1 /*
   2  * Copyright (c) 1994, 2013, 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.StringJoiner;
  38 import java.util.regex.Matcher;
  39 import java.util.regex.Pattern;
  40 import java.util.regex.PatternSyntaxException;
  41 
  42 /**
  43  * The {@code String} class represents character strings. All
  44  * string literals in Java programs, such as {@code "abc"}, are
  45  * implemented as instances of this class.
  46  * <p>
  47  * Strings are constant; their values cannot be changed after they
  48  * are created. String buffers support mutable strings.
  49  * Because String objects are immutable they can be shared. For example:
  50  * <p><blockquote><pre>
  51  *     String str = "abc";
  52  * </pre></blockquote><p>
  53  * is equivalent to:
  54  * <p><blockquote><pre>
  55  *     char data[] = {'a', 'b', 'c'};
  56  *     String str = new String(data);
  57  * </pre></blockquote><p>
  58  * Here are some more examples of how strings can be used:
  59  * <p><blockquote><pre>
  60  *     System.out.println("abc");
  61  *     String cde = "cde";
  62  *     System.out.println("abc" + cde);
  63  *     String c = "abc".substring(2,3);
  64  *     String d = cde.substring(1, 2);
  65  * </pre></blockquote>
  66  * <p>
  67  * The class {@code String} includes methods for examining
  68  * individual characters of the sequence, for comparing strings, for
  69  * searching strings, for extracting substrings, and for creating a
  70  * copy of a string with all characters translated to uppercase or to
  71  * lowercase. Case mapping is based on the Unicode Standard version
  72  * specified by the {@link java.lang.Character Character} class.
  73  * <p>
  74  * The Java language provides special support for the string
  75  * concatenation operator (&nbsp;+&nbsp;), and for conversion of
  76  * other objects to strings. String concatenation is implemented
  77  * through the {@code StringBuilder}(or {@code StringBuffer})
  78  * class and its {@code append} method.
  79  * String conversions are implemented through the method
  80  * {@code toString}, defined by {@code Object} and
  81  * inherited by all classes in Java. For additional information on
  82  * string concatenation and conversion, see Gosling, Joy, and Steele,
  83  * <i>The Java Language Specification</i>.
  84  *
  85  * <p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor
  86  * or method in this class will cause a {@link NullPointerException} to be
  87  * thrown.
  88  *
  89  * <p>A {@code String} represents a string in the UTF-16 format
  90  * in which <em>supplementary characters</em> are represented by <em>surrogate
  91  * pairs</em> (see the section <a href="Character.html#unicode">Unicode
  92  * Character Representations</a> in the {@code Character} class for
  93  * more information).
  94  * Index values refer to {@code char} code units, so a supplementary
  95  * character uses two positions in a {@code String}.
  96  * <p>The {@code String} class provides methods for dealing with
  97  * Unicode code points (i.e., characters), in addition to those for
  98  * dealing with Unicode code units (i.e., {@code char} values).
  99  *
 100  * @author  Lee Boynton
 101  * @author  Arthur van Hoff
 102  * @author  Martin Buchholz
 103  * @author  Ulf Zibis
 104  * @see     java.lang.Object#toString()
 105  * @see     java.lang.StringBuffer
 106  * @see     java.lang.StringBuilder
 107  * @see     java.nio.charset.Charset
 108  * @since   JDK1.0
 109  */
 110 
 111 public final class String
 112     implements java.io.Serializable, Comparable<String>, CharSequence {
 113     /** The value is used for character storage. */
 114     private final char value[];
 115 
 116     /** Cache the hash code for the string */
 117     private int hash; // Default to 0
 118 
 119     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 120     private static final long serialVersionUID = -6849794470754667710L;
 121 
 122     /**
 123      * Class String is special cased within the Serialization Stream Protocol.
 124      *
 125      * A String instance is written initially into an ObjectOutputStream in the
 126      * following format:
 127      * <pre>
 128      *      {@code TC_STRING} (utf String)
 129      * </pre>
 130      * The String is written by method {@code DataOutput.writeUTF}.
 131      * A new handle is generated to  refer to all future references to the
 132      * string instance within the stream.
 133      */
 134     private static final ObjectStreamField[] serialPersistentFields =
 135         new ObjectStreamField[0];
 136 
 137     /**
 138      * Initializes a newly created {@code String} object so that it represents
 139      * an empty character sequence.  Note that use of this constructor is
 140      * unnecessary since Strings are immutable.
 141      */
 142     public String() {
 143         this.value = new char[0];
 144     }
 145 
 146     /**
 147      * Initializes a newly created {@code String} object so that it represents
 148      * the same sequence of characters as the argument; in other words, the
 149      * newly created string is a copy of the argument string. Unless an
 150      * explicit copy of {@code original} is needed, use of this constructor is
 151      * unnecessary since Strings are immutable.
 152      *
 153      * @param  original
 154      *         A {@code String}
 155      */
 156     public String(String original) {
 157         this.value = original.value;
 158         this.hash = original.hash;
 159     }
 160 
 161     /**
 162      * Allocates a new {@code String} so that it represents the sequence of
 163      * characters currently contained in the character array argument. The
 164      * contents of the character array are copied; subsequent modification of
 165      * the character array does not affect the newly created string.
 166      *
 167      * @param  value
 168      *         The initial value of the string
 169      */
 170     public String(char value[]) {
 171         this.value = Arrays.copyOf(value, value.length);
 172     }
 173 
 174     /**
 175      * Allocates a new {@code String} that contains characters from a subarray
 176      * of the character array argument. The {@code offset} argument is the
 177      * index of the first character of the subarray and the {@code count}
 178      * argument specifies the length of the subarray. The contents of the
 179      * subarray are copied; subsequent modification of the character array does
 180      * not affect the newly created string.
 181      *
 182      * @param  value
 183      *         Array that is the source of characters
 184      *
 185      * @param  offset
 186      *         The initial offset
 187      *
 188      * @param  count
 189      *         The length
 190      *
 191      * @throws  IndexOutOfBoundsException
 192      *          If the {@code offset} and {@code count} arguments index
 193      *          characters outside the bounds of the {@code value} array
 194      */
 195     public String(char value[], int offset, int count) {
 196         if (offset < 0) {
 197             throw new StringIndexOutOfBoundsException(offset);
 198         }
 199         if (count < 0) {
 200             throw new StringIndexOutOfBoundsException(count);
 201         }
 202         // Note: offset or count might be near -1>>>1.
 203         if (offset > value.length - count) {
 204             throw new StringIndexOutOfBoundsException(offset + count);
 205         }
 206         this.value = Arrays.copyOfRange(value, offset, offset+count);
 207     }
 208 
 209     /**
 210      * Allocates a new {@code String} that contains characters from a subarray
 211      * of the <a href="Character.html#unicode">Unicode code point</a> array
 212      * argument.  The {@code offset} argument is the index of the first code
 213      * point of the subarray and the {@code count} argument specifies the
 214      * length of the subarray.  The contents of the subarray are converted to
 215      * {@code char}s; subsequent modification of the {@code int} array does not
 216      * affect the newly created string.
 217      *
 218      * @param  codePoints
 219      *         Array that is the source of Unicode code points
 220      *
 221      * @param  offset
 222      *         The initial offset
 223      *
 224      * @param  count
 225      *         The length
 226      *
 227      * @throws  IllegalArgumentException
 228      *          If any invalid Unicode code point is found in {@code
 229      *          codePoints}
 230      *
 231      * @throws  IndexOutOfBoundsException
 232      *          If the {@code offset} and {@code count} arguments index
 233      *          characters outside the bounds of the {@code codePoints} array
 234      *
 235      * @since  1.5
 236      */
 237     public String(int[] codePoints, int offset, int count) {
 238         if (offset < 0) {
 239             throw new StringIndexOutOfBoundsException(offset);
 240         }
 241         if (count < 0) {
 242             throw new StringIndexOutOfBoundsException(count);
 243         }
 244         // Note: offset or count might be near -1>>>1.
 245         if (offset > codePoints.length - count) {
 246             throw new StringIndexOutOfBoundsException(offset + count);
 247         }
 248 
 249         final int end = offset + count;
 250 
 251         // Pass 1: Compute precise size of char[]
 252         int n = count;
 253         for (int i = offset; i < end; i++) {
 254             int c = codePoints[i];
 255             if (Character.isBmpCodePoint(c))
 256                 continue;
 257             else if (Character.isValidCodePoint(c))
 258                 n++;
 259             else throw new IllegalArgumentException(Integer.toString(c));
 260         }
 261 
 262         // Pass 2: Allocate and fill in char[]
 263         final char[] v = new char[n];
 264 
 265         for (int i = offset, j = 0; i < end; i++, j++) {
 266             int c = codePoints[i];
 267             if (Character.isBmpCodePoint(c))
 268                 v[j] = (char)c;
 269             else
 270                 Character.toSurrogates(c, v, j++);
 271         }
 272 
 273         this.value = v;
 274     }
 275 
 276     /**
 277      * Allocates a new {@code String} constructed from a subarray of an array
 278      * of 8-bit integer values.
 279      *
 280      * <p> The {@code offset} argument is the index of the first byte of the
 281      * subarray, and the {@code count} argument specifies the length of the
 282      * subarray.
 283      *
 284      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 285      * specified in the method above.
 286      *
 287      * @deprecated This method does not properly convert bytes into characters.
 288      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 289      * {@code String} constructors that take a {@link
 290      * java.nio.charset.Charset}, charset name, or that use the platform's
 291      * default charset.
 292      *
 293      * @param  ascii
 294      *         The bytes to be converted to characters
 295      *
 296      * @param  hibyte
 297      *         The top 8 bits of each 16-bit Unicode code unit
 298      *
 299      * @param  offset
 300      *         The initial offset
 301      * @param  count
 302      *         The length
 303      *
 304      * @throws  IndexOutOfBoundsException
 305      *          If the {@code offset} or {@code count} argument is invalid
 306      *
 307      * @see  #String(byte[], int)
 308      * @see  #String(byte[], int, int, java.lang.String)
 309      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 310      * @see  #String(byte[], int, int)
 311      * @see  #String(byte[], java.lang.String)
 312      * @see  #String(byte[], java.nio.charset.Charset)
 313      * @see  #String(byte[])
 314      */
 315     @Deprecated
 316     public String(byte ascii[], int hibyte, int offset, int count) {
 317         checkBounds(ascii, offset, count);
 318         char value[] = new char[count];
 319 
 320         if (hibyte == 0) {
 321             for (int i = count; i-- > 0;) {
 322                 value[i] = (char)(ascii[i + offset] & 0xff);
 323             }
 324         } else {
 325             hibyte <<= 8;
 326             for (int i = count; i-- > 0;) {
 327                 value[i] = (char)(hibyte | (ascii[i + offset] & 0xff));
 328             }
 329         }
 330         this.value = value;
 331     }
 332 
 333     /**
 334      * Allocates a new {@code String} containing characters constructed from
 335      * an array of 8-bit integer values. Each character <i>c</i>in the
 336      * resulting string is constructed from the corresponding component
 337      * <i>b</i> in the byte array such that:
 338      *
 339      * <blockquote><pre>
 340      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 341      *                         | (<b><i>b</i></b> &amp; 0xff))
 342      * </pre></blockquote>
 343      *
 344      * @deprecated  This method does not properly convert bytes into
 345      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 346      * {@code String} constructors that take a {@link
 347      * java.nio.charset.Charset}, charset name, or that use the platform's
 348      * default charset.
 349      *
 350      * @param  ascii
 351      *         The bytes to be converted to characters
 352      *
 353      * @param  hibyte
 354      *         The top 8 bits of each 16-bit Unicode code unit
 355      *
 356      * @see  #String(byte[], int, int, java.lang.String)
 357      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 358      * @see  #String(byte[], int, int)
 359      * @see  #String(byte[], java.lang.String)
 360      * @see  #String(byte[], java.nio.charset.Charset)
 361      * @see  #String(byte[])
 362      */
 363     @Deprecated
 364     public String(byte ascii[], int hibyte) {
 365         this(ascii, hibyte, 0, ascii.length);
 366     }
 367 
 368     /* Common private utility method used to bounds check the byte array
 369      * and requested offset & length values used by the String(byte[],..)
 370      * constructors.
 371      */
 372     private static void checkBounds(byte[] bytes, int offset, int length) {
 373         if (length < 0)
 374             throw new StringIndexOutOfBoundsException(length);
 375         if (offset < 0)
 376             throw new StringIndexOutOfBoundsException(offset);
 377         if (offset > bytes.length - length)
 378             throw new StringIndexOutOfBoundsException(offset + length);
 379     }
 380 
 381     /**
 382      * Constructs a new {@code String} by decoding the specified subarray of
 383      * bytes using the specified charset.  The length of the new {@code String}
 384      * is a function of the charset, and hence may not be equal to the length
 385      * of the subarray.
 386      *
 387      * <p> The behavior of this constructor when the given bytes are not valid
 388      * in the given charset is unspecified.  The {@link
 389      * java.nio.charset.CharsetDecoder} class should be used when more control
 390      * over the decoding process is required.
 391      *
 392      * @param  bytes
 393      *         The bytes to be decoded into characters
 394      *
 395      * @param  offset
 396      *         The index of the first byte to decode
 397      *
 398      * @param  length
 399      *         The number of bytes to decode
 400 
 401      * @param  charsetName
 402      *         The name of a supported {@linkplain java.nio.charset.Charset
 403      *         charset}
 404      *
 405      * @throws  UnsupportedEncodingException
 406      *          If the named charset is not supported
 407      *
 408      * @throws  IndexOutOfBoundsException
 409      *          If the {@code offset} and {@code length} arguments index
 410      *          characters outside the bounds of the {@code bytes} array
 411      *
 412      * @since  JDK1.1
 413      */
 414     public String(byte bytes[], int offset, int length, String charsetName)
 415             throws UnsupportedEncodingException {
 416         if (charsetName == null)
 417             throw new NullPointerException("charsetName");
 418         checkBounds(bytes, offset, length);
 419         this.value = StringCoding.decode(charsetName, bytes, offset, length);
 420     }
 421 
 422     /**
 423      * Constructs a new {@code String} by decoding the specified subarray of
 424      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 425      * The length of the new {@code String} is a function of the charset, and
 426      * hence may not be equal to the length of the subarray.
