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  * <blockquote><pre>
  51  *     String str = "abc";
  52  * </pre></blockquote><p>
  53  * is equivalent to:
  54  * <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  * <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 into an ObjectOutputStream according to
 126      * <a href="{@docroot}../platform/serialization/spec/output.html">
 127      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
 128      */
 129     private static final ObjectStreamField[] serialPersistentFields =
 130         new ObjectStreamField[0];
 131 
 132     /**
 133      * Initializes a newly created {@code String} object so that it represents
 134      * an empty character sequence.  Note that use of this constructor is
 135      * unnecessary since Strings are immutable.
 136      */
 137     public String() {
 138         this.value = new char[0];
 139     }
 140 
 141     /**
 142      * Initializes a newly created {@code String} object so that it represents
 143      * the same sequence of characters as the argument; in other words, the
 144      * newly created string is a copy of the argument string. Unless an
 145      * explicit copy of {@code original} is needed, use of this constructor is
 146      * unnecessary since Strings are immutable.
 147      *
 148      * @param  original
 149      *         A {@code String}
 150      */
 151     public String(String original) {
 152         this.value = original.value;
 153         this.hash = original.hash;
 154     }
 155 
 156     /**
 157      * Allocates a new {@code String} so that it represents the sequence of
 158      * characters currently contained in the character array argument. The
 159      * contents of the character array are copied; subsequent modification of
 160      * the character array does not affect the newly created string.
 161      *
 162      * @param  value
 163      *         The initial value of the string
 164      */
 165     public String(char value[]) {
 166         this.value = Arrays.copyOf(value, value.length);
 167     }
 168 
 169     /**
 170      * Allocates a new {@code String} that contains characters from a subarray
 171      * of the character array argument. The {@code offset} argument is the
 172      * index of the first character of the subarray and the {@code count}
 173      * argument specifies the length of the subarray. The contents of the
 174      * subarray are copied; subsequent modification of the character array does
 175      * not affect the newly created string.
 176      *
 177      * @param  value
 178      *         Array that is the source of characters
 179      *
 180      * @param  offset
 181      *         The initial offset
 182      *
 183      * @param  count
 184      *         The length
 185      *
 186      * @throws  IndexOutOfBoundsException
 187      *          If the {@code offset} and {@code count} arguments index
 188      *          characters outside the bounds of the {@code value} array
 189      */
 190     public String(char value[], int offset, int count) {
 191         if (offset < 0) {
 192             throw new StringIndexOutOfBoundsException(offset);
 193         }
 194         if (count < 0) {
 195             throw new StringIndexOutOfBoundsException(count);
 196         }
 197         // Note: offset or count might be near -1>>>1.
 198         if (offset > value.length - count) {
 199             throw new StringIndexOutOfBoundsException(offset + count);
 200         }
 201         this.value = Arrays.copyOfRange(value, offset, offset+count);
 202     }
 203 
 204     /**
 205      * Allocates a new {@code String} that contains characters from a subarray
 206      * of the <a href="Character.html#unicode">Unicode code point</a> array
 207      * argument.  The {@code offset} argument is the index of the first code
 208      * point of the subarray and the {@code count} argument specifies the
 209      * length of the subarray.  The contents of the subarray are converted to
 210      * {@code char}s; subsequent modification of the {@code int} array does not
 211      * affect the newly created string.
 212      *
 213      * @param  codePoints
 214      *         Array that is the source of Unicode code points
 215      *
 216      * @param  offset
 217      *         The initial offset
 218      *
 219      * @param  count
 220      *         The length
 221      *
 222      * @throws  IllegalArgumentException
 223      *          If any invalid Unicode code point is found in {@code
 224      *          codePoints}
 225      *
 226      * @throws  IndexOutOfBoundsException
 227      *          If the {@code offset} and {@code count} arguments index
 228      *          characters outside the bounds of the {@code codePoints} array
 229      *
 230      * @since  1.5
 231      */
 232     public String(int[] codePoints, int offset, int count) {
 233         if (offset < 0) {
 234             throw new StringIndexOutOfBoundsException(offset);
 235         }
 236         if (count < 0) {
 237             throw new StringIndexOutOfBoundsException(count);
 238         }
 239         // Note: offset or count might be near -1>>>1.
 240         if (offset > codePoints.length - count) {
 241             throw new StringIndexOutOfBoundsException(offset + count);
 242         }
 243 
 244         final int end = offset + count;
 245 
 246         // Pass 1: Compute precise size of char[]
 247         int n = count;
 248         for (int i = offset; i < end; i++) {
 249             int c = codePoints[i];
 250             if (Character.isBmpCodePoint(c))
 251                 continue;
 252             else if (Character.isValidCodePoint(c))
 253                 n++;
 254             else throw new IllegalArgumentException(Integer.toString(c));
 255         }
 256 
 257         // Pass 2: Allocate and fill in char[]
 258         final char[] v = new char[n];
 259 
 260         for (int i = offset, j = 0; i < end; i++, j++) {
 261             int c = codePoints[i];
 262             if (Character.isBmpCodePoint(c))
 263                 v[j] = (char)c;
 264             else
 265                 Character.toSurrogates(c, v, j++);
 266         }
 267 
 268         this.value = v;
 269     }
 270 
 271     /**
 272      * Allocates a new {@code String} constructed from a subarray of an array
 273      * of 8-bit integer values.
 274      *
 275      * <p> The {@code offset} argument is the index of the first byte of the
 276      * subarray, and the {@code count} argument specifies the length of the
 277      * subarray.
 278      *
 279      * <p> Each {@code byte} in the subarray is converted to a {@code char} as
 280      * specified in the method above.
 281      *
 282      * @deprecated This method does not properly convert bytes into characters.
