1 /*
   2  * Copyright (c) 1994, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.ObjectStreamField;
  29 import java.io.UnsupportedEncodingException;
  30 import java.nio.charset.Charset;
  31 import java.util.ArrayList;
  32 import java.util.Arrays;
  33 import java.util.Comparator;
  34 import java.util.Formatter;
  35 import java.util.Locale;
  36 import java.util.Objects;
  37 import java.util.Spliterator;
  38 import java.util.StringJoiner;
  39 import java.util.regex.Matcher;
  40 import java.util.regex.Pattern;
  41 import java.util.regex.PatternSyntaxException;
  42 import java.util.stream.IntStream;
  43 import java.util.stream.StreamSupport;
  44 import jdk.internal.HotSpotIntrinsicCandidate;
  45 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. String concatenation is implemented
  82  * through the {@code StringBuilder}(or {@code StringBuffer})
  83  * class and its {@code append} method.
  84  * String conversions are implemented through the method
  85  * {@code toString}, defined by {@code Object} and
  86  * inherited by all classes in Java. For additional information on
  87  * string concatenation and conversion, see Gosling, Joy, and Steele,
  88  * <i>The Java Language Specification</i>.
  89  *
  90  * <p> Unless otherwise noted, passing a {@code null} argument to a constructor
  91  * or method in this class will cause a {@link NullPointerException} to be
  92  * thrown.
  93  *
  94  * <p>A {@code String} represents a string in the UTF-16 format
  95  * in which <em>supplementary characters</em> are represented by <em>surrogate
  96  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  97  * Character Representations</a> in the {@code Character} class for
  98  * more information).
  99  * Index values refer to {@code char} code units, so a supplementary
 100  * character uses two positions in a {@code String}.
 101  * <p>The {@code String} class provides methods for dealing with
 102  * Unicode code points (i.e., characters), in addition to those for
 103  * dealing with Unicode code units (i.e., {@code char} values).
 104  *
 105  * <p>Unless otherwise noted, methods for comparing Strings do not take locale
 106  * into account.  The {@link java.text.Collator} class provides methods for
 107  * finer-grain, locale-sensitive String comparison.
 108  *
 109  * @author  Lee Boynton
 110  * @author  Arthur van Hoff
 111  * @author  Martin Buchholz
 112  * @author  Ulf Zibis
 113  * @see     java.lang.Object#toString()
 114  * @see     java.lang.StringBuffer
 115  * @see     java.lang.StringBuilder
 116  * @see     java.nio.charset.Charset
 117  * @since   1.0
 118  */
 119 
 120 public final class String
 121     implements java.io.Serializable, Comparable<String>, CharSequence {
 122 
 123     /**
 124      * The value is used for character storage.
 125      *
 126      * @implNote This field is trusted by the VM, and is a subject to
 127      * constant folding if String instance is constant. Overwriting this
 128      * field after construction will cause problems.
 129      *
 130      * Additionally, it is marked with {@link Stable} to trust the contents
 131      * of the array. No other facility in JDK provides this functionality (yet).
 132      * {@link Stable} is safe here, because value is never null.
 133      */
 134     @Stable
 135     private final byte[] value;
 136 
 137     /**
 138      * The identifier of the encoding used to encode the bytes in
 139      * {@code value}. The supported values in this implementation are
 140      *
 141      * LATIN1
 142      * UTF16
 143      *
 144      * @implNote This field is trusted by the VM, and is a subject to
 145      * constant folding if String instance is constant. Overwriting this
 146      * field after construction will cause problems.
 147      */
 148     private final byte coder;
 149 
 150     /** Cache the hash code for the string */
 151     private int hash; // Default to 0
 152 
 153     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 154     private static final long serialVersionUID = -6849794470754667710L;
 155 
 156     /**
 157      * If String compaction is disabled, the bytes in {@code value} are
 158      * always encoded in UTF16.
 159      *
 160      * For methods with several possible implementation paths, when String
 161      * compaction is disabled, only one code path is taken.
 162      *
 163      * The instance field value is generally opaque to optimizing JIT
 164      * compilers. Therefore, in performance-sensitive place, an explicit
 165      * check of the static boolean {@code COMPACT_STRINGS} is done first
 166      * before checking the {@code coder} field since the static boolean
 167      * {@code COMPACT_STRINGS} would be constant folded away by an
 168      * optimizing JIT compiler. The idioms for these cases are as follows.
 169      *
 170      * For code such as:
 171      *
 172      *    if (coder == LATIN1) { ... }
 173      *
 174      * can be written more optimally as
 175      *
 176      *    if (coder() == LATIN1) { ... }
 177      *
 178      * or:
 179      *
 180      *    if (COMPACT_STRINGS && coder == LATIN1) { ... }
 181      *
 182      * An optimizing JIT compiler can fold the above conditional as:
 183      *
 184      *    COMPACT_STRINGS == true  => if (coder == LATIN1) { ... }
 185      *    COMPACT_STRINGS == false => if (false)           { ... }
 186      *
 187      * @implNote
 188      * The actual value for this field is injected by JVM. The static
 189      * initialization block is used to set the value here to communicate
 190      * that this static final field is not statically foldable, and to
 191      * avoid any possible circular dependency during vm initialization.
 192      */
 193     static final boolean COMPACT_STRINGS;
 194 
 195     static {
 196         COMPACT_STRINGS = true;
 197     }
 198 
 199     /**
 200      * Class String is special cased within the Serialization Stream Protocol.
 201      *
 202      * A String instance is written into an ObjectOutputStream according to
 203      * <a href="{@docRoot}/../platform/serialization/spec/output.html">
 204      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 205      */
 206     private static final ObjectStreamField[] serialPersistentFields =
 207         new ObjectStreamField[0];
 208 
 209     /**
 210      * Initializes a newly created {@code String} object so that it represents
 211      * an empty character sequence.  Note that use of this constructor is
 212      * unnecessary since Strings are immutable.
 213      */
 214     public String() {
 215         this.value = "".value;
 216         this.coder = "".coder;
 217     }
 218 
 219     /**
 220      * Initializes a newly created {@code String} object so that it represents
 221      * the same sequence of characters as the argument; in other words, the
 222      * newly created string is a copy of the argument string. Unless an
 223      * explicit copy of {@code original} is needed, use of this constructor is
 224      * unnecessary since Strings are immutable.
 225      *
 226      * @param  original
 227      *         A {@code String}
 228      */
 229     @HotSpotIntrinsicCandidate
 230     public String(String original) {
 231         this.value = original.value;
 232         this.coder = original.coder;
 233         this.hash = original.hash;
 234     }
 235 
 236     /**
 237      * Allocates a new {@code String} so that it represents the sequence of
 238      * characters currently contained in the character array argument. The
 239      * contents of the character array are copied; subsequent modification of
 240      * the character array does not affect the newly created string.
 241      *
 242      * @param  value
 243      *         The initial value of the string
 244      */
 245     public String(char value[]) {
 246         this(value, 0, value.length, null);
 247     }
 248 
 249     /**
 250      * Allocates a new {@code String} that contains characters from a subarray
 251      * of the character array argument. The {@code offset} argument is the
 252      * index of the first character of the subarray and the {@code count}
 253      * argument specifies the length of the subarray. The contents of the
 254      * subarray are copied; subsequent modification of the character array does
 255      * not affect the newly created string.
 256      *
 257      * @param  value
 258      *         Array that is the source of characters
 259      *
 260      * @param  offset
 261      *         The initial offset
 262      *
 263      * @param  count
 264      *         The length
 265      *
 266      * @throws  IndexOutOfBoundsException
 267      *          If {@code offset} is negative, {@code count} is negative, or
 268      *          {@code offset} is greater than {@code value.length - count}
 269      */
 270     public String(char value[], int offset, int count) {
 271         this(value, offset, count, rangeCheck(value, offset, count));
 272     }
 273 
 274     private static Void rangeCheck(char[] value, int offset, int count) {
 275         checkBoundsOffCount(offset, count, value.length);
 276         return null;
 277     }
 278 
 279     /**
 280      * Allocates a new {@code String} that contains characters from a subarray
 281      * of the <a href="Character.html#unicode">Unicode code point</a> array
 282      * argument.  The {@code offset} argument is the index of the first code
 283      * point of the subarray and the {@code count} argument specifies the
 284      * length of the subarray.  The contents of the subarray are converted to
 285      * {@code char}s; subsequent modification of the {@code int} array does not
 286      * affect the newly created string.
 287      *
 288      * @param  codePoints
 289      *         Array that is the source of Unicode code points
 290      *
 291      * @param  offset
 292      *         The initial offset
 293      *
 294      * @param  count
 295      *         The length
 296      *
 297      * @throws  IllegalArgumentException
 298      *          If any invalid Unicode code point is found in {@code
 299      *          codePoints}
 300      *
 301      * @throws  IndexOutOfBoundsException
 302      *          If {@code offset} is negative, {@code count} is negative, or
 303      *          {@code offset} is greater than {@code codePoints.length - count}
 304      *
 305      * @since  1.5
 306      */
 307     public String(int[] codePoints, int offset, int count) {
 308         checkBoundsOffCount(offset, count, codePoints.length);
 309         if (count == 0) {
 310             this.value = "".value;
 311             this.coder = "".coder;
 312             return;
 313         }
 314         if (COMPACT_STRINGS) {
 315             byte[] val = StringLatin1.toBytes(codePoints, offset, count);
 316             if (val != null) {
 317                 this.coder = LATIN1;
 318                 this.value = val;
 319                 return;
 320             }
 321         }
 322         this.coder = UTF16;
 323         this.value = StringUTF16.toBytes(codePoints, offset, count);
 324     }
 325 
 326     /**
 327      * Allocates a new {@code String} constructed from a subarray of an array
 328      * of 8-bit integer values.
 329      *
 330      * <p> The {@code offset} argument is the index of the first byte of the
 331      * subarray, and the {@code count} argument specifies the length of the
 332      * subarray.
 333      *
 334      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 335      * specified in the method above.
 336      *
 337      * @deprecated This method does not properly convert bytes into characters.
 338      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 339      * {@code String} constructors that take a {@link
 340      * java.nio.charset.Charset}, charset name, or that use the platform's
 341      * default charset.
 342      *
 343      * @param  ascii
 344      *         The bytes to be converted to characters
 345      *
 346      * @param  hibyte
 347      *         The top 8 bits of each 16-bit Unicode code unit
 348      *
 349      * @param  offset
 350      *         The initial offset
 351      * @param  count
 352      *         The length
 353      *
 354      * @throws  IndexOutOfBoundsException
 355      *          If {@code offset} is negative, {@code count} is negative, or
 356      *          {@code offset} is greater than {@code ascii.length - count}
 357      *
 358      * @see  #String(byte[], int)
 359      * @see  #String(byte[], int, int, java.lang.String)
 360      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 361      * @see  #String(byte[], int, int)
 362      * @see  #String(byte[], java.lang.String)
 363      * @see  #String(byte[], java.nio.charset.Charset)
 364      * @see  #String(byte[])
 365      */
 366     @Deprecated(since="1.1")
 367     public String(byte ascii[], int hibyte, int offset, int count) {
 368         checkBoundsOffCount(offset, count, ascii.length);
 369         if (count == 0) {
 370             this.value = "".value;
 371             this.coder = "".coder;
 372             return;
 373         }
 374         if (COMPACT_STRINGS && (byte)hibyte == 0) {
 375             this.value = Arrays.copyOfRange(ascii, offset, offset + count);
 376             this.coder = LATIN1;
 377         } else {
 378             hibyte <<= 8;
 379             byte[] val = StringUTF16.newBytesFor(count);
 380             for (int i = 0; i < count; i++) {
 381                 StringUTF16.putChar(val, i, hibyte | (ascii[offset++] & 0xff));
 382             }
 383             this.value = val;
 384             this.coder = UTF16;
 385         }
 386     }
 387 
 388     /**
 389      * Allocates a new {@code String} containing characters constructed from
 390      * an array of 8-bit integer values. Each character <i>c</i>in the
 391      * resulting string is constructed from the corresponding component
 392      * <i>b</i> in the byte array such that:
 393      *
 394      * <blockquote><pre>
 395      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 396      *                         | (<b><i>b</i></b> &amp; 0xff))
 397      * </pre></blockquote>
 398      *
 399      * @deprecated  This method does not properly convert bytes into
 400      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 401      * {@code String} constructors that take a {@link
 402      * java.nio.charset.Charset}, charset name, or that use the platform's
 403      * default charset.
 404      *
 405      * @param  ascii
 406      *         The bytes to be converted to characters
 407      *
 408      * @param  hibyte
 409      *         The top 8 bits of each 16-bit Unicode code unit
 410      *
 411      * @see  #String(byte[], int, int, java.lang.String)
 412      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 413      * @see  #String(byte[], int, int)
 414      * @see  #String(byte[], java.lang.String)
 415      * @see  #String(byte[], java.nio.charset.Charset)
 416      * @see  #String(byte[])
 417      */
 418     @Deprecated(since="1.1")
 419     public String(byte ascii[], int hibyte) {
 420         this(ascii, hibyte, 0, ascii.length);
 421     }
 422 
 423     /**
 424      * Constructs a new {@code String} by decoding the specified subarray of
 425      * bytes using the specified charset.  The length of the new {@code String}
 426      * is a function of the charset, and hence may not be equal to the length
 427      * of the subarray.
 428      *
 429      * <p> The behavior of this constructor when the given bytes are not valid
 430      * in the given charset is unspecified.  The {@link
 431      * java.nio.charset.CharsetDecoder} class should be used when more control
 432      * over the decoding process is required.