 427      *
 428      * <p> This method always replaces malformed-input and unmappable-character
 429      * sequences with this charset's default replacement string.  The {@link
 430      * java.nio.charset.CharsetDecoder} class should be used when more control
 431      * over the decoding process is required.
 432      *
 433      * @param  bytes
 434      *         The bytes to be decoded into characters
 435      *
 436      * @param  offset
 437      *         The index of the first byte to decode
 438      *
 439      * @param  length
 440      *         The number of bytes to decode
 441      *
 442      * @param  charset
 443      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 444      *         decode the {@code bytes}
 445      *
 446      * @throws  IndexOutOfBoundsException
 447      *          If the {@code offset} and {@code length} arguments index
 448      *          characters outside the bounds of the {@code bytes} array
 449      *
 450      * @since  1.6
 451      */
 452     public String(byte bytes[], int offset, int length, Charset charset) {
 453         if (charset == null)
 454             throw new NullPointerException("charset");
 455         checkBounds(bytes, offset, length);
 456         this.value =  StringCoding.decode(charset, bytes, offset, length);
 457     }
 458 
 459     /**
 460      * Constructs a new {@code String} by decoding the specified array of bytes
 461      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 462      * length of the new {@code String} is a function of the charset, and hence
 463      * may not be equal to the length of the byte array.
 464      *
 465      * <p> The behavior of this constructor when the given bytes are not valid
 466      * in the given charset is unspecified.  The {@link
 467      * java.nio.charset.CharsetDecoder} class should be used when more control
 468      * over the decoding process is required.
 469      *
 470      * @param  bytes
 471      *         The bytes to be decoded into characters
 472      *
 473      * @param  charsetName
 474      *         The name of a supported {@linkplain java.nio.charset.Charset
 475      *         charset}
 476      *
 477      * @throws  UnsupportedEncodingException
 478      *          If the named charset is not supported
 479      *
 480      * @since  JDK1.1
 481      */
 482     public String(byte bytes[], String charsetName)
 483             throws UnsupportedEncodingException {
 484         this(bytes, 0, bytes.length, charsetName);
 485     }
 486 
 487     /**
 488      * Constructs a new {@code String} by decoding the specified array of
 489      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 490      * The length of the new {@code String} is a function of the charset, and
 491      * hence may not be equal to the length of the byte array.
 492      *
 493      * <p> This method always replaces malformed-input and unmappable-character
 494      * sequences with this charset's default replacement string.  The {@link
 495      * java.nio.charset.CharsetDecoder} class should be used when more control
 496      * over the decoding process is required.
 497      *
 498      * @param  bytes
 499      *         The bytes to be decoded into characters
 500      *
 501      * @param  charset
 502      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 503      *         decode the {@code bytes}
 504      *
 505      * @since  1.6
 506      */
 507     public String(byte bytes[], Charset charset) {
 508         this(bytes, 0, bytes.length, charset);
 509     }
 510 
 511     /**
 512      * Constructs a new {@code String} by decoding the specified subarray of
 513      * bytes using the platform's default charset.  The length of the new
 514      * {@code String} is a function of the charset, and hence may not be equal
 515      * to the length of the subarray.
 516      *
 517      * <p> The behavior of this constructor when the given bytes are not valid
 518      * in the default charset is unspecified.  The {@link
 519      * java.nio.charset.CharsetDecoder} class should be used when more control
 520      * over the decoding process is required.
 521      *
 522      * @param  bytes
 523      *         The bytes to be decoded into characters
 524      *
 525      * @param  offset
 526      *         The index of the first byte to decode
 527      *
 528      * @param  length
 529      *         The number of bytes to decode
 530      *
 531      * @throws  IndexOutOfBoundsException
 532      *          If the {@code offset} and the {@code length} arguments index
 533      *          characters outside the bounds of the {@code bytes} array
 534      *
 535      * @since  JDK1.1
 536      */
 537     public String(byte bytes[], int offset, int length) {
 538         checkBounds(bytes, offset, length);
 539         this.value = StringCoding.decode(bytes, offset, length);
 540     }
 541 
 542     /**
 543      * Constructs a new {@code String} by decoding the specified array of bytes
 544      * using the platform's default charset.  The length of the new {@code
 545      * String} is a function of the charset, and hence may not be equal to the
 546      * length of the byte array.
 547      *
 548      * <p> The behavior of this constructor when the given bytes are not valid
 549      * in the default charset is unspecified.  The {@link
 550      * java.nio.charset.CharsetDecoder} class should be used when more control
 551      * over the decoding process is required.
 552      *
 553      * @param  bytes
 554      *         The bytes to be decoded into characters
 555      *
 556      * @since  JDK1.1
 557      */
 558     public String(byte bytes[]) {
 559         this(bytes, 0, bytes.length);
 560     }
 561 
 562     /**
 563      * Allocates a new string that contains the sequence of characters
 564      * currently contained in the string buffer argument. The contents of the
 565      * string buffer are copied; subsequent modification of the string buffer
 566      * does not affect the newly created string.
 567      *
 568      * @param  buffer
 569      *         A {@code StringBuffer}
 570      */
 571     public String(StringBuffer buffer) {
 572         synchronized(buffer) {
 573             this.value = Arrays.copyOf(buffer.getValue(), buffer.length());
 574         }
 575     }
 576 
 577     /**
 578      * Allocates a new string that contains the sequence of characters
 579      * currently contained in the string builder argument. The contents of the
 580      * string builder are copied; subsequent modification of the string builder
 581      * does not affect the newly created string.
 582      *
 583      * <p> This constructor is provided to ease migration to {@code
 584      * StringBuilder}. Obtaining a string from a string builder via the {@code
 585      * toString} method is likely to run faster and is generally preferred.
 586      *
 587      * @param   builder
 588      *          A {@code StringBuilder}
 589      *
 590      * @since  1.5
 591      */
 592     public String(StringBuilder builder) {
 593         this.value = Arrays.copyOf(builder.getValue(), builder.length());
 594     }
 595 
 596     /*
 597     * Package private constructor which shares value array for speed.
 598     * this constructor is always expected to be called with share==true.
 599     * a separate constructor is needed because we already have a public
 600     * String(char[]) constructor that makes a copy of the given char[].
 601     */
 602     String(char[] value, boolean share) {
 603         // assert share : "unshared not supported";
 604         this.value = value;
 605     }
 606 
 607     /**
 608      * Returns the length of this string.
 609      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 610      * code units</a> in the string.
 611      *
 612      * @return  the length of the sequence of characters represented by this
 613      *          object.
 614      */
 615     public int length() {
 616         return value.length;
 617     }
 618 
 619     /**
 620      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 621      *
 622      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 623      * {@code false}
 624      *
 625      * @since 1.6
 626      */
 627     public boolean isEmpty() {
 628         return value.length == 0;
 629     }
 630 
 631     /**
 632      * Returns the {@code char} value at the
 633      * specified index. An index ranges from {@code 0} to
 634      * {@code length() - 1}. The first {@code char} value of the sequence
 635      * is at index {@code 0}, the next at index {@code 1},
 636      * and so on, as for array indexing.
 637      *
 638      * <p>If the {@code char} value specified by the index is a
 639      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 640      * value is returned.
 641      *
 642      * @param      index   the index of the {@code char} value.
 643      * @return     the {@code char} value at the specified index of this string.
 644      *             The first {@code char} value is at index {@code 0}.
 645      * @exception  IndexOutOfBoundsException  if the {@code index}
 646      *             argument is negative or not less than the length of this
 647      *             string.
 648      */
 649     public char charAt(int index) {
 650         if ((index < 0) || (index >= value.length)) {
 651             throw new StringIndexOutOfBoundsException(index);
 652         }
 653         return value[index];
 654     }
 655 
 656     /**
 657      * Returns the character (Unicode code point) at the specified
 658      * index. The index refers to {@code char} values
 659      * (Unicode code units) and ranges from {@code 0} to
 660      * {@link #length()}{@code  - 1}.
 661      *
 662      * <p> If the {@code char} value specified at the given index
 663      * is in the high-surrogate range, the following index is less
 664      * than the length of this {@code String}, and the
 665      * {@code char} value at the following index is in the
 666      * low-surrogate range, then the supplementary code point
 667      * corresponding to this surrogate pair is returned. Otherwise,
 668      * the {@code char} value at the given index is returned.
 669      *
 670      * @param      index the index to the {@code char} values
 671      * @return     the code point value of the character at the
 672      *             {@code index}
 673      * @exception  IndexOutOfBoundsException  if the {@code index}
 674      *             argument is negative or not less than the length of this
 675      *             string.
 676      * @since      1.5
 677      */
 678     public int codePointAt(int index) {
 679         if ((index < 0) || (index >= value.length)) {
 680             throw new StringIndexOutOfBoundsException(index);
 681         }
 682         return Character.codePointAtImpl(value, index, value.length);
 683     }
 684 
 685     /**
 686      * Returns the character (Unicode code point) before the specified
 687      * index. The index refers to {@code char} values
 688      * (Unicode code units) and ranges from {@code 1} to {@link
 689      * CharSequence#length() length}.
 690      *
 691      * <p> If the {@code char} value at {@code (index - 1)}
 692      * is in the low-surrogate range, {@code (index - 2)} is not
 693      * negative, and the {@code char} value at {@code (index -
 694      * 2)} is in the high-surrogate range, then the
 695      * supplementary code point value of the surrogate pair is
 696      * returned. If the {@code char} value at {@code index -
 697      * 1} is an unpaired low-surrogate or a high-surrogate, the
 698      * surrogate value is returned.
 699      *
 700      * @param     index the index following the code point that should be returned
 701      * @return    the Unicode code point value before the given index.
 702      * @exception IndexOutOfBoundsException if the {@code index}
 703      *            argument is less than 1 or greater than the length
 704      *            of this string.
 705      * @since     1.5
 706      */
 707     public int codePointBefore(int index) {
 708         int i = index - 1;
 709         if ((i < 0) || (i >= value.length)) {
 710             throw new StringIndexOutOfBoundsException(index);
 711         }
 712         return Character.codePointBeforeImpl(value, index, 0);
 713     }
 714 
 715     /**
 716      * Returns the number of Unicode code points in the specified text
 717      * range of this {@code String}. The text range begins at the
 718      * specified {@code beginIndex} and extends to the
 719      * {@code char} at index {@code endIndex - 1}. Thus the
 720      * length (in {@code char}s) of the text range is
 721      * {@code endIndex-beginIndex}. Unpaired surrogates within
 722      * the text range count as one code point each.
 723      *
 724      * @param beginIndex the index to the first {@code char} of
 725      * the text range.
 726      * @param endIndex the index after the last {@code char} of
 727      * the text range.
 728      * @return the number of Unicode code points in the specified text
 729      * range
 730      * @exception IndexOutOfBoundsException if the
 731      * {@code beginIndex} is negative, or {@code endIndex}
 732      * is larger than the length of this {@code String}, or
 733      * {@code beginIndex} is larger than {@code endIndex}.
 734      * @since  1.5
 735      */
 736     public int codePointCount(int beginIndex, int endIndex) {
 737         if (beginIndex < 0 || endIndex > value.length || beginIndex > endIndex) {
 738             throw new IndexOutOfBoundsException();
 739         }
 740         return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
 741     }
 742 
 743     /**
 744      * Returns the index within this {@code String} that is
 745      * offset from the given {@code index} by
 746      * {@code codePointOffset} code points. Unpaired surrogates
 747      * within the text range given by {@code index} and
 748      * {@code codePointOffset} count as one code point each.
 749      *
 750      * @param index the index to be offset
 751      * @param codePointOffset the offset in code points
 752      * @return the index within this {@code String}
 753      * @exception IndexOutOfBoundsException if {@code index}
 754      *   is negative or larger then the length of this
 755      *   {@code String}, or if {@code codePointOffset} is positive
 756      *   and the substring starting with {@code index} has fewer
 757      *   than {@code codePointOffset} code points,
 758      *   or if {@code codePointOffset} is negative and the substring
 759      *   before {@code index} has fewer than the absolute value
 760      *   of {@code codePointOffset} code points.
 761      * @since 1.5
 762      */
 763     public int offsetByCodePoints(int index, int codePointOffset) {
 764         if (index < 0 || index > value.length) {
 765             throw new IndexOutOfBoundsException();
 766         }
 767         return Character.offsetByCodePointsImpl(value, 0, value.length,
 768                 index, codePointOffset);
 769     }
 770 
 771     /**
 772      * Copy characters from this string into dst starting at dstBegin.
 773      * This method doesn't perform any range checking.
 774      */
 775     void getChars(char dst[], int dstBegin) {
 776         System.arraycopy(value, 0, dst, dstBegin, value.length);
 777     }
 778 
 779     /**
 780      * Copies characters from this string into the destination character
 781      * array.
 782      * <p>
 783      * The first character to be copied is at index {@code srcBegin};
 784      * the last character to be copied is at index {@code srcEnd-1}
 785      * (thus the total number of characters to be copied is
 786      * {@code srcEnd-srcBegin}). The characters are copied into the
 787      * subarray of {@code dst} starting at index {@code dstBegin}
 788      * and ending at index:
 789      * <p><blockquote><pre>
 790      *     dstbegin + (srcEnd-srcBegin) - 1
 791      * </pre></blockquote>
 792      *
 793      * @param      srcBegin   index of the first character in the string
 794      *                        to copy.
 795      * @param      srcEnd     index after the last character in the string
 796      *                        to copy.
 797      * @param      dst        the destination array.
 798      * @param      dstBegin   the start offset in the destination array.
 799      * @exception IndexOutOfBoundsException If any of the following
 800      *            is true:
 801      *            <ul><li>{@code srcBegin} is negative.
 802      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 803      *            <li>{@code srcEnd} is greater than the length of this
 804      *                string
 805      *            <li>{@code dstBegin} is negative
 806      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 807      *                {@code dst.length}</ul>
 808      */
 809     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 810         if (srcBegin < 0) {
 811             throw new StringIndexOutOfBoundsException(srcBegin);
 812         }
 813         if (srcEnd > value.length) {
 814             throw new StringIndexOutOfBoundsException(srcEnd);
 815         }
 816         if (srcBegin > srcEnd) {
 817             throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
 818         }
 819         System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
 820     }
 821 
 822     /**
 823      * Copies characters from this string into the destination byte array. Each
 824      * byte receives the 8 low-order bits of the corresponding character. The
 825      * eight high-order bits of each character are not copied and do not
 826      * participate in the transfer in any way.