 283      * As of JDK&nbsp;1.1, the preferred way to do this is via the
 284      * {@code String} constructors that take a {@link
 285      * java.nio.charset.Charset}, charset name, or that use the platform's
 286      * default charset.
 287      *
 288      * @param  ascii
 289      *         The bytes to be converted to characters
 290      *
 291      * @param  hibyte
 292      *         The top 8 bits of each 16-bit Unicode code unit
 293      *
 294      * @param  offset
 295      *         The initial offset
 296      * @param  count
 297      *         The length
 298      *
 299      * @throws  IndexOutOfBoundsException
 300      *          If the {@code offset} or {@code count} argument is invalid
 301      *
 302      * @see  #String(byte[], int)
 303      * @see  #String(byte[], int, int, java.lang.String)
 304      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 305      * @see  #String(byte[], int, int)
 306      * @see  #String(byte[], java.lang.String)
 307      * @see  #String(byte[], java.nio.charset.Charset)
 308      * @see  #String(byte[])
 309      */
 310     @Deprecated
 311     public String(byte ascii[], int hibyte, int offset, int count) {
 312         checkBounds(ascii, offset, count);
 313         char value[] = new char[count];
 314 
 315         if (hibyte == 0) {
 316             for (int i = count; i-- > 0;) {
 317                 value[i] = (char)(ascii[i + offset] & 0xff);
 318             }
 319         } else {
 320             hibyte <<= 8;
 321             for (int i = count; i-- > 0;) {
 322                 value[i] = (char)(hibyte | (ascii[i + offset] & 0xff));
 323             }
 324         }
 325         this.value = value;
 326     }
 327 
 328     /**
 329      * Allocates a new {@code String} containing characters constructed from
 330      * an array of 8-bit integer values. Each character <i>c</i>in the
 331      * resulting string is constructed from the corresponding component
 332      * <i>b</i> in the byte array such that:
 333      *
 334      * <blockquote><pre>
 335      *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
 336      *                         | (<b><i>b</i></b> &amp; 0xff))
 337      * </pre></blockquote>
 338      *
 339      * @deprecated  This method does not properly convert bytes into
 340      * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 341      * {@code String} constructors that take a {@link
 342      * java.nio.charset.Charset}, charset name, or that use the platform's
 343      * default charset.
 344      *
 345      * @param  ascii
 346      *         The bytes to be converted to characters
 347      *
 348      * @param  hibyte
 349      *         The top 8 bits of each 16-bit Unicode code unit
 350      *
 351      * @see  #String(byte[], int, int, java.lang.String)
 352      * @see  #String(byte[], int, int, java.nio.charset.Charset)
 353      * @see  #String(byte[], int, int)
 354      * @see  #String(byte[], java.lang.String)
 355      * @see  #String(byte[], java.nio.charset.Charset)
 356      * @see  #String(byte[])
 357      */
 358     @Deprecated
 359     public String(byte ascii[], int hibyte) {
 360         this(ascii, hibyte, 0, ascii.length);
 361     }
 362 
 363     /* Common private utility method used to bounds check the byte array
 364      * and requested offset & length values used by the String(byte[],..)
 365      * constructors.
 366      */
 367     private static void checkBounds(byte[] bytes, int offset, int length) {
 368         if (length < 0)
 369             throw new StringIndexOutOfBoundsException(length);
 370         if (offset < 0)
 371             throw new StringIndexOutOfBoundsException(offset);
 372         if (offset > bytes.length - length)
 373             throw new StringIndexOutOfBoundsException(offset + length);
 374     }
 375 
 376     /**
 377      * Constructs a new {@code String} by decoding the specified subarray of
 378      * bytes using the specified charset.  The length of the new {@code String}
 379      * is a function of the charset, and hence may not be equal to the length
 380      * of the subarray.
 381      *
 382      * <p> The behavior of this constructor when the given bytes are not valid
 383      * in the given charset is unspecified.  The {@link
 384      * java.nio.charset.CharsetDecoder} class should be used when more control
 385      * over the decoding process is required.
 386      *
 387      * @param  bytes
 388      *         The bytes to be decoded into characters
 389      *
 390      * @param  offset
 391      *         The index of the first byte to decode
 392      *
 393      * @param  length
 394      *         The number of bytes to decode
 395 
 396      * @param  charsetName
 397      *         The name of a supported {@linkplain java.nio.charset.Charset
 398      *         charset}
 399      *
 400      * @throws  UnsupportedEncodingException
 401      *          If the named charset is not supported
 402      *
 403      * @throws  IndexOutOfBoundsException
 404      *          If the {@code offset} and {@code length} arguments index
 405      *          characters outside the bounds of the {@code bytes} array
 406      *
 407      * @since  JDK1.1
 408      */
 409     public String(byte bytes[], int offset, int length, String charsetName)
 410             throws UnsupportedEncodingException {
 411         if (charsetName == null)
 412             throw new NullPointerException("charsetName");
 413         checkBounds(bytes, offset, length);
 414         this.value = StringCoding.decode(charsetName, bytes, offset, length);
 415     }
 416 
 417     /**
 418      * Constructs a new {@code String} by decoding the specified subarray of
 419      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 420      * The length of the new {@code String} is a function of the charset, and
 421      * hence may not be equal to the length of the subarray.
 422      *
 423      * <p> This method always replaces malformed-input and unmappable-character
 424      * sequences with this charset's default replacement string.  The {@link
 425      * java.nio.charset.CharsetDecoder} class should be used when more control
 426      * over the decoding process is required.