 433      *
 434      * @param  bytes
 435      *         The bytes to be decoded into characters
 436      *
 437      * @param  offset
 438      *         The index of the first byte to decode
 439      *
 440      * @param  length
 441      *         The number of bytes to decode
 442 
 443      * @param  charsetName
 444      *         The name of a supported {@linkplain java.nio.charset.Charset
 445      *         charset}
 446      *
 447      * @throws  UnsupportedEncodingException
 448      *          If the named charset is not supported
 449      *
 450      * @throws  IndexOutOfBoundsException
 451      *          If {@code offset} is negative, {@code length} is negative, or
 452      *          {@code offset} is greater than {@code bytes.length - length}
 453      *
 454      * @since  1.1
 455      */
 456     public String(byte bytes[], int offset, int length, String charsetName)
 457             throws UnsupportedEncodingException {
 458         if (charsetName == null)
 459             throw new NullPointerException("charsetName");
 460         checkBoundsOffCount(offset, length, bytes.length);
 461         StringCoding.Result ret =
 462             StringCoding.decode(charsetName, bytes, offset, length);
 463         this.value = ret.value;
 464         this.coder = ret.coder;
 465     }
 466 
 467     /**
 468      * Constructs a new {@code String} by decoding the specified subarray of
 469      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 470      * The length of the new {@code String} is a function of the charset, and
 471      * hence may not be equal to the length of the subarray.
 472      *
 473      * <p> This method always replaces malformed-input and unmappable-character
 474      * sequences with this charset's default replacement string.  The {@link
 475      * java.nio.charset.CharsetDecoder} class should be used when more control
 476      * over the decoding process is required.
 477      *
 478      * @param  bytes
 479      *         The bytes to be decoded into characters
 480      *
 481      * @param  offset
 482      *         The index of the first byte to decode
 483      *
 484      * @param  length
 485      *         The number of bytes to decode
 486      *
 487      * @param  charset
 488      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 489      *         decode the {@code bytes}
 490      *
 491      * @throws  IndexOutOfBoundsException
 492      *          If {@code offset} is negative, {@code length} is negative, or
 493      *          {@code offset} is greater than {@code bytes.length - length}
 494      *
 495      * @since  1.6
 496      */
 497     public String(byte bytes[], int offset, int length, Charset charset) {
 498         if (charset == null)
 499             throw new NullPointerException("charset");
 500         checkBoundsOffCount(offset, length, bytes.length);
 501         StringCoding.Result ret =
 502             StringCoding.decode(charset, bytes, offset, length);
 503         this.value = ret.value;
 504         this.coder = ret.coder;
 505     }
 506 
 507     /**
 508      * Constructs a new {@code String} by decoding the specified array of bytes
 509      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 510      * length of the new {@code String} is a function of the charset, and hence
 511      * may not be equal to the length of the byte array.
 512      *
 513      * <p> The behavior of this constructor when the given bytes are not valid
 514      * in the given charset is unspecified.  The {@link
 515      * java.nio.charset.CharsetDecoder} class should be used when more control
 516      * over the decoding process is required.
 517      *
 518      * @param  bytes
 519      *         The bytes to be decoded into characters
 520      *
 521      * @param  charsetName
 522      *         The name of a supported {@linkplain java.nio.charset.Charset
 523      *         charset}
 524      *
 525      * @throws  UnsupportedEncodingException
 526      *          If the named charset is not supported
 527      *
 528      * @since  1.1
 529      */
 530     public String(byte bytes[], String charsetName)
 531             throws UnsupportedEncodingException {
 532         this(bytes, 0, bytes.length, charsetName);
 533     }
 534 
 535     /**
 536      * Constructs a new {@code String} by decoding the specified array of
 537      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 538      * The length of the new {@code String} is a function of the charset, and
 539      * hence may not be equal to the length of the byte array.
 540      *
 541      * <p> This method always replaces malformed-input and unmappable-character
 542      * sequences with this charset's default replacement string.  The {@link
 543      * java.nio.charset.CharsetDecoder} class should be used when more control
 544      * over the decoding process is required.
 545      *
 546      * @param  bytes
 547      *         The bytes to be decoded into characters
 548      *
 549      * @param  charset
 550      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 551      *         decode the {@code bytes}
 552      *
 553      * @since  1.6
 554      */
 555     public String(byte bytes[], Charset charset) {
 556         this(bytes, 0, bytes.length, charset);
 557     }
 558 
 559     /**
 560      * Constructs a new {@code String} by decoding the specified subarray of
 561      * bytes using the platform's default charset.  The length of the new
 562      * {@code String} is a function of the charset, and hence may not be equal
 563      * to the length of the subarray.
 564      *
 565      * <p> The behavior of this constructor when the given bytes are not valid
 566      * in the default charset is unspecified.  The {@link
 567      * java.nio.charset.CharsetDecoder} class should be used when more control
 568      * over the decoding process is required.
 569      *
 570      * @param  bytes
 571      *         The bytes to be decoded into characters
 572      *
 573      * @param  offset
 574      *         The index of the first byte to decode
 575      *
 576      * @param  length
 577      *         The number of bytes to decode
 578      *
 579      * @throws  IndexOutOfBoundsException
 580      *          If {@code offset} is negative, {@code length} is negative, or
 581      *          {@code offset} is greater than {@code bytes.length - length}
 582      *
 583      * @since  1.1
 584      */
 585     public String(byte bytes[], int offset, int length) {
 586         checkBoundsOffCount(offset, length, bytes.length);
 587         StringCoding.Result ret = StringCoding.decode(bytes, offset, length);
 588         this.value = ret.value;
 589         this.coder = ret.coder;
 590     }
 591 
 592     /**
 593      * Constructs a new {@code String} by decoding the specified array of bytes
 594      * using the platform's default charset.  The length of the new {@code
 595      * String} is a function of the charset, and hence may not be equal to the
 596      * length of the byte array.
 597      *
 598      * <p> The behavior of this constructor when the given bytes are not valid
 599      * in the default charset is unspecified.  The {@link
 600      * java.nio.charset.CharsetDecoder} class should be used when more control
 601      * over the decoding process is required.
 602      *
 603      * @param  bytes
 604      *         The bytes to be decoded into characters
 605      *
 606      * @since  1.1
 607      */
 608     public String(byte[] bytes) {
 609         this(bytes, 0, bytes.length);
 610     }
 611 
 612     /**
 613      * Allocates a new string that contains the sequence of characters
 614      * currently contained in the string buffer argument. The contents of the
 615      * string buffer are copied; subsequent modification of the string buffer
 616      * does not affect the newly created string.
 617      *
 618      * @param  buffer
 619      *         A {@code StringBuffer}
 620      */
 621     public String(StringBuffer buffer) {
 622         this(buffer.toString());
 623     }
 624 
 625     /**
 626      * Allocates a new string that contains the sequence of characters
 627      * currently contained in the string builder argument. The contents of the
 628      * string builder are copied; subsequent modification of the string builder
 629      * does not affect the newly created string.
 630      *
 631      * <p> This constructor is provided to ease migration to {@code
 632      * StringBuilder}. Obtaining a string from a string builder via the {@code
 633      * toString} method is likely to run faster and is generally preferred.
 634      *
 635      * @param   builder
 636      *          A {@code StringBuilder}
 637      *
 638      * @since  1.5
 639      */
 640     public String(StringBuilder builder) {
 641         this(builder, null);
 642     }
 643 
 644    /*
 645     * Package private constructor which shares value array for speed.
 646     * this constructor is always expected to be called with share==true.
 647     * a separate constructor is needed because we already have a public
 648     * String(char[]) constructor that makes a copy of the given char[].
 649     */
 650     // TBD: this is kept for package internal use (Thread/System),
 651     // should be removed if they all have a byte[] version
 652     String(char[] val, boolean share) {
 653         // assert share : "unshared not supported";
 654         this(val, 0, val.length, null);
 655     }
 656 
 657     /**
 658      * Returns the length of this string.
 659      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 660      * code units</a> in the string.
 661      *
 662      * @return  the length of the sequence of characters represented by this
 663      *          object.
 664      */
 665     public int length() {
 666         return value.length >> coder();
 667     }
 668 
 669     /**
 670      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 671      *
 672      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 673      * {@code false}
 674      *
 675      * @since 1.6
 676      */
 677     public boolean isEmpty() {
 678         return value.length == 0;
 679     }
 680 
 681     /**
 682      * Returns the {@code char} value at the
 683      * specified index. An index ranges from {@code 0} to
 684      * {@code length() - 1}. The first {@code char} value of the sequence
 685      * is at index {@code 0}, the next at index {@code 1},
 686      * and so on, as for array indexing.
 687      *
 688      * <p>If the {@code char} value specified by the index is a
 689      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 690      * value is returned.
 691      *
 692      * @param      index   the index of the {@code char} value.
 693      * @return     the {@code char} value at the specified index of this string.
 694      *             The first {@code char} value is at index {@code 0}.
 695      * @exception  IndexOutOfBoundsException  if the {@code index}
 696      *             argument is negative or not less than the length of this
 697      *             string.
 698      */
 699     public char charAt(int index) {
 700         if (isLatin1()) {
 701             return StringLatin1.charAt(value, index);
 702         } else {
 703             return StringUTF16.charAt(value, index);
 704         }
 705     }
 706 
 707     /**
 708      * Returns the character (Unicode code point) at the specified
 709      * index. The index refers to {@code char} values
 710      * (Unicode code units) and ranges from {@code 0} to
 711      * {@link #length()}{@code  - 1}.
 712      *
 713      * <p> If the {@code char} value specified at the given index
 714      * is in the high-surrogate range, the following index is less
 715      * than the length of this {@code String}, and the
 716      * {@code char} value at the following index is in the
 717      * low-surrogate range, then the supplementary code point
 718      * corresponding to this surrogate pair is returned. Otherwise,
 719      * the {@code char} value at the given index is returned.
 720      *
 721      * @param      index the index to the {@code char} values
 722      * @return     the code point value of the character at the
 723      *             {@code index}
 724      * @exception  IndexOutOfBoundsException  if the {@code index}
 725      *             argument is negative or not less than the length of this
 726      *             string.
 727      * @since      1.5
 728      */
 729     public int codePointAt(int index) {
 730         if (isLatin1()) {
 731             checkIndex(index, value.length);
 732             return value[index] & 0xff;
 733         }
 734         int length = value.length >> 1;
 735         checkIndex(index, length);
 736         return StringUTF16.codePointAt(value, index, length);
 737     }
 738 
 739     /**
 740      * Returns the character (Unicode code point) before the specified
 741      * index. The index refers to {@code char} values
 742      * (Unicode code units) and ranges from {@code 1} to {@link
 743      * CharSequence#length() length}.
 744      *
 745      * <p> If the {@code char} value at {@code (index - 1)}
 746      * is in the low-surrogate range, {@code (index - 2)} is not
 747      * negative, and the {@code char} value at {@code (index -
 748      * 2)} is in the high-surrogate range, then the
 749      * supplementary code point value of the surrogate pair is
 750      * returned. If the {@code char} value at {@code index -
 751      * 1} is an unpaired low-surrogate or a high-surrogate, the
 752      * surrogate value is returned.
 753      *
 754      * @param     index the index following the code point that should be returned
 755      * @return    the Unicode code point value before the given index.
 756      * @exception IndexOutOfBoundsException if the {@code index}
 757      *            argument is less than 1 or greater than the length
 758      *            of this string.
 759      * @since     1.5
 760      */
 761     public int codePointBefore(int index) {
 762         int i = index - 1;
 763         if (i < 0 || i >= length()) {
 764             throw new StringIndexOutOfBoundsException(index);
 765         }
 766         if (isLatin1()) {
 767             return (value[i] & 0xff);
 768         }
 769         return StringUTF16.codePointBefore(value, index);
 770     }
 771 
 772     /**
 773      * Returns the number of Unicode code points in the specified text
 774      * range of this {@code String}. The text range begins at the
 775      * specified {@code beginIndex} and extends to the
 776      * {@code char} at index {@code endIndex - 1}. Thus the
 777      * length (in {@code char}s) of the text range is
 778      * {@code endIndex-beginIndex}. Unpaired surrogates within
 779      * the text range count as one code point each.
 780      *
 781      * @param beginIndex the index to the first {@code char} of
 782      * the text range.
 783      * @param endIndex the index after the last {@code char} of
 784      * the text range.
 785      * @return the number of Unicode code points in the specified text
 786      * range
 787      * @exception IndexOutOfBoundsException if the
 788      * {@code beginIndex} is negative, or {@code endIndex}
 789      * is larger than the length of this {@code String}, or
 790      * {@code beginIndex} is larger than {@code endIndex}.
 791      * @since  1.5
 792      */
 793     public int codePointCount(int beginIndex, int endIndex) {
 794         if (beginIndex < 0 || beginIndex > endIndex ||
 795             endIndex > length()) {
 796             throw new IndexOutOfBoundsException();
 797         }
 798         if (isLatin1()) {
 799             return endIndex - beginIndex;
 800         }
 801         return StringUTF16.codePointCount(value, beginIndex, endIndex);
 802     }
 803 
 804     /**
 805      * Returns the index within this {@code String} that is
 806      * offset from the given {@code index} by
 807      * {@code codePointOffset} code points. Unpaired surrogates
 808      * within the text range given by {@code index} and
 809      * {@code codePointOffset} count as one code point each.
 810      *
 811      * @param index the index to be offset
 812      * @param codePointOffset the offset in code points
 813      * @return the index within this {@code String}
 814      * @exception IndexOutOfBoundsException if {@code index}
 815      *   is negative or larger then the length of this
 816      *   {@code String}, or if {@code codePointOffset} is positive
 817      *   and the substring starting with {@code index} has fewer
 818      *   than {@code codePointOffset} code points,
 819      *   or if {@code codePointOffset} is negative and the substring
 820      *   before {@code index} has fewer than the absolute value
 821      *   of {@code codePointOffset} code points.
 822      * @since 1.5
 823      */
 824     public int offsetByCodePoints(int index, int codePointOffset) {
 825         if (index < 0 || index > length()) {
 826             throw new IndexOutOfBoundsException();
 827         }
 828         return Character.offsetByCodePoints(this, index, codePointOffset);
 829     }
 830 
 831     /**
 832      * Copies characters from this string into the destination character
 833      * array.
