restriction on the value of {@code fromIndex}. If it is
1644      *          greater than or equal to the length of this string, it has
1645      *          the same effect as if it were equal to one less than the
1646      *          length of this string: this entire string may be searched.
1647      *          If it is negative, it has the same effect as if it were -1:
1648      *          -1 is returned.
1649      * @return  the index of the last occurrence of the character in the
1650      *          character sequence represented by this object that is less
1651      *          than or equal to {@code fromIndex}, or {@code -1}
1652      *          if the character does not occur before that point.
1653      */
1654     public int lastIndexOf(int ch, int fromIndex) {
1655         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1656                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1657     }
1658 
1659     /**
1660      * Returns the index within this string of the first occurrence of the
1661      * specified substring.
1662      *
1663      * <p>The returned index is the smallest value {@code k} for which:
1664      * <pre>{@code
1665      * this.startsWith(str, k)
1666      * }</pre>
1667      * If no such value of {@code k} exists, then {@code -1} is returned.
1668      *
1669      * @param   str   the substring to search for.
1670      * @return  the index of the first occurrence of the specified substring,
1671      *          or {@code -1} if there is no such occurrence.
1672      */
1673     public int indexOf(String str) {
1674         if (coder() == str.coder()) {
1675             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1676                               : StringUTF16.indexOf(value, str.value);
1677         }
1678         if (coder() == LATIN1) {  // str.coder == UTF16
1679             return -1;
1680         }
1681         return StringUTF16.indexOfLatin1(value, str.value);
1682     }
1683 
1684     /**
1685      * Returns the index within this string of the first occurrence of the
1686      * specified substring, starting at the specified index.
1687      *
1688      * <p>The returned index is the smallest value {@code k} for which:
1689      * <pre>{@code
1690      *     k >= Math.min(fromIndex, this.length()) &&
1691      *                   this.startsWith(str, k)
1692      * }</pre>
1693      * If no such value of {@code k} exists, then {@code -1} is returned.
1694      *
1695      * @param   str         the substring to search for.
1696      * @param   fromIndex   the index from which to start the search.
1697      * @return  the index of the first occurrence of the specified substring,
1698      *          starting at the specified index,
1699      *          or {@code -1} if there is no such occurrence.
1700      */
1701     public int indexOf(String str, int fromIndex) {
1702         return indexOf(value, coder(), length(), str, fromIndex);
1703     }
1704 
1705     /**
1706      * Code shared by String and AbstractStringBuilder to do searches. The
1707      * source is the character array being searched, and the target
1708      * is the string being searched for.
1709      *
1710      * @param   src       the characters being searched.
1711      * @param   srcCoder  the coder of the source string.
1712      * @param   srcCount  length of the source string.
1713      * @param   tgtStr    the characters being searched for.
1714      * @param   fromIndex the index to begin searching from.
1715      */
1716     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1717                        String tgtStr, int fromIndex) {
1718         byte[] tgt    = tgtStr.value;
1719         byte tgtCoder = tgtStr.coder();
1720         int tgtCount  = tgtStr.length();
1721 
1722         if (fromIndex >= srcCount) {
1723             return (tgtCount == 0 ? srcCount : -1);
1724         }
1725         if (fromIndex < 0) {
1726             fromIndex = 0;
1727         }
1728         if (tgtCount == 0) {
1729             return fromIndex;
1730         }
1731         if (tgtCount > srcCount) {
1732             return -1;
1733         }
1734         if (srcCoder == tgtCoder) {
1735             return srcCoder == LATIN1
1736                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1737                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1738         }
1739         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1740             return -1;
1741         }
1742         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1743         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1744     }
1745 
1746     /**
1747      * Returns the index within this string of the last occurrence of the
1748      * specified substring.  The last occurrence of the empty string ""
1749      * is considered to occur at the index value {@code this.length()}.
1750      *
1751      * <p>The returned index is the largest value {@code k} for which:
1752      * <pre>{@code
1753      * this.startsWith(str, k)
1754      * }</pre>
1755      * If no such value of {@code k} exists, then {@code -1} is returned.
1756      *
1757      * @param   str   the substring to search for.
1758      * @return  the index of the last occurrence of the specified substring,
1759      *          or {@code -1} if there is no such occurrence.
1760      */
1761     public int lastIndexOf(String str) {
1762         return lastIndexOf(str, length());
1763     }
1764 
1765     /**
1766      * Returns the index within this string of the last occurrence of the
1767      * specified substring, searching backward starting at the specified index.
1768      *
1769      * <p>The returned index is the largest value {@code k} for which:
1770      * <pre>{@code
1771      *     k <= Math.min(fromIndex, this.length()) &&
1772      *                   this.startsWith(str, k)
1773      * }</pre>
1774      * If no such value of {@code k} exists, then {@code -1} is returned.
1775      *
1776      * @param   str         the substring to search for.
1777      * @param   fromIndex   the index to start the search from.
1778      * @return  the index of the last occurrence of the specified substring,
1779      *          searching backward from the specified index,
1780      *          or {@code -1} if there is no such occurrence.
1781      */
1782     public int lastIndexOf(String str, int fromIndex) {
1783         return lastIndexOf(value, coder(), length(), str, fromIndex);
1784     }
1785 
1786     /**
1787      * Code shared by String and AbstractStringBuilder to do searches. The
1788      * source is the character array being searched, and the target
1789      * is the string being searched for.
1790      *
1791      * @param   src         the characters being searched.
1792      * @param   srcCoder    coder handles the mapping between bytes/chars
1793      * @param   srcCount    count of the source string.
1794      * @param   tgt         the characters being searched for.
1795      * @param   fromIndex   the index to begin searching from.
1796      */
1797     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1798                            String tgtStr, int fromIndex) {
1799         byte[] tgt = tgtStr.value;
1800         byte tgtCoder = tgtStr.coder();
1801         int tgtCount = tgtStr.length();
1802         /*
1803          * Check arguments; return immediately where possible. For
1804          * consistency, don't check for null str.