 827      *
 828      * <p> The first character to be copied is at index {@code srcBegin}; the
 829      * last character to be copied is at index {@code srcEnd-1}.  The total
 830      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 831      * characters, converted to bytes, are copied into the subarray of {@code
 832      * dst} starting at index {@code dstBegin} and ending at index:
 833      *
 834      * <blockquote><pre>
 835      *     dstbegin + (srcEnd-srcBegin) - 1
 836      * </pre></blockquote>
 837      *
 838      * @deprecated  This method does not properly convert characters into
 839      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 840      * {@link #getBytes()} method, which uses the platform's default charset.
 841      *
 842      * @param  srcBegin
 843      *         Index of the first character in the string to copy
 844      *
 845      * @param  srcEnd
 846      *         Index after the last character in the string to copy
 847      *
 848      * @param  dst
 849      *         The destination array
 850      *
 851      * @param  dstBegin
 852      *         The start offset in the destination array
 853      *
 854      * @throws  IndexOutOfBoundsException
 855      *          If any of the following is true:
 856      *          <ul>
 857      *            <li> {@code srcBegin} is negative
 858      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 859      *            <li> {@code srcEnd} is greater than the length of this String
 860      *            <li> {@code dstBegin} is negative
 861      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 862      *                 dst.length}
 863      *          </ul>
 864      */
 865     @Deprecated
 866     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 867         if (srcBegin < 0) {
 868             throw new StringIndexOutOfBoundsException(srcBegin);
 869         }
 870         if (srcEnd > value.length) {
 871             throw new StringIndexOutOfBoundsException(srcEnd);
 872         }
 873         if (srcBegin > srcEnd) {
 874             throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
 875         }
 876         Objects.requireNonNull(dst);
 877 
 878         int j = dstBegin;
 879         int n = srcEnd;
 880         int i = srcBegin;
 881         char[] val = value;   /* avoid getfield opcode */
 882 
 883         while (i < n) {
 884             dst[j++] = (byte)val[i++];
 885         }
 886     }
 887 
 888     /**
 889      * Encodes this {@code String} into a sequence of bytes using the named
 890      * charset, storing the result into a new byte array.
 891      *
 892      * <p> The behavior of this method when this string cannot be encoded in
 893      * the given charset is unspecified.  The {@link
 894      * java.nio.charset.CharsetEncoder} class should be used when more control
 895      * over the encoding process is required.
 896      *
 897      * @param  charsetName
 898      *         The name of a supported {@linkplain java.nio.charset.Charset
 899      *         charset}
 900      *
 901      * @return  The resultant byte array
 902      *
 903      * @throws  UnsupportedEncodingException
 904      *          If the named charset is not supported
 905      *
 906      * @since  JDK1.1
 907      */
 908     public byte[] getBytes(String charsetName)
 909             throws UnsupportedEncodingException {
 910         if (charsetName == null) throw new NullPointerException();
 911         return StringCoding.encode(charsetName, value, 0, value.length);
 912     }
 913 
 914     /**
 915      * Encodes this {@code String} into a sequence of bytes using the given
 916      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 917      * new byte array.
 918      *
 919      * <p> This method always replaces malformed-input and unmappable-character
 920      * sequences with this charset's default replacement byte array.  The
 921      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 922      * control over the encoding process is required.
 923      *
 924      * @param  charset
 925      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 926      *         the {@code String}
 927      *
 928      * @return  The resultant byte array
 929      *
 930      * @since  1.6
 931      */
 932     public byte[] getBytes(Charset charset) {
 933         if (charset == null) throw new NullPointerException();
 934         return StringCoding.encode(charset, value, 0, value.length);
 935     }
 936 
 937     /**
 938      * Encodes this {@code String} into a sequence of bytes using the
 939      * platform's default charset, storing the result into a new byte array.
 940      *
 941      * <p> The behavior of this method when this string cannot be encoded in
 942      * the default charset is unspecified.  The {@link
 943      * java.nio.charset.CharsetEncoder} class should be used when more control
 944      * over the encoding process is required.
 945      *
 946      * @return  The resultant byte array
 947      *
 948      * @since      JDK1.1
 949      */
 950     public byte[] getBytes() {
 951         return StringCoding.encode(value, 0, value.length);
 952     }
 953 
 954     /**
 955      * Compares this string to the specified object.  The result is {@code
 956      * true} if and only if the argument is not {@code null} and is a {@code
 957      * String} object that represents the same sequence of characters as this
 958      * object.
 959      *
 960      * @param  anObject
 961      *         The object to compare this {@code String} against
 962      *
 963      * @return  {@code true} if the given object represents a {@code String}
 964      *          equivalent to this string, {@code false} otherwise
 965      *
 966      * @see  #compareTo(String)
 967      * @see  #equalsIgnoreCase(String)
 968      */
 969     public boolean equals(Object anObject) {
 970         if (this == anObject) {
 971             return true;
 972         }
 973         if (anObject instanceof String) {
 974             String anotherString = (String)anObject;
 975             int n = value.length;
 976             if (n == anotherString.value.length) {
 977                 char v1[] = value;
 978                 char v2[] = anotherString.value;
 979                 int i = 0;
 980                 while (n-- != 0) {
 981                     if (v1[i] != v2[i])
 982                         return false;
 983                     i++;
 984                 }
 985                 return true;
 986             }
 987         }
 988         return false;
 989     }
 990 
 991     /**
 992      * Compares this string to the specified {@code StringBuffer}.  The result
 993      * is {@code true} if and only if this {@code String} represents the same
 994      * sequence of characters as the specified {@code StringBuffer}. This method
 995      * synchronizes on the {@code StringBuffer}.
 996      *
 997      * @param  sb
 998      *         The {@code StringBuffer} to compare this {@code String} against
 999      *
1000      * @return  {@code true} if this {@code String} represents the same
1001      *          sequence of characters as the specified {@code StringBuffer},
1002      *          {@code false} otherwise
1003      *
1004      * @since  1.4
1005      */
1006     public boolean contentEquals(StringBuffer sb) {
1007         return contentEquals((CharSequence)sb);
1008     }
1009 
1010     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1011         char v1[] = value;
1012         char v2[] = sb.getValue();
1013         int n = v1.length;
1014         if (n != sb.length()) {
1015             return false;
1016         }
1017         for (int i = 0; i < n; i++) {
1018             if (v1[i] != v2[i]) {
1019                 return false;
1020             }
1021         }
1022         return true;
1023     }
1024 
1025     /**
1026      * Compares this string to the specified {@code CharSequence}.  The
1027      * result is {@code true} if and only if this {@code String} represents the
1028      * same sequence of char values as the specified sequence. Note that if the
1029      * {@code CharSequence} is a {@code StringBuffer} then the method
1030      * synchronizes on it.
1031      *
1032      * @param  cs
1033      *         The sequence to compare this {@code String} against
1034      *
1035      * @return  {@code true} if this {@code String} represents the same
1036      *          sequence of char values as the specified sequence, {@code
1037      *          false} otherwise
1038      *
1039      * @since  1.5
1040      */
1041     public boolean contentEquals(CharSequence cs) {
1042         // Argument is a StringBuffer, StringBuilder
1043         if (cs instanceof AbstractStringBuilder) {
1044             if (cs instanceof StringBuffer) {
1045                 synchronized(cs) {
1046                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1047                 }
1048             } else {
1049                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1050             }
1051         }
1052         // Argument is a String
1053         if (cs.equals(this))
1054             return true;
1055         // Argument is a generic CharSequence
1056         char v1[] = value;
1057         int n = v1.length;
1058         if (n != cs.length()) {
1059             return false;
1060         }
1061         for (int i = 0; i < n; i++) {
1062             if (v1[i] != cs.charAt(i)) {
1063                 return false;
1064             }
1065         }
1066         return true;
1067     }
1068 
1069     /**
1070      * Compares this {@code String} to another {@code String}, ignoring case
1071      * considerations.  Two strings are considered equal ignoring case if they
1072      * are of the same length and corresponding characters in the two strings
1073      * are equal ignoring case.
1074      *
1075      * <p> Two characters {@code c1} and {@code c2} are considered the same
1076      * ignoring case if at least one of the following is true:
1077      * <ul>
1078      *   <li> The two characters are the same (as compared by the
1079      *        {@code ==} operator)
1080      *   <li> Applying the method {@link
1081      *        java.lang.Character#toUpperCase(char)} to each character
1082      *        produces the same result
1083      *   <li> Applying the method {@link
1084      *        java.lang.Character#toLowerCase(char)} to each character
1085      *        produces the same result
1086      * </ul>
1087      *
1088      * @param  anotherString
1089      *         The {@code String} to compare this {@code String} against
1090      *
1091      * @return  {@code true} if the argument is not {@code null} and it
1092      *          represents an equivalent {@code String} ignoring case; {@code
1093      *          false} otherwise
1094      *
1095      * @see  #equals(Object)
1096      */
1097     public boolean equalsIgnoreCase(String anotherString) {
1098         return (this == anotherString) ? true
1099                 : (anotherString != null)
1100                 && (anotherString.value.length == value.length)
1101                 && regionMatches(true, 0, anotherString, 0, value.length);
1102     }
1103 
1104     /**
1105      * Compares two strings lexicographically.
1106      * The comparison is based on the Unicode value of each character in
1107      * the strings. The character sequence represented by this
1108      * {@code String} object is compared lexicographically to the
1109      * character sequence represented by the argument string. The result is
1110      * a negative integer if this {@code String} object
1111      * lexicographically precedes the argument string. The result is a
1112      * positive integer if this {@code String} object lexicographically
1113      * follows the argument string. The result is zero if the strings
1114      * are equal; {@code compareTo} returns {@code 0} exactly when
1115      * the {@link #equals(Object)} method would return {@code true}.
1116      * <p>
1117      * This is the definition of lexicographic ordering. If two strings are
1118      * different, then either they have different characters at some index
1119      * that is a valid index for both strings, or their lengths are different,
1120      * or both. If they have different characters at one or more index
1121      * positions, let <i>k</i> be the smallest such index; then the string
1122      * whose character at position <i>k</i> has the smaller value, as
1123      * determined by using the &lt; operator, lexicographically precedes the
1124      * other string. In this case, {@code compareTo} returns the
1125      * difference of the two character values at position {@code k} in
1126      * the two string -- that is, the value:
1127      * <blockquote><pre>
1128      * this.charAt(k)-anotherString.charAt(k)
1129      * </pre></blockquote>
1130      * If there is no index position at which they differ, then the shorter
1131      * string lexicographically precedes the longer string. In this case,
1132      * {@code compareTo} returns the difference of the lengths of the
1133      * strings -- that is, the value:
1134      * <blockquote><pre>
1135      * this.length()-anotherString.length()
1136      * </pre></blockquote>
1137      *
1138      * @param   anotherString   the {@code String} to be compared.
1139      * @return  the value {@code 0} if the argument string is equal to
1140      *          this string; a value less than {@code 0} if this string
1141      *          is lexicographically less than the string argument; and a
1142      *          value greater than {@code 0} if this string is
1143      *          lexicographically greater than the string argument.
1144      */
1145     public int compareTo(String anotherString) {
1146         int len1 = value.length;
1147         int len2 = anotherString.value.length;
1148         int lim = Math.min(len1, len2);
1149         char v1[] = value;
1150         char v2[] = anotherString.value;
1151 
1152         int k = 0;
1153         while (k < lim) {
1154             char c1 = v1[k];
1155             char c2 = v2[k];
1156             if (c1 != c2) {
1157                 return c1 - c2;
1158             }
1159             k++;
1160         }
1161         return len1 - len2;
1162     }
1163 
1164     /**
1165      * A Comparator that orders {@code String} objects as by
1166      * {@code compareToIgnoreCase}. This comparator is serializable.
1167      * <p>
1168      * Note that this Comparator does <em>not</em> take locale into account,
1169      * and will result in an unsatisfactory ordering for certain locales.
1170      * The java.text package provides <em>Collators</em> to allow
1171      * locale-sensitive ordering.
1172      *
1173      * @see     java.text.Collator#compare(String, String)
1174      * @since   1.2
1175      */
1176     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1177                                          = new CaseInsensitiveComparator();
1178     private static class CaseInsensitiveComparator
1179             implements Comparator<String>, java.io.Serializable {
1180         // use serialVersionUID from JDK 1.2.2 for interoperability
1181         private static final long serialVersionUID = 8575799808933029326L;
1182 
1183         public int compare(String s1, String s2) {
1184             int n1 = s1.length();
1185             int n2 = s2.length();
1186             int min = Math.min(n1, n2);
1187             for (int i = 0; i < min; i++) {
1188                 char c1 = s1.charAt(i);
1189                 char c2 = s2.charAt(i);
1190                 if (c1 != c2) {
1191                     c1 = Character.toUpperCase(c1);
1192                     c2 = Character.toUpperCase(c2);
1193                     if (c1 != c2) {
1194                         c1 = Character.toLowerCase(c1);
1195                         c2 = Character.toLowerCase(c2);
1196                         if (c1 != c2) {
1197                             // No overflow because of numeric promotion
1198                             return c1 - c2;
1199                         }
1200                     }
1201                 }
1202             }
1203             return n1 - n2;
1204         }
1205 
1206         /** Replaces the de-serialized object. */
1207         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1208     }
1209 
1210     /**
1211      * Compares two strings lexicographically, ignoring case
1212      * differences. This method returns an integer whose sign is that of
1213      * calling {@code compareTo} with normalized versions of the strings
1214      * where case differences have been eliminated by calling
1215      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1216      * each character.
1217      * <p>
1218      * Note that this method does <em>not</em> take locale into account,
1219      * and will result in an unsatisfactory ordering for certain locales.
1220      * The java.text package provides <em>collators</em> to allow
1221      * locale-sensitive ordering.
1222      *
1223      * @param   str   the {@code String} to be compared.
1224      * @return  a negative integer, zero, or a positive integer as the
1225      *          specified String is greater than, equal to, or less
1226      *          than this String, ignoring case considerations.
1227      * @see     java.text.Collator#compare(String, String)
1228      * @since   1.2
1229      */
1230     public int compareToIgnoreCase(String str) {
1231         return CASE_INSENSITIVE_ORDER.compare(this, str);
1232     }
1233 
1234     /**
1235      * Tests if two string regions are equal.