 427      *
 428      * @param  bytes
 429      *         The bytes to be decoded into characters
 430      *
 431      * @param  offset
 432      *         The index of the first byte to decode
 433      *
 434      * @param  length
 435      *         The number of bytes to decode
 436      *
 437      * @param  charset
 438      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 439      *         decode the {@code bytes}
 440      *
 441      * @throws  IndexOutOfBoundsException
 442      *          If the {@code offset} and {@code length} arguments index
 443      *          characters outside the bounds of the {@code bytes} array
 444      *
 445      * @since  1.6
 446      */
 447     public String(byte bytes[], int offset, int length, Charset charset) {
 448         if (charset == null)
 449             throw new NullPointerException("charset");
 450         checkBounds(bytes, offset, length);
 451         this.value =  StringCoding.decode(charset, bytes, offset, length);
 452     }
 453 
 454     /**
 455      * Constructs a new {@code String} by decoding the specified array of bytes
 456      * using the specified {@linkplain java.nio.charset.Charset charset}.  The
 457      * length of the new {@code String} is a function of the charset, and hence
 458      * may not be equal to the length of the byte array.
 459      *
 460      * <p> The behavior of this constructor when the given bytes are not valid
 461      * in the given charset is unspecified.  The {@link
 462      * java.nio.charset.CharsetDecoder} class should be used when more control
 463      * over the decoding process is required.
 464      *
 465      * @param  bytes
 466      *         The bytes to be decoded into characters
 467      *
 468      * @param  charsetName
 469      *         The name of a supported {@linkplain java.nio.charset.Charset
 470      *         charset}
 471      *
 472      * @throws  UnsupportedEncodingException
 473      *          If the named charset is not supported
 474      *
 475      * @since  JDK1.1
 476      */
 477     public String(byte bytes[], String charsetName)
 478             throws UnsupportedEncodingException {
 479         this(bytes, 0, bytes.length, charsetName);
 480     }
 481 
 482     /**
 483      * Constructs a new {@code String} by decoding the specified array of
 484      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
 485      * The length of the new {@code String} is a function of the charset, and
 486      * hence may not be equal to the length of the byte array.
 487      *
 488      * <p> This method always replaces malformed-input and unmappable-character
 489      * sequences with this charset's default replacement string.  The {@link
 490      * java.nio.charset.CharsetDecoder} class should be used when more control
 491      * over the decoding process is required.
 492      *
 493      * @param  bytes
 494      *         The bytes to be decoded into characters
 495      *
 496      * @param  charset
 497      *         The {@linkplain java.nio.charset.Charset charset} to be used to
 498      *         decode the {@code bytes}
 499      *
 500      * @since  1.6
 501      */
 502     public String(byte bytes[], Charset charset) {
 503         this(bytes, 0, bytes.length, charset);
 504     }
 505 
 506     /**
 507      * Constructs a new {@code String} by decoding the specified subarray of
 508      * bytes using the platform's default charset.  The length of the new
 509      * {@code String} is a function of the charset, and hence may not be equal
 510      * to the length of the subarray.
 511      *
 512      * <p> The behavior of this constructor when the given bytes are not valid
 513      * in the default charset is unspecified.  The {@link
 514      * java.nio.charset.CharsetDecoder} class should be used when more control
 515      * over the decoding process is required.
 516      *
 517      * @param  bytes
 518      *         The bytes to be decoded into characters
 519      *
 520      * @param  offset
 521      *         The index of the first byte to decode
 522      *
 523      * @param  length
 524      *         The number of bytes to decode
 525      *
 526      * @throws  IndexOutOfBoundsException
 527      *          If the {@code offset} and the {@code length} arguments index
 528      *          characters outside the bounds of the {@code bytes} array
 529      *
 530      * @since  JDK1.1
 531      */
 532     public String(byte bytes[], int offset, int length) {
 533         checkBounds(bytes, offset, length);
 534         this.value = StringCoding.decode(bytes, offset, length);
 535     }
 536 
 537     /**
 538      * Constructs a new {@code String} by decoding the specified array of bytes
 539      * using the platform's default charset.  The length of the new {@code
 540      * String} is a function of the charset, and hence may not be equal to the
 541      * length of the byte array.
 542      *
 543      * <p> The behavior of this constructor when the given bytes are not valid
 544      * in the default charset is unspecified.  The {@link
 545      * java.nio.charset.CharsetDecoder} class should be used when more control
 546      * over the decoding process is required.
 547      *
 548      * @param  bytes
 549      *         The bytes to be decoded into characters
 550      *
 551      * @since  JDK1.1
 552      */
 553     public String(byte bytes[]) {
 554         this(bytes, 0, bytes.length);
 555     }
 556 
 557     /**
 558      * Allocates a new string that contains the sequence of characters
 559      * currently contained in the string buffer argument. The contents of the
 560      * string buffer are copied; subsequent modification of the string buffer
 561      * does not affect the newly created string.
 562      *
 563      * @param  buffer
 564      *         A {@code StringBuffer}
 565      */
 566     public String(StringBuffer buffer) {
 567         synchronized(buffer) {
 568             this.value = Arrays.copyOf(buffer.getValue(), buffer.length());
 569         }
 570     }
 571 
 572     /**
 573      * Allocates a new string that contains the sequence of characters
 574      * currently contained in the string builder argument. The contents of the
 575      * string builder are copied; subsequent modification of the string builder
 576      * does not affect the newly created string.
 577      *
 578      * <p> This constructor is provided to ease migration to {@code
 579      * StringBuilder}. Obtaining a string from a string builder via the {@code
 580      * toString} method is likely to run faster and is generally preferred.
 581      *
 582      * @param   builder
 583      *          A {@code StringBuilder}
 584      *
 585      * @since  1.5
 586      */
 587     public String(StringBuilder builder) {
 588         this.value = Arrays.copyOf(builder.getValue(), builder.length());
 589     }
 590 
 591     /*
 592     * Package private constructor which shares value array for speed.