1805          */
1806         int rightIndex = srcCount - tgtCount;
1807         if (fromIndex > rightIndex) {
1808             fromIndex = rightIndex;
1809         }
1810         if (fromIndex < 0) {
1811             return -1;
1812         }
1813         /* Empty string always matches. */
1814         if (tgtCount == 0) {
1815             return fromIndex;
1816         }
1817         if (srcCoder == tgtCoder) {
1818             return srcCoder == LATIN1
1819                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1820                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1821         }
1822         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1823             return -1;
1824         }
1825         // srcCoder == UTF16 && tgtCoder == LATIN1
1826         return StringUTF16.lastIndexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1827     }
1828 
1829     /**
1830      * Returns a string that is a substring of this string. The
1831      * substring begins with the character at the specified index and
1832      * extends to the end of this string. <p>
1833      * Examples:
1834      * <blockquote><pre>
1835      * "unhappy".substring(2) returns "happy"
1836      * "Harbison".substring(3) returns "bison"
1837      * "emptiness".substring(9) returns "" (an empty string)
1838      * </pre></blockquote>
1839      *
1840      * @param      beginIndex   the beginning index, inclusive.
1841      * @return     the specified substring.
1842      * @exception  IndexOutOfBoundsException  if
1843      *             {@code beginIndex} is negative or larger than the
1844      *             length of this {@code String} object.
1845      */
1846     public String substring(int beginIndex) {
1847         if (beginIndex < 0) {
1848             throw new StringIndexOutOfBoundsException(beginIndex);
1849         }
1850         int subLen = length() - beginIndex;
1851         if (subLen < 0) {
1852             throw new StringIndexOutOfBoundsException(subLen);
1853         }
1854         if (beginIndex == 0) {
1855             return this;
1856         }
1857         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1858                           : StringUTF16.newString(value, beginIndex, subLen);
1859     }
1860 
1861     /**
1862      * Returns a string that is a substring of this string. The
1863      * substring begins at the specified {@code beginIndex} and
1864      * extends to the character at index {@code endIndex - 1}.
1865      * Thus the length of the substring is {@code endIndex-beginIndex}.
1866      * <p>
1867      * Examples:
1868      * <blockquote><pre>
1869      * "hamburger".substring(4, 8) returns "urge"
1870      * "smiles".substring(1, 5) returns "mile"
1871      * </pre></blockquote>
1872      *
1873      * @param      beginIndex   the beginning index, inclusive.
1874      * @param      endIndex     the ending index, exclusive.
1875      * @return     the specified substring.
1876      * @exception  IndexOutOfBoundsException  if the
1877      *             {@code beginIndex} is negative, or
1878      *             {@code endIndex} is larger than the length of
1879      *             this {@code String} object, or
1880      *             {@code beginIndex} is larger than
1881      *             {@code endIndex}.
1882      */
1883     public String substring(int beginIndex, int endIndex) {
1884         int length = length();
1885         checkBoundsBeginEnd(beginIndex, endIndex, length);
1886         int subLen = endIndex - beginIndex;
1887         if (beginIndex == 0 && endIndex == length) {
1888             return this;
1889         }
1890         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1891                           : StringUTF16.newString(value, beginIndex, subLen);
1892     }
1893 
1894     /**
1895      * Returns a character sequence that is a subsequence of this sequence.
1896      *
1897      * <p> An invocation of this method of the form
1898      *
1899      * <blockquote><pre>
1900      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1901      *
1902      * behaves in exactly the same way as the invocation
1903      *
1904      * <blockquote><pre>
1905      * str.substring(begin,&nbsp;end)</pre></blockquote>
1906      *
1907      * @apiNote
1908      * This method is defined so that the {@code String} class can implement
1909      * the {@link CharSequence} interface.
1910      *
1911      * @param   beginIndex   the begin index, inclusive.
1912      * @param   endIndex     the end index, exclusive.
1913      * @return  the specified subsequence.
1914      *
1915      * @throws  IndexOutOfBoundsException
1916      *          if {@code beginIndex} or {@code endIndex} is negative,
1917      *          if {@code endIndex} is greater than {@code length()},
1918      *          or if {@code beginIndex} is greater than {@code endIndex}
1919      *
1920      * @since 1.4
1921      * @spec JSR-51
1922      */
1923     public CharSequence subSequence(int beginIndex, int endIndex) {
1924         return this.substring(beginIndex, endIndex);
1925     }
1926 
1927     /**
1928      * Concatenates the specified string to the end of this string.
1929      * <p>
1930      * If the length of the argument string is {@code 0}, then this
1931      * {@code String} object is returned. Otherwise, a
1932      * {@code String} object is returned that represents a character
1933      * sequence that is the concatenation of the character sequence
1934      * represented by this {@code String} object and the character
1935      * sequence represented by the argument string.<p>
1936      * Examples:
1937      * <blockquote><pre>
1938      * "cares".concat("s") returns "caress"
1939      * "to".concat("get").concat("her") returns "together"
1940      * </pre></blockquote>
1941      *
1942      * @param   str   the {@code String} that is concatenated to the end
1943      *                of this {@code String}.
1944      * @return  a string that represents the concatenation of this object's
1945      *          characters followed by the string argument's characters.
1946      */
1947     public String concat(String str) {
1948         int olen = str.length();
1949         if (olen == 0) {
1950             return this;
1951         }
1952         if (coder() == str.coder()) {
1953             byte[] val = this.value;
1954             byte[] oval = str.value;
1955             int len = val.length + oval.length;
1956             byte[] buf = Arrays.copyOf(val, len);
1957             System.arraycopy(oval, 0, buf, val.length, oval.length);
1958             return new String(buf, coder);
1959         }
1960         int len = length();
1961         byte[] buf = StringUTF16.newBytesFor(len + olen);
1962         getBytes(buf, 0, UTF16);
1963         str.getBytes(buf, len, UTF16);
1964         return new String(buf, UTF16);
1965     }
1966 
1967     /**
1968      * Returns a string resulting from replacing all occurrences of
1969      * {@code oldChar} in this string with {@code newChar}.
1970      * <p>
1971      * If the character {@code oldChar} does not occur in the
1972      * character sequence represented by this {@code String} object,
1973      * then a reference to this {@code String} object is returned.
1974      * Otherwise, a {@code String} object is returned that
1975      * represents a character sequence identical to the character sequence
1976      * represented by this {@code String} object, except that every
1977      * occurrence of {@code oldChar} is replaced by an occurrence
1978      * of {@code newChar}.
1979      * <p>
1980      * Examples:
1981      * <blockquote><pre>
1982      * "mesquite in your cellar".replace('e', 'o')
1983      *         returns "mosquito in your collar"
1984      * "the war of baronets".replace('r', 'y')
1985      *         returns "the way of bayonets"
1986      * "sparring with a purple porpoise".replace('p', 't')
1987      *         returns "starring with a turtle tortoise"
1988      * "JonL".replace('q', 'x') returns "JonL" (no change)
1989      * </pre></blockquote>
1990      *
1991      * @param   oldChar   the old character.