 834      * <p>
 835      * The first character to be copied is at index {@code srcBegin};
 836      * the last character to be copied is at index {@code srcEnd-1}
 837      * (thus the total number of characters to be copied is
 838      * {@code srcEnd-srcBegin}). The characters are copied into the
 839      * subarray of {@code dst} starting at index {@code dstBegin}
 840      * and ending at index:
 841      * <blockquote><pre>
 842      *     dstBegin + (srcEnd-srcBegin) - 1
 843      * </pre></blockquote>
 844      *
 845      * @param      srcBegin   index of the first character in the string
 846      *                        to copy.
 847      * @param      srcEnd     index after the last character in the string
 848      *                        to copy.
 849      * @param      dst        the destination array.
 850      * @param      dstBegin   the start offset in the destination array.
 851      * @exception IndexOutOfBoundsException If any of the following
 852      *            is true:
 853      *            <ul><li>{@code srcBegin} is negative.
 854      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 855      *            <li>{@code srcEnd} is greater than the length of this
 856      *                string
 857      *            <li>{@code dstBegin} is negative
 858      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 859      *                {@code dst.length}</ul>
 860      */
 861     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 862         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 863         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 864         if (isLatin1()) {
 865             StringLatin1.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 866         } else {
 867             StringUTF16.getChars(value, srcBegin, srcEnd, dst, dstBegin);
 868         }
 869     }
 870 
 871     /**
 872      * Copies characters from this string into the destination byte array. Each
 873      * byte receives the 8 low-order bits of the corresponding character. The
 874      * eight high-order bits of each character are not copied and do not
 875      * participate in the transfer in any way.
 876      *
 877      * <p> The first character to be copied is at index {@code srcBegin}; the
 878      * last character to be copied is at index {@code srcEnd-1}.  The total
 879      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 880      * characters, converted to bytes, are copied into the subarray of {@code
 881      * dst} starting at index {@code dstBegin} and ending at index:
 882      *
 883      * <blockquote><pre>
 884      *     dstBegin + (srcEnd-srcBegin) - 1
 885      * </pre></blockquote>
 886      *
 887      * @deprecated  This method does not properly convert characters into
 888      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 889      * {@link #getBytes()} method, which uses the platform's default charset.
 890      *
 891      * @param  srcBegin
 892      *         Index of the first character in the string to copy
 893      *
 894      * @param  srcEnd
 895      *         Index after the last character in the string to copy
 896      *
 897      * @param  dst
 898      *         The destination array
 899      *
 900      * @param  dstBegin
 901      *         The start offset in the destination array
 902      *
 903      * @throws  IndexOutOfBoundsException
 904      *          If any of the following is true:
 905      *          <ul>
 906      *            <li> {@code srcBegin} is negative
 907      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 908      *            <li> {@code srcEnd} is greater than the length of this String
 909      *            <li> {@code dstBegin} is negative
 910      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 911      *                 dst.length}
 912      *          </ul>
 913      */
 914     @Deprecated(since="1.1")
 915     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 916         checkBoundsBeginEnd(srcBegin, srcEnd, length());
 917         Objects.requireNonNull(dst);
 918         checkBoundsOffCount(dstBegin, srcEnd - srcBegin, dst.length);
 919         if (isLatin1()) {
 920             StringLatin1.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 921         } else {
 922             StringUTF16.getBytes(value, srcBegin, srcEnd, dst, dstBegin);
 923         }
 924     }
 925 
 926     /**
 927      * Encodes this {@code String} into a sequence of bytes using the named
 928      * charset, storing the result into a new byte array.
 929      *
 930      * <p> The behavior of this method when this string cannot be encoded in
 931      * the given charset is unspecified.  The {@link
 932      * java.nio.charset.CharsetEncoder} class should be used when more control
 933      * over the encoding process is required.
 934      *
 935      * @param  charsetName
 936      *         The name of a supported {@linkplain java.nio.charset.Charset
 937      *         charset}
 938      *
 939      * @return  The resultant byte array
 940      *
 941      * @throws  UnsupportedEncodingException
 942      *          If the named charset is not supported
 943      *
 944      * @since  1.1
 945      */
 946     public byte[] getBytes(String charsetName)
 947             throws UnsupportedEncodingException {
 948         if (charsetName == null) throw new NullPointerException();
 949         return StringCoding.encode(charsetName, coder(), value);
 950     }
 951 
 952     /**
 953      * Encodes this {@code String} into a sequence of bytes using the given
 954      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 955      * new byte array.
 956      *
 957      * <p> This method always replaces malformed-input and unmappable-character
 958      * sequences with this charset's default replacement byte array.  The
 959      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 960      * control over the encoding process is required.
 961      *
 962      * @param  charset
 963      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 964      *         the {@code String}
 965      *
 966      * @return  The resultant byte array
 967      *
 968      * @since  1.6
 969      */
 970     public byte[] getBytes(Charset charset) {
 971         if (charset == null) throw new NullPointerException();
 972         return StringCoding.encode(charset, coder(), value);
 973      }
 974 
 975     /**
 976      * Encodes this {@code String} into a sequence of bytes using the
 977      * platform's default charset, storing the result into a new byte array.
 978      *
 979      * <p> The behavior of this method when this string cannot be encoded in
 980      * the default charset is unspecified.  The {@link
 981      * java.nio.charset.CharsetEncoder} class should be used when more control
 982      * over the encoding process is required.
 983      *
 984      * @return  The resultant byte array
 985      *
 986      * @since      1.1
 987      */
 988     public byte[] getBytes() {
 989         return StringCoding.encode(coder(), value);
 990     }
 991 
 992     /**
 993      * Compares this string to the specified object.  The result is {@code
 994      * true} if and only if the argument is not {@code null} and is a {@code
 995      * String} object that represents the same sequence of characters as this
 996      * object.
 997      *
 998      * <p>For finer-grained String comparison, refer to
 999      * {@link java.text.Collator}.
1000      *
1001      * @param  anObject
1002      *         The object to compare this {@code String} against
1003      *
1004      * @return  {@code true} if the given object represents a {@code String}
1005      *          equivalent to this string, {@code false} otherwise
1006      *
1007      * @see  #compareTo(String)
1008      * @see  #equalsIgnoreCase(String)
1009      */
1010     public boolean equals(Object anObject) {
1011         if (this == anObject) {
1012             return true;
1013         }
1014         if (anObject instanceof String) {
1015             String aString = (String)anObject;
1016             if (coder() == aString.coder()) {
1017                 return isLatin1() ? StringLatin1.equals(value, aString.value)
1018                                   : StringUTF16.equals(value, aString.value);
1019             }
1020         }
1021         return false;
1022     }
1023 
1024     /**
1025      * Compares this string to the specified {@code StringBuffer}.  The result
1026      * is {@code true} if and only if this {@code String} represents the same
1027      * sequence of characters as the specified {@code StringBuffer}. This method
1028      * synchronizes on the {@code StringBuffer}.
1029      *
1030      * <p>For finer-grained String comparison, refer to
1031      * {@link java.text.Collator}.
1032      *
1033      * @param  sb
1034      *         The {@code StringBuffer} to compare this {@code String} against
1035      *
1036      * @return  {@code true} if this {@code String} represents the same
1037      *          sequence of characters as the specified {@code StringBuffer},
1038      *          {@code false} otherwise
1039      *
1040      * @since  1.4
1041      */
1042     public boolean contentEquals(StringBuffer sb) {
1043         return contentEquals((CharSequence)sb);
1044     }
1045 
1046     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1047         int len = length();
1048         if (len != sb.length()) {
1049             return false;
1050         }
1051         byte v1[] = value;
1052         byte v2[] = sb.getValue();
1053         if (coder() == sb.getCoder()) {
1054             int n = v1.length;
1055             for (int i = 0; i < n; i++) {
1056                 if (v1[i] != v2[i]) {
1057                     return false;
1058                 }
1059             }
1060         } else {
1061             if (!isLatin1()) {  // utf16 str and latin1 abs can never be "equal"
1062                 return false;
1063             }
1064             for (int i = 0; i < len; i++) {
1065                 if ((char)(v1[i] & 0xff) != StringUTF16.getChar(v2, i)) {
1066                     return false;
1067                 }
1068             }
1069         }
1070         return true;
1071     }
1072 
1073     /**
1074      * Compares this string to the specified {@code CharSequence}.  The
1075      * result is {@code true} if and only if this {@code String} represents the
1076      * same sequence of char values as the specified sequence. Note that if the
1077      * {@code CharSequence} is a {@code StringBuffer} then the method
1078      * synchronizes on it.
1079      *
1080      * <p>For finer-grained String comparison, refer to
1081      * {@link java.text.Collator}.
1082      *
1083      * @param  cs
1084      *         The sequence to compare this {@code String} against
1085      *
1086      * @return  {@code true} if this {@code String} represents the same
1087      *          sequence of char values as the specified sequence, {@code
1088      *          false} otherwise
1089      *
1090      * @since  1.5
1091      */
1092     public boolean contentEquals(CharSequence cs) {
1093         // Argument is a StringBuffer, StringBuilder
1094         if (cs instanceof AbstractStringBuilder) {
1095             if (cs instanceof StringBuffer) {
1096                 synchronized(cs) {
1097                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1098                 }
1099             } else {
1100                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1101             }
1102         }
1103         // Argument is a String
1104         if (cs instanceof String) {
1105             return equals(cs);
1106         }
1107         // Argument is a generic CharSequence
1108         int n = cs.length();
1109         if (n != length()) {
1110             return false;
1111         }
1112         byte[] val = this.value;
1113         if (isLatin1()) {
1114             for (int i = 0; i < n; i++) {
1115                 if ((val[i] & 0xff) != cs.charAt(i)) {
1116                     return false;
1117                 }
1118             }
1119         } else {
1120             for (int i = 0; i < n; i++) {
1121                 if (StringUTF16.getChar(val, i) != cs.charAt(i)) {
1122                     return false;
1123                 }
1124             }
1125         }
1126         return true;
1127     }
1128 
1129     /**
1130      * Compares this {@code String} to another {@code String}, ignoring case
1131      * considerations.  Two strings are considered equal ignoring case if they
1132      * are of the same length and corresponding characters in the two strings
1133      * are equal ignoring case.
1134      *
1135      * <p> Two characters {@code c1} and {@code c2} are considered the same
1136      * ignoring case if at least one of the following is true:
1137      * <ul>
1138      *   <li> The two characters are the same (as compared by the
1139      *        {@code ==} operator)
1140      *   <li> Calling {@code Character.toLowerCase(Character.toUpperCase(char))}
1141      *        on each character produces the same result
1142      * </ul>
1143      *
1144      * <p>Note that this method does <em>not</em> take locale into account, and
1145      * will result in unsatisfactory results for certain locales.  The
1146      * {@link java.text.Collator} class provides locale-sensitive comparison.
1147      *
1148      * @param  anotherString
1149      *         The {@code String} to compare this {@code String} against
1150      *
1151      * @return  {@code true} if the argument is not {@code null} and it
1152      *          represents an equivalent {@code String} ignoring case; {@code
1153      *          false} otherwise
1154      *
1155      * @see  #equals(Object)
1156      */
1157     public boolean equalsIgnoreCase(String anotherString) {
1158         return (this == anotherString) ? true
1159                 : (anotherString != null)
1160                 && (anotherString.length() == length())
1161                 && regionMatches(true, 0, anotherString, 0, length());
1162     }
1163 
1164     /**
1165      * Compares two strings lexicographically.
1166      * The comparison is based on the Unicode value of each character in
1167      * the strings. The character sequence represented by this
1168      * {@code String} object is compared lexicographically to the
1169      * character sequence represented by the argument string. The result is
1170      * a negative integer if this {@code String} object
1171      * lexicographically precedes the argument string. The result is a
1172      * positive integer if this {@code String} object lexicographically
1173      * follows the argument string. The result is zero if the strings
1174      * are equal; {@code compareTo} returns {@code 0} exactly when
1175      * the {@link #equals(Object)} method would return {@code true}.
1176      * <p>
1177      * This is the definition of lexicographic ordering. If two strings are
1178      * different, then either they have different characters at some index
1179      * that is a valid index for both strings, or their lengths are different,
1180      * or both. If they have different characters at one or more index
1181      * positions, let <i>k</i> be the smallest such index; then the string
1182      * whose character at position <i>k</i> has the smaller value, as
1183      * determined by using the {@code <} operator, lexicographically precedes the
1184      * other string. In this case, {@code compareTo} returns the
1185      * difference of the two character values at position {@code k} in
1186      * the two string -- that is, the value:
1187      * <blockquote><pre>
1188      * this.charAt(k)-anotherString.charAt(k)
1189      * </pre></blockquote>
1190      * If there is no index position at which they differ, then the shorter
1191      * string lexicographically precedes the longer string. In this case,
1192      * {@code compareTo} returns the difference of the lengths of the
1193      * strings -- that is, the value:
1194      * <blockquote><pre>
1195      * this.length()-anotherString.length()
1196      * </pre></blockquote>
1197      *
1198      * <p>For finer-grained String comparison, refer to
1199      * {@link java.text.Collator}.
1200      *
1201      * @param   anotherString   the {@code String} to be compared.
1202      * @return  the value {@code 0} if the argument string is equal to
1203      *          this string; a value less than {@code 0} if this string
1204      *          is lexicographically less than the string argument; and a
1205      *          value greater than {@code 0} if this string is
1206      *          lexicographically greater than the string argument.
1207      */
1208     public int compareTo(String anotherString) {
1209         byte v1[] = value;
1210         byte v2[] = anotherString.value;
1211         if (coder() == anotherString.coder()) {
1212             return isLatin1() ? StringLatin1.compareTo(v1, v2)
1213                               : StringUTF16.compareTo(v1, v2);
1214         }
1215         return isLatin1() ? StringLatin1.compareToUTF16(v1, v2)
1216                           : StringUTF16.compareToLatin1(v1, v2);
1217      }
1218 
1219     /**
1220      * A Comparator that orders {@code String} objects as by
1221      * {@code compareToIgnoreCase}. This comparator is serializable.