 593     * this constructor is always expected to be called with share==true.
 594     * a separate constructor is needed because we already have a public
 595     * String(char[]) constructor that makes a copy of the given char[].
 596     */
 597     String(char[] value, boolean share) {
 598         // assert share : "unshared not supported";
 599         this.value = value;
 600     }
 601 
 602     /**
 603      * Returns the length of this string.
 604      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 605      * code units</a> in the string.
 606      *
 607      * @return  the length of the sequence of characters represented by this
 608      *          object.
 609      */
 610     public int length() {
 611         return value.length;
 612     }
 613 
 614     /**
 615      * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
 616      *
 617      * @return {@code true} if {@link #length()} is {@code 0}, otherwise
 618      * {@code false}
 619      *
 620      * @since 1.6
 621      */
 622     public boolean isEmpty() {
 623         return value.length == 0;
 624     }
 625 
 626     /**
 627      * Returns the {@code char} value at the
 628      * specified index. An index ranges from {@code 0} to
 629      * {@code length() - 1}. The first {@code char} value of the sequence
 630      * is at index {@code 0}, the next at index {@code 1},
 631      * and so on, as for array indexing.
 632      *
 633      * <p>If the {@code char} value specified by the index is a
 634      * <a href="Character.html#unicode">surrogate</a>, the surrogate
 635      * value is returned.
 636      *
 637      * @param      index   the index of the {@code char} value.
 638      * @return     the {@code char} value at the specified index of this string.
 639      *             The first {@code char} value is at index {@code 0}.
 640      * @exception  IndexOutOfBoundsException  if the {@code index}
 641      *             argument is negative or not less than the length of this
 642      *             string.
 643      */
 644     public char charAt(int index) {
 645         if ((index < 0) || (index >= value.length)) {
 646             throw new StringIndexOutOfBoundsException(index);
 647         }
 648         return value[index];
 649     }
 650 
 651     /**
 652      * Returns the character (Unicode code point) at the specified
 653      * index. The index refers to {@code char} values
 654      * (Unicode code units) and ranges from {@code 0} to
 655      * {@link #length()}{@code  - 1}.
 656      *
 657      * <p> If the {@code char} value specified at the given index
 658      * is in the high-surrogate range, the following index is less
 659      * than the length of this {@code String}, and the
 660      * {@code char} value at the following index is in the
 661      * low-surrogate range, then the supplementary code point
 662      * corresponding to this surrogate pair is returned. Otherwise,
 663      * the {@code char} value at the given index is returned.
 664      *
 665      * @param      index the index to the {@code char} values
 666      * @return     the code point value of the character at the
 667      *             {@code index}
 668      * @exception  IndexOutOfBoundsException  if the {@code index}
 669      *             argument is negative or not less than the length of this
 670      *             string.
 671      * @since      1.5
 672      */
 673     public int codePointAt(int index) {
 674         if ((index < 0) || (index >= value.length)) {
 675             throw new StringIndexOutOfBoundsException(index);
 676         }
 677         return Character.codePointAtImpl(value, index, value.length);
 678     }
 679 
 680     /**
 681      * Returns the character (Unicode code point) before the specified
 682      * index. The index refers to {@code char} values
 683      * (Unicode code units) and ranges from {@code 1} to {@link
 684      * CharSequence#length() length}.
 685      *
 686      * <p> If the {@code char} value at {@code (index - 1)}
 687      * is in the low-surrogate range, {@code (index - 2)} is not
 688      * negative, and the {@code char} value at {@code (index -
 689      * 2)} is in the high-surrogate range, then the
 690      * supplementary code point value of the surrogate pair is
 691      * returned. If the {@code char} value at {@code index -
 692      * 1} is an unpaired low-surrogate or a high-surrogate, the
 693      * surrogate value is returned.
 694      *
 695      * @param     index the index following the code point that should be returned
 696      * @return    the Unicode code point value before the given index.
 697      * @exception IndexOutOfBoundsException if the {@code index}
 698      *            argument is less than 1 or greater than the length
 699      *            of this string.
 700      * @since     1.5
 701      */
 702     public int codePointBefore(int index) {
 703         int i = index - 1;
 704         if ((i < 0) || (i >= value.length)) {
 705             throw new StringIndexOutOfBoundsException(index);
 706         }
 707         return Character.codePointBeforeImpl(value, index, 0);
 708     }
 709 
 710     /**
 711      * Returns the number of Unicode code points in the specified text
 712      * range of this {@code String}. The text range begins at the
 713      * specified {@code beginIndex} and extends to the
 714      * {@code char} at index {@code endIndex - 1}. Thus the
 715      * length (in {@code char}s) of the text range is
 716      * {@code endIndex-beginIndex}. Unpaired surrogates within
 717      * the text range count as one code point each.
 718      *
 719      * @param beginIndex the index to the first {@code char} of
 720      * the text range.
 721      * @param endIndex the index after the last {@code char} of
 722      * the text range.
 723      * @return the number of Unicode code points in the specified text
 724      * range
 725      * @exception IndexOutOfBoundsException if the
 726      * {@code beginIndex} is negative, or {@code endIndex}
 727      * is larger than the length of this {@code String}, or
 728      * {@code beginIndex} is larger than {@code endIndex}.
 729      * @since  1.5
 730      */
 731     public int codePointCount(int beginIndex, int endIndex) {
 732         if (beginIndex < 0 || endIndex > value.length || beginIndex > endIndex) {
 733             throw new IndexOutOfBoundsException();
 734         }
 735         return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
 736     }
 737 
 738     /**
 739      * Returns the index within this {@code String} that is
 740      * offset from the given {@code index} by
 741      * {@code codePointOffset} code points. Unpaired surrogates
 742      * within the text range given by {@code index} and
 743      * {@code codePointOffset} count as one code point each.