1992      * @param   newChar   the new character.
1993      * @return  a string derived from this string by replacing every
1994      *          occurrence of {@code oldChar} with {@code newChar}.
1995      */
1996     public String replace(char oldChar, char newChar) {
1997         if (oldChar != newChar) {
1998             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
1999                                     : StringUTF16.replace(value, oldChar, newChar);
2000             if (ret != null) {
2001                 return ret;
2002             }
2003         }
2004         return this;
2005     }
2006 
2007     /**
2008      * Tells whether or not this string matches the given <a
2009      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2010      *
2011      * <p> An invocation of this method of the form
2012      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2013      * same result as the expression
2014      *
2015      * <blockquote>
2016      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2017      * matches(<i>regex</i>, <i>str</i>)}
2018      * </blockquote>
2019      *
2020      * @param   regex
2021      *          the regular expression to which this string is to be matched
2022      *
2023      * @return  {@code true} if, and only if, this string matches the
2024      *          given regular expression
2025      *
2026      * @throws  PatternSyntaxException
2027      *          if the regular expression's syntax is invalid
2028      *
2029      * @see java.util.regex.Pattern
2030      *
2031      * @since 1.4
2032      * @spec JSR-51
2033      */
2034     public boolean matches(String regex) {
2035         return Pattern.matches(regex, this);
2036     }
2037 
2038     /**
2039      * Returns true if and only if this string contains the specified
2040      * sequence of char values.
2041      *
2042      * @param s the sequence to search for
2043      * @return true if this string contains {@code s}, false otherwise
2044      * @since 1.5
2045      */
2046     public boolean contains(CharSequence s) {
2047         return indexOf(s.toString()) >= 0;
2048     }
2049 
2050     /**
2051      * Replaces the first substring of this string that matches the given <a
2052      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2053      * given replacement.
2054      *
2055      * <p> An invocation of this method of the form
2056      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2057      * yields exactly the same result as the expression
2058      *
2059      * <blockquote>
2060      * <code>
2061      * {@link java.util.regex.Pattern}.{@link
2062      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2063      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2064      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2065      * </code>
2066      * </blockquote>
2067      *
2068      *<p>
2069      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2070      * replacement string may cause the results to be different than if it were
2071      * being treated as a literal replacement string; see
2072      * {@link java.util.regex.Matcher#replaceFirst}.
2073      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2074      * meaning of these characters, if desired.
2075      *
2076      * @param   regex
2077      *          the regular expression to which this string is to be matched
2078      * @param   replacement
2079      *          the string to be substituted for the first match
2080      *
2081      * @return  The resulting {@code String}
2082      *
2083      * @throws  PatternSyntaxException
2084      *          if the regular expression's syntax is invalid
2085      *
2086      * @see java.util.regex.Pattern
2087      *
2088      * @since 1.4
2089      * @spec JSR-51
2090      */
2091     public String replaceFirst(String regex, String replacement) {
2092         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2093     }
2094 
2095     /**
2096      * Replaces each substring of this string that matches the given <a
2097      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2098      * given replacement.
2099      *
2100      * <p> An invocation of this method of the form
2101      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2102      * yields exactly the same result as the expression
2103      *
2104      * <blockquote>
2105      * <code>
2106      * {@link java.util.regex.Pattern}.{@link
2107      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2108      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2109      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2110      * </code>
2111      * </blockquote>
2112      *
2113      *<p>
2114      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2115      * replacement string may cause the results to be different than if it were
2116      * being treated as a literal replacement string; see
2117      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2118      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2119      * meaning of these characters, if desired.
2120      *
2121      * @param   regex
2122      *          the regular expression to which this string is to be matched
2123      * @param   replacement
2124      *          the string to be substituted for each match
2125      *
2126      * @return  The resulting {@code String}
2127      *
2128      * @throws  PatternSyntaxException
2129      *          if the regular expression's syntax is invalid
2130      *
2131      * @see java.util.regex.Pattern
2132      *
2133      * @since 1.4
2134      * @spec JSR-51
2135      */
2136     public String replaceAll(String regex, String replacement) {
2137         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2138     }
2139 
2140     /**
2141      * Replaces each substring of this string that matches the literal target
2142      * sequence with the specified literal replacement sequence. The
2143      * replacement proceeds from the beginning of the string to the end, for
2144      * example, replacing "aa" with "b" in the string "aaa" will result in
2145      * "ba" rather than "ab".
2146      *
2147      * @param  target The sequence of char values to be replaced
2148      * @param  replacement The replacement sequence of char values
2149      * @return  The resulting string
2150      * @since 1.5
2151      */
2152     public String replace(CharSequence target, CharSequence replacement) {
2153         String tgtStr = target.toString();
2154         String replStr = replacement.toString();
2155         int j = indexOf(tgtStr);
2156         if (j < 0) {
2157             return this;
2158         }
2159         int tgtLen = tgtStr.length();
2160         int tgtLen1 = Math.max(tgtLen, 1);
2161         int thisLen = length();
2162 
2163         int newLenHint = thisLen - tgtLen + replStr.length();
2164         if (newLenHint < 0) {
2165             throw new OutOfMemoryError();
2166         }
2167         StringBuilder sb = new StringBuilder(newLenHint);
2168         int i = 0;
2169         do {
2170             sb.append(this, i, j).append(replStr);
2171             i = j + tgtLen;
2172         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2173         return sb.append(this, i, thisLen).toString();
2174     }
2175 
2176     /**
2177      * Splits this string around matches of the given
2178      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2179      *
2180      * <p> The array returned by this method contains each substring of this
2181      * string that is terminated by another substring that matches the given
2182      * expression or is terminated by the end of the string.  The substrings in
2183      * the array are in the order in which they occur in this string.  If the
2184      * expression does not match any part of the input then the resulting array
2185      * has just one element, namely this string.
2186      *
2187      * <p> When there is a positive-width match at the beginning of this
2188      * string then an empty leading substring is included at the beginning
2189      * of the resulting array. A zero-width match at the beginning however
2190      * never produces such empty leading substring.