1222      * <p>
1223      * Note that this Comparator does <em>not</em> take locale into account,
1224      * and will result in an unsatisfactory ordering for certain locales.
1225      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1226      *
1227      * @see     java.text.Collator
1228      * @since   1.2
1229      */
1230     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1231                                          = new CaseInsensitiveComparator();
1232     private static class CaseInsensitiveComparator
1233             implements Comparator<String>, java.io.Serializable {
1234         // use serialVersionUID from JDK 1.2.2 for interoperability
1235         private static final long serialVersionUID = 8575799808933029326L;
1236 
1237         public int compare(String s1, String s2) {
1238             byte v1[] = s1.value;
1239             byte v2[] = s2.value;
1240             if (s1.coder() == s2.coder()) {
1241                 return s1.isLatin1() ? StringLatin1.compareToCI(v1, v2)
1242                                      : StringUTF16.compareToCI(v1, v2);
1243             }
1244             return s1.isLatin1() ? StringLatin1.compareToCI_UTF16(v1, v2)
1245                                  : StringUTF16.compareToCI_Latin1(v1, v2);
1246         }
1247 
1248         /** Replaces the de-serialized object. */
1249         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1250     }
1251 
1252     /**
1253      * Compares two strings lexicographically, ignoring case
1254      * differences. This method returns an integer whose sign is that of
1255      * calling {@code compareTo} with normalized versions of the strings
1256      * where case differences have been eliminated by calling
1257      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1258      * each character.
1259      * <p>
1260      * Note that this method does <em>not</em> take locale into account,
1261      * and will result in an unsatisfactory ordering for certain locales.
1262      * The {@link java.text.Collator} class provides locale-sensitive comparison.
1263      *
1264      * @param   str   the {@code String} to be compared.
1265      * @return  a negative integer, zero, or a positive integer as the
1266      *          specified String is greater than, equal to, or less
1267      *          than this String, ignoring case considerations.
1268      * @see     java.text.Collator
1269      * @since   1.2
1270      */
1271     public int compareToIgnoreCase(String str) {
1272         return CASE_INSENSITIVE_ORDER.compare(this, str);
1273     }
1274 
1275     /**
1276      * Tests if two string regions are equal.
1277      * <p>
1278      * A substring of this {@code String} object is compared to a substring
1279      * of the argument other. The result is true if these substrings
1280      * represent identical character sequences. The substring of this
1281      * {@code String} object to be compared begins at index {@code toffset}
1282      * and has length {@code len}. The substring of other to be compared
1283      * begins at index {@code ooffset} and has length {@code len}. The
1284      * result is {@code false} if and only if at least one of the following
1285      * is true:
1286      * <ul><li>{@code toffset} is negative.
1287      * <li>{@code ooffset} is negative.
1288      * <li>{@code toffset+len} is greater than the length of this
1289      * {@code String} object.
1290      * <li>{@code ooffset+len} is greater than the length of the other
1291      * argument.
1292      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1293      * such that:
1294      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1295      * <i>k</i>{@code )}
1296      * </ul>
1297      *
1298      * <p>Note that this method does <em>not</em> take locale into account.  The
1299      * {@link java.text.Collator} class provides locale-sensitive comparison.
1300      *
1301      * @param   toffset   the starting offset of the subregion in this string.
1302      * @param   other     the string argument.
1303      * @param   ooffset   the starting offset of the subregion in the string
1304      *                    argument.
1305      * @param   len       the number of characters to compare.
1306      * @return  {@code true} if the specified subregion of this string
1307      *          exactly matches the specified subregion of the string argument;
1308      *          {@code false} otherwise.
1309      */
1310     public boolean regionMatches(int toffset, String other, int ooffset, int len) {
1311         byte tv[] = value;
1312         byte ov[] = other.value;
1313         // Note: toffset, ooffset, or len might be near -1>>>1.
1314         if ((ooffset < 0) || (toffset < 0) ||
1315              (toffset > (long)length() - len) ||
1316              (ooffset > (long)other.length() - len)) {
1317             return false;
1318         }
1319         if (coder() == other.coder()) {
1320             if (!isLatin1() && (len > 0)) {
1321                 toffset = toffset << 1;
1322                 ooffset = ooffset << 1;
1323                 len = len << 1;
1324             }
1325             while (len-- > 0) {
1326                 if (tv[toffset++] != ov[ooffset++]) {
1327                     return false;
1328                 }
1329             }
1330         } else {
1331             if (coder() == LATIN1) {
1332                 while (len-- > 0) {
1333                     if (StringLatin1.getChar(tv, toffset++) !=
1334                         StringUTF16.getChar(ov, ooffset++)) {
1335                         return false;
1336                     }
1337                 }
1338             } else {
1339                 while (len-- > 0) {
1340                     if (StringUTF16.getChar(tv, toffset++) !=
1341                         StringLatin1.getChar(ov, ooffset++)) {
1342                         return false;
1343                     }
1344                 }
1345             }
1346         }
1347         return true;
1348     }
1349 
1350     /**
1351      * Tests if two string regions are equal.
1352      * <p>
1353      * A substring of this {@code String} object is compared to a substring
1354      * of the argument {@code other}. The result is {@code true} if these
1355      * substrings represent character sequences that are the same, ignoring
1356      * case if and only if {@code ignoreCase} is true. The substring of
1357      * this {@code String} object to be compared begins at index
1358      * {@code toffset} and has length {@code len}. The substring of
1359      * {@code other} to be compared begins at index {@code ooffset} and
1360      * has length {@code len}. The result is {@code false} if and only if
1361      * at least one of the following is true:
1362      * <ul><li>{@code toffset} is negative.
1363      * <li>{@code ooffset} is negative.
1364      * <li>{@code toffset+len} is greater than the length of this
1365      * {@code String} object.
1366      * <li>{@code ooffset+len} is greater than the length of the other
1367      * argument.
1368      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1369      * integer <i>k</i> less than {@code len} such that:
1370      * <blockquote><pre>
1371      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1372      * </pre></blockquote>
1373      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1374      * integer <i>k</i> less than {@code len} such that:
1375      * <blockquote><pre>
1376      * Character.toLowerCase(Character.toUpperCase(this.charAt(toffset+k))) !=
1377      Character.toLowerCase(Character.toUpperCase(other.charAt(ooffset+k)))
1378      * </pre></blockquote>
1379      * </ul>
1380      *
1381      * <p>Note that this method does <em>not</em> take locale into account,
1382      * and will result in unsatisfactory results for certain locales when
1383      * {@code ignoreCase} is {@code true}.  The {@link java.text.Collator} class
1384      * provides locale-sensitive comparison.
1385      *
1386      * @param   ignoreCase   if {@code true}, ignore case when comparing
1387      *                       characters.
1388      * @param   toffset      the starting offset of the subregion in this
1389      *                       string.
1390      * @param   other        the string argument.
1391      * @param   ooffset      the starting offset of the subregion in the string
1392      *                       argument.
1393      * @param   len          the number of characters to compare.
1394      * @return  {@code true} if the specified subregion of this string
1395      *          matches the specified subregion of the string argument;
1396      *          {@code false} otherwise. Whether the matching is exact
1397      *          or case insensitive depends on the {@code ignoreCase}
1398      *          argument.
1399      */
1400     public boolean regionMatches(boolean ignoreCase, int toffset,
1401             String other, int ooffset, int len) {
1402         if (!ignoreCase) {
1403             return regionMatches(toffset, other, ooffset, len);
1404         }
1405         // Note: toffset, ooffset, or len might be near -1>>>1.
1406         if ((ooffset < 0) || (toffset < 0)
1407                 || (toffset > (long)length() - len)
1408                 || (ooffset > (long)other.length() - len)) {
1409             return false;
1410         }
1411         byte tv[] = value;
1412         byte ov[] = other.value;
1413         if (coder() == other.coder()) {
1414             return isLatin1()
1415               ? StringLatin1.regionMatchesCI(tv, toffset, ov, ooffset, len)
1416               : StringUTF16.regionMatchesCI(tv, toffset, ov, ooffset, len);
1417         }
1418         return isLatin1()
1419               ? StringLatin1.regionMatchesCI_UTF16(tv, toffset, ov, ooffset, len)
1420               : StringUTF16.regionMatchesCI_Latin1(tv, toffset, ov, ooffset, len);
1421     }
1422 
1423     /**
1424      * Tests if the substring of this string beginning at the
1425      * specified index starts with the specified prefix.
1426      *
1427      * @param   prefix    the prefix.
1428      * @param   toffset   where to begin looking in this string.
1429      * @return  {@code true} if the character sequence represented by the
1430      *          argument is a prefix of the substring of this object starting
1431      *          at index {@code toffset}; {@code false} otherwise.
1432      *          The result is {@code false} if {@code toffset} is
1433      *          negative or greater than the length of this
1434      *          {@code String} object; otherwise the result is the same
1435      *          as the result of the expression
1436      *          <pre>
1437      *          this.substring(toffset).startsWith(prefix)
1438      *          </pre>
1439      */
1440     public boolean startsWith(String prefix, int toffset) {
1441         // Note: toffset might be near -1>>>1.
1442         if (toffset < 0 || toffset > length() - prefix.length()) {
1443             return false;
1444         }
1445         byte ta[] = value;
1446         byte pa[] = prefix.value;
1447         int po = 0;
1448         int pc = pa.length;
1449         if (coder() == prefix.coder()) {
1450             int to = isLatin1() ? toffset : toffset << 1;
1451             while (po < pc) {
1452                 if (ta[to++] != pa[po++]) {
1453                     return false;
1454                 }
1455             }
1456         } else {
1457             if (isLatin1()) {  // && pcoder == UTF16
1458                 return false;
1459             }
1460             // coder == UTF16 && pcoder == LATIN1)
1461             while (po < pc) {
1462                 if (StringUTF16.getChar(ta, toffset++) != (pa[po++] & 0xff)) {
1463                     return false;
1464                }
1465             }
1466         }
1467         return true;
1468     }
1469 
1470     /**
1471      * Tests if this string starts with the specified prefix.
1472      *
1473      * @param   prefix   the prefix.
1474      * @return  {@code true} if the character sequence represented by the
1475      *          argument is a prefix of the character sequence represented by
1476      *          this string; {@code false} otherwise.
1477      *          Note also that {@code true} will be returned if the
1478      *          argument is an empty string or is equal to this
1479      *          {@code String} object as determined by the
1480      *          {@link #equals(Object)} method.
1481      * @since   1.0
1482      */
1483     public boolean startsWith(String prefix) {
1484         return startsWith(prefix, 0);
1485     }
1486 
1487     /**
1488      * Tests if this string ends with the specified suffix.
1489      *
1490      * @param   suffix   the suffix.
1491      * @return  {@code true} if the character sequence represented by the
1492      *          argument is a suffix of the character sequence represented by
1493      *          this object; {@code false} otherwise. Note that the
1494      *          result will be {@code true} if the argument is the
1495      *          empty string or is equal to this {@code String} object
1496      *          as determined by the {@link #equals(Object)} method.
1497      */
1498     public boolean endsWith(String suffix) {
1499         return startsWith(suffix, length() - suffix.length());
1500     }
1501 
1502     /**
1503      * Returns a hash code for this string. The hash code for a
1504      * {@code String} object is computed as
1505      * <blockquote><pre>
1506      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1507      * </pre></blockquote>
1508      * using {@code int} arithmetic, where {@code s[i]} is the
1509      * <i>i</i>th character of the string, {@code n} is the length of
1510      * the string, and {@code ^} indicates exponentiation.
1511      * (The hash value of the empty string is zero.)
1512      *
1513      * @return  a hash code value for this object.
1514      */
1515     public int hashCode() {
1516         if (hash == 0 && value.length > 0) {
1517             hash = isLatin1() ? StringLatin1.hashCode(value)
1518                               : StringUTF16.hashCode(value);
1519         }
1520         return hash;
1521     }
1522 
1523     /**
1524      * Returns the index within this string of the first occurrence of
1525      * the specified character. If a character with value
1526      * {@code ch} occurs in the character sequence represented by
1527      * this {@code String} object, then the index (in Unicode
1528      * code units) of the first such occurrence is returned. For
1529      * values of {@code ch} in the range from 0 to 0xFFFF
1530      * (inclusive), this is the smallest value <i>k</i> such that:
1531      * <blockquote><pre>
1532      * this.charAt(<i>k</i>) == ch
1533      * </pre></blockquote>
1534      * is true. For other values of {@code ch}, it is the
1535      * smallest value <i>k</i> such that:
1536      * <blockquote><pre>
1537      * this.codePointAt(<i>k</i>) == ch
1538      * </pre></blockquote>
1539      * is true. In either case, if no such character occurs in this
1540      * string, then {@code -1} is returned.
1541      *
1542      * @param   ch   a character (Unicode code point).
1543      * @return  the index of the first occurrence of the character in the
1544      *          character sequence represented by this object, or
1545      *          {@code -1} if the character does not occur.
1546      */
1547     public int indexOf(int ch) {
1548         return indexOf(ch, 0);
1549     }
1550 
1551     /**
1552      * Returns the index within this string of the first occurrence of the
1553      * specified character, starting the search at the specified index.
1554      * <p>
1555      * If a character with value {@code ch} occurs in the
1556      * character sequence represented by this {@code String}
1557      * object at an index no smaller than {@code fromIndex}, then
1558      * the index of the first such occurrence is returned. For values
1559      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1560      * this is the smallest value <i>k</i> such that:
1561      * <blockquote><pre>
1562      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1563      * </pre></blockquote>
1564      * is true. For other values of {@code ch}, it is the
1565      * smallest value <i>k</i> such that:
1566      * <blockquote><pre>
1567      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1568      * </pre></blockquote>
1569      * is true. In either case, if no such character occurs in this
1570      * string at or after position {@code fromIndex}, then
1571      * {@code -1} is returned.