1236      * <p>
1237      * A substring of this {@code String} object is compared to a substring
1238      * of the argument other. The result is true if these substrings
1239      * represent identical character sequences. The substring of this
1240      * {@code String} object to be compared begins at index {@code toffset}
1241      * and has length {@code len}. The substring of other to be compared
1242      * begins at index {@code ooffset} and has length {@code len}. The
1243      * result is {@code false} if and only if at least one of the following
1244      * is true:
1245      * <ul><li>{@code toffset} is negative.
1246      * <li>{@code ooffset} is negative.
1247      * <li>{@code toffset+len} is greater than the length of this
1248      * {@code String} object.
1249      * <li>{@code ooffset+len} is greater than the length of the other
1250      * argument.
1251      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1252      * such that:
1253      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1254      * <i>k</i>{@code )}
1255      * </ul>
1256      *
1257      * @param   toffset   the starting offset of the subregion in this string.
1258      * @param   other     the string argument.
1259      * @param   ooffset   the starting offset of the subregion in the string
1260      *                    argument.
1261      * @param   len       the number of characters to compare.
1262      * @return  {@code true} if the specified subregion of this string
1263      *          exactly matches the specified subregion of the string argument;
1264      *          {@code false} otherwise.
1265      */
1266     public boolean regionMatches(int toffset, String other, int ooffset,
1267             int len) {
1268         char ta[] = value;
1269         int to = toffset;
1270         char pa[] = other.value;
1271         int po = ooffset;
1272         // Note: toffset, ooffset, or len might be near -1>>>1.
1273         if ((ooffset < 0) || (toffset < 0)
1274                 || (toffset > (long)value.length - len)
1275                 || (ooffset > (long)other.value.length - len)) {
1276             return false;
1277         }
1278         while (len-- > 0) {
1279             if (ta[to++] != pa[po++]) {
1280                 return false;
1281             }
1282         }
1283         return true;
1284     }
1285 
1286     /**
1287      * Tests if two string regions are equal.
1288      * <p>
1289      * A substring of this {@code String} object is compared to a substring
1290      * of the argument {@code other}. The result is {@code true} if these
1291      * substrings represent character sequences that are the same, ignoring
1292      * case if and only if {@code ignoreCase} is true. The substring of
1293      * this {@code String} object to be compared begins at index
1294      * {@code toffset} and has length {@code len}. The substring of
1295      * {@code other} to be compared begins at index {@code ooffset} and
1296      * has length {@code len}. The result is {@code false} if and only if
1297      * at least one of the following is true:
1298      * <ul><li>{@code toffset} is negative.
1299      * <li>{@code ooffset} is negative.
1300      * <li>{@code toffset+len} is greater than the length of this
1301      * {@code String} object.
1302      * <li>{@code ooffset+len} is greater than the length of the other
1303      * argument.
1304      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1305      * integer <i>k</i> less than {@code len} such that:
1306      * <blockquote><pre>
1307      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1308      * </pre></blockquote>
1309      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1310      * integer <i>k</i> less than {@code len} such that:
1311      * <blockquote><pre>
1312      * Character.toLowerCase(this.charAt(toffset+k)) !=
1313      Character.toLowerCase(other.charAt(ooffset+k))
1314      * </pre></blockquote>
1315      * and:
1316      * <blockquote><pre>
1317      * Character.toUpperCase(this.charAt(toffset+k)) !=
1318      *         Character.toUpperCase(other.charAt(ooffset+k))
1319      * </pre></blockquote>
1320      * </ul>
1321      *
1322      * @param   ignoreCase   if {@code true}, ignore case when comparing
1323      *                       characters.
1324      * @param   toffset      the starting offset of the subregion in this
1325      *                       string.
1326      * @param   other        the string argument.
1327      * @param   ooffset      the starting offset of the subregion in the string
1328      *                       argument.
1329      * @param   len          the number of characters to compare.
1330      * @return  {@code true} if the specified subregion of this string
1331      *          matches the specified subregion of the string argument;
1332      *          {@code false} otherwise. Whether the matching is exact
1333      *          or case insensitive depends on the {@code ignoreCase}
1334      *          argument.
1335      */
1336     public boolean regionMatches(boolean ignoreCase, int toffset,
1337             String other, int ooffset, int len) {
1338         char ta[] = value;
1339         int to = toffset;
1340         char pa[] = other.value;
1341         int po = ooffset;
1342         // Note: toffset, ooffset, or len might be near -1>>>1.
1343         if ((ooffset < 0) || (toffset < 0)
1344                 || (toffset > (long)value.length - len)
1345                 || (ooffset > (long)other.value.length - len)) {
1346             return false;
1347         }
1348         while (len-- > 0) {
1349             char c1 = ta[to++];
1350             char c2 = pa[po++];
1351             if (c1 == c2) {
1352                 continue;
1353             }
1354             if (ignoreCase) {
1355                 // If characters don't match but case may be ignored,
1356                 // try converting both characters to uppercase.
1357                 // If the results match, then the comparison scan should
1358                 // continue.
1359                 char u1 = Character.toUpperCase(c1);
1360                 char u2 = Character.toUpperCase(c2);
1361                 if (u1 == u2) {
1362                     continue;
1363                 }
1364                 // Unfortunately, conversion to uppercase does not work properly
1365                 // for the Georgian alphabet, which has strange rules about case
1366                 // conversion.  So we need to make one last check before
1367                 // exiting.
1368                 if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
1369                     continue;
1370                 }
1371             }
1372             return false;
1373         }
1374         return true;
1375     }
1376 
1377     /**
1378      * Tests if the substring of this string beginning at the
1379      * specified index starts with the specified prefix.
1380      *
1381      * @param   prefix    the prefix.
1382      * @param   toffset   where to begin looking in this string.
1383      * @return  {@code true} if the character sequence represented by the
1384      *          argument is a prefix of the substring of this object starting
1385      *          at index {@code toffset}; {@code false} otherwise.
1386      *          The result is {@code false} if {@code toffset} is
1387      *          negative or greater than the length of this
1388      *          {@code String} object; otherwise the result is the same
1389      *          as the result of the expression
1390      *          <pre>
1391      *          this.substring(toffset).startsWith(prefix)
1392      *          </pre>
1393      */
1394     public boolean startsWith(String prefix, int toffset) {
1395         char ta[] = value;
1396         int to = toffset;
1397         char pa[] = prefix.value;
1398         int po = 0;
1399         int pc = prefix.value.length;
1400         // Note: toffset might be near -1>>>1.
1401         if ((toffset < 0) || (toffset > value.length - pc)) {
1402             return false;
1403         }
1404         while (--pc >= 0) {
1405             if (ta[to++] != pa[po++]) {
1406                 return false;
1407             }
1408         }
1409         return true;
1410     }
1411 
1412     /**
1413      * Tests if this string starts with the specified prefix.
1414      *
1415      * @param   prefix   the prefix.
1416      * @return  {@code true} if the character sequence represented by the
1417      *          argument is a prefix of the character sequence represented by
1418      *          this string; {@code false} otherwise.
1419      *          Note also that {@code true} will be returned if the
1420      *          argument is an empty string or is equal to this
1421      *          {@code String} object as determined by the
1422      *          {@link #equals(Object)} method.
1423      * @since   1. 0
1424      */
1425     public boolean startsWith(String prefix) {
1426         return startsWith(prefix, 0);
1427     }
1428 
1429     /**
1430      * Tests if this string ends with the specified suffix.
1431      *
1432      * @param   suffix   the suffix.
1433      * @return  {@code true} if the character sequence represented by the
1434      *          argument is a suffix of the character sequence represented by
1435      *          this object; {@code false} otherwise. Note that the
1436      *          result will be {@code true} if the argument is the
1437      *          empty string or is equal to this {@code String} object
1438      *          as determined by the {@link #equals(Object)} method.
1439      */
1440     public boolean endsWith(String suffix) {
1441         return startsWith(suffix, value.length - suffix.value.length);
1442     }
1443 
1444     /**
1445      * Returns a hash code for this string. The hash code for a
1446      * {@code String} object is computed as
1447      * <blockquote><pre>
1448      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1449      * </pre></blockquote>
1450      * using {@code int} arithmetic, where {@code s[i]} is the
1451      * <i>i</i>th character of the string, {@code n} is the length of
1452      * the string, and {@code ^} indicates exponentiation.
1453      * (The hash value of the empty string is zero.)
1454      *
1455      * @return  a hash code value for this object.
1456      */
1457     public int hashCode() {
1458         int h = hash;
1459         if (h == 0 && value.length > 0) {
1460             char val[] = value;
1461 
1462             for (int i = 0; i < value.length; i++) {
1463                 h = 31 * h + val[i];
1464             }
1465             hash = h;
1466         }
1467         return h;
1468     }
1469 
1470     /**
1471      * Returns the index within this string of the first occurrence of
1472      * the specified character. If a character with value
1473      * {@code ch} occurs in the character sequence represented by
1474      * this {@code String} object, then the index (in Unicode
1475      * code units) of the first such occurrence is returned. For
1476      * values of {@code ch} in the range from 0 to 0xFFFF
1477      * (inclusive), this is the smallest value <i>k</i> such that:
1478      * <blockquote><pre>
1479      * this.charAt(<i>k</i>) == ch
1480      * </pre></blockquote>
1481      * is true. For other values of {@code ch}, it is the
1482      * smallest value <i>k</i> such that:
1483      * <blockquote><pre>
1484      * this.codePointAt(<i>k</i>) == ch
1485      * </pre></blockquote>
1486      * is true. In either case, if no such character occurs in this
1487      * string, then {@code -1} is returned.
1488      *
1489      * @param   ch   a character (Unicode code point).
1490      * @return  the index of the first occurrence of the character in the
1491      *          character sequence represented by this object, or
1492      *          {@code -1} if the character does not occur.
1493      */
1494     public int indexOf(int ch) {
1495         return indexOf(ch, 0);
1496     }
1497 
1498     /**
1499      * Returns the index within this string of the first occurrence of the
1500      * specified character, starting the search at the specified index.
1501      * <p>
1502      * If a character with value {@code ch} occurs in the
1503      * character sequence represented by this {@code String}
1504      * object at an index no smaller than {@code fromIndex}, then
1505      * the index of the first such occurrence is returned. For values
1506      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1507      * this is the smallest value <i>k</i> such that:
1508      * <blockquote><pre>
1509      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1510      * </pre></blockquote>
1511      * is true. For other values of {@code ch}, it is the
1512      * smallest value <i>k</i> such that:
1513      * <blockquote><pre>
1514      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1515      * </pre></blockquote>
1516      * is true. In either case, if no such character occurs in this
1517      * string at or after position {@code fromIndex}, then
1518      * {@code -1} is returned.
1519      *
1520      * <p>
1521      * There is no restriction on the value of {@code fromIndex}. If it
1522      * is negative, it has the same effect as if it were zero: this entire
1523      * string may be searched. If it is greater than the length of this
1524      * string, it has the same effect as if it were equal to the length of
1525      * this string: {@code -1} is returned.
1526      *
1527      * <p>All indices are specified in {@code char} values
1528      * (Unicode code units).
1529      *
1530      * @param   ch          a character (Unicode code point).
1531      * @param   fromIndex   the index to start the search from.
1532      * @return  the index of the first occurrence of the character in the
1533      *          character sequence represented by this object that is greater
1534      *          than or equal to {@code fromIndex}, or {@code -1}
1535      *          if the character does not occur.
1536      */
1537     public int indexOf(int ch, int fromIndex) {
1538         final int max = value.length;
1539         if (fromIndex < 0) {
1540             fromIndex = 0;
1541         } else if (fromIndex >= max) {
1542             // Note: fromIndex might be near -1>>>1.
1543             return -1;
1544         }
1545 
1546         if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
1547             // handle most cases here (ch is a BMP code point or a
1548             // negative value (invalid code point))
1549             final char[] value = this.value;
1550             for (int i = fromIndex; i < max; i++) {
1551                 if (value[i] == ch) {
1552                     return i;
1553                 }
1554             }
1555             return -1;
1556         } else {
1557             return indexOfSupplementary(ch, fromIndex);
1558         }
1559     }
1560 
1561     /**
1562      * Handles (rare) calls of indexOf with a supplementary character.
1563      */
1564     private int indexOfSupplementary(int ch, int fromIndex) {
1565         if (Character.isValidCodePoint(ch)) {
1566             final char[] value = this.value;
1567             final char hi = Character.highSurrogate(ch);
1568             final char lo = Character.lowSurrogate(ch);
1569             final int max = value.length - 1;
1570             for (int i = fromIndex; i < max; i++) {
1571                 if (value[i] == hi && value[i + 1] == lo) {
1572                     return i;
1573                 }
1574             }
1575         }
1576         return -1;
1577     }
1578 
1579     /**
1580      * Returns the index within this string of the last occurrence of
1581      * the specified character. For values of {@code ch} in the
1582      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1583      * units) returned is the largest value <i>k</i> such that:
1584      * <blockquote><pre>
1585      * this.charAt(<i>k</i>) == ch
1586      * </pre></blockquote>
1587      * is true. For other values of {@code ch}, it is the
1588      * largest value <i>k</i> such that:
1589      * <blockquote><pre>
1590      * this.codePointAt(<i>k</i>) == ch
1591      * </pre></blockquote>
1592      * is true.  In either case, if no such character occurs in this
1593      * string, then {@code -1} is returned.  The
1594      * {@code String} is searched backwards starting at the last
1595      * character.
1596      *
1597      * @param   ch   a character (Unicode code point).
1598      * @return  the index of the last occurrence of the character in the
1599      *          character sequence represented by this object, or
1600      *          {@code -1} if the character does not occur.
1601      */
1602     public int lastIndexOf(int ch) {
1603         return lastIndexOf(ch, value.length - 1);
1604     }
1605 
1606     /**
1607      * Returns the index within this string of the last occurrence of
1608      * the specified character, searching backward starting at the
1609      * specified index. For values of {@code ch} in the range
1610      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1611      * value <i>k</i> such that:
1612      * <blockquote><pre>
1613      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1614      * </pre></blockquote>
1615      * is true. For other values of {@code ch}, it is the
1616      * largest value <i>k</i> such that:
1617      * <blockquote><pre>
1618      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1619      * </pre></blockquote>
1620      * is true. In either case, if no such character occurs in this
1621      * string at or before position {@code fromIndex}, then
1622      * {@code -1} is returned.