 744      *
 745      * @param index the index to be offset
 746      * @param codePointOffset the offset in code points
 747      * @return the index within this {@code String}
 748      * @exception IndexOutOfBoundsException if {@code index}
 749      *   is negative or larger then the length of this
 750      *   {@code String}, or if {@code codePointOffset} is positive
 751      *   and the substring starting with {@code index} has fewer
 752      *   than {@code codePointOffset} code points,
 753      *   or if {@code codePointOffset} is negative and the substring
 754      *   before {@code index} has fewer than the absolute value
 755      *   of {@code codePointOffset} code points.
 756      * @since 1.5
 757      */
 758     public int offsetByCodePoints(int index, int codePointOffset) {
 759         if (index < 0 || index > value.length) {
 760             throw new IndexOutOfBoundsException();
 761         }
 762         return Character.offsetByCodePointsImpl(value, 0, value.length,
 763                 index, codePointOffset);
 764     }
 765 
 766     /**
 767      * Copy characters from this string into dst starting at dstBegin.
 768      * This method doesn't perform any range checking.
 769      */
 770     void getChars(char dst[], int dstBegin) {
 771         System.arraycopy(value, 0, dst, dstBegin, value.length);
 772     }
 773 
 774     /**
 775      * Copies characters from this string into the destination character
 776      * array.
 777      * <p>
 778      * The first character to be copied is at index {@code srcBegin};
 779      * the last character to be copied is at index {@code srcEnd-1}
 780      * (thus the total number of characters to be copied is
 781      * {@code srcEnd-srcBegin}). The characters are copied into the
 782      * subarray of {@code dst} starting at index {@code dstBegin}
 783      * and ending at index:
 784      * <blockquote><pre>
 785      *     dstbegin + (srcEnd-srcBegin) - 1
 786      * </pre></blockquote>
 787      *
 788      * @param      srcBegin   index of the first character in the string
 789      *                        to copy.
 790      * @param      srcEnd     index after the last character in the string
 791      *                        to copy.
 792      * @param      dst        the destination array.
 793      * @param      dstBegin   the start offset in the destination array.
 794      * @exception IndexOutOfBoundsException If any of the following
 795      *            is true:
 796      *            <ul><li>{@code srcBegin} is negative.
 797      *            <li>{@code srcBegin} is greater than {@code srcEnd}
 798      *            <li>{@code srcEnd} is greater than the length of this
 799      *                string
 800      *            <li>{@code dstBegin} is negative
 801      *            <li>{@code dstBegin+(srcEnd-srcBegin)} is larger than
 802      *                {@code dst.length}</ul>
 803      */
 804     public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
 805         if (srcBegin < 0) {
 806             throw new StringIndexOutOfBoundsException(srcBegin);
 807         }
 808         if (srcEnd > value.length) {
 809             throw new StringIndexOutOfBoundsException(srcEnd);
 810         }
 811         if (srcBegin > srcEnd) {
 812             throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
 813         }
 814         System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
 815     }
 816 
 817     /**
 818      * Copies characters from this string into the destination byte array. Each
 819      * byte receives the 8 low-order bits of the corresponding character. The
 820      * eight high-order bits of each character are not copied and do not
 821      * participate in the transfer in any way.
 822      *
 823      * <p> The first character to be copied is at index {@code srcBegin}; the
 824      * last character to be copied is at index {@code srcEnd-1}.  The total
 825      * number of characters to be copied is {@code srcEnd-srcBegin}. The
 826      * characters, converted to bytes, are copied into the subarray of {@code
 827      * dst} starting at index {@code dstBegin} and ending at index:
 828      *
 829      * <blockquote><pre>
 830      *     dstbegin + (srcEnd-srcBegin) - 1
 831      * </pre></blockquote>
 832      *
 833      * @deprecated  This method does not properly convert characters into
 834      * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
 835      * {@link #getBytes()} method, which uses the platform's default charset.
 836      *
 837      * @param  srcBegin
 838      *         Index of the first character in the string to copy
 839      *
 840      * @param  srcEnd
 841      *         Index after the last character in the string to copy
 842      *
 843      * @param  dst
 844      *         The destination array
 845      *
 846      * @param  dstBegin
 847      *         The start offset in the destination array
 848      *
 849      * @throws  IndexOutOfBoundsException
 850      *          If any of the following is true:
 851      *          <ul>
 852      *            <li> {@code srcBegin} is negative
 853      *            <li> {@code srcBegin} is greater than {@code srcEnd}
 854      *            <li> {@code srcEnd} is greater than the length of this String
 855      *            <li> {@code dstBegin} is negative
 856      *            <li> {@code dstBegin+(srcEnd-srcBegin)} is larger than {@code
 857      *                 dst.length}
 858      *          </ul>
 859      */
 860     @Deprecated
 861     public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
 862         if (srcBegin < 0) {
 863             throw new StringIndexOutOfBoundsException(srcBegin);
 864         }
 865         if (srcEnd > value.length) {
 866             throw new StringIndexOutOfBoundsException(srcEnd);
 867         }
 868         if (srcBegin > srcEnd) {
 869             throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
 870         }
 871         Objects.requireNonNull(dst);
 872 
 873         int j = dstBegin;
 874         int n = srcEnd;
 875         int i = srcBegin;
 876         char[] val = value;   /* avoid getfield opcode */
 877 
 878         while (i < n) {
 879             dst[j++] = (byte)val[i++];
 880         }
 881     }
 882 
 883     /**
 884      * Encodes this {@code String} into a sequence of bytes using the named
 885      * charset, storing the result into a new byte array.