2191      *
2192      * <p> The {@code limit} parameter controls the number of times the
2193      * pattern is applied and therefore affects the length of the resulting
2194      * array.  If the limit <i>n</i> is greater than zero then the pattern
2195      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2196      * length will be no greater than <i>n</i>, and the array's last entry
2197      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2198      * is non-positive then the pattern will be applied as many times as
2199      * possible and the array can have any length.  If <i>n</i> is zero then
2200      * the pattern will be applied as many times as possible, the array can
2201      * have any length, and trailing empty strings will be discarded.
2202      *
2203      * <p> The string {@code "boo:and:foo"}, for example, yields the
2204      * following results with these parameters:
2205      *
2206      * <blockquote><table class="plain">
2207      * <caption style="display:none">Split example showing regex, limit, and result</caption>
2208      * <thead>
2209      * <tr>
2210      *     <th>Regex</th>
2211      *     <th>Limit</th>
2212      *     <th>Result</th>
2213      * </tr>
2214      * </thead>
2215      * <tbody>
2216      * <tr><td style="text-align:center">:</td>
2217      *     <td style="text-align:center">2</td>
2218      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2219      * <tr><td style="text-align:center">:</td>
2220      *     <td style="text-align:center">5</td>
2221      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2222      * <tr><td style="text-align:center">:</td>
2223      *     <td style="text-align:center">-2</td>
2224      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2225      * <tr><td style="text-align:center">o</td>
2226      *     <td style="text-align:center">5</td>
2227      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2228      * <tr><td style="text-align:center">o</td>
2229      *     <td style="text-align:center">-2</td>
2230      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2231      * <tr><td style="text-align:center">o</td>
2232      *     <td style="text-align:center">0</td>
2233      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2234      * </tbody>
2235      * </table></blockquote>
2236      *
2237      * <p> An invocation of this method of the form
2238      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2239      * yields the same result as the expression
2240      *
2241      * <blockquote>
2242      * <code>
2243      * {@link java.util.regex.Pattern}.{@link
2244      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2245      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2246      * </code>
2247      * </blockquote>
2248      *
2249      *
2250      * @param  regex
2251      *         the delimiting regular expression
2252      *
2253      * @param  limit
2254      *         the result threshold, as described above
2255      *
2256      * @return  the array of strings computed by splitting this string
2257      *          around matches of the given regular expression
2258      *
2259      * @throws  PatternSyntaxException
2260      *          if the regular expression's syntax is invalid
2261      *
2262      * @see java.util.regex.Pattern
2263      *
2264      * @since 1.4
2265      * @spec JSR-51
2266      */
2267     public String[] split(String regex, int limit) {
2268         /* fastpath if the regex is a
2269          (1)one-char String and this character is not one of the
2270             RegEx's meta characters ".$|()[{^?*+\\", or
2271          (2)two-char String and the first char is the backslash and
2272             the second is not the ascii digit or ascii letter.
2273          */
2274         char ch = 0;
2275         if (((regex.length() == 1 &&
2276              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2277              (regex.length() == 2 &&
2278               regex.charAt(0) == '\\' &&
2279               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2280               ((ch-'a')|('z'-ch)) < 0 &&
2281               ((ch-'A')|('Z'-ch)) < 0)) &&
2282             (ch < Character.MIN_HIGH_SURROGATE ||
2283              ch > Character.MAX_LOW_SURROGATE))
2284         {
2285             int off = 0;
2286             int next = 0;
2287             boolean limited = limit > 0;
2288             ArrayList<String> list = new ArrayList<>();
2289             while ((next = indexOf(ch, off)) != -1) {
2290                 if (!limited || list.size() < limit - 1) {
2291                     list.add(substring(off, next));
2292                     off = next + 1;
2293                 } else {    // last one
2294                     //assert (list.size() == limit - 1);
2295                     int last = length();
2296                     list.add(substring(off, last));
2297                     off = last;
2298                     break;
2299                 }
2300             }
2301             // If no match was found, return this
2302             if (off == 0)
2303                 return new String[]{this};
2304 
2305             // Add remaining segment
2306             if (!limited || list.size() < limit)
2307                 list.add(substring(off, length()));
2308 
2309             // Construct result
2310             int resultSize = list.size();
2311             if (limit == 0) {
2312                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2313                     resultSize--;
2314                 }
2315             }
2316             String[] result = new String[resultSize];
2317             return list.subList(0, resultSize).toArray(result);
2318         }
2319         return Pattern.compile(regex).split(this, limit);
2320     }
2321 
2322     /**
2323      * Splits this string around matches of the given <a
2324      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2325      *
2326      * <p> This method works as if by invoking the two-argument {@link
2327      * #split(String, int) split} method with the given expression and a limit
2328      * argument of zero.  Trailing empty strings are therefore not included in
2329      * the resulting array.
2330      *
2331      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2332      * results with these expressions:
2333      *
2334      * <blockquote><table class="plain">
2335      * <caption style="display:none">Split examples showing regex and result</caption>
2336      * <thead>
2337      * <tr>
2338      *  <th>Regex</th>
2339      *  <th>Result</th>
2340      * </tr>
2341      * </thead>
2342      * <tbody>
2343      * <tr><td style="text-align:center">:</td>
2344      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2345      * <tr><td style="text-align:center">o</td>
2346      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2347      * </tbody>
2348      * </table></blockquote>
2349      *
2350      *
2351      * @param  regex
2352      *         the delimiting regular expression
2353      *
2354      * @return  the array of strings computed by splitting this string
2355      *          around matches of the given regular expression
2356      *
2357      * @throws  PatternSyntaxException
2358      *          if the regular expression's syntax is invalid
2359      *
2360      * @see java.util.regex.Pattern
2361      *
2362      * @since 1.4
2363      * @spec JSR-51
2364      */
2365     public String[] split(String regex) {
2366         return split(regex, 0);
2367     }
2368 
2369     /**
2370      * Returns a new String composed of copies of the
2371      * {@code CharSequence elements} joined together with a copy of
2372      * the specified {@code delimiter}.
2373      *
2374      * <blockquote>For example,
2375      * <pre>{@code
2376      *     String message = String.join("-", "Java", "is", "cool");
2377      *     // message returned is: "Java-is-cool"
2378      * }</pre></blockquote>
2379      *
2380      * Note that if an element is null, then {@code "null"} is added.
2381      *
2382      * @param  delimiter the delimiter that separates each element
2383      * @param  elements the elements to join together.