1623      *
1624      * <p>All indices are specified in {@code char} values
1625      * (Unicode code units).
1626      *
1627      * @param   ch          a character (Unicode code point).
1628      * @param   fromIndex   the index to start the search from. There is no
1629      *          restriction on the value of {@code fromIndex}. If it is
1630      *          greater than or equal to the length of this string, it has
1631      *          the same effect as if it were equal to one less than the
1632      *          length of this string: this entire string may be searched.
1633      *          If it is negative, it has the same effect as if it were -1:
1634      *          -1 is returned.
1635      * @return  the index of the last occurrence of the character in the
1636      *          character sequence represented by this object that is less
1637      *          than or equal to {@code fromIndex}, or {@code -1}
1638      *          if the character does not occur before that point.
1639      */
1640     public int lastIndexOf(int ch, int fromIndex) {
1641         if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
1642             // handle most cases here (ch is a BMP code point or a
1643             // negative value (invalid code point))
1644             final char[] value = this.value;
1645             int i = Math.min(fromIndex, value.length - 1);
1646             for (; i >= 0; i--) {
1647                 if (value[i] == ch) {
1648                     return i;
1649                 }
1650             }
1651             return -1;
1652         } else {
1653             return lastIndexOfSupplementary(ch, fromIndex);
1654         }
1655     }
1656 
1657     /**
1658      * Handles (rare) calls of lastIndexOf with a supplementary character.
1659      */
1660     private int lastIndexOfSupplementary(int ch, int fromIndex) {
1661         if (Character.isValidCodePoint(ch)) {
1662             final char[] value = this.value;
1663             char hi = Character.highSurrogate(ch);
1664             char lo = Character.lowSurrogate(ch);
1665             int i = Math.min(fromIndex, value.length - 2);
1666             for (; i >= 0; i--) {
1667                 if (value[i] == hi && value[i + 1] == lo) {
1668                     return i;
1669                 }
1670             }
1671         }
1672         return -1;
1673     }
1674 
1675     /**
1676      * Returns the index within this string of the first occurrence of the
1677      * specified substring.
1678      *
1679      * <p>The returned index is the smallest value <i>k</i> for which:
1680      * <blockquote><pre>
1681      * this.startsWith(str, <i>k</i>)
1682      * </pre></blockquote>
1683      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1684      *
1685      * @param   str   the substring to search for.
1686      * @return  the index of the first occurrence of the specified substring,
1687      *          or {@code -1} if there is no such occurrence.
1688      */
1689     public int indexOf(String str) {
1690         return indexOf(str, 0);
1691     }
1692 
1693     /**
1694      * Returns the index within this string of the first occurrence of the
1695      * specified substring, starting at the specified index.
1696      *
1697      * <p>The returned index is the smallest value <i>k</i> for which:
1698      * <blockquote><pre>
1699      * <i>k</i> &gt;= fromIndex {@code &&} this.startsWith(str, <i>k</i>)
1700      * </pre></blockquote>
1701      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1702      *
1703      * @param   str         the substring to search for.
1704      * @param   fromIndex   the index from which to start the search.
1705      * @return  the index of the first occurrence of the specified substring,
1706      *          starting at the specified index,
1707      *          or {@code -1} if there is no such occurrence.
1708      */
1709     public int indexOf(String str, int fromIndex) {
1710         return indexOf(value, 0, value.length,
1711                 str.value, 0, str.value.length, fromIndex);
1712     }
1713 
1714     /**
1715      * Code shared by String and AbstractStringBuilder to do searches. The
1716      * source is the character array being searched, and the target
1717      * is the string being searched for.
1718      *
1719      * @param   source       the characters being searched.
1720      * @param   sourceOffset offset of the source string.
1721      * @param   sourceCount  count of the source string.
1722      * @param   target       the characters being searched for.
1723      * @param   fromIndex    the index to begin searching from.
1724      */
1725     static int indexOf(char[] source, int sourceOffset, int sourceCount,
1726             String target, int fromIndex) {
1727         return indexOf(source, sourceOffset, sourceCount,
1728                        target.value, 0, target.value.length,
1729                        fromIndex);
1730     }
1731 
1732     /**
1733      * Code shared by String and StringBuffer to do searches. The
1734      * source is the character array being searched, and the target
1735      * is the string being searched for.
1736      *
1737      * @param   source       the characters being searched.
1738      * @param   sourceOffset offset of the source string.
1739      * @param   sourceCount  count of the source string.
1740      * @param   target       the characters being searched for.
1741      * @param   targetOffset offset of the target string.
1742      * @param   targetCount  count of the target string.
1743      * @param   fromIndex    the index to begin searching from.
1744      */
1745     static int indexOf(char[] source, int sourceOffset, int sourceCount,
1746             char[] target, int targetOffset, int targetCount,
1747             int fromIndex) {
1748         if (fromIndex >= sourceCount) {
1749             return (targetCount == 0 ? sourceCount : -1);
1750         }
1751         if (fromIndex < 0) {
1752             fromIndex = 0;
1753         }
1754         if (targetCount == 0) {
1755             return fromIndex;
1756         }
1757 
1758         char first = target[targetOffset];
1759         int max = sourceOffset + (sourceCount - targetCount);
1760 
1761         for (int i = sourceOffset + fromIndex; i <= max; i++) {
1762             /* Look for first character. */
1763             if (source[i] != first) {
1764                 while (++i <= max && source[i] != first);
1765             }
1766 
1767             /* Found first character, now look at the rest of v2 */
1768             if (i <= max) {
1769                 int j = i + 1;
1770                 int end = j + targetCount - 1;
1771                 for (int k = targetOffset + 1; j < end && source[j]
1772                         == target[k]; j++, k++);
1773 
1774                 if (j == end) {
1775                     /* Found whole string. */
1776                     return i - sourceOffset;
1777                 }
1778             }
1779         }
1780         return -1;
1781     }
1782 
1783     /**
1784      * Returns the index within this string of the last occurrence of the
1785      * specified substring.  The last occurrence of the empty string ""
1786      * is considered to occur at the index value {@code this.length()}.
1787      *
1788      * <p>The returned index is the largest value <i>k</i> for which:
1789      * <blockquote><pre>
1790      * this.startsWith(str, <i>k</i>)
1791      * </pre></blockquote>
1792      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1793      *
1794      * @param   str   the substring to search for.
1795      * @return  the index of the last occurrence of the specified substring,
1796      *          or {@code -1} if there is no such occurrence.
1797      */
1798     public int lastIndexOf(String str) {
1799         return lastIndexOf(str, value.length);
1800     }
1801 
1802     /**
1803      * Returns the index within this string of the last occurrence of the
1804      * specified substring, searching backward starting at the specified index.
1805      *
1806      * <p>The returned index is the largest value <i>k</i> for which:
1807      * <blockquote><pre>
1808      * <i>k</i> {@code <=} fromIndex {@code &&} this.startsWith(str, <i>k</i>)
1809      * </pre></blockquote>
1810      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1811      *
1812      * @param   str         the substring to search for.
1813      * @param   fromIndex   the index to start the search from.
1814      * @return  the index of the last occurrence of the specified substring,
1815      *          searching backward from the specified index,
1816      *          or {@code -1} if there is no such occurrence.
1817      */
1818     public int lastIndexOf(String str, int fromIndex) {
1819         return lastIndexOf(value, 0, value.length,
1820                 str.value, 0, str.value.length, fromIndex);
1821     }
1822 
1823     /**
1824      * Code shared by String and AbstractStringBuilder to do searches. The
1825      * source is the character array being searched, and the target
1826      * is the string being searched for.
1827      *
1828      * @param   source       the characters being searched.
1829      * @param   sourceOffset offset of the source string.
1830      * @param   sourceCount  count of the source string.
1831      * @param   target       the characters being searched for.
1832      * @param   fromIndex    the index to begin searching from.
1833      */
1834     static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
1835             String target, int fromIndex) {
1836         return lastIndexOf(source, sourceOffset, sourceCount,
1837                        target.value, 0, target.value.length,
1838                        fromIndex);
1839     }
1840 
1841     /**
1842      * Code shared by String and StringBuffer to do searches. The
1843      * source is the character array being searched, and the target
1844      * is the string being searched for.
1845      *
1846      * @param   source       the characters being searched.
1847      * @param   sourceOffset offset of the source string.
1848      * @param   sourceCount  count of the source string.
1849      * @param   target       the characters being searched for.
1850      * @param   targetOffset offset of the target string.
1851      * @param   targetCount  count of the target string.
1852      * @param   fromIndex    the index to begin searching from.
1853      */
1854     static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
1855             char[] target, int targetOffset, int targetCount,
1856             int fromIndex) {
1857         /*
1858          * Check arguments; return immediately where possible. For
1859          * consistency, don't check for null str.
1860          */
1861         int rightIndex = sourceCount - targetCount;
1862         if (fromIndex < 0) {
1863             return -1;
1864         }
1865         if (fromIndex > rightIndex) {
1866             fromIndex = rightIndex;
1867         }
1868         /* Empty string always matches. */
1869         if (targetCount == 0) {
1870             return fromIndex;
1871         }
1872 
1873         int strLastIndex = targetOffset + targetCount - 1;
1874         char strLastChar = target[strLastIndex];
1875         int min = sourceOffset + targetCount - 1;
1876         int i = min + fromIndex;
1877 
1878     startSearchForLastChar:
1879         while (true) {
1880             while (i >= min && source[i] != strLastChar) {
1881                 i--;
1882             }
1883             if (i < min) {
1884                 return -1;
1885             }
1886             int j = i - 1;
1887             int start = j - (targetCount - 1);
1888             int k = strLastIndex - 1;
1889 
1890             while (j > start) {
1891                 if (source[j--] != target[k--]) {
1892                     i--;
1893                     continue startSearchForLastChar;
1894                 }
1895             }
1896             return start - sourceOffset + 1;
1897         }
1898     }
1899 
1900     /**
1901      * Returns a new string that is a substring of this string. The
1902      * substring begins with the character at the specified index and
1903      * extends to the end of this string. <p>
1904      * Examples:
1905      * <blockquote><pre>
1906      * "unhappy".substring(2) returns "happy"
1907      * "Harbison".substring(3) returns "bison"
1908      * "emptiness".substring(9) returns "" (an empty string)
1909      * </pre></blockquote>
1910      *
1911      * @param      beginIndex   the beginning index, inclusive.
1912      * @return     the specified substring.
1913      * @exception  IndexOutOfBoundsException  if
1914      *             {@code beginIndex} is negative or larger than the
1915      *             length of this {@code String} object.
1916      */
1917     public String substring(int beginIndex) {
1918         if (beginIndex < 0) {
1919             throw new StringIndexOutOfBoundsException(beginIndex);
1920         }
1921         int subLen = value.length - beginIndex;
1922         if (subLen < 0) {
1923             throw new StringIndexOutOfBoundsException(subLen);
1924         }
1925         return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
1926     }
1927 
1928     /**
1929      * Returns a new string that is a substring of this string. The
1930      * substring begins at the specified {@code beginIndex} and
1931      * extends to the character at index {@code endIndex - 1}.
1932      * Thus the length of the substring is {@code endIndex-beginIndex}.
1933      * <p>
1934      * Examples:
1935      * <blockquote><pre>
1936      * "hamburger".substring(4, 8) returns "urge"
1937      * "smiles".substring(1, 5) returns "mile"
1938      * </pre></blockquote>
1939      *
1940      * @param      beginIndex   the beginning index, inclusive.
1941      * @param      endIndex     the ending index, exclusive.
1942      * @return     the specified substring.
1943      * @exception  IndexOutOfBoundsException  if the
1944      *             {@code beginIndex} is negative, or
1945      *             {@code endIndex} is larger than the length of
1946      *             this {@code String} object, or
1947      *             {@code beginIndex} is larger than
1948      *             {@code endIndex}.
1949      */
1950     public String substring(int beginIndex, int endIndex) {
1951         if (beginIndex < 0) {
1952             throw new StringIndexOutOfBoundsException(beginIndex);
1953         }
1954         if (endIndex > value.length) {
1955             throw new StringIndexOutOfBoundsException(endIndex);
1956         }
1957         int subLen = endIndex - beginIndex;
1958         if (subLen < 0) {
1959             throw new StringIndexOutOfBoundsException(subLen);
1960         }
1961         return ((beginIndex == 0) && (endIndex == value.length)) ? this
1962                 : new String(value, beginIndex, subLen);
1963     }
1964 
1965     /**
1966      * Returns a new character sequence that is a subsequence of this sequence.
1967      *
1968      * <p> An invocation of this method of the form
1969      *
1970      * <blockquote><pre>
1971      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1972      *
1973      * behaves in exactly the same way as the invocation
1974      *
1975      * <blockquote><pre>
1976      * str.substring(begin,&nbsp;end)</pre></blockquote>
1977      *
1978      * This method is defined so that the {@code String} class can implement
1979      * the {@link CharSequence} interface.
1980      *
1981      * @param   beginIndex   the begin index, inclusive.
1982      * @param   endIndex     the end index, exclusive.
1983      * @return  the specified subsequence.
1984      *
1985      * @throws  IndexOutOfBoundsException
1986      *          if {@code beginIndex} or {@code endIndex} is negative,
1987      *          if {@code endIndex} is greater than {@code length()},
1988      *          or if {@code beginIndex} is greater than {@code endIndex}
1989      *
1990      * @since 1.4
1991      * @spec JSR-51
1992      */
1993     public CharSequence subSequence(int beginIndex, int endIndex) {
1994         return this.substring(beginIndex, endIndex);
1995     }
1996 
1997     /**
1998      * Concatenates the specified string to the end of this string.
1999      * <p>
2000      * If the length of the argument string is {@code 0}, then this
2001      * {@code String} object is returned. Otherwise, a new
2002      * {@code String} object is created, representing a character
2003      * sequence that is the concatenation of the character sequence
2004      * represented by this {@code String} object and the character
2005      * sequence represented by the argument string.<p>
2006      * Examples:
2007      * <blockquote><pre>
2008      * "cares".concat("s") returns "caress"
2009      * "to".concat("get").concat("her") returns "together"
2010      * </pre></blockquote>
2011      *
2012      * @param   str   the {@code String} that is concatenated to the end
2013      *                of this {@code String}.