 886      *
 887      * <p> The behavior of this method when this string cannot be encoded in
 888      * the given charset is unspecified.  The {@link
 889      * java.nio.charset.CharsetEncoder} class should be used when more control
 890      * over the encoding process is required.
 891      *
 892      * @param  charsetName
 893      *         The name of a supported {@linkplain java.nio.charset.Charset
 894      *         charset}
 895      *
 896      * @return  The resultant byte array
 897      *
 898      * @throws  UnsupportedEncodingException
 899      *          If the named charset is not supported
 900      *
 901      * @since  JDK1.1
 902      */
 903     public byte[] getBytes(String charsetName)
 904             throws UnsupportedEncodingException {
 905         if (charsetName == null) throw new NullPointerException();
 906         return StringCoding.encode(charsetName, value, 0, value.length);
 907     }
 908 
 909     /**
 910      * Encodes this {@code String} into a sequence of bytes using the given
 911      * {@linkplain java.nio.charset.Charset charset}, storing the result into a
 912      * new byte array.
 913      *
 914      * <p> This method always replaces malformed-input and unmappable-character
 915      * sequences with this charset's default replacement byte array.  The
 916      * {@link java.nio.charset.CharsetEncoder} class should be used when more
 917      * control over the encoding process is required.
 918      *
 919      * @param  charset
 920      *         The {@linkplain java.nio.charset.Charset} to be used to encode
 921      *         the {@code String}
 922      *
 923      * @return  The resultant byte array
 924      *
 925      * @since  1.6
 926      */
 927     public byte[] getBytes(Charset charset) {
 928         if (charset == null) throw new NullPointerException();
 929         return StringCoding.encode(charset, value, 0, value.length);
 930     }
 931 
 932     /**
 933      * Encodes this {@code String} into a sequence of bytes using the
 934      * platform's default charset, storing the result into a new byte array.
 935      *
 936      * <p> The behavior of this method when this string cannot be encoded in
 937      * the default charset is unspecified.  The {@link
 938      * java.nio.charset.CharsetEncoder} class should be used when more control
 939      * over the encoding process is required.
 940      *
 941      * @return  The resultant byte array
 942      *
 943      * @since      JDK1.1
 944      */
 945     public byte[] getBytes() {
 946         return StringCoding.encode(value, 0, value.length);
 947     }
 948 
 949     /**
 950      * Compares this string to the specified object.  The result is {@code
 951      * true} if and only if the argument is not {@code null} and is a {@code
 952      * String} object that represents the same sequence of characters as this
 953      * object.
 954      *
 955      * @param  anObject
 956      *         The object to compare this {@code String} against
 957      *
 958      * @return  {@code true} if the given object represents a {@code String}
 959      *          equivalent to this string, {@code false} otherwise
 960      *
 961      * @see  #compareTo(String)
 962      * @see  #equalsIgnoreCase(String)
 963      */
 964     public boolean equals(Object anObject) {
 965         if (this == anObject) {
 966             return true;
 967         }
 968         if (anObject instanceof String) {
 969             String anotherString = (String)anObject;
 970             int n = value.length;
 971             if (n == anotherString.value.length) {
 972                 char v1[] = value;
 973                 char v2[] = anotherString.value;
 974                 int i = 0;
 975                 while (n-- != 0) {
 976                     if (v1[i] != v2[i])
 977                         return false;
 978                     i++;
 979                 }
 980                 return true;
 981             }
 982         }
 983         return false;
 984     }
 985 
 986     /**
 987      * Compares this string to the specified {@code StringBuffer}.  The result
 988      * is {@code true} if and only if this {@code String} represents the same
 989      * sequence of characters as the specified {@code StringBuffer}. This method
 990      * synchronizes on the {@code StringBuffer}.
 991      *
 992      * @param  sb
 993      *         The {@code StringBuffer} to compare this {@code String} against
 994      *
 995      * @return  {@code true} if this {@code String} represents the same
 996      *          sequence of characters as the specified {@code StringBuffer},
 997      *          {@code false} otherwise
 998      *
 999      * @since  1.4
1000      */
1001     public boolean contentEquals(StringBuffer sb) {
1002         return contentEquals((CharSequence)sb);
1003     }
1004 
1005     private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
1006         char v1[] = value;
1007         char v2[] = sb.getValue();
1008         int n = v1.length;
1009         if (n != sb.length()) {
1010             return false;
1011         }
1012         for (int i = 0; i < n; i++) {
1013             if (v1[i] != v2[i]) {
1014                 return false;
1015             }
1016         }
1017         return true;
1018     }
1019 
1020     /**
1021      * Compares this string to the specified {@code CharSequence}.  The
1022      * result is {@code true} if and only if this {@code String} represents the
1023      * same sequence of char values as the specified sequence. Note that if the
1024      * {@code CharSequence} is a {@code StringBuffer} then the method
1025      * synchronizes on it.