2384      *
2385      * @return a new {@code String} that is composed of the {@code elements}
2386      *         separated by the {@code delimiter}
2387      *
2388      * @throws NullPointerException If {@code delimiter} or {@code elements}
2389      *         is {@code null}
2390      *
2391      * @see java.util.StringJoiner
2392      * @since 1.8
2393      */
2394     public static String join(CharSequence delimiter, CharSequence... elements) {
2395         Objects.requireNonNull(delimiter);
2396         Objects.requireNonNull(elements);
2397         // Number of elements not likely worth Arrays.stream overhead.
2398         StringJoiner joiner = new StringJoiner(delimiter);
2399         for (CharSequence cs: elements) {
2400             joiner.add(cs);
2401         }
2402         return joiner.toString();
2403     }
2404 
2405     /**
2406      * Returns a new {@code String} composed of copies of the
2407      * {@code CharSequence elements} joined together with a copy of the
2408      * specified {@code delimiter}.
2409      *
2410      * <blockquote>For example,
2411      * <pre>{@code
2412      *     List<String> strings = List.of("Java", "is", "cool");
2413      *     String message = String.join(" ", strings);
2414      *     //message returned is: "Java is cool"
2415      *
2416      *     Set<String> strings =
2417      *         new LinkedHashSet<>(List.of("Java", "is", "very", "cool"));
2418      *     String message = String.join("-", strings);
2419      *     //message returned is: "Java-is-very-cool"
2420      * }</pre></blockquote>
2421      *
2422      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2423      *
2424      * @param  delimiter a sequence of characters that is used to separate each
2425      *         of the {@code elements} in the resulting {@code String}
2426      * @param  elements an {@code Iterable} that will have its {@code elements}
2427      *         joined together.
2428      *
2429      * @return a new {@code String} that is composed from the {@code elements}
2430      *         argument
2431      *
2432      * @throws NullPointerException If {@code delimiter} or {@code elements}
2433      *         is {@code null}
2434      *
2435      * @see    #join(CharSequence,CharSequence...)
2436      * @see    java.util.StringJoiner
2437      * @since 1.8
2438      */
2439     public static String join(CharSequence delimiter,
2440             Iterable<? extends CharSequence> elements) {
2441         Objects.requireNonNull(delimiter);
2442         Objects.requireNonNull(elements);
2443         StringJoiner joiner = new StringJoiner(delimiter);
2444         for (CharSequence cs: elements) {
2445             joiner.add(cs);
2446         }
2447         return joiner.toString();
2448     }
2449 
2450     /**
2451      * Converts all of the characters in this {@code String} to lower
2452      * case using the rules of the given {@code Locale}.  Case mapping is based
2453      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2454      * class. Since case mappings are not always 1:1 char mappings, the resulting
2455      * {@code String} may be a different length than the original {@code String}.
2456      * <p>
2457      * Examples of lowercase  mappings are in the following table:
2458      * <table class="plain">
2459      * <caption style="display:none">Lowercase mapping examples showing language code of locale, upper case, lower case, and description</caption>
2460      * <thead>
2461      * <tr>
2462      *   <th>Language Code of Locale</th>
2463      *   <th>Upper Case</th>
2464      *   <th>Lower Case</th>
2465      *   <th>Description</th>
2466      * </tr>
2467      * </thead>
2468      * <tbody>
2469      * <tr>
2470      *   <td>tr (Turkish)</td>
2471      *   <td>\u0130</td>
2472      *   <td>\u0069</td>
2473      *   <td>capital letter I with dot above -&gt; small letter i</td>
2474      * </tr>
2475      * <tr>
2476      *   <td>tr (Turkish)</td>
2477      *   <td>\u0049</td>
2478      *   <td>\u0131</td>
2479      *   <td>capital letter I -&gt; small letter dotless i </td>
2480      * </tr>
2481      * <tr>
2482      *   <td>(all)</td>
2483      *   <td>French Fries</td>
2484      *   <td>french fries</td>
2485      *   <td>lowercased all chars in String</td>
2486      * </tr>
2487      * <tr>
2488      *   <td>(all)</td>
2489      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2490      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2491      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2492      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2493      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2494      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2495      *   <td>lowercased all chars in String</td>
2496      * </tr>
2497      * </tbody>
2498      * </table>
2499      *
2500      * @param locale use the case transformation rules for this locale
2501      * @return the {@code String}, converted to lowercase.
2502      * @see     java.lang.String#toLowerCase()
2503      * @see     java.lang.String#toUpperCase()
2504      * @see     java.lang.String#toUpperCase(Locale)
2505      * @since   1.1
2506      */
2507     public String toLowerCase(Locale locale) {
2508         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2509                           : StringUTF16.toLowerCase(this, value, locale);
2510     }
2511 
2512     /**
2513      * Converts all of the characters in this {@code String} to lower
2514      * case using the rules of the default locale. This is equivalent to calling
2515      * {@code toLowerCase(Locale.getDefault())}.
2516      * <p>
2517      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2518      * results if used for strings that are intended to be interpreted locale
2519      * independently.
2520      * Examples are programming language identifiers, protocol keys, and HTML
2521      * tags.
2522      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2523      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2524      * LATIN SMALL LETTER DOTLESS I character.
2525      * To obtain correct results for locale insensitive strings, use
2526      * {@code toLowerCase(Locale.ROOT)}.
2527      *
2528      * @return  the {@code String}, converted to lowercase.
2529      * @see     java.lang.String#toLowerCase(Locale)
2530      */
2531     public String toLowerCase() {
2532         return toLowerCase(Locale.getDefault());
2533     }
2534 
2535     /**
2536      * Converts all of the characters in this {@code String} to upper
2537      * case using the rules of the given {@code Locale}. Case mapping is based
2538      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2539      * class. Since case mappings are not always 1:1 char mappings, the resulting
2540      * {@code String} may be a different length than the original {@code String}.
2541      * <p>
2542      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2543      *
2544      * <table class="plain">
2545      * <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>
2546      * <thead>
2547      * <tr>
2548      *   <th>Language Code of Locale</th>
2549      *   <th>Lower Case</th>
2550      *   <th>Upper Case</th>
2551      *   <th>Description</th>
2552      * </tr>
2553      * </thead>
2554      * <tbody>
2555      * <tr>
2556      *   <td>tr (Turkish)</td>
2557      *   <td>\u0069</td>
2558      *   <td>\u0130</td>
2559      *   <td>small letter i -&gt; capital letter I with dot above</td>
2560      * </tr>
2561      * <tr>
2562      *   <td>tr (Turkish)</td>
2563      *   <td>\u0131</td>
2564      *   <td>\u0049</td>
2565      *   <td>small letter dotless i -&gt; capital letter I</td>
2566      * </tr>
2567      * <tr>
2568      *   <td>(all)</td>
2569      *   <td>\u00df</td>
2570      *   <td>\u0053 \u0053</td>
2571      *   <td>small letter sharp s -&gt; two letters: SS</td>
2572      * </tr>
2573      * <tr>
2574      *   <td>(all)</td>
2575      *   <td>Fahrvergn&uuml;gen</td>
2576      *   <td>FAHRVERGN&Uuml;GEN</td>
2577      *   <td></td>
2578      * </tr>
2579      * </tbody>
2580      * </table>
2581      * @param locale use the case transformation rules for this locale
2582      * @return the {@code String}, converted to uppercase.