1572      *
1573      * <p>
1574      * There is no restriction on the value of {@code fromIndex}. If it
1575      * is negative, it has the same effect as if it were zero: this entire
1576      * string may be searched. If it is greater than the length of this
1577      * string, it has the same effect as if it were equal to the length of
1578      * this string: {@code -1} is returned.
1579      *
1580      * <p>All indices are specified in {@code char} values
1581      * (Unicode code units).
1582      *
1583      * @param   ch          a character (Unicode code point).
1584      * @param   fromIndex   the index to start the search from.
1585      * @return  the index of the first occurrence of the character in the
1586      *          character sequence represented by this object that is greater
1587      *          than or equal to {@code fromIndex}, or {@code -1}
1588      *          if the character does not occur.
1589      */
1590     public int indexOf(int ch, int fromIndex) {
1591         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex)
1592                           : StringUTF16.indexOf(value, ch, fromIndex);
1593     }
1594 
1595     /**
1596      * Returns the index within this string of the last occurrence of
1597      * the specified character. For values of {@code ch} in the
1598      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1599      * units) returned is the largest value <i>k</i> such that:
1600      * <blockquote><pre>
1601      * this.charAt(<i>k</i>) == ch
1602      * </pre></blockquote>
1603      * is true. For other values of {@code ch}, it is the
1604      * largest value <i>k</i> such that:
1605      * <blockquote><pre>
1606      * this.codePointAt(<i>k</i>) == ch
1607      * </pre></blockquote>
1608      * is true.  In either case, if no such character occurs in this
1609      * string, then {@code -1} is returned.  The
1610      * {@code String} is searched backwards starting at the last
1611      * character.
1612      *
1613      * @param   ch   a character (Unicode code point).
1614      * @return  the index of the last occurrence of the character in the
1615      *          character sequence represented by this object, or
1616      *          {@code -1} if the character does not occur.
1617      */
1618     public int lastIndexOf(int ch) {
1619         return lastIndexOf(ch, length() - 1);
1620     }
1621 
1622     /**
1623      * Returns the index within this string of the last occurrence of
1624      * the specified character, searching backward starting at the
1625      * specified index. For values of {@code ch} in the range
1626      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1627      * value <i>k</i> such that:
1628      * <blockquote><pre>
1629      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1630      * </pre></blockquote>
1631      * is true. For other values of {@code ch}, it is the
1632      * largest value <i>k</i> such that:
1633      * <blockquote><pre>
1634      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1635      * </pre></blockquote>
1636      * is true. In either case, if no such character occurs in this
1637      * string at or before position {@code fromIndex}, then
1638      * {@code -1} is returned.
1639      *
1640      * <p>All indices are specified in {@code char} values
1641      * (Unicode code units).
1642      *
1643      * @param   ch          a character (Unicode code point).
1644      * @param   fromIndex   the index to start the search from. There is no
1645      *          restriction on the value of {@code fromIndex}. If it is
1646      *          greater than or equal to the length of this string, it has
1647      *          the same effect as if it were equal to one less than the
1648      *          length of this string: this entire string may be searched.
1649      *          If it is negative, it has the same effect as if it were -1:
1650      *          -1 is returned.
1651      * @return  the index of the last occurrence of the character in the
1652      *          character sequence represented by this object that is less
1653      *          than or equal to {@code fromIndex}, or {@code -1}
1654      *          if the character does not occur before that point.
1655      */
1656     public int lastIndexOf(int ch, int fromIndex) {
1657         return isLatin1() ? StringLatin1.lastIndexOf(value, ch, fromIndex)
1658                           : StringUTF16.lastIndexOf(value, ch, fromIndex);
1659     }
1660 
1661     /**
1662      * Returns the index within this string of the first occurrence of the
1663      * specified substring.
1664      *
1665      * <p>The returned index is the smallest value {@code k} for which:
1666      * <pre>{@code
1667      * this.startsWith(str, k)
1668      * }</pre>
1669      * If no such value of {@code k} exists, then {@code -1} is returned.
1670      *
1671      * @param   str   the substring to search for.
1672      * @return  the index of the first occurrence of the specified substring,
1673      *          or {@code -1} if there is no such occurrence.
1674      */
1675     public int indexOf(String str) {
1676         if (coder() == str.coder()) {
1677             return isLatin1() ? StringLatin1.indexOf(value, str.value)
1678                               : StringUTF16.indexOf(value, str.value);
1679         }
1680         if (coder() == LATIN1) {  // str.coder == UTF16
1681             return -1;
1682         }
1683         return StringUTF16.indexOfLatin1(value, str.value);
1684     }
1685 
1686     /**
1687      * Returns the index within this string of the first occurrence of the
1688      * specified substring, starting at the specified index.
1689      *
1690      * <p>The returned index is the smallest value {@code k} for which:
1691      * <pre>{@code
1692      *     k >= Math.min(fromIndex, this.length()) &&
1693      *                   this.startsWith(str, k)
1694      * }</pre>
1695      * If no such value of {@code k} exists, then {@code -1} is returned.
1696      *
1697      * @param   str         the substring to search for.
1698      * @param   fromIndex   the index from which to start the search.
1699      * @return  the index of the first occurrence of the specified substring,
1700      *          starting at the specified index,
1701      *          or {@code -1} if there is no such occurrence.
1702      */
1703     public int indexOf(String str, int fromIndex) {
1704         return indexOf(value, coder(), length(), str, fromIndex);
1705     }
1706 
1707     /**
1708      * Code shared by String and AbstractStringBuilder to do searches. The
1709      * source is the character array being searched, and the target
1710      * is the string being searched for.
1711      *
1712      * @param   src       the characters being searched.
1713      * @param   srcCoder  the coder of the source string.
1714      * @param   srcCount  length of the source string.
1715      * @param   tgtStr    the characters being searched for.
1716      * @param   fromIndex the index to begin searching from.
1717      */
1718     static int indexOf(byte[] src, byte srcCoder, int srcCount,
1719                        String tgtStr, int fromIndex) {
1720         byte[] tgt    = tgtStr.value;
1721         byte tgtCoder = tgtStr.coder();
1722         int tgtCount  = tgtStr.length();
1723 
1724         if (fromIndex >= srcCount) {
1725             return (tgtCount == 0 ? srcCount : -1);
1726         }
1727         if (fromIndex < 0) {
1728             fromIndex = 0;
1729         }
1730         if (tgtCount == 0) {
1731             return fromIndex;
1732         }
1733         if (srcCoder == tgtCoder) {
1734             return srcCoder == LATIN1
1735                 ? StringLatin1.indexOf(src, srcCount, tgt, tgtCount, fromIndex)
1736                 : StringUTF16.indexOf(src, srcCount, tgt, tgtCount, fromIndex);
1737         }
1738         if (srcCoder == LATIN1) {    //  && tgtCoder == UTF16
1739             return -1;
1740         }
1741         // srcCoder == UTF16 && tgtCoder == LATIN1) {
1742         return StringUTF16.indexOfLatin1(src, srcCount, tgt, tgtCount, fromIndex);
1743     }
1744 
1745     /**
1746      * Returns the index within this string of the last occurrence of the
1747      * specified substring.  The last occurrence of the empty string ""
1748      * is considered to occur at the index value {@code this.length()}.
1749      *
1750      * <p>The returned index is the largest value {@code k} for which:
1751      * <pre>{@code
1752      * this.startsWith(str, k)
1753      * }</pre>
1754      * If no such value of {@code k} exists, then {@code -1} is returned.
1755      *
1756      * @param   str   the substring to search for.
1757      * @return  the index of the last occurrence of the specified substring,
1758      *          or {@code -1} if there is no such occurrence.
1759      */
1760     public int lastIndexOf(String str) {
1761         return lastIndexOf(str, length());
1762     }
1763 
1764     /**
1765      * Returns the index within this string of the last occurrence of the
1766      * specified substring, searching backward starting at the specified index.
1767      *
1768      * <p>The returned index is the largest value {@code k} for which:
1769      * <pre>{@code
1770      *     k <= Math.min(fromIndex, this.length()) &&
1771      *                   this.startsWith(str, k)
1772      * }</pre>
1773      * If no such value of {@code k} exists, then {@code -1} is returned.
1774      *
1775      * @param   str         the substring to search for.
1776      * @param   fromIndex   the index to start the search from.
1777      * @return  the index of the last occurrence of the specified substring,
1778      *          searching backward from the specified index,
1779      *          or {@code -1} if there is no such occurrence.
1780      */
1781     public int lastIndexOf(String str, int fromIndex) {
1782         return lastIndexOf(value, coder(), length(), str, fromIndex);
1783     }
1784 
1785     /**
1786      * Code shared by String and AbstractStringBuilder to do searches. The
1787      * source is the character array being searched, and the target
1788      * is the string being searched for.
1789      *
1790      * @param   src         the characters being searched.
1791      * @param   srcCoder  coder handles the mapping between bytes/chars
1792      * @param   srcCount    count of the source string.
1793      * @param   tgt         the characters being searched for.
1794      * @param   fromIndex   the index to begin searching from.
1795      */
1796     static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
1797                            String tgtStr, int fromIndex) {
1798         byte[] tgt = tgtStr.value;
1799         byte tgtCoder = tgtStr.coder();
1800         int tgtCount = tgtStr.length();
1801         /*
1802          * Check arguments; return immediately where possible. For
1803          * consistency, don't check for null str.
1804          */
1805         int rightIndex = srcCount - tgtCount;
1806         if (fromIndex < 0) {
1807             return -1;
1808         }
1809         if (fromIndex > rightIndex) {
1810             fromIndex = rightIndex;
1811         }
1812         /* Empty string always matches. */
1813         if (tgtCount == 0) {
1814             return fromIndex;
1815         }
1816         if (srcCoder == tgtCoder) {
1817             return srcCoder == LATIN1
1818                 ? StringLatin1.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex)
1819                 : StringUTF16.lastIndexOf(src, srcCount, tgt, tgtCount, fromIndex);
1820         }
1821         if (srcCoder == LATIN1) {    // && tgtCoder == UTF16
1822             return -1;
1823         }
1824                                      // srcCoder == UTF16 && tgtCoder == LATIN1
1825         int min = tgtCount - 1;
1826         int i = min + fromIndex;
1827         int strLastIndex = tgtCount - 1;
1828 
1829         char strLastChar = (char)(tgt[strLastIndex] & 0xff);
1830     startSearchForLastChar:
1831         while (true) {
1832             while (i >= min && StringUTF16.getChar(src, i) != strLastChar) {
1833                 i--;
1834             }
1835             if (i < min) {
1836                 return -1;
1837             }
1838             int j = i - 1;
1839             int start = j - strLastIndex;
1840             int k = strLastIndex - 1;
1841             while (j > start) {
1842                 if (StringUTF16.getChar(src, j--) != (tgt[k--] & 0xff)) {
1843                     i--;
1844                     continue startSearchForLastChar;
1845                 }
1846             }
1847             return start + 1;
1848         }
1849     }
1850 
1851     /**
1852      * Returns a string that is a substring of this string. The
1853      * substring begins with the character at the specified index and
1854      * extends to the end of this string. <p>
1855      * Examples:
1856      * <blockquote><pre>
1857      * "unhappy".substring(2) returns "happy"
1858      * "Harbison".substring(3) returns "bison"
1859      * "emptiness".substring(9) returns "" (an empty string)
1860      * </pre></blockquote>
1861      *
1862      * @param      beginIndex   the beginning index, inclusive.
1863      * @return     the specified substring.
1864      * @exception  IndexOutOfBoundsException  if
1865      *             {@code beginIndex} is negative or larger than the
1866      *             length of this {@code String} object.
1867      */
1868     public String substring(int beginIndex) {
1869         if (beginIndex < 0) {
1870             throw new StringIndexOutOfBoundsException(beginIndex);
1871         }
1872         int subLen = length() - beginIndex;
1873         if (subLen < 0) {
1874             throw new StringIndexOutOfBoundsException(subLen);
1875         }
1876         if (beginIndex == 0) {
1877             return this;
1878         }
1879         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1880                           : StringUTF16.newString(value, beginIndex, subLen);
1881     }
1882 
1883     /**
1884      * Returns a string that is a substring of this string. The
1885      * substring begins at the specified {@code beginIndex} and
1886      * extends to the character at index {@code endIndex - 1}.
1887      * Thus the length of the substring is {@code endIndex-beginIndex}.
1888      * <p>
1889      * Examples:
1890      * <blockquote><pre>
1891      * "hamburger".substring(4, 8) returns "urge"
1892      * "smiles".substring(1, 5) returns "mile"
1893      * </pre></blockquote>
1894      *
1895      * @param      beginIndex   the beginning index, inclusive.
1896      * @param      endIndex     the ending index, exclusive.
1897      * @return     the specified substring.
1898      * @exception  IndexOutOfBoundsException  if the
1899      *             {@code beginIndex} is negative, or
1900      *             {@code endIndex} is larger than the length of
1901      *             this {@code String} object, or
1902      *             {@code beginIndex} is larger than
1903      *             {@code endIndex}.
1904      */
1905     public String substring(int beginIndex, int endIndex) {
1906         int length = length();
1907         checkBoundsBeginEnd(beginIndex, endIndex, length);
1908         int subLen = endIndex - beginIndex;
1909         if (beginIndex == 0 && endIndex == length) {
1910             return this;
1911         }
1912         return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
1913                           : StringUTF16.newString(value, beginIndex, subLen);
1914     }
1915 
1916     /**
1917      * Returns a character sequence that is a subsequence of this sequence.
1918      *
1919      * <p> An invocation of this method of the form
1920      *
1921      * <blockquote><pre>
1922      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1923      *
1924      * behaves in exactly the same way as the invocation
1925      *
1926      * <blockquote><pre>
1927      * str.substring(begin,&nbsp;end)</pre></blockquote>
1928      *
1929      * @apiNote
1930      * This method is defined so that the {@code String} class can implement
1931      * the {@link CharSequence} interface.