2014      * @return  a string that represents the concatenation of this object's
2015      *          characters followed by the string argument's characters.
2016      */
2017     public String concat(String str) {
2018         int otherLen = str.length();
2019         if (otherLen == 0) {
2020             return this;
2021         }
2022         int len = value.length;
2023         char buf[] = Arrays.copyOf(value, len + otherLen);
2024         str.getChars(buf, len);
2025         return new String(buf, true);
2026     }
2027 
2028     /**
2029      * Returns a new string resulting from replacing all occurrences of
2030      * {@code oldChar} in this string with {@code newChar}.
2031      * <p>
2032      * If the character {@code oldChar} does not occur in the
2033      * character sequence represented by this {@code String} object,
2034      * then a reference to this {@code String} object is returned.
2035      * Otherwise, a new {@code String} object is created that
2036      * represents a character sequence identical to the character sequence
2037      * represented by this {@code String} object, except that every
2038      * occurrence of {@code oldChar} is replaced by an occurrence
2039      * of {@code newChar}.
2040      * <p>
2041      * Examples:
2042      * <blockquote><pre>
2043      * "mesquite in your cellar".replace('e', 'o')
2044      *         returns "mosquito in your collar"
2045      * "the war of baronets".replace('r', 'y')
2046      *         returns "the way of bayonets"
2047      * "sparring with a purple porpoise".replace('p', 't')
2048      *         returns "starring with a turtle tortoise"
2049      * "JonL".replace('q', 'x') returns "JonL" (no change)
2050      * </pre></blockquote>
2051      *
2052      * @param   oldChar   the old character.
2053      * @param   newChar   the new character.
2054      * @return  a string derived from this string by replacing every
2055      *          occurrence of {@code oldChar} with {@code newChar}.
2056      */
2057     public String replace(char oldChar, char newChar) {
2058         if (oldChar != newChar) {
2059             int len = value.length;
2060             int i = -1;
2061             char[] val = value; /* avoid getfield opcode */
2062 
2063             while (++i < len) {
2064                 if (val[i] == oldChar) {
2065                     break;
2066                 }
2067             }
2068             if (i < len) {
2069                 char buf[] = new char[len];
2070                 for (int j = 0; j < i; j++) {
2071                     buf[j] = val[j];
2072                 }
2073                 while (i < len) {
2074                     char c = val[i];
2075                     buf[i] = (c == oldChar) ? newChar : c;
2076                     i++;
2077                 }
2078                 return new String(buf, true);
2079             }
2080         }
2081         return this;
2082     }
2083 
2084     /**
2085      * Tells whether or not this string matches the given <a
2086      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2087      *
2088      * <p> An invocation of this method of the form
2089      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2090      * same result as the expression
2091      *
2092      * <blockquote>
2093      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2094      * matches(<i>regex</i>, <i>str</i>)}
2095      * </blockquote>
2096      *
2097      * @param   regex
2098      *          the regular expression to which this string is to be matched
2099      *
2100      * @return  {@code true} if, and only if, this string matches the
2101      *          given regular expression
2102      *
2103      * @throws  PatternSyntaxException
2104      *          if the regular expression's syntax is invalid
2105      *
2106      * @see java.util.regex.Pattern
2107      *
2108      * @since 1.4
2109      * @spec JSR-51
2110      */
2111     public boolean matches(String regex) {
2112         return Pattern.matches(regex, this);
2113     }
2114 
2115     /**
2116      * Returns true if and only if this string contains the specified
2117      * sequence of char values.
2118      *
2119      * @param s the sequence to search for
2120      * @return true if this string contains {@code s}, false otherwise
2121      * @since 1.5
2122      */
2123     public boolean contains(CharSequence s) {
2124         return indexOf(s.toString()) > -1;
2125     }
2126 
2127     /**
2128      * Replaces the first substring of this string that matches the given <a
2129      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2130      * given replacement.
2131      *
2132      * <p> An invocation of this method of the form
2133      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2134      * yields exactly the same result as the expression
2135      *
2136      * <blockquote>
2137      * <code>
2138      * {@link java.util.regex.Pattern}.{@link
2139      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2140      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2141      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2142      * </code>
2143      * </blockquote>
2144      *
2145      *<p>
2146      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2147      * replacement string may cause the results to be different than if it were
2148      * being treated as a literal replacement string; see
2149      * {@link java.util.regex.Matcher#replaceFirst}.
2150      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2151      * meaning of these characters, if desired.
2152      *
2153      * @param   regex
2154      *          the regular expression to which this string is to be matched
2155      * @param   replacement
2156      *          the string to be substituted for the first match
2157      *
2158      * @return  The resulting {@code String}
2159      *
2160      * @throws  PatternSyntaxException
2161      *          if the regular expression's syntax is invalid
2162      *
2163      * @see java.util.regex.Pattern
2164      *
2165      * @since 1.4
2166      * @spec JSR-51
2167      */
2168     public String replaceFirst(String regex, String replacement) {
2169         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2170     }
2171 
2172     /**
2173      * Replaces each substring of this string that matches the given <a
2174      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2175      * given replacement.
2176      *
2177      * <p> An invocation of this method of the form
2178      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2179      * yields exactly the same result as the expression
2180      *
2181      * <blockquote>
2182      * <code>
2183      * {@link java.util.regex.Pattern}.{@link
2184      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2185      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2186      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2187      * </code>
2188      * </blockquote>
2189      *
2190      *<p>
2191      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2192      * replacement string may cause the results to be different than if it were
2193      * being treated as a literal replacement string; see
2194      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2195      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2196      * meaning of these characters, if desired.
2197      *
2198      * @param   regex
2199      *          the regular expression to which this string is to be matched
2200      * @param   replacement
2201      *          the string to be substituted for each match
2202      *
2203      * @return  The resulting {@code String}
2204      *
2205      * @throws  PatternSyntaxException
2206      *          if the regular expression's syntax is invalid
2207      *
2208      * @see java.util.regex.Pattern
2209      *
2210      * @since 1.4
2211      * @spec JSR-51
2212      */
2213     public String replaceAll(String regex, String replacement) {
2214         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2215     }
2216 
2217     /**
2218      * Replaces each substring of this string that matches the literal target
2219      * sequence with the specified literal replacement sequence. The
2220      * replacement proceeds from the beginning of the string to the end, for
2221      * example, replacing "aa" with "b" in the string "aaa" will result in
2222      * "ba" rather than "ab".
2223      *
2224      * @param  target The sequence of char values to be replaced
2225      * @param  replacement The replacement sequence of char values
2226      * @return  The resulting string
2227      * @since 1.5
2228      */
2229     public String replace(CharSequence target, CharSequence replacement) {
2230         return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(
2231                 this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
2232     }
2233 
2234     /**
2235      * Splits this string around matches of the given
2236      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2237      *
2238      * <p> The array returned by this method contains each substring of this
2239      * string that is terminated by another substring that matches the given
2240      * expression or is terminated by the end of the string.  The substrings in
2241      * the array are in the order in which they occur in this string.  If the
2242      * expression does not match any part of the input then the resulting array
2243      * has just one element, namely this string.
2244      *
2245      * <p> The {@code limit} parameter controls the number of times the
2246      * pattern is applied and therefore affects the length of the resulting
2247      * array.  If the limit <i>n</i> is greater than zero then the pattern
2248      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2249      * length will be no greater than <i>n</i>, and the array's last entry
2250      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2251      * is non-positive then the pattern will be applied as many times as
2252      * possible and the array can have any length.  If <i>n</i> is zero then
2253      * the pattern will be applied as many times as possible, the array can
2254      * have any length, and trailing empty strings will be discarded.
2255      *
2256      * <p> The string {@code "boo:and:foo"}, for example, yields the
2257      * following results with these parameters:
2258      *
2259      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and result">
2260      * <tr>
2261      *     <th>Regex</th>
2262      *     <th>Limit</th>
2263      *     <th>Result</th>
2264      * </tr>
2265      * <tr><td align=center>:</td>
2266      *     <td align=center>2</td>
2267      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2268      * <tr><td align=center>:</td>
2269      *     <td align=center>5</td>
2270      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2271      * <tr><td align=center>:</td>
2272      *     <td align=center>-2</td>
2273      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2274      * <tr><td align=center>o</td>
2275      *     <td align=center>5</td>
2276      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2277      * <tr><td align=center>o</td>
2278      *     <td align=center>-2</td>
2279      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2280      * <tr><td align=center>o</td>
2281      *     <td align=center>0</td>
2282      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2283      * </table></blockquote>
2284      *
2285      * <p> An invocation of this method of the form
2286      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2287      * yields the same result as the expression
2288      *
2289      * <blockquote>
2290      * <code>
2291      * {@link java.util.regex.Pattern}.{@link
2292      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2293      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2294      * </code>
2295      * </blockquote>
2296      *
2297      *
2298      * @param  regex
2299      *         the delimiting regular expression
2300      *
2301      * @param  limit
2302      *         the result threshold, as described above
2303      *
2304      * @return  the array of strings computed by splitting this string
2305      *          around matches of the given regular expression
2306      *
2307      * @throws  PatternSyntaxException
2308      *          if the regular expression's syntax is invalid
2309      *
2310      * @see java.util.regex.Pattern
2311      *
2312      * @since 1.4
2313      * @spec JSR-51
2314      */
2315     public String[] split(String regex, int limit) {
2316         /* fastpath if the regex is a
2317          (1)one-char String and this character is not one of the
2318             RegEx's meta characters ".$|()[{^?*+\\", or
2319          (2)two-char String and the first char is the backslash and
2320             the second is not the ascii digit or ascii letter.
2321          */
2322         char ch = 0;
2323         if (((regex.value.length == 1 &&
2324              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2325              (regex.length() == 2 &&
2326               regex.charAt(0) == '\\' &&
2327               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2328               ((ch-'a')|('z'-ch)) < 0 &&
2329               ((ch-'A')|('Z'-ch)) < 0)) &&
2330             (ch < Character.MIN_HIGH_SURROGATE ||
2331              ch > Character.MAX_LOW_SURROGATE))
2332         {
2333             int off = 0;
2334             int next = 0;
2335             boolean limited = limit > 0;
2336             ArrayList<String> list = new ArrayList<>();
2337             while ((next = indexOf(ch, off)) != -1) {
2338                 if (!limited || list.size() < limit - 1) {
2339                     list.add(substring(off, next));
2340                     off = next + 1;
2341                 } else {    // last one
2342                     //assert (list.size() == limit - 1);
2343                     list.add(substring(off, value.length));
2344                     off = value.length;
2345                     break;
2346                 }
2347             }
2348             // If no match was found, return this
2349             if (off == 0)
2350                 return new String[]{this};
2351 
2352             // Add remaining segment
2353             if (!limited || list.size() < limit)
2354                 list.add(substring(off, value.length));
2355 
2356             // Construct result
2357             int resultSize = list.size();
2358             if (limit == 0) {
2359                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2360                     resultSize--;
2361                 }
2362             }
2363             String[] result = new String[resultSize];
2364             return list.subList(0, resultSize).toArray(result);
2365         }
2366         return Pattern.compile(regex).split(this, limit);
2367     }
2368 
2369     /**
2370      * Splits this string around matches of the given <a
2371      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2372      *
2373      * <p> This method works as if by invoking the two-argument {@link
2374      * #split(String, int) split} method with the given expression and a limit
2375      * argument of zero.  Trailing empty strings are therefore not included in
2376      * the resulting array.
2377      *
2378      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2379      * results with these expressions:
2380      *
2381      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and result">
2382      * <tr>
2383      *  <th>Regex</th>
2384      *  <th>Result</th>
2385      * </tr>
2386      * <tr><td align=center>:</td>
2387      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2388      * <tr><td align=center>o</td>
2389      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2390      * </table></blockquote>
2391      *
2392      *
2393      * @param  regex
2394      *         the delimiting regular expression
2395      *
2396      * @return  the array of strings computed by splitting this string
2397      *          around matches of the given regular expression
2398      *
2399      * @throws  PatternSyntaxException
2400      *          if the regular expression's syntax is invalid
2401      *
2402      * @see java.util.regex.Pattern
2403      *
2404      * @since 1.4
2405      * @spec JSR-51
2406      */
2407     public String[] split(String regex) {
2408         return split(regex, 0);
2409     }
2410 
2411     /**
2412      * Returns a new String composed of copies of the
2413      * {@code CharSequence elements} joined together with a copy of
2414      * the specified {@code delimiter}.
2415      *
2416      * <blockquote>For example,
2417      * <pre>{@code
2418      *     String message = String.join("-", "Java", "is", "cool");
2419      *     // message returned is: "Java-is-cool"
2420      * }</pre></blockquote>
2421      *
2422      * Note that if an element is null, then {@code "null"} is added.
2423      *
2424      * @param  delimiter the delimiter that separates each element
2425      * @param  elements the elements to join together.
2426      *
2427      * @return a new {@code String} that is composed of the {@code elements}
2428      *         separated by the {@code delimiter}
2429      *
2430      * @throws NullPointerException If {@code delimiter} or {@code elements}
2431      *         is {@code null}
2432      *
2433      * @see java.util.StringJoiner
2434      * @since 1.8
2435      */
2436     public static String join(CharSequence delimiter, CharSequence... elements) {
2437         Objects.requireNonNull(delimiter);
2438         Objects.requireNonNull(elements);
2439         // Number of elements not likely worth Arrays.stream overhead.
2440         StringJoiner joiner = new StringJoiner(delimiter);
2441         for (CharSequence cs: elements) {
2442             joiner.add(cs);
2443         }
2444         return joiner.toString();
2445     }
2446 
2447     /**
2448      * Returns a new {@code String} composed of copies of the
2449      * {@code CharSequence elements} joined together with a copy of the
2450      * specified {@code delimiter}.
2451      *
2452      * <blockquote>For example,
2453      * <pre>{@code
2454      *     List<String> strings = new LinkedList<>();
2455      *     strings.add("Java");strings.add("is");
2456      *     strings.add("cool");
2457      *     String message = String.join(" ", strings);
2458      *     //message returned is: "Java is cool"
2459      *
2460      *     Set<String> strings = new HashSet<>();
2461      *     Strings.add("Java"); strings.add("is");
2462      *     strings.add("very"); strings.add("cool");
2463      *     String message = String.join("-", strings);
2464      *     //message returned is: "Java-is-very-cool"
2465      * }</pre></blockquote>
2466      *
2467      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2468      *
2469      * @param  delimiter a sequence of characters that is used to separate each
2470      *         of the {@code elements} in the resulting {@code String}
2471      * @param  elements an {@code Iterable} that will have its {@code elements}
2472      *         joined together.