2583      * @see     java.lang.String#toUpperCase()
2584      * @see     java.lang.String#toLowerCase()
2585      * @see     java.lang.String#toLowerCase(Locale)
2586      * @since   1.1
2587      */
2588     public String toUpperCase(Locale locale) {
2589         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2590                           : StringUTF16.toUpperCase(this, value, locale);
2591     }
2592 
2593     /**
2594      * Converts all of the characters in this {@code String} to upper
2595      * case using the rules of the default locale. This method is equivalent to
2596      * {@code toUpperCase(Locale.getDefault())}.
2597      * <p>
2598      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2599      * results if used for strings that are intended to be interpreted locale
2600      * independently.
2601      * Examples are programming language identifiers, protocol keys, and HTML
2602      * tags.
2603      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2604      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2605      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2606      * To obtain correct results for locale insensitive strings, use
2607      * {@code toUpperCase(Locale.ROOT)}.
2608      *
2609      * @return  the {@code String}, converted to uppercase.
2610      * @see     java.lang.String#toUpperCase(Locale)
2611      */
2612     public String toUpperCase() {
2613         return toUpperCase(Locale.getDefault());
2614     }
2615 
2616     /**
2617      * Returns a string whose value is this string, with any leading and trailing
2618      * whitespace removed.
2619      * <p>
2620      * If this {@code String} object represents an empty character
2621      * sequence, or the first and last characters of character sequence
2622      * represented by this {@code String} object both have codes
2623      * greater than {@code '\u005Cu0020'} (the space character), then a
2624      * reference to this {@code String} object is returned.
2625      * <p>
2626      * Otherwise, if there is no character with a code greater than
2627      * {@code '\u005Cu0020'} in the string, then a
2628      * {@code String} object representing an empty string is
2629      * returned.
2630      * <p>
2631      * Otherwise, let <i>k</i> be the index of the first character in the
2632      * string whose code is greater than {@code '\u005Cu0020'}, and let
2633      * <i>m</i> be the index of the last character in the string whose code
2634      * is greater than {@code '\u005Cu0020'}. 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 whitespace (as defined above) from
2641      * the beginning and end of a string.
2642      *
2643      * @return  A string whose value is this string, with any leading and trailing white
2644      *          space removed, or this string if it has no leading or
2645      *          trailing white 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      * This object (which is already a string!) is itself returned.
2655      *
2656      * @return  the string itself.
2657      */
2658     public String toString() {
2659         return this;
2660     }
2661 
2662     /**
2663      * Returns a stream of {@code int} zero-extending the {@code char} values
2664      * from this sequence.  Any char which maps to a <a
2665      * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
2666      * point</a> is passed through uninterpreted.
2667      *
2668      * @return an IntStream of char values from this sequence
2669      */
2670     @Override
2671     public IntStream chars() {
2672         return StreamSupport.intStream(
2673             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2674                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
2675             false);
2676     }
2677 
2678 
2679     /**
2680      * Returns a stream of code point values from this sequence.  Any surrogate
2681      * pairs encountered in the sequence are combined as if by {@linkplain
2682      * Character#toCodePoint Character.toCodePoint} and the result is passed
2683      * to the stream. Any other code units, including ordinary BMP characters,
2684      * unpaired surrogates, and undefined code units, are zero-extended to
2685      * {@code int} values which are then passed to the stream.
2686      *
2687      * @return an IntStream of Unicode code points from this sequence
2688      */
2689     @Override
2690     public IntStream codePoints() {
2691         return StreamSupport.intStream(
2692             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2693                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
2694             false);
2695     }
2696 
2697     /**
2698      * Converts this string to a new character array.
2699      *
2700      * @return  a newly allocated character array whose length is the length
2701      *          of this string and whose contents are initialized to contain
2702      *          the character sequence represented by this string.
2703      */
2704     public char[] toCharArray() {
2705         return isLatin1() ? StringLatin1.toChars(value)
2706                           : StringUTF16.toChars(value);
2707     }
2708 
2709     /**
2710      * Returns a formatted string using the specified format string and
2711      * arguments.
2712      *
2713      * <p> The locale always used is the one returned by {@link
2714      * java.util.Locale#getDefault(java.util.Locale.Category)
2715      * Locale.getDefault(Locale.Category)} with
2716      * {@link java.util.Locale.Category#FORMAT FORMAT} category specified.
2717      *
2718      * @param  format
2719      *         A <a href="../util/Formatter.html#syntax">format string</a>
2720      *
2721      * @param  args
2722      *         Arguments referenced by the format specifiers in the format
2723      *         string.  If there are more arguments than format specifiers, the
2724      *         extra arguments are ignored.  The number of arguments is
2725      *         variable and may be zero.  The maximum number of arguments is
2726      *         limited by the maximum dimension of a Java array as defined by
2727      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2728      *         The behaviour on a
2729      *         {@code null} argument depends on the <a
2730      *         href="../util/Formatter.html#syntax">conversion</a>.
2731      *
2732      * @throws  java.util.IllegalFormatException
2733      *          If a format string contains an illegal syntax, a format
2734      *          specifier that is incompatible with the given arguments,
2735      *          insufficient arguments given the format string, or other
2736      *          illegal conditions.  For specification of all possible
2737      *          formatting errors, see the <a
2738      *          href="../util/Formatter.html#detail">Details</a> section of the
2739      *          formatter class specification.
2740      *
2741      * @return  A formatted string
2742      *
2743      * @see  java.util.Formatter
2744      * @since  1.5
2745      */
2746     public static String format(String format, Object... args) {
2747         return new Formatter().format(format, args).toString();
2748     }
2749 
2750     /**
2751      * Returns a formatted string using the specified locale, format string,
2752      * and arguments.