1932      *
1933      * @param   beginIndex   the begin index, inclusive.
1934      * @param   endIndex     the end index, exclusive.
1935      * @return  the specified subsequence.
1936      *
1937      * @throws  IndexOutOfBoundsException
1938      *          if {@code beginIndex} or {@code endIndex} is negative,
1939      *          if {@code endIndex} is greater than {@code length()},
1940      *          or if {@code beginIndex} is greater than {@code endIndex}
1941      *
1942      * @since 1.4
1943      * @spec JSR-51
1944      */
1945     public CharSequence subSequence(int beginIndex, int endIndex) {
1946         return this.substring(beginIndex, endIndex);
1947     }
1948 
1949     /**
1950      * Concatenates the specified string to the end of this string.
1951      * <p>
1952      * If the length of the argument string is {@code 0}, then this
1953      * {@code String} object is returned. Otherwise, a
1954      * {@code String} object is returned that represents a character
1955      * sequence that is the concatenation of the character sequence
1956      * represented by this {@code String} object and the character
1957      * sequence represented by the argument string.<p>
1958      * Examples:
1959      * <blockquote><pre>
1960      * "cares".concat("s") returns "caress"
1961      * "to".concat("get").concat("her") returns "together"
1962      * </pre></blockquote>
1963      *
1964      * @param   str   the {@code String} that is concatenated to the end
1965      *                of this {@code String}.
1966      * @return  a string that represents the concatenation of this object's
1967      *          characters followed by the string argument's characters.
1968      */
1969     public String concat(String str) {
1970         int olen = str.length();
1971         if (olen == 0) {
1972             return this;
1973         }
1974         if (coder() == str.coder()) {
1975             byte[] val = this.value;
1976             byte[] oval = str.value;
1977             int len = val.length + oval.length;
1978             byte[] buf = Arrays.copyOf(val, len);
1979             System.arraycopy(oval, 0, buf, val.length, oval.length);
1980             return new String(buf, coder);
1981         }
1982         int len = length();
1983         byte[] buf = StringUTF16.newBytesFor(len + olen);
1984         getBytes(buf, 0, UTF16);
1985         str.getBytes(buf, len, UTF16);
1986         return new String(buf, UTF16);
1987     }
1988 
1989     /**
1990      * Returns a string resulting from replacing all occurrences of
1991      * {@code oldChar} in this string with {@code newChar}.
1992      * <p>
1993      * If the character {@code oldChar} does not occur in the
1994      * character sequence represented by this {@code String} object,
1995      * then a reference to this {@code String} object is returned.
1996      * Otherwise, a {@code String} object is returned that
1997      * represents a character sequence identical to the character sequence
1998      * represented by this {@code String} object, except that every
1999      * occurrence of {@code oldChar} is replaced by an occurrence
2000      * of {@code newChar}.
2001      * <p>
2002      * Examples:
2003      * <blockquote><pre>
2004      * "mesquite in your cellar".replace('e', 'o')
2005      *         returns "mosquito in your collar"
2006      * "the war of baronets".replace('r', 'y')
2007      *         returns "the way of bayonets"
2008      * "sparring with a purple porpoise".replace('p', 't')
2009      *         returns "starring with a turtle tortoise"
2010      * "JonL".replace('q', 'x') returns "JonL" (no change)
2011      * </pre></blockquote>
2012      *
2013      * @param   oldChar   the old character.
2014      * @param   newChar   the new character.
2015      * @return  a string derived from this string by replacing every
2016      *          occurrence of {@code oldChar} with {@code newChar}.
2017      */
2018     public String replace(char oldChar, char newChar) {
2019         if (oldChar != newChar) {
2020             String ret = isLatin1() ? StringLatin1.replace(value, oldChar, newChar)
2021                                     : StringUTF16.replace(value, oldChar, newChar);
2022             if (ret != null) {
2023                 return ret;
2024             }
2025         }
2026         return this;
2027     }
2028 
2029     /**
2030      * Tells whether or not this string matches the given <a
2031      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2032      *
2033      * <p> An invocation of this method of the form
2034      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2035      * same result as the expression
2036      *
2037      * <blockquote>
2038      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2039      * matches(<i>regex</i>, <i>str</i>)}
2040      * </blockquote>
2041      *
2042      * @param   regex
2043      *          the regular expression to which this string is to be matched
2044      *
2045      * @return  {@code true} if, and only if, this string matches the
2046      *          given regular expression
2047      *
2048      * @throws  PatternSyntaxException
2049      *          if the regular expression's syntax is invalid
2050      *
2051      * @see java.util.regex.Pattern
2052      *
2053      * @since 1.4
2054      * @spec JSR-51
2055      */
2056     public boolean matches(String regex) {
2057         return Pattern.matches(regex, this);
2058     }
2059 
2060     /**
2061      * Returns true if and only if this string contains the specified
2062      * sequence of char values.
2063      *
2064      * @param s the sequence to search for
2065      * @return true if this string contains {@code s}, false otherwise
2066      * @since 1.5
2067      */
2068     public boolean contains(CharSequence s) {
2069         return indexOf(s.toString()) >= 0;
2070     }
2071 
2072     /**
2073      * Replaces the first substring of this string that matches the given <a
2074      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2075      * given replacement.
2076      *
2077      * <p> An invocation of this method of the form
2078      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2079      * yields exactly the same result as the expression
2080      *
2081      * <blockquote>
2082      * <code>
2083      * {@link java.util.regex.Pattern}.{@link
2084      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2085      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2086      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2087      * </code>
2088      * </blockquote>
2089      *
2090      *<p>
2091      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2092      * replacement string may cause the results to be different than if it were
2093      * being treated as a literal replacement string; see
2094      * {@link java.util.regex.Matcher#replaceFirst}.
2095      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2096      * meaning of these characters, if desired.
2097      *
2098      * @param   regex
2099      *          the regular expression to which this string is to be matched
2100      * @param   replacement
2101      *          the string to be substituted for the first match
2102      *
2103      * @return  The resulting {@code String}
2104      *
2105      * @throws  PatternSyntaxException
2106      *          if the regular expression's syntax is invalid
2107      *
2108      * @see java.util.regex.Pattern
2109      *
2110      * @since 1.4
2111      * @spec JSR-51
2112      */
2113     public String replaceFirst(String regex, String replacement) {
2114         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2115     }
2116 
2117     /**
2118      * Replaces each substring of this string that matches the given <a
2119      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2120      * given replacement.
2121      *
2122      * <p> An invocation of this method of the form
2123      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2124      * yields exactly the same result as the expression
2125      *
2126      * <blockquote>
2127      * <code>
2128      * {@link java.util.regex.Pattern}.{@link
2129      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2130      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2131      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2132      * </code>
2133      * </blockquote>
2134      *
2135      *<p>
2136      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2137      * replacement string may cause the results to be different than if it were
2138      * being treated as a literal replacement string; see
2139      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2140      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2141      * meaning of these characters, if desired.
2142      *
2143      * @param   regex
2144      *          the regular expression to which this string is to be matched
2145      * @param   replacement
2146      *          the string to be substituted for each match
2147      *
2148      * @return  The resulting {@code String}
2149      *
2150      * @throws  PatternSyntaxException
2151      *          if the regular expression's syntax is invalid
2152      *
2153      * @see java.util.regex.Pattern
2154      *
2155      * @since 1.4
2156      * @spec JSR-51
2157      */
2158     public String replaceAll(String regex, String replacement) {
2159         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2160     }
2161 
2162     /**
2163      * Replaces each substring of this string that matches the literal target
2164      * sequence with the specified literal replacement sequence. The
2165      * replacement proceeds from the beginning of the string to the end, for
2166      * example, replacing "aa" with "b" in the string "aaa" will result in
2167      * "ba" rather than "ab".
2168      *
2169      * @param  target The sequence of char values to be replaced
2170      * @param  replacement The replacement sequence of char values
2171      * @return  The resulting string
2172      * @since 1.5
2173      */
2174     public String replace(CharSequence target, CharSequence replacement) {
2175         String tgtStr = target.toString();
2176         String replStr = replacement.toString();
2177         int j = indexOf(tgtStr);
2178         if (j < 0) {
2179             return this;
2180         }
2181         int tgtLen = tgtStr.length();
2182         int tgtLen1 = Math.max(tgtLen, 1);
2183         int thisLen = length();
2184 
2185         int newLenHint = thisLen - tgtLen + replStr.length();
2186         if (newLenHint < 0) {
2187             throw new OutOfMemoryError();
2188         }
2189         StringBuilder sb = new StringBuilder(newLenHint);
2190         int i = 0;
2191         do {
2192             sb.append(this, i, j).append(replStr);
2193             i = j + tgtLen;
2194         } while (j < thisLen && (j = indexOf(tgtStr, j + tgtLen1)) > 0);
2195         return sb.append(this, i, thisLen).toString();
2196     }
2197 
2198     /**
2199      * Splits this string around matches of the given
2200      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2201      *
2202      * <p> The array returned by this method contains each substring of this
2203      * string that is terminated by another substring that matches the given
2204      * expression or is terminated by the end of the string.  The substrings in
2205      * the array are in the order in which they occur in this string.  If the
2206      * expression does not match any part of the input then the resulting array
2207      * has just one element, namely this string.
2208      *
2209      * <p> When there is a positive-width match at the beginning of this
2210      * string then an empty leading substring is included at the beginning
2211      * of the resulting array. A zero-width match at the beginning however
2212      * never produces such empty leading substring.
2213      *
2214      * <p> The {@code limit} parameter controls the number of times the
2215      * pattern is applied and therefore affects the length of the resulting
2216      * array.  If the limit <i>n</i> is greater than zero then the pattern
2217      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2218      * length will be no greater than <i>n</i>, and the array's last entry
2219      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2220      * is non-positive then the pattern will be applied as many times as
2221      * possible and the array can have any length.  If <i>n</i> is zero then
2222      * the pattern will be applied as many times as possible, the array can
2223      * have any length, and trailing empty strings will be discarded.
2224      *
2225      * <p> The string {@code "boo:and:foo"}, for example, yields the
2226      * following results with these parameters:
2227      *
2228      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and result">
2229      * <tr>
2230      *     <th>Regex</th>
2231      *     <th>Limit</th>
2232      *     <th>Result</th>
2233      * </tr>
2234      * <tr><td align=center>:</td>
2235      *     <td align=center>2</td>
2236      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2237      * <tr><td align=center>:</td>
2238      *     <td align=center>5</td>
2239      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2240      * <tr><td align=center>:</td>
2241      *     <td align=center>-2</td>
2242      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2243      * <tr><td align=center>o</td>
2244      *     <td align=center>5</td>
2245      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2246      * <tr><td align=center>o</td>
2247      *     <td align=center>-2</td>
2248      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2249      * <tr><td align=center>o</td>
2250      *     <td align=center>0</td>
2251      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2252      * </table></blockquote>
2253      *
2254      * <p> An invocation of this method of the form
2255      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2256      * yields the same result as the expression
2257      *
2258      * <blockquote>
2259      * <code>
2260      * {@link java.util.regex.Pattern}.{@link
2261      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2262      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2263      * </code>
2264      * </blockquote>
2265      *
2266      *
2267      * @param  regex
2268      *         the delimiting regular expression
2269      *
2270      * @param  limit
2271      *         the result threshold, as described above
2272      *
2273      * @return  the array of strings computed by splitting this string
2274      *          around matches of the given regular expression
2275      *
2276      * @throws  PatternSyntaxException
2277      *          if the regular expression's syntax is invalid
2278      *
2279      * @see java.util.regex.Pattern
2280      *
2281      * @since 1.4
2282      * @spec JSR-51
2283      */
2284     public String[] split(String regex, int limit) {
2285         /* fastpath if the regex is a
2286          (1)one-char String and this character is not one of the
2287             RegEx's meta characters ".$|()[{^?*+\\", or
2288          (2)two-char String and the first char is the backslash and
2289             the second is not the ascii digit or ascii letter.
2290          */
2291         char ch = 0;
2292         if (((regex.length() == 1 &&
2293              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2294              (regex.length() == 2 &&
2295               regex.charAt(0) == '\\' &&
2296               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2297               ((ch-'a')|('z'-ch)) < 0 &&
2298               ((ch-'A')|('Z'-ch)) < 0)) &&
2299             (ch < Character.MIN_HIGH_SURROGATE ||
2300              ch > Character.MAX_LOW_SURROGATE))
2301         {
2302             int off = 0;
2303             int next = 0;
2304             boolean limited = limit > 0;
2305             ArrayList<String> list = new ArrayList<>();
2306             while ((next = indexOf(ch, off)) != -1) {
2307                 if (!limited || list.size() < limit - 1) {
2308                     list.add(substring(off, next));
2309                     off = next + 1;
2310                 } else {    // last one
2311                     //assert (list.size() == limit - 1);
2312                     int last = length();
2313                     list.add(substring(off, last));
2314                     off = last;
2315                     break;
2316                 }
2317             }
2318             // If no match was found, return this
2319             if (off == 0)
2320                 return new String[]{this};
2321 
2322             // Add remaining segment
2323             if (!limited || list.size() < limit)
2324                 list.add(substring(off, length()));
2325 
2326             // Construct result
2327             int resultSize = list.size();
2328             if (limit == 0) {
2329                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2330                     resultSize--;
2331                 }
2332             }
2333             String[] result = new String[resultSize];
2334             return list.subList(0, resultSize).toArray(result);
2335         }
2336         return Pattern.compile(regex).split(this, limit);
2337     }
2338 
2339     /**
2340      * Splits this string around matches of the given <a
2341      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2342      *
2343      * <p> This method works as if by invoking the two-argument {@link
2344      * #split(String, int) split} method with the given expression and a limit
2345      * argument of zero.  Trailing empty strings are therefore not included in
2346      * the resulting array.