1026      *
1027      * @param  cs
1028      *         The sequence to compare this {@code String} against
1029      *
1030      * @return  {@code true} if this {@code String} represents the same
1031      *          sequence of char values as the specified sequence, {@code
1032      *          false} otherwise
1033      *
1034      * @since  1.5
1035      */
1036     public boolean contentEquals(CharSequence cs) {
1037         // Argument is a StringBuffer, StringBuilder
1038         if (cs instanceof AbstractStringBuilder) {
1039             if (cs instanceof StringBuffer) {
1040                 synchronized(cs) {
1041                    return nonSyncContentEquals((AbstractStringBuilder)cs);
1042                 }
1043             } else {
1044                 return nonSyncContentEquals((AbstractStringBuilder)cs);
1045             }
1046         }
1047         // Argument is a String
1048         if (cs.equals(this))
1049             return true;
1050         // Argument is a generic CharSequence
1051         char v1[] = value;
1052         int n = v1.length;
1053         if (n != cs.length()) {
1054             return false;
1055         }
1056         for (int i = 0; i < n; i++) {
1057             if (v1[i] != cs.charAt(i)) {
1058                 return false;
1059             }
1060         }
1061         return true;
1062     }
1063 
1064     /**
1065      * Compares this {@code String} to another {@code String}, ignoring case
1066      * considerations.  Two strings are considered equal ignoring case if they
1067      * are of the same length and corresponding characters in the two strings
1068      * are equal ignoring case.
1069      *
1070      * <p> Two characters {@code c1} and {@code c2} are considered the same
1071      * ignoring case if at least one of the following is true:
1072      * <ul>
1073      *   <li> The two characters are the same (as compared by the
1074      *        {@code ==} operator)
1075      *   <li> Applying the method {@link
1076      *        java.lang.Character#toUpperCase(char)} to each character
1077      *        produces the same result
1078      *   <li> Applying the method {@link
1079      *        java.lang.Character#toLowerCase(char)} to each character
1080      *        produces the same result
1081      * </ul>
1082      *
1083      * @param  anotherString
1084      *         The {@code String} to compare this {@code String} against
1085      *
1086      * @return  {@code true} if the argument is not {@code null} and it
1087      *          represents an equivalent {@code String} ignoring case; {@code
1088      *          false} otherwise
1089      *
1090      * @see  #equals(Object)
1091      */
1092     public boolean equalsIgnoreCase(String anotherString) {
1093         return (this == anotherString) ? true
1094                 : (anotherString != null)
1095                 && (anotherString.value.length == value.length)
1096                 && regionMatches(true, 0, anotherString, 0, value.length);
1097     }
1098 
1099     /**
1100      * Compares two strings lexicographically.
1101      * The comparison is based on the Unicode value of each character in
1102      * the strings. The character sequence represented by this
1103      * {@code String} object is compared lexicographically to the
1104      * character sequence represented by the argument string. The result is
1105      * a negative integer if this {@code String} object
1106      * lexicographically precedes the argument string. The result is a
1107      * positive integer if this {@code String} object lexicographically
1108      * follows the argument string. The result is zero if the strings
1109      * are equal; {@code compareTo} returns {@code 0} exactly when
1110      * the {@link #equals(Object)} method would return {@code true}.
1111      * <p>
1112      * This is the definition of lexicographic ordering. If two strings are
1113      * different, then either they have different characters at some index
1114      * that is a valid index for both strings, or their lengths are different,
1115      * or both. If they have different characters at one or more index
1116      * positions, let <i>k</i> be the smallest such index; then the string
1117      * whose character at position <i>k</i> has the smaller value, as
1118      * determined by using the &lt; operator, lexicographically precedes the
1119      * other string. In this case, {@code compareTo} returns the
1120      * difference of the two character values at position {@code k} in
1121      * the two string -- that is, the value:
1122      * <blockquote><pre>
1123      * this.charAt(k)-anotherString.charAt(k)
1124      * </pre></blockquote>
1125      * If there is no index position at which they differ, then the shorter
1126      * string lexicographically precedes the longer string. In this case,
1127      * {@code compareTo} returns the difference of the lengths of the
1128      * strings -- that is, the value:
1129      * <blockquote><pre>
1130      * this.length()-anotherString.length()
1131      * </pre></blockquote>
1132      *
1133      * @param   anotherString   the {@code String} to be compared.
1134      * @return  the value {@code 0} if the argument string is equal to
1135      *          this string; a value less than {@code 0} if this string
1136      *          is lexicographically less than the string argument; and a
1137      *          value greater than {@code 0} if this string is
1138      *          lexicographically greater than the string argument.
1139      */
1140     public int compareTo(String anotherString) {
1141         int len1 = value.length;
1142         int len2 = anotherString.value.length;
1143         int lim = Math.min(len1, len2);
1144         char v1[] = value;
1145         char v2[] = anotherString.value;
1146 
1147         int k = 0;
1148         while (k < lim) {
1149             char c1 = v1[k];
1150             char c2 = v2[k];
1151             if (c1 != c2) {
1152                 return c1 - c2;
1153             }
1154             k++;
1155         }
1156         return len1 - len2;
1157     }
1158 
1159     /**
1160      * A Comparator that orders {@code String} objects as by
1161      * {@code compareToIgnoreCase}. This comparator is serializable.
1162      * <p>
1163      * Note that this Comparator does <em>not</em> take locale into account,
1164      * and will result in an unsatisfactory ordering for certain locales.
1165      * The java.text package provides <em>Collators</em> to allow
1166      * locale-sensitive ordering.
1167      *
1168      * @see     java.text.Collator#compare(String, String)
1169      * @since   1.2
1170      */
1171     public static final Comparator<String> CASE_INSENSITIVE_ORDER
1172                                          = new CaseInsensitiveComparator();
1173     private static class CaseInsensitiveComparator
1174             implements Comparator<String>, java.io.Serializable {
1175         // use serialVersionUID from JDK 1.2.2 for interoperability
1176         private static final long serialVersionUID = 8575799808933029326L;
1177 
1178         public int compare(String s1, String s2) {
1179             int n1 = s1.length();
1180             int n2 = s2.length();
1181             int min = Math.min(n1, n2);
1182             for (int i = 0; i < min; i++) {
1183                 char c1 = s1.charAt(i);
1184                 char c2 = s2.charAt(i);
1185                 if (c1 != c2) {
1186                     c1 = Character.toUpperCase(c1);
1187                     c2 = Character.toUpperCase(c2);
1188                     if (c1 != c2) {
1189                         c1 = Character.toLowerCase(c1);
1190                         c2 = Character.toLowerCase(c2);
1191                         if (c1 != c2) {
1192                             // No overflow because of numeric promotion
1193                             return c1 - c2;
1194                         }
1195                     }
1196                 }
1197             }
1198             return n1 - n2;
1199         }
1200 
1201         /** Replaces the de-serialized object. */
1202         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
1203     }
1204 
1205     /**
1206      * Compares two strings lexicographically, ignoring case
1207      * differences. This method returns an integer whose sign is that of
1208      * calling {@code compareTo} with normalized versions of the strings
1209      * where case differences have been eliminated by calling
1210      * {@code Character.toLowerCase(Character.toUpperCase(character))} on
1211      * each character.
1212      * <p>
1213      * Note that this method does <em>not</em> take locale into account,
1214      * and will result in an unsatisfactory ordering for certain locales.
1215      * The java.text package provides <em>collators</em> to allow
1216      * locale-sensitive ordering.
1217      *
1218      * @param   str   the {@code String} to be compared.
1219      * @return  a negative integer, zero, or a positive integer as the
1220      *          specified String is greater than, equal to, or less
1221      *          than this String, ignoring case considerations.
1222      * @see     java.text.Collator#compare(String, String)
1223      * @since   1.2
1224      */
1225     public int compareToIgnoreCase(String str) {
1226         return CASE_INSENSITIVE_ORDER.compare(this, str);
1227     }
1228 
1229     /**
1230      * Tests if two string regions are equal.
1231      * <p>
1232      * A substring of this {@code String} object is compared to a substring
1233      * of the argument other. The result is true if these substrings
1234      * represent identical character sequences. The substring of this
1235      * {@code String} object to be compared begins at index {@code toffset}
1236      * and has length {@code len}. The substring of other to be compared
1237      * begins at index {@code ooffset} and has length {@code len}. The
1238      * result is {@code false} if and only if at least one of the following
1239      * is true:
1240      * <ul><li>{@code toffset} is negative.
1241      * <li>{@code ooffset} is negative.
1242      * <li>{@code toffset+len} is greater than the length of this
1243      * {@code String} object.
1244      * <li>{@code ooffset+len} is greater than the length of the other
1245      * argument.
1246      * <li>There is some nonnegative integer <i>k</i> less than {@code len}
1247      * such that:
1248      * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
1249      * <i>k</i>{@code )}
1250      * </ul>
1251      *
1252      * @param   toffset   the starting offset of the subregion in this string.
1253      * @param   other     the string argument.
1254      * @param   ooffset   the starting offset of the subregion in the string
1255      *                    argument.
1256      * @param   len       the number of characters to compare.
1257      * @return  {@code true} if the specified subregion of this string
1258      *          exactly matches the specified subregion of the string argument;
1259      *          {@code false} otherwise.
1260      */
1261     public boolean regionMatches(int toffset, String other, int ooffset,
1262             int len) {
1263         char ta[] = value;
1264         int to = toffset;
1265         char pa[] = other.value;
1266         int po = ooffset;
1267         // Note: toffset, ooffset, or len might be near -1>>>1.
1268         if ((ooffset < 0) || (toffset < 0)
1269                 || (toffset > (long)value.length - len)
1270                 || (ooffset > (long)other.value.length - len)) {
1271             return false;
1272         }
1273         while (len-- > 0) {
1274             if (ta[to++] != pa[po++]) {
1275                 return false;
1276             }
1277         }
1278         return true;
1279     }
1280 
1281     /**
1282      * Tests if two string regions are equal.
1283      * <p>
1284      * A substring of this {@code String} object is compared to a substring
1285      * of the argument {@code other}. The result is {@code true} if these
1286      * substrings represent character sequences that are the same, ignoring
1287      * case if and only if {@code ignoreCase} is true. The substring of
1288      * this {@code String} object to be compared begins at index
1289      * {@code toffset} and has length {@code len}. The substring of
1290      * {@code other} to be compared begins at index {@code ooffset} and
1291      * has length {@code len}. The result is {@code false} if and only if
1292      * at least one of the following is true:
1293      * <ul><li>{@code toffset} is negative.
1294      * <li>{@code ooffset} is negative.
1295      * <li>{@code toffset+len} is greater than the length of this
1296      * {@code String} object.
1297      * <li>{@code ooffset+len} is greater than the length of the other
1298      * argument.
1299      * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
1300      * integer <i>k</i> less than {@code len} such that:
1301      * <blockquote><pre>
1302      * this.charAt(toffset+k) != other.charAt(ooffset+k)
1303      * </pre></blockquote>
1304      * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
1305      * integer <i>k</i> less than {@code len} such that:
1306      * <blockquote><pre>
1307      * Character.toLowerCase(this.charAt(toffset+k)) !=
1308      Character.toLowerCase(other.charAt(ooffset+k))
1309      * </pre></blockquote>
1310      * and:
1311      * <blockquote><pre>
1312      * Character.toUpperCase(this.charAt(toffset+k)) !=
1313      *         Character.toUpperCase(other.charAt(ooffset+k))
1314      * </pre></blockquote>
1315      * </ul>
1316      *
1317      * @param   ignoreCase   if {@code true}, ignore case when comparing
1318      *                       characters.
1319      * @param   toffset      the starting offset of the subregion in this
1320      *                       string.
1321      * @param   other        the string argument.
1322      * @param   ooffset      the starting offset of the subregion in the string
1323      *                       argument.
1324      * @param   len          the number of characters to compare.
1325      * @return  