2753      *
2754      * @param  l
2755      *         The {@linkplain java.util.Locale locale} to apply during
2756      *         formatting.  If {@code l} is {@code null} then no localization
2757      *         is applied.
2758      *
2759      * @param  format
2760      *         A <a href="../util/Formatter.html#syntax">format string</a>
2761      *
2762      * @param  args
2763      *         Arguments referenced by the format specifiers in the format
2764      *         string.  If there are more arguments than format specifiers, the
2765      *         extra arguments are ignored.  The number of arguments is
2766      *         variable and may be zero.  The maximum number of arguments is
2767      *         limited by the maximum dimension of a Java array as defined by
2768      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2769      *         The behaviour on a
2770      *         {@code null} argument depends on the
2771      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2772      *
2773      * @throws  java.util.IllegalFormatException
2774      *          If a format string contains an illegal syntax, a format
2775      *          specifier that is incompatible with the given arguments,
2776      *          insufficient arguments given the format string, or other
2777      *          illegal conditions.  For specification of all possible
2778      *          formatting errors, see the <a
2779      *          href="../util/Formatter.html#detail">Details</a> section of the
2780      *          formatter class specification
2781      *
2782      * @return  A formatted string
2783      *
2784      * @see  java.util.Formatter
2785      * @since  1.5
2786      */
2787     public static String format(Locale l, String format, Object... args) {
2788         return new Formatter(l).format(format, args).toString();
2789     }
2790 
2791     /**
2792      * Returns the string representation of the {@code Object} argument.
2793      *
2794      * @param   obj   an {@code Object}.
2795      * @return  if the argument is {@code null}, then a string equal to
2796      *          {@code "null"}; otherwise, the value of
2797      *          {@code obj.toString()} is returned.
2798      * @see     java.lang.Object#toString()
2799      */
2800     public static String valueOf(Object obj) {
2801         return (obj == null) ? "null" : obj.toString();
2802     }
2803 
2804     /**
2805      * Returns the string representation of the {@code char} array
2806      * argument. The contents of the character array are copied; subsequent
2807      * modification of the character array does not affect the returned
2808      * string.
2809      *
2810      * @param   data     the character array.
2811      * @return  a {@code String} that contains the characters of the
2812      *          character array.
2813      */
2814     public static String valueOf(char data[]) {
2815         return new String(data);
2816     }
2817 
2818     /**
2819      * Returns the string representation of a specific subarray of the
2820      * {@code char} array argument.
2821      * <p>
2822      * The {@code offset} argument is the index of the first
2823      * character of the subarray. The {@code count} argument
2824      * specifies the length of the subarray. The contents of the subarray
2825      * are copied; subsequent modification of the character array does not
2826      * affect the returned string.
2827      *
2828      * @param   data     the character array.
2829      * @param   offset   initial offset of the subarray.
2830      * @param   count    length of the subarray.
2831      * @return  a {@code String} that contains the characters of the
2832      *          specified subarray of the character array.
2833      * @exception IndexOutOfBoundsException if {@code offset} is
2834      *          negative, or {@code count} is negative, or
2835      *          {@code offset+count} is larger than
2836      *          {@code data.length}.
2837      */
2838     public static String valueOf(char data[], int offset, int count) {
2839         return new String(data, offset, count);
2840     }
2841 
2842     /**
2843      * Equivalent to {@link #valueOf(char[], int, int)}.
2844      *
2845      * @param   data     the character array.
2846      * @param   offset   initial offset of the subarray.
2847      * @param   count    length of the subarray.
2848      * @return  a {@code String} that contains the characters of the
2849      *          specified subarray of the character array.
2850      * @exception IndexOutOfBoundsException if {@code offset} is
2851      *          negative, or {@code count} is negative, or
2852      *          {@code offset+count} is larger than
2853      *          {@code data.length}.
2854      */
2855     public static String copyValueOf(char data[], int offset, int count) {
2856         return new String(data, offset, count);
2857     }
2858 
2859     /**
2860      * Equivalent to {@link #valueOf(char[])}.
2861      *
2862      * @param   data   the character array.
2863      * @return  a {@code String} that contains the characters of the
2864      *          character array.
2865      */
2866     public static String copyValueOf(char data[]) {
2867         return new String(data);
2868     }
2869 
2870     /**
2871      * Returns the string representation of the {@code boolean} argument.
2872      *
2873      * @param   b   a {@code boolean}.
2874      * @return  if the argument is {@code true}, a string equal to
2875      *          {@code "true"} is returned; otherwise, a string equal to
2876      *          {@code "false"} is returned.
2877      */
2878     public static String valueOf(boolean b) {
2879         return b ? "true" : "false";
2880     }
2881 
2882     /**
2883      * Returns the string representation of the {@code char}
2884      * argument.
2885      *
2886      * @param   c   a {@code char}.
2887      * @return  a string of length {@code 1} containing
2888      *          as its single character the argument {@code c}.
2889      */
2890     public static String valueOf(char c) {
2891         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
2892             return new String(StringLatin1.toBytes(c), LATIN1);
2893         }
2894         return new String(StringUTF16.toBytes(c), UTF16);
2895     }
2896 
2897     /**
2898      * Returns the string representation of the {@code int} argument.
2899      * <p>
2900      * The representation is exactly the one returned by the
2901      * {@code Integer.toString} method of one argument.
2902      *
2903      * @param   i   an {@code int}.
2904      * @return  a string representation of the {@code int} argument.
2905      * @see     java.lang.Integer#toString(int, int)
2906      */
2907     public static String valueOf(int i) {
2908         return Integer.toString(i);
2909     }
2910 
2911     /**
2912      * Returns the string representation of the {@code long} argument.
2913      * <p>
2914      * The representation is exactly the one returned by the
2915      * {@code Long.toString} method of one argument.
2916      *
2917      * @param   l   a {@code long}.
2918      * @return  a string representation of the {@code long} argument.
2919      * @see     java.lang.Long#toString(long)
2920      */
2921     public static String valueOf(long l) {
2922         return Long.toString(l);
2923     }
2924 
2925     /**
2926      * Returns the string representation of the {@code float} argument.
2927      * <p>
2928      * The representation is exactly the one returned by the
2929      * {@code Float.toString} method of one argument.
2930      *
2931      * @param   f   a {@code float}.
2932      * @return  a string representation of the {@code float} argument.
2933      * @see     java.lang.Float#toString(float)
2934      */
2935     public static String valueOf(float f) {
2936         return Float.toString(f);
2937     }
2938 
2939     /**
2940      * Returns the string representation of the {@code double} argument.