2347      *
2348      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2349      * results with these expressions:
2350      *
2351      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and result">
2352      * <tr>
2353      *  <th>Regex</th>
2354      *  <th>Result</th>
2355      * </tr>
2356      * <tr><td align=center>:</td>
2357      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2358      * <tr><td align=center>o</td>
2359      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2360      * </table></blockquote>
2361      *
2362      *
2363      * @param  regex
2364      *         the delimiting regular expression
2365      *
2366      * @return  the array of strings computed by splitting this string
2367      *          around matches of the given regular expression
2368      *
2369      * @throws  PatternSyntaxException
2370      *          if the regular expression's syntax is invalid
2371      *
2372      * @see java.util.regex.Pattern
2373      *
2374      * @since 1.4
2375      * @spec JSR-51
2376      */
2377     public String[] split(String regex) {
2378         return split(regex, 0);
2379     }
2380 
2381     /**
2382      * Returns a new String composed of copies of the
2383      * {@code CharSequence elements} joined together with a copy of
2384      * the specified {@code delimiter}.
2385      *
2386      * <blockquote>For example,
2387      * <pre>{@code
2388      *     String message = String.join("-", "Java", "is", "cool");
2389      *     // message returned is: "Java-is-cool"
2390      * }</pre></blockquote>
2391      *
2392      * Note that if an element is null, then {@code "null"} is added.
2393      *
2394      * @param  delimiter the delimiter that separates each element
2395      * @param  elements the elements to join together.
2396      *
2397      * @return a new {@code String} that is composed of the {@code elements}
2398      *         separated by the {@code delimiter}
2399      *
2400      * @throws NullPointerException If {@code delimiter} or {@code elements}
2401      *         is {@code null}
2402      *
2403      * @see java.util.StringJoiner
2404      * @since 1.8
2405      */
2406     public static String join(CharSequence delimiter, CharSequence... elements) {
2407         Objects.requireNonNull(delimiter);
2408         Objects.requireNonNull(elements);
2409         // Number of elements not likely worth Arrays.stream overhead.
2410         StringJoiner joiner = new StringJoiner(delimiter);
2411         for (CharSequence cs: elements) {
2412             joiner.add(cs);
2413         }
2414         return joiner.toString();
2415     }
2416 
2417     /**
2418      * Returns a new {@code String} composed of copies of the
2419      * {@code CharSequence elements} joined together with a copy of the
2420      * specified {@code delimiter}.
2421      *
2422      * <blockquote>For example,
2423      * <pre>{@code
2424      *     List<String> strings = new LinkedList<>();
2425      *     strings.add("Java");strings.add("is");
2426      *     strings.add("cool");
2427      *     String message = String.join(" ", strings);
2428      *     //message returned is: "Java is cool"
2429      *
2430      *     Set<String> strings = new LinkedHashSet<>();
2431      *     strings.add("Java"); strings.add("is");
2432      *     strings.add("very"); strings.add("cool");
2433      *     String message = String.join("-", strings);
2434      *     //message returned is: "Java-is-very-cool"
2435      * }</pre></blockquote>
2436      *
2437      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2438      *
2439      * @param  delimiter a sequence of characters that is used to separate each
2440      *         of the {@code elements} in the resulting {@code String}
2441      * @param  elements an {@code Iterable} that will have its {@code elements}
2442      *         joined together.
2443      *
2444      * @return a new {@code String} that is composed from the {@code elements}
2445      *         argument
2446      *
2447      * @throws NullPointerException If {@code delimiter} or {@code elements}
2448      *         is {@code null}
2449      *
2450      * @see    #join(CharSequence,CharSequence...)
2451      * @see    java.util.StringJoiner
2452      * @since 1.8
2453      */
2454     public static String join(CharSequence delimiter,
2455             Iterable<? extends CharSequence> elements) {
2456         Objects.requireNonNull(delimiter);
2457         Objects.requireNonNull(elements);
2458         StringJoiner joiner = new StringJoiner(delimiter);
2459         for (CharSequence cs: elements) {
2460             joiner.add(cs);
2461         }
2462         return joiner.toString();
2463     }
2464 
2465     /**
2466      * Converts all of the characters in this {@code String} to lower
2467      * case using the rules of the given {@code Locale}.  Case mapping is based
2468      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2469      * class. Since case mappings are not always 1:1 char mappings, the resulting
2470      * {@code String} may be a different length than the original {@code String}.
2471      * <p>
2472      * Examples of lowercase  mappings are in the following table:
2473      * <table border="1" summary="Lowercase mapping examples showing language code of locale, upper case, lower case, and description">
2474      * <tr>
2475      *   <th>Language Code of Locale</th>
2476      *   <th>Upper Case</th>
2477      *   <th>Lower Case</th>
2478      *   <th>Description</th>
2479      * </tr>
2480      * <tr>
2481      *   <td>tr (Turkish)</td>
2482      *   <td>\u0130</td>
2483      *   <td>\u0069</td>
2484      *   <td>capital letter I with dot above -&gt; small letter i</td>
2485      * </tr>
2486      * <tr>
2487      *   <td>tr (Turkish)</td>
2488      *   <td>\u0049</td>
2489      *   <td>\u0131</td>
2490      *   <td>capital letter I -&gt; small letter dotless i </td>
2491      * </tr>
2492      * <tr>
2493      *   <td>(all)</td>
2494      *   <td>French Fries</td>
2495      *   <td>french fries</td>
2496      *   <td>lowercased all chars in String</td>
2497      * </tr>
2498      * <tr>
2499      *   <td>(all)</td>
2500      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2501      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2502      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2503      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2504      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2505      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2506      *   <td>lowercased all chars in String</td>
2507      * </tr>
2508      * </table>
2509      *
2510      * @param locale use the case transformation rules for this locale
2511      * @return the {@code String}, converted to lowercase.
2512      * @see     java.lang.String#toLowerCase()
2513      * @see     java.lang.String#toUpperCase()
2514      * @see     java.lang.String#toUpperCase(Locale)
2515      * @since   1.1
2516      */
2517     public String toLowerCase(Locale locale) {
2518         return isLatin1() ? StringLatin1.toLowerCase(this, value, locale)
2519                           : StringUTF16.toLowerCase(this, value, locale);
2520     }
2521 
2522     /**
2523      * Converts all of the characters in this {@code String} to lower
2524      * case using the rules of the default locale. This is equivalent to calling
2525      * {@code toLowerCase(Locale.getDefault())}.
2526      * <p>
2527      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2528      * results if used for strings that are intended to be interpreted locale
2529      * independently.
2530      * Examples are programming language identifiers, protocol keys, and HTML
2531      * tags.
2532      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2533      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2534      * LATIN SMALL LETTER DOTLESS I character.
2535      * To obtain correct results for locale insensitive strings, use
2536      * {@code toLowerCase(Locale.ROOT)}.
2537      *
2538      * @return  the {@code String}, converted to lowercase.
2539      * @see     java.lang.String#toLowerCase(Locale)
2540      */
2541     public String toLowerCase() {
2542         return toLowerCase(Locale.getDefault());
2543     }
2544 
2545     /**
2546      * Converts all of the characters in this {@code String} to upper
2547      * case using the rules of the given {@code Locale}. Case mapping is based
2548      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2549      * class. Since case mappings are not always 1:1 char mappings, the resulting
2550      * {@code String} may be a different length than the original {@code String}.
2551      * <p>
2552      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2553      *
2554      * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.">
2555      * <tr>
2556      *   <th>Language Code of Locale</th>
2557      *   <th>Lower Case</th>
2558      *   <th>Upper Case</th>
2559      *   <th>Description</th>
2560      * </tr>
2561      * <tr>
2562      *   <td>tr (Turkish)</td>
2563      *   <td>\u0069</td>
2564      *   <td>\u0130</td>
2565      *   <td>small letter i -&gt; capital letter I with dot above</td>
2566      * </tr>
2567      * <tr>
2568      *   <td>tr (Turkish)</td>
2569      *   <td>\u0131</td>
2570      *   <td>\u0049</td>
2571      *   <td>small letter dotless i -&gt; capital letter I</td>
2572      * </tr>
2573      * <tr>
2574      *   <td>(all)</td>
2575      *   <td>\u00df</td>
2576      *   <td>\u0053 \u0053</td>
2577      *   <td>small letter sharp s -&gt; two letters: SS</td>
2578      * </tr>
2579      * <tr>
2580      *   <td>(all)</td>
2581      *   <td>Fahrvergn&uuml;gen</td>
2582      *   <td>FAHRVERGN&Uuml;GEN</td>
2583      *   <td></td>
2584      * </tr>
2585      * </table>
2586      * @param locale use the case transformation rules for this locale
2587      * @return the {@code String}, converted to uppercase.
2588      * @see     java.lang.String#toUpperCase()
2589      * @see     java.lang.String#toLowerCase()
2590      * @see     java.lang.String#toLowerCase(Locale)
2591      * @since   1.1
2592      */
2593     public String toUpperCase(Locale locale) {
2594         return isLatin1() ? StringLatin1.toUpperCase(this, value, locale)
2595                           : StringUTF16.toUpperCase(this, value, locale);
2596     }
2597 
2598     /**
2599      * Converts all of the characters in this {@code String} to upper
2600      * case using the rules of the default locale. This method is equivalent to
2601      * {@code toUpperCase(Locale.getDefault())}.
2602      * <p>
2603      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2604      * results if used for strings that are intended to be interpreted locale
2605      * independently.
2606      * Examples are programming language identifiers, protocol keys, and HTML
2607      * tags.
2608      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2609      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2610      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2611      * To obtain correct results for locale insensitive strings, use
2612      * {@code toUpperCase(Locale.ROOT)}.
2613      *
2614      * @return  the {@code String}, converted to uppercase.
2615      * @see     java.lang.String#toUpperCase(Locale)
2616      */
2617     public String toUpperCase() {
2618         return toUpperCase(Locale.getDefault());
2619     }
2620 
2621     /**
2622      * Returns a string whose value is this string, with any leading and trailing
2623      * whitespace removed.
2624      * <p>
2625      * If this {@code String} object represents an empty character
2626      * sequence, or the first and last characters of character sequence
2627      * represented by this {@code String} object both have codes
2628      * greater than {@code '\u005Cu0020'} (the space character), then a
2629      * reference to this {@code String} object is returned.
2630      * <p>
2631      * Otherwise, if there is no character with a code greater than
2632      * {@code '\u005Cu0020'} in the string, then a
2633      * {@code String} object representing an empty string is
2634      * returned.
2635      * <p>
2636      * Otherwise, let <i>k</i> be the index of the first character in the
2637      * string whose code is greater than {@code '\u005Cu0020'}, and let
2638      * <i>m</i> be the index of the last character in the string whose code
2639      * is greater than {@code '\u005Cu0020'}. A {@code String}
2640      * object is returned, representing the substring of this string that
2641      * begins with the character at index <i>k</i> and ends with the
2642      * character at index <i>m</i>-that is, the result of
2643      * {@code this.substring(k, m + 1)}.
2644      * <p>
2645      * This method may be used to trim whitespace (as defined above) from
2646      * the beginning and end of a string.
2647      *
2648      * @return  A string whose value is this string, with any leading and trailing white
2649      *          space removed, or this string if it has no leading or
2650      *          trailing white space.
2651      */
2652     public String trim() {
2653         String ret = isLatin1() ? StringLatin1.trim(value)
2654                                 : StringUTF16.trim(value);
2655         return ret == null ? this : ret;
2656     }
2657 
2658     /**
2659      * This object (which is already a string!) is itself returned.
2660      *
2661      * @return  the string itself.
2662      */
2663     public String toString() {
2664         return this;
2665     }
2666 
2667     /**
2668      * Returns a stream of {@code int} zero-extending the {@code char} values
2669      * from this sequence.  Any char which maps to a <a
2670      * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
2671      * point</a> is passed through uninterpreted.
2672      *
2673      * @return an IntStream of char values from this sequence
2674      * @since 9
2675      */
2676     @Override
2677     public IntStream chars() {
2678         return StreamSupport.intStream(
2679             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2680                        : new StringUTF16.CharsSpliterator(value, Spliterator.IMMUTABLE),
2681             false);
2682     }
2683 
2684 
2685     /**
2686      * Returns a stream of code point values from this sequence.  Any surrogate
2687      * pairs encountered in the sequence are combined as if by {@linkplain
2688      * Character#toCodePoint Character.toCodePoint} and the result is passed
2689      * to the stream. Any other code units, including ordinary BMP characters,
2690      * unpaired surrogates, and undefined code units, are zero-extended to
2691      * {@code int} values which are then passed to the stream.
2692      *
2693      * @return an IntStream of Unicode code points from this sequence
2694      * @since 9
2695      */
2696     @Override
2697     public IntStream codePoints() {
2698         return StreamSupport.intStream(
2699             isLatin1() ? new StringLatin1.CharsSpliterator(value, Spliterator.IMMUTABLE)
2700                        : new StringUTF16.CodePointsSpliterator(value, Spliterator.IMMUTABLE),
2701             false);
2702     }
2703 
2704     /**
2705      * Converts this string to a new character array.
2706      *
2707      * @return  a newly allocated character array whose length is the length
2708      *          of this string and whose contents are initialized to contain
2709      *          the character sequence represented by this string.
2710      */
2711     public char[] toCharArray() {
2712         return isLatin1() ? StringLatin1.toChars(value)
2713                           : StringUTF16.toChars(value);
2714     }
2715 
2716     /**
2717      * Returns a formatted string using the specified format string and
2718      * arguments.
2719      *
2720      * <p> The locale always used is the one returned by {@link
2721      * java.util.Locale#getDefault() Locale.getDefault()}.
2722      *
2723      * @param  format
2724      *         A <a href="../util/Formatter.html#syntax">format string</a>
2725      *
2726      * @param  args
2727      *         Arguments referenced by the format specifiers in the format
2728      *         string.  If there are more arguments than format specifiers, the
2729      *         extra arguments are ignored.  The number of arguments is
2730      *         variable and may be zero.  The maximum number of arguments is
2731      *         limited by the maximum dimension of a Java array as defined by
2732      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2733      *         The behaviour on a
2734      *         {@code null} argument depends on the <a
2735      *         href="../util/Formatter.html#syntax">conversion</a>.