2473      *
2474      * @return a new {@code String} that is composed from the {@code elements}
2475      *         argument
2476      *
2477      * @throws NullPointerException If {@code delimiter} or {@code elements}
2478      *         is {@code null}
2479      *
2480      * @see    #join(CharSequence,CharSequence...)
2481      * @see    java.util.StringJoiner
2482      * @since 1.8
2483      */
2484     public static String join(CharSequence delimiter,
2485             Iterable<? extends CharSequence> elements) {
2486         Objects.requireNonNull(delimiter);
2487         Objects.requireNonNull(elements);
2488         StringJoiner joiner = new StringJoiner(delimiter);
2489         for (CharSequence cs: elements) {
2490             joiner.add(cs);
2491         }
2492         return joiner.toString();
2493     }
2494 
2495     /**
2496      * Converts all of the characters in this {@code String} to lower
2497      * case using the rules of the given {@code Locale}.  Case mapping is based
2498      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2499      * class. Since case mappings are not always 1:1 char mappings, the resulting
2500      * {@code String} may be a different length than the original {@code String}.
2501      * <p>
2502      * Examples of lowercase  mappings are in the following table:
2503      * <table border="1" summary="Lowercase mapping examples showing language code of locale, upper case, lower case, and description">
2504      * <tr>
2505      *   <th>Language Code of Locale</th>
2506      *   <th>Upper Case</th>
2507      *   <th>Lower Case</th>
2508      *   <th>Description</th>
2509      * </tr>
2510      * <tr>
2511      *   <td>tr (Turkish)</td>
2512      *   <td>&#92;u0130</td>
2513      *   <td>&#92;u0069</td>
2514      *   <td>capital letter I with dot above -&gt; small letter i</td>
2515      * </tr>
2516      * <tr>
2517      *   <td>tr (Turkish)</td>
2518      *   <td>&#92;u0049</td>
2519      *   <td>&#92;u0131</td>
2520      *   <td>capital letter I -&gt; small letter dotless i </td>
2521      * </tr>
2522      * <tr>
2523      *   <td>(all)</td>
2524      *   <td>French Fries</td>
2525      *   <td>french fries</td>
2526      *   <td>lowercased all chars in String</td>
2527      * </tr>
2528      * <tr>
2529      *   <td>(all)</td>
2530      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2531      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2532      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2533      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2534      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2535      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2536      *   <td>lowercased all chars in String</td>
2537      * </tr>
2538      * </table>
2539      *
2540      * @param locale use the case transformation rules for this locale
2541      * @return the {@code String}, converted to lowercase.
2542      * @see     java.lang.String#toLowerCase()
2543      * @see     java.lang.String#toUpperCase()
2544      * @see     java.lang.String#toUpperCase(Locale)
2545      * @since   1.1
2546      */
2547     public String toLowerCase(Locale locale) {
2548         if (locale == null) {
2549             throw new NullPointerException();
2550         }
2551 
2552         int firstUpper;
2553         final int len = value.length;
2554 
2555         /* Now check if there are any characters that need to be changed. */
2556         scan: {
2557             for (firstUpper = 0 ; firstUpper < len; ) {
2558                 char c = value[firstUpper];
2559                 if ((c >= Character.MIN_HIGH_SURROGATE)
2560                         && (c <= Character.MAX_HIGH_SURROGATE)) {
2561                     int supplChar = codePointAt(firstUpper);
2562                     if (supplChar != Character.toLowerCase(supplChar)) {
2563                         break scan;
2564                     }
2565                     firstUpper += Character.charCount(supplChar);
2566                 } else {
2567                     if (c != Character.toLowerCase(c)) {
2568                         break scan;
2569                     }
2570                     firstUpper++;
2571                 }
2572             }
2573             return this;
2574         }
2575 
2576         char[] result = new char[len];
2577         int resultOffset = 0;  /* result may grow, so i+resultOffset
2578                                 * is the write location in result */
2579 
2580         /* Just copy the first few lowerCase characters. */
2581         System.arraycopy(value, 0, result, 0, firstUpper);
2582 
2583         String lang = locale.getLanguage();
2584         boolean localeDependent =
2585                 (lang == "tr" || lang == "az" || lang == "lt");
2586         char[] lowerCharArray;
2587         int lowerChar;
2588         int srcChar;
2589         int srcCount;
2590         for (int i = firstUpper; i < len; i += srcCount) {
2591             srcChar = (int)value[i];
2592             if ((char)srcChar >= Character.MIN_HIGH_SURROGATE
2593                     && (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
2594                 srcChar = codePointAt(i);
2595                 srcCount = Character.charCount(srcChar);
2596             } else {
2597                 srcCount = 1;
2598             }
2599             if (localeDependent || srcChar == '\u03A3') { // GREEK CAPITAL LETTER SIGMA
2600                 lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
2601             } else if (srcChar == '\u0130') { // LATIN CAPITAL LETTER I DOT
2602                 lowerChar = Character.ERROR;
2603             } else {
2604                 lowerChar = Character.toLowerCase(srcChar);
2605             }
2606             if ((lowerChar == Character.ERROR)
2607                     || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
2608                 if (lowerChar == Character.ERROR) {
2609                     if (!localeDependent && srcChar == '\u0130') {
2610                         lowerCharArray =
2611                                 ConditionalSpecialCasing.toLowerCaseCharArray(this, i, Locale.ENGLISH);
2612                     } else {
2613                         lowerCharArray =
2614                                 ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
2615                     }
2616                 } else if (srcCount == 2) {
2617                     resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
2618                     continue;
2619                 } else {
2620                     lowerCharArray = Character.toChars(lowerChar);
2621                 }
2622 
2623                 /* Grow result if needed */
2624                 int mapLen = lowerCharArray.length;
2625                 if (mapLen > srcCount) {
2626                     char[] result2 = new char[result.length + mapLen - srcCount];
2627                     System.arraycopy(result, 0, result2, 0, i + resultOffset);
2628                     result = result2;
2629                 }
2630                 for (int x = 0; x < mapLen; ++x) {
2631                     result[i + resultOffset + x] = lowerCharArray[x];
2632                 }
2633                 resultOffset += (mapLen - srcCount);
2634             } else {
2635                 result[i + resultOffset] = (char)lowerChar;
2636             }
2637         }
2638         return new String(result, 0, len + resultOffset);
2639     }
2640 
2641     /**
2642      * Converts all of the characters in this {@code String} to lower
2643      * case using the rules of the default locale. This is equivalent to calling
2644      * {@code toLowerCase(Locale.getDefault())}.
2645      * <p>
2646      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2647      * results if used for strings that are intended to be interpreted locale
2648      * independently.
2649      * Examples are programming language identifiers, protocol keys, and HTML
2650      * tags.
2651      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2652      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2653      * LATIN SMALL LETTER DOTLESS I character.
2654      * To obtain correct results for locale insensitive strings, use
2655      * {@code toLowerCase(Locale.ENGLISH)}.
2656      * <p>
2657      * @return  the {@code String}, converted to lowercase.
2658      * @see     java.lang.String#toLowerCase(Locale)
2659      */
2660     public String toLowerCase() {
2661         return toLowerCase(Locale.getDefault());
2662     }
2663 
2664     /**
2665      * Converts all of the characters in this {@code String} to upper
2666      * case using the rules of the given {@code Locale}. Case mapping is based
2667      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2668      * class. Since case mappings are not always 1:1 char mappings, the resulting
2669      * {@code String} may be a different length than the original {@code String}.
2670      * <p>
2671      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2672      * <p>
2673      * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.">
2674      * <tr>
2675      *   <th>Language Code of Locale</th>
2676      *   <th>Lower Case</th>
2677      *   <th>Upper Case</th>
2678      *   <th>Description</th>
2679      * </tr>
2680      * <tr>
2681      *   <td>tr (Turkish)</td>
2682      *   <td>&#92;u0069</td>
2683      *   <td>&#92;u0130</td>
2684      *   <td>small letter i -&gt; capital letter I with dot above</td>
2685      * </tr>
2686      * <tr>
2687      *   <td>tr (Turkish)</td>
2688      *   <td>&#92;u0131</td>
2689      *   <td>&#92;u0049</td>
2690      *   <td>small letter dotless i -&gt; capital letter I</td>
2691      * </tr>
2692      * <tr>
2693      *   <td>(all)</td>
2694      *   <td>&#92;u00df</td>
2695      *   <td>&#92;u0053 &#92;u0053</td>
2696      *   <td>small letter sharp s -&gt; two letters: SS</td>
2697      * </tr>
2698      * <tr>
2699      *   <td>(all)</td>
2700      *   <td>Fahrvergn&uuml;gen</td>
2701      *   <td>FAHRVERGN&Uuml;GEN</td>
2702      *   <td></td>
2703      * </tr>
2704      * </table>
2705      * @param locale use the case transformation rules for this locale
2706      * @return the {@code String}, converted to uppercase.
2707      * @see     java.lang.String#toUpperCase()
2708      * @see     java.lang.String#toLowerCase()
2709      * @see     java.lang.String#toLowerCase(Locale)
2710      * @since   1.1
2711      */
2712     public String toUpperCase(Locale locale) {
2713         if (locale == null) {
2714             throw new NullPointerException();
2715         }
2716 
2717         int firstLower;
2718         final int len = value.length;
2719 
2720         /* Now check if there are any characters that need to be changed. */
2721         scan: {
2722             for (firstLower = 0 ; firstLower < len; ) {
2723                 int c = (int)value[firstLower];
2724                 int srcCount;
2725                 if ((c >= Character.MIN_HIGH_SURROGATE)
2726                         && (c <= Character.MAX_HIGH_SURROGATE)) {
2727                     c = codePointAt(firstLower);
2728                     srcCount = Character.charCount(c);
2729                 } else {
2730                     srcCount = 1;
2731                 }
2732                 int upperCaseChar = Character.toUpperCaseEx(c);
2733                 if ((upperCaseChar == Character.ERROR)
2734                         || (c != upperCaseChar)) {
2735                     break scan;
2736                 }
2737                 firstLower += srcCount;
2738             }
2739             return this;
2740         }
2741 
2742         /* result may grow, so i+resultOffset is the write location in result */
2743         int resultOffset = 0;
2744         char[] result = new char[len]; /* may grow */
2745 
2746         /* Just copy the first few upperCase characters. */
2747         System.arraycopy(value, 0, result, 0, firstLower);
2748 
2749         String lang = locale.getLanguage();
2750         boolean localeDependent =
2751                 (lang == "tr" || lang == "az" || lang == "lt");
2752         char[] upperCharArray;
2753         int upperChar;
2754         int srcChar;
2755         int srcCount;
2756         for (int i = firstLower; i < len; i += srcCount) {
2757             srcChar = (int)value[i];
2758             if ((char)srcChar >= Character.MIN_HIGH_SURROGATE &&
2759                 (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
2760                 srcChar = codePointAt(i);
2761                 srcCount = Character.charCount(srcChar);
2762             } else {
2763                 srcCount = 1;
2764             }
2765             if (localeDependent) {
2766                 upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);
2767             } else {
2768                 upperChar = Character.toUpperCaseEx(srcChar);
2769             }
2770             if ((upperChar == Character.ERROR)
2771                     || (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
2772                 if (upperChar == Character.ERROR) {
2773                     if (localeDependent) {
2774                         upperCharArray =
2775                                 ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);
2776                     } else {
2777                         upperCharArray = Character.toUpperCaseCharArray(srcChar);
2778                     }
2779                 } else if (srcCount == 2) {
2780                     resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;
2781                     continue;
2782                 } else {
2783                     upperCharArray = Character.toChars(upperChar);
2784                 }
2785 
2786                 /* Grow result if needed */
2787                 int mapLen = upperCharArray.length;
2788                 if (mapLen > srcCount) {
2789                     char[] result2 = new char[result.length + mapLen - srcCount];
2790                     System.arraycopy(result, 0, result2, 0, i + resultOffset);
2791                     result = result2;
2792                 }
2793                 for (int x = 0; x < mapLen; ++x) {
2794                     result[i + resultOffset + x] = upperCharArray[x];
2795                 }
2796                 resultOffset += (mapLen - srcCount);
2797             } else {
2798                 result[i + resultOffset] = (char)upperChar;
2799             }
2800         }
2801         return new String(result, 0, len + resultOffset);
2802     }
2803 
2804     /**
2805      * Converts all of the characters in this {@code String} to upper
2806      * case using the rules of the default locale. This method is equivalent to
2807      * {@code toUpperCase(Locale.getDefault())}.
2808      * <p>
2809      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2810      * results if used for strings that are intended to be interpreted locale
2811      * independently.
2812      * Examples are programming language identifiers, protocol keys, and HTML
2813      * tags.
2814      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2815      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2816      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2817      * To obtain correct results for locale insensitive strings, use
2818      * {@code toUpperCase(Locale.ENGLISH)}.
2819      * <p>
2820      * @return  the {@code String}, converted to uppercase.
2821      * @see     java.lang.String#toUpperCase(Locale)
2822      */
2823     public String toUpperCase() {
2824         return toUpperCase(Locale.getDefault());
2825     }
2826 
2827     /**
2828      * Returns a copy of the string, with leading and trailing whitespace
2829      * omitted.
2830      * <p>
2831      * If this {@code String} object represents an empty character
2832      * sequence, or the first and last characters of character sequence
2833      * represented by this {@code String} object both have codes
2834      * greater than {@code '\u005Cu0020'} (the space character), then a
2835      * reference to this {@code String} object is returned.
2836      * <p>
2837      * Otherwise, if there is no character with a code greater than
2838      * {@code '\u005Cu0020'} in the string, then a new
2839      * {@code String} object representing an empty string is created
2840      * and returned.
2841      * <p>
2842      * Otherwise, let <i>k</i> be the index of the first character in the
2843      * string whose code is greater than {@code '\u005Cu0020'}, and let
2844      * <i>m</i> be the index of the last character in the string whose code
2845      * is greater than {@code '\u005Cu0020'}. A new {@code String}
2846      * object is created, representing the substring of this string that
2847      * begins with the character at index <i>k</i> and ends with the
2848      * character at index <i>m</i>-that is, the result of
2849      * {@code this.substring(k, m + 1)}.