2941      * <p>
2942      * The representation is exactly the one returned by the
2943      * {@code Double.toString} method of one argument.
2944      *
2945      * @param   d   a {@code double}.
2946      * @return  a  string representation of the {@code double} argument.
2947      * @see     java.lang.Double#toString(double)
2948      */
2949     public static String valueOf(double d) {
2950         return Double.toString(d);
2951     }
2952 
2953     /**
2954      * Returns a canonical representation for the string object.
2955      * <p>
2956      * A pool of strings, initially empty, is maintained privately by the
2957      * class {@code String}.
2958      * <p>
2959      * When the intern method is invoked, if the pool already contains a
2960      * string equal to this {@code String} object as determined by
2961      * the {@link #equals(Object)} method, then the string from the pool is
2962      * returned. Otherwise, this {@code String} object is added to the
2963      * pool and a reference to this {@code String} object is returned.
2964      * <p>
2965      * It follows that for any two strings {@code s} and {@code t},
2966      * {@code s.intern() == t.intern()} is {@code true}
2967      * if and only if {@code s.equals(t)} is {@code true}.
2968      * <p>
2969      * All literal strings and string-valued constant expressions are
2970      * interned. String literals are defined in section 3.10.5 of the
2971      * <cite>The Java&trade; Language Specification</cite>.
2972      *
2973      * @return  a string that has the same contents as this string, but is
2974      *          guaranteed to be from a pool of unique strings.
2975      * @jls 3.10.5 String Literals
2976      */
2977     public native String intern();
2978 
2979     ////////////////////////////////////////////////////////////////
2980 
2981     /**
2982      * Copy character bytes from this string into dst starting at dstBegin.
2983      * This method doesn't perform any range checking.
2984      *
2985      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
2986      * coders are different, and dst is big enough (range check)
2987      *
2988      * @param dstBegin  the char index, not offset of byte[]
2989      * @param coder     the coder of dst[]
2990      */
2991     void getBytes(byte dst[], int dstBegin, byte coder) {
2992         if (coder() == coder) {
2993             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
2994         } else {    // this.coder == LATIN && coder == UTF16
2995             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
2996         }
2997     }
2998 
2999     /*
3000      * Package private constructor. Trailing Void argument is there for
3001      * disambiguating it against other (public) constructors.
3002      *
3003      * Stores the char[] value into a byte[] that each byte represents
3004      * the8 low-order bits of the corresponding character, if the char[]
3005      * contains only latin1 character. Or a byte[] that stores all
3006      * characters in their byte sequences defined by the {@code StringUTF16}.
3007      */
3008     String(char[] value, int off, int len, Void sig) {
3009         if (len == 0) {
3010             this.value = "".value;
3011             this.coder = "".coder;
3012             return;
3013         }
3014         if (COMPACT_STRINGS) {
3015             byte[] val = StringUTF16.compress(value, off, len);
3016             if (val != null) {
3017                 this.value = val;
3018                 this.coder = LATIN1;
3019                 return;
3020             }
3021         }
3022         this.coder = UTF16;
3023         this.value = StringUTF16.toBytes(value, off, len);
3024     }
3025 
3026     /*
3027      * Package private constructor. Trailing Void argument is there for
3028      * disambiguating it against other (public) constructors.
3029      */
3030     String(AbstractStringBuilder asb, Void sig) {
3031         byte[] val = asb.getValue();
3032         int length = asb.length();
3033         if (asb.isLatin1()) {
3034             this.coder = LATIN1;
3035             this.value = Arrays.copyOfRange(val, 0, length);
3036         } else {
3037             if (COMPACT_STRINGS) {
3038                 byte[] buf = StringUTF16.compress(val, 0, length);
3039                 if (buf != null) {
3040                     this.coder = LATIN1;
3041                     this.value = buf;
3042                     return;
3043                 }
3044             }
3045             this.coder = UTF16;
3046             this.value = Arrays.copyOfRange(val, 0, length << 1);
3047         }
3048     }
3049 
3050    /*
3051     * Package private constructor which shares value array for speed.
3052     */
3053     String(byte[] value, byte coder) {
3054         this.value = value;
3055         this.coder = coder;
3056     }
3057 
3058     byte coder() {
3059         return COMPACT_STRINGS ? coder : UTF16;
3060     }
3061 
3062     private boolean isLatin1() {
3063         return COMPACT_STRINGS && coder == LATIN1;
3064     }
3065 
3066     static final byte LATIN1 = 0;
3067     static final byte UTF16  = 1;
3068 
3069     /*
3070      * StringIndexOutOfBoundsException  if {@code index} is
3071      * negative or greater than or equal to {@code length}.
3072      */
3073     static void checkIndex(int index, int length) {
3074         if (index < 0 || index >= length) {
3075             throw new StringIndexOutOfBoundsException("index " + index +
3076                                                       ",length " + length);
3077         }
3078     }
3079 
3080     /*
3081      * StringIndexOutOfBoundsException  if {@code offset}
3082      * is negative or greater than {@code length}.
3083      */
3084     static void checkOffset(int offset, int length) {
3085         if (offset < 0 || offset > length) {
3086             throw new StringIndexOutOfBoundsException("offset " + offset +
3087                                                       ",length " + length);
3088         }
3089     }
3090 
3091     /*
3092      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3093      * bounds.
3094      *
3095      * @throws  StringIndexOutOfBoundsException
3096      *          If {@code offset} is negative, {@code count} is negative,
3097      *          or {@code offset} is greater than {@code length - count}
3098      */
3099     static void checkBoundsOffCount(int offset, int count, int length) {
3100         if (offset < 0 || count < 0 || offset > length - count) {
3101             throw new StringIndexOutOfBoundsException(
3102                 "offset " + offset + ", count " + count + ", length " + length);
3103         }
3104     }
3105 
3106     /*
3107      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3108      * bounds.
3109      *
3110      * @throws  StringIndexOutOfBoundsException
3111      *          If {@code begin} is negative, {@code begin} is greater than
3112      *          {@code end}, or {@code end} is greater than {@code length}.
3113      */
3114     static void checkBoundsBeginEnd(int begin, int end, int length) {
3115         if (begin < 0 || begin > end || end > length) {
3116             throw new StringIndexOutOfBoundsException(
3117                 "begin " + begin + ", end " + end + ", length " + length);
3118         }
3119     }
3120 }