2736      *
2737      * @throws  java.util.IllegalFormatException
2738      *          If a format string contains an illegal syntax, a format
2739      *          specifier that is incompatible with the given arguments,
2740      *          insufficient arguments given the format string, or other
2741      *          illegal conditions.  For specification of all possible
2742      *          formatting errors, see the <a
2743      *          href="../util/Formatter.html#detail">Details</a> section of the
2744      *          formatter class specification.
2745      *
2746      * @return  A formatted string
2747      *
2748      * @see  java.util.Formatter
2749      * @since  1.5
2750      */
2751     public static String format(String format, Object... args) {
2752         return new Formatter().format(format, args).toString();
2753     }
2754 
2755     /**
2756      * Returns a formatted string using the specified locale, format string,
2757      * and arguments.
2758      *
2759      * @param  l
2760      *         The {@linkplain java.util.Locale locale} to apply during
2761      *         formatting.  If {@code l} is {@code null} then no localization
2762      *         is applied.
2763      *
2764      * @param  format
2765      *         A <a href="../util/Formatter.html#syntax">format string</a>
2766      *
2767      * @param  args
2768      *         Arguments referenced by the format specifiers in the format
2769      *         string.  If there are more arguments than format specifiers, the
2770      *         extra arguments are ignored.  The number of arguments is
2771      *         variable and may be zero.  The maximum number of arguments is
2772      *         limited by the maximum dimension of a Java array as defined by
2773      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2774      *         The behaviour on a
2775      *         {@code null} argument depends on the
2776      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2777      *
2778      * @throws  java.util.IllegalFormatException
2779      *          If a format string contains an illegal syntax, a format
2780      *          specifier that is incompatible with the given arguments,
2781      *          insufficient arguments given the format string, or other
2782      *          illegal conditions.  For specification of all possible
2783      *          formatting errors, see the <a
2784      *          href="../util/Formatter.html#detail">Details</a> section of the
2785      *          formatter class specification
2786      *
2787      * @return  A formatted string
2788      *
2789      * @see  java.util.Formatter
2790      * @since  1.5
2791      */
2792     public static String format(Locale l, String format, Object... args) {
2793         return new Formatter(l).format(format, args).toString();
2794     }
2795 
2796     /**
2797      * Returns the string representation of the {@code Object} argument.
2798      *
2799      * @param   obj   an {@code Object}.
2800      * @return  if the argument is {@code null}, then a string equal to
2801      *          {@code "null"}; otherwise, the value of
2802      *          {@code obj.toString()} is returned.
2803      * @see     java.lang.Object#toString()
2804      */
2805     public static String valueOf(Object obj) {
2806         return (obj == null) ? "null" : obj.toString();
2807     }
2808 
2809     /**
2810      * Returns the string representation of the {@code char} array
2811      * argument. The contents of the character array are copied; subsequent
2812      * modification of the character array does not affect the returned
2813      * string.
2814      *
2815      * @param   data     the character array.
2816      * @return  a {@code String} that contains the characters of the
2817      *          character array.
2818      */
2819     public static String valueOf(char data[]) {
2820         return new String(data);
2821     }
2822 
2823     /**
2824      * Returns the string representation of a specific subarray of the
2825      * {@code char} array argument.
2826      * <p>
2827      * The {@code offset} argument is the index of the first
2828      * character of the subarray. The {@code count} argument
2829      * specifies the length of the subarray. The contents of the subarray
2830      * are copied; subsequent modification of the character array does not
2831      * affect the returned string.
2832      *
2833      * @param   data     the character array.
2834      * @param   offset   initial offset of the subarray.
2835      * @param   count    length of the subarray.
2836      * @return  a {@code String} that contains the characters of the
2837      *          specified subarray of the character array.
2838      * @exception IndexOutOfBoundsException if {@code offset} is
2839      *          negative, or {@code count} is negative, or
2840      *          {@code offset+count} is larger than
2841      *          {@code data.length}.
2842      */
2843     public static String valueOf(char data[], int offset, int count) {
2844         return new String(data, offset, count);
2845     }
2846 
2847     /**
2848      * Equivalent to {@link #valueOf(char[], int, int)}.
2849      *
2850      * @param   data     the character array.
2851      * @param   offset   initial offset of the subarray.
2852      * @param   count    length of the subarray.
2853      * @return  a {@code String} that contains the characters of the
2854      *          specified subarray of the character array.
2855      * @exception IndexOutOfBoundsException if {@code offset} is
2856      *          negative, or {@code count} is negative, or
2857      *          {@code offset+count} is larger than
2858      *          {@code data.length}.
2859      */
2860     public static String copyValueOf(char data[], int offset, int count) {
2861         return new String(data, offset, count);
2862     }
2863 
2864     /**
2865      * Equivalent to {@link #valueOf(char[])}.
2866      *
2867      * @param   data   the character array.
2868      * @return  a {@code String} that contains the characters of the
2869      *          character array.
2870      */
2871     public static String copyValueOf(char data[]) {
2872         return new String(data);
2873     }
2874 
2875     /**
2876      * Returns the string representation of the {@code boolean} argument.
2877      *
2878      * @param   b   a {@code boolean}.
2879      * @return  if the argument is {@code true}, a string equal to
2880      *          {@code "true"} is returned; otherwise, a string equal to
2881      *          {@code "false"} is returned.
2882      */
2883     public static String valueOf(boolean b) {
2884         return b ? "true" : "false";
2885     }
2886 
2887     /**
2888      * Returns the string representation of the {@code char}
2889      * argument.
2890      *
2891      * @param   c   a {@code char}.
2892      * @return  a string of length {@code 1} containing
2893      *          as its single character the argument {@code c}.
2894      */
2895     public static String valueOf(char c) {
2896         if (COMPACT_STRINGS && StringLatin1.canEncode(c)) {
2897             return new String(StringLatin1.toBytes(c), LATIN1);
2898         }
2899         return new String(StringUTF16.toBytes(c), UTF16);
2900     }
2901 
2902     /**
2903      * Returns the string representation of the {@code int} argument.
2904      * <p>
2905      * The representation is exactly the one returned by the
2906      * {@code Integer.toString} method of one argument.
2907      *
2908      * @param   i   an {@code int}.
2909      * @return  a string representation of the {@code int} argument.
2910      * @see     java.lang.Integer#toString(int, int)
2911      */
2912     public static String valueOf(int i) {
2913         return Integer.toString(i);
2914     }
2915 
2916     /**
2917      * Returns the string representation of the {@code long} argument.
2918      * <p>
2919      * The representation is exactly the one returned by the
2920      * {@code Long.toString} method of one argument.
2921      *
2922      * @param   l   a {@code long}.
2923      * @return  a string representation of the {@code long} argument.
2924      * @see     java.lang.Long#toString(long)
2925      */
2926     public static String valueOf(long l) {
2927         return Long.toString(l);
2928     }
2929 
2930     /**
2931      * Returns the string representation of the {@code float} argument.
2932      * <p>
2933      * The representation is exactly the one returned by the
2934      * {@code Float.toString} method of one argument.
2935      *
2936      * @param   f   a {@code float}.
2937      * @return  a string representation of the {@code float} argument.
2938      * @see     java.lang.Float#toString(float)
2939      */
2940     public static String valueOf(float f) {
2941         return Float.toString(f);
2942     }
2943 
2944     /**
2945      * Returns the string representation of the {@code double} argument.
2946      * <p>
2947      * The representation is exactly the one returned by the
2948      * {@code Double.toString} method of one argument.
2949      *
2950      * @param   d   a {@code double}.
2951      * @return  a  string representation of the {@code double} argument.
2952      * @see     java.lang.Double#toString(double)
2953      */
2954     public static String valueOf(double d) {
2955         return Double.toString(d);
2956     }
2957 
2958     /**
2959      * Returns a canonical representation for the string object.
2960      * <p>
2961      * A pool of strings, initially empty, is maintained privately by the
2962      * class {@code String}.
2963      * <p>
2964      * When the intern method is invoked, if the pool already contains a
2965      * string equal to this {@code String} object as determined by
2966      * the {@link #equals(Object)} method, then the string from the pool is
2967      * returned. Otherwise, this {@code String} object is added to the
2968      * pool and a reference to this {@code String} object is returned.
2969      * <p>
2970      * It follows that for any two strings {@code s} and {@code t},
2971      * {@code s.intern() == t.intern()} is {@code true}
2972      * if and only if {@code s.equals(t)} is {@code true}.
2973      * <p>
2974      * All literal strings and string-valued constant expressions are
2975      * interned. String literals are defined in section 3.10.5 of the
2976      * <cite>The Java&trade; Language Specification</cite>.
2977      *
2978      * @return  a string that has the same contents as this string, but is
2979      *          guaranteed to be from a pool of unique strings.
2980      */
2981     public native String intern();
2982 
2983     ////////////////////////////////////////////////////////////////
2984 
2985     /**
2986      * Copy character bytes from this string into dst starting at dstBegin.
2987      * This method doesn't perform any range checking.
2988      *
2989      * Invoker guarantees: dst is in UTF16 (inflate itself for asb), if two
2990      * coders are different, and dst is big enough (range check)
2991      *
2992      * @param dstBegin  the char index, not offset of byte[]
2993      * @param coder     the coder of dst[]
2994      */
2995     void getBytes(byte dst[], int dstBegin, byte coder) {
2996         if (coder() == coder) {
2997             System.arraycopy(value, 0, dst, dstBegin << coder, value.length);
2998         } else {    // this.coder == LATIN && coder == UTF16
2999             StringLatin1.inflate(value, 0, dst, dstBegin, value.length);
3000         }
3001     }
3002 
3003     /*
3004      * Package private constructor. Trailing Void argument is there for
3005      * disambiguating it against other (public) constructors.
3006      *
3007      * Stores the char[] value into a byte[] that each byte represents
3008      * the8 low-order bits of the corresponding character, if the char[]
3009      * contains only latin1 character. Or a byte[] that stores all
3010      * characters in their byte sequences defined by the {@code StringUTF16}.
3011      */
3012     String(char[] value, int off, int len, Void sig) {
3013         if (len == 0) {
3014             this.value = "".value;
3015             this.coder = "".coder;
3016             return;
3017         }
3018         if (COMPACT_STRINGS) {
3019             byte[] val = StringUTF16.compress(value, off, len);
3020             if (val != null) {
3021                 this.value = val;
3022                 this.coder = LATIN1;
3023                 return;
3024             }
3025         }
3026         this.coder = UTF16;
3027         this.value = StringUTF16.toBytes(value, off, len);
3028     }
3029 
3030     /*
3031      * Package private constructor. Trailing Void argument is there for
3032      * disambiguating it against other (public) constructors.
3033      */
3034     String(AbstractStringBuilder asb, Void sig) {
3035         byte[] val = asb.getValue();
3036         int length = asb.length();
3037         if (asb.isLatin1()) {
3038             this.coder = LATIN1;
3039             this.value = Arrays.copyOfRange(val, 0, length);
3040         } else {
3041             if (COMPACT_STRINGS) {
3042                 byte[] buf = StringUTF16.compress(val, 0, length);
3043                 if (buf != null) {
3044                     this.coder = LATIN1;
3045                     this.value = buf;
3046                     return;
3047                 }
3048             }
3049             this.coder = UTF16;
3050             this.value = Arrays.copyOfRange(val, 0, length << 1);
3051         }
3052     }
3053 
3054    /*
3055     * Package private constructor which shares value array for speed.
3056     */
3057     String(byte[] value, byte coder) {
3058         this.value = value;
3059         this.coder = coder;
3060     }
3061 
3062     byte coder() {
3063         return COMPACT_STRINGS ? coder : UTF16;
3064     }
3065 
3066     private boolean isLatin1() {
3067         return COMPACT_STRINGS && coder == LATIN1;
3068     }
3069 
3070     static final byte LATIN1 = 0;
3071     static final byte UTF16  = 1;
3072 
3073     /*
3074      * StringIndexOutOfBoundsException  if {@code index} is
3075      * negative or greater than or equal to {@code length}.
3076      */
3077     static void checkIndex(int index, int length) {
3078         if (index < 0 || index >= length) {
3079             throw new StringIndexOutOfBoundsException("index " + index);
3080         }
3081     }
3082 
3083     /*
3084      * StringIndexOutOfBoundsException  if {@code offset}
3085      * is negative or greater than {@code length}.
3086      */
3087     static void checkOffset(int offset, int length) {
3088         if (offset < 0 || offset > length) {
3089             throw new StringIndexOutOfBoundsException("offset " + offset +
3090                                                       ",length " + length);
3091         }
3092     }
3093 
3094     /*
3095      * Check {@code offset}, {@code count} against {@code 0} and {@code length}
3096      * bounds.
3097      *
3098      * @throws  StringIndexOutOfBoundsException
3099      *          If {@code offset} is negative, {@code count} is negative,
3100      *          or {@code offset} is greater than {@code length - count}
3101      */
3102     static void checkBoundsOffCount(int offset, int count, int length) {
3103         if (offset < 0 || count < 0 || offset > length - count) {
3104             throw new StringIndexOutOfBoundsException(
3105                 "offset " + offset + ", count " + count + ", length " + length);
3106         }
3107     }
3108 
3109     /*
3110      * Check {@code begin}, {@code end} against {@code 0} and {@code length}
3111      * bounds.
3112      *
3113      * @throws  StringIndexOutOfBoundsException
3114      *          If {@code begin} is negative, {@code begin} is greater than
3115      *          {@code end}, or {@code end} is greater than {@code length}.
3116      */
3117     private static void checkBoundsBeginEnd(int begin, int end, int length) {
3118         if (begin < 0 || begin > end || end > length) {
3119             throw new StringIndexOutOfBoundsException(
3120                 "begin " + begin + ", end " + end + ", length " + length);
3121         }
3122     }
3123 }