2850      * <p>
2851      * This method may be used to trim whitespace (as defined above) from
2852      * the beginning and end of a string.
2853      *
2854      * @return  A copy of this string with leading and trailing white
2855      *          space removed, or this string if it has no leading or
2856      *          trailing white space.
2857      */
2858     public String trim() {
2859         int len = value.length;
2860         int st = 0;
2861         char[] val = value;    /* avoid getfield opcode */
2862 
2863         while ((st < len) && (val[st] <= ' ')) {
2864             st++;
2865         }
2866         while ((st < len) && (val[len - 1] <= ' ')) {
2867             len--;
2868         }
2869         return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
2870     }
2871 
2872     /**
2873      * This object (which is already a string!) is itself returned.
2874      *
2875      * @return  the string itself.
2876      */
2877     public String toString() {
2878         return this;
2879     }
2880 
2881     /**
2882      * Converts this string to a new character array.
2883      *
2884      * @return  a newly allocated character array whose length is the length
2885      *          of this string and whose contents are initialized to contain
2886      *          the character sequence represented by this string.
2887      */
2888     public char[] toCharArray() {
2889         // Cannot use Arrays.copyOf because of class initialization order issues
2890         char result[] = new char[value.length];
2891         System.arraycopy(value, 0, result, 0, value.length);
2892         return result;
2893     }
2894 
2895     /**
2896      * Returns a formatted string using the specified format string and
2897      * arguments.
2898      *
2899      * <p> The locale always used is the one returned by {@link
2900      * java.util.Locale#getDefault() Locale.getDefault()}.
2901      *
2902      * @param  format
2903      *         A <a href="../util/Formatter.html#syntax">format string</a>
2904      *
2905      * @param  args
2906      *         Arguments referenced by the format specifiers in the format
2907      *         string.  If there are more arguments than format specifiers, the
2908      *         extra arguments are ignored.  The number of arguments is
2909      *         variable and may be zero.  The maximum number of arguments is
2910      *         limited by the maximum dimension of a Java array as defined by
2911      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2912      *         The behaviour on a
2913      *         {@code null} argument depends on the <a
2914      *         href="../util/Formatter.html#syntax">conversion</a>.
2915      *
2916      * @throws  java.util.IllegalFormatException
2917      *          If a format string contains an illegal syntax, a format
2918      *          specifier that is incompatible with the given arguments,
2919      *          insufficient arguments given the format string, or other
2920      *          illegal conditions.  For specification of all possible
2921      *          formatting errors, see the <a
2922      *          href="../util/Formatter.html#detail">Details</a> section of the
2923      *          formatter class specification.
2924      *
2925      * @return  A formatted string
2926      *
2927      * @see  java.util.Formatter
2928      * @since  1.5
2929      */
2930     public static String format(String format, Object... args) {
2931         return new Formatter().format(format, args).toString();
2932     }
2933 
2934     /**
2935      * Returns a formatted string using the specified locale, format string,
2936      * and arguments.
2937      *
2938      * @param  l
2939      *         The {@linkplain java.util.Locale locale} to apply during
2940      *         formatting.  If {@code l} is {@code null} then no localization
2941      *         is applied.
2942      *
2943      * @param  format
2944      *         A <a href="../util/Formatter.html#syntax">format string</a>
2945      *
2946      * @param  args
2947      *         Arguments referenced by the format specifiers in the format
2948      *         string.  If there are more arguments than format specifiers, the
2949      *         extra arguments are ignored.  The number of arguments is
2950      *         variable and may be zero.  The maximum number of arguments is
2951      *         limited by the maximum dimension of a Java array as defined by
2952      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2953      *         The behaviour on a
2954      *         {@code null} argument depends on the
2955      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2956      *
2957      * @throws  java.util.IllegalFormatException
2958      *          If a format string contains an illegal syntax, a format
2959      *          specifier that is incompatible with the given arguments,
2960      *          insufficient arguments given the format string, or other
2961      *          illegal conditions.  For specification of all possible
2962      *          formatting errors, see the <a
2963      *          href="../util/Formatter.html#detail">Details</a> section of the
2964      *          formatter class specification
2965      *
2966      * @return  A formatted string
2967      *
2968      * @see  java.util.Formatter
2969      * @since  1.5
2970      */
2971     public static String format(Locale l, String format, Object... args) {
2972         return new Formatter(l).format(format, args).toString();
2973     }
2974 
2975     /**
2976      * Returns the string representation of the {@code Object} argument.
2977      *
2978      * @param   obj   an {@code Object}.
2979      * @return  if the argument is {@code null}, then a string equal to
2980      *          {@code "null"}; otherwise, the value of
2981      *          {@code obj.toString()} is returned.
2982      * @see     java.lang.Object#toString()
2983      */
2984     public static String valueOf(Object obj) {
2985         return (obj == null) ? "null" : obj.toString();
2986     }
2987 
2988     /**
2989      * Returns the string representation of the {@code char} array
2990      * argument. The contents of the character array are copied; subsequent
2991      * modification of the character array does not affect the newly
2992      * created string.
2993      *
2994      * @param   data   a {@code char} array.
2995      * @return  a newly allocated string representing the same sequence of
2996      *          characters contained in the character array argument.
2997      */
2998     public static String valueOf(char data[]) {
2999         return new String(data);
3000     }
3001 
3002     /**
3003      * Returns the string representation of a specific subarray of the
3004      * {@code char} array argument.
3005      * <p>
3006      * The {@code offset} argument is the index of the first
3007      * character of the subarray. The {@code count} argument
3008      * specifies the length of the subarray. The contents of the subarray
3009      * are copied; subsequent modification of the character array does not
3010      * affect the newly created string.
3011      *
3012      * @param   data     the character array.
3013      * @param   offset   the initial offset into the value of the
3014      *                  {@code String}.
3015      * @param   count    the length of the value of the {@code String}.
3016      * @return  a string representing the sequence of characters contained
3017      *          in the subarray of the character array argument.
3018      * @exception IndexOutOfBoundsException if {@code offset} is
3019      *          negative, or {@code count} is negative, or
3020      *          {@code offset+count} is larger than
3021      *          {@code data.length}.
3022      */
3023     public static String valueOf(char data[], int offset, int count) {
3024         return new String(data, offset, count);
3025     }
3026 
3027     /**
3028      * Returns a String that represents the character sequence in the
3029      * array specified.
3030      *
3031      * @param   data     the character array.
3032      * @param   offset   initial offset of the subarray.
3033      * @param   count    length of the subarray.
3034      * @return  a {@code String} that contains the characters of the
3035      *          specified subarray of the character array.
3036      */
3037     public static String copyValueOf(char data[], int offset, int count) {
3038         // All public String constructors now copy the data.
3039         return new String(data, offset, count);
3040     }
3041 
3042     /**
3043      * Returns a String that represents the character sequence in the
3044      * array specified.
3045      *
3046      * @param   data   the character array.
3047      * @return  a {@code String} that contains the characters of the
3048      *          character array.
3049      */
3050     public static String copyValueOf(char data[]) {
3051         return new String(data);
3052     }
3053 
3054     /**
3055      * Returns the string representation of the {@code boolean} argument.
3056      *
3057      * @param   b   a {@code boolean}.
3058      * @return  if the argument is {@code true}, a string equal to
3059      *          {@code "true"} is returned; otherwise, a string equal to
3060      *          {@code "false"} is returned.
3061      */
3062     public static String valueOf(boolean b) {
3063         return b ? "true" : "false";
3064     }
3065 
3066     /**
3067      * Returns the string representation of the {@code char}
3068      * argument.
3069      *
3070      * @param   c   a {@code char}.
3071      * @return  a string of length {@code 1} containing
3072      *          as its single character the argument {@code c}.
3073      */
3074     public static String valueOf(char c) {
3075         char data[] = {c};
3076         return new String(data, true);
3077     }
3078 
3079     /**
3080      * Returns the string representation of the {@code int} argument.
3081      * <p>
3082      * The representation is exactly the one returned by the
3083      * {@code Integer.toString} method of one argument.
3084      *
3085      * @param   i   an {@code int}.
3086      * @return  a string representation of the {@code int} argument.
3087      * @see     java.lang.Integer#toString(int, int)
3088      */
3089     public static String valueOf(int i) {
3090         return Integer.toString(i);
3091     }
3092 
3093     /**
3094      * Returns the string representation of the {@code long} argument.
3095      * <p>
3096      * The representation is exactly the one returned by the
3097      * {@code Long.toString} method of one argument.
3098      *
3099      * @param   l   a {@code long}.
3100      * @return  a string representation of the {@code long} argument.
3101      * @see     java.lang.Long#toString(long)
3102      */
3103     public static String valueOf(long l) {
3104         return Long.toString(l);
3105     }
3106 
3107     /**
3108      * Returns the string representation of the {@code float} argument.
3109      * <p>
3110      * The representation is exactly the one returned by the
3111      * {@code Float.toString} method of one argument.
3112      *
3113      * @param   f   a {@code float}.
3114      * @return  a string representation of the {@code float} argument.
3115      * @see     java.lang.Float#toString(float)
3116      */
3117     public static String valueOf(float f) {
3118         return Float.toString(f);
3119     }
3120 
3121     /**
3122      * Returns the string representation of the {@code double} argument.
3123      * <p>
3124      * The representation is exactly the one returned by the
3125      * {@code Double.toString} method of one argument.
3126      *
3127      * @param   d   a {@code double}.
3128      * @return  a  string representation of the {@code double} argument.
3129      * @see     java.lang.Double#toString(double)
3130      */
3131     public static String valueOf(double d) {
3132         return Double.toString(d);
3133     }
3134 
3135     /**
3136      * Returns a canonical representation for the string object.
3137      * <p>
3138      * A pool of strings, initially empty, is maintained privately by the
3139      * class {@code String}.
3140      * <p>
3141      * When the intern method is invoked, if the pool already contains a
3142      * string equal to this {@code String} object as determined by
3143      * the {@link #equals(Object)} method, then the string from the pool is
3144      * returned. Otherwise, this {@code String} object is added to the
3145      * pool and a reference to this {@code String} object is returned.
3146      * <p>
3147      * It follows that for any two strings {@code s} and {@code t},
3148      * {@code s.intern() == t.intern()} is {@code true}
3149      * if and only if {@code s.equals(t)} is {@code true}.
3150      * <p>
3151      * All literal strings and string-valued constant expressions are
3152      * interned. String literals are defined in section 3.10.5 of the
3153      * <cite>The Java&trade; Language Specification</cite>.
3154      *
3155      * @return  a string that has the same contents as this string, but is
3156      *          guaranteed to be from a pool of unique strings.
3157      */
3158     public native String intern();
3159 
3160     /**
3161      * Seed value used for each alternative hash calculated.
3162      */
3163     private static final int HASHING_SEED;
3164 
3165     static {
3166         long nanos = System.nanoTime();
3167         long now = System.currentTimeMillis();
3168         int SEED_MATERIAL[] = {
3169                 System.identityHashCode(String.class),
3170                 System.identityHashCode(System.class),
3171                 (int) (nanos >>> 32),
3172                 (int) nanos,
3173                 (int) (now >>> 32),
3174                 (int) now,
3175                 (int) (System.nanoTime() >>> 2)
3176         };
3177 
3178         // Use murmur3 to scramble the seeding material.
3179         // Inline implementation to avoid loading classes
3180         int h1 = 0;
3181 
3182         // body
3183         for(int k1 : SEED_MATERIAL) {
3184             k1 *= 0xcc9e2d51;
3185             k1 = (k1 << 15) | (k1 >>> 17);
3186             k1 *= 0x1b873593;
3187 
3188             h1 ^= k1;
3189             h1 = (h1 << 13) | (h1 >>> 19);
3190             h1 = h1 * 5 + 0xe6546b64;
3191         }
3192 
3193         // tail (always empty, as body is always 32-bit chunks)
3194 
3195         // finalization
3196 
3197         h1 ^= SEED_MATERIAL.length * 4;
3198 
3199         // finalization mix force all bits of a hash block to avalanche
3200         h1 ^= h1 >>> 16;
3201         h1 *= 0x85ebca6b;
3202         h1 ^= h1 >>> 13;
3203         h1 *= 0xc2b2ae35;
3204         h1 ^= h1 >>> 16;
3205 
3206         HASHING_SEED = h1;
3207     }
3208 
3209     /**
3210      * Cached value of the hashing algorithm result
3211      */
3212     private transient int hash32 = 0;
3213 
3214     /**
3215     * Return a 32-bit hash code value for this object.
3216     * <p>
3217     * The general contract of {@code hash32} is:
3218     * <ul>
3219     * <li>Whenever it is invoked on the same object more than once during
3220     *     an execution of a Java application, the {@code hash32} method
3221     *     must consistently return the same integer, provided no information
3222     *     used in {@code equals} comparisons on the object is modified.
3223     *     This integer need not remain consistent from one execution of an
3224     *     application to another execution of the same application.
3225     * <li>If two objects are equal according to the {@code equals(Object)}
3226     *     method, then calling the {@code hash32} method on each of
3227     *     the two objects must produce the same integer result.
3228     * <li>It is <em>not</em> required that if two objects are unequal
3229     *     according to the {@link java.lang.Object#equals(java.lang.Object)}
3230     *     method, then calling the {@code hash32} method on each of the
3231     *     two objects must produce distinct integer results.  However, the
3232     *     programmer should be aware that producing distinct integer results
3233     *     for unequal objects may improve the performance of hash tables.
3234     * </ul>
3235     *
3236     * The hash value will never be zero.
3237     *
3238     * @return  a hash code value for this object.
3239     * @see     java.lang.Object#equals(java.lang.Object)
3240     */
3241     public int hash32() {
3242         int h = hash32;
3243         if (0 == h) {
3244            // harmless data race on hash32 here.
3245            h = sun.misc.Hashing.murmur3_32(HASHING_SEED, value, 0, value.length);
3246 
3247            // ensure result is not zero to avoid recalcing
3248            h = (0 != h) ? h : 1;
3249 
3250            hash32 = h;
3251         }
3252 
3253         return h;
3254     }
3255 
3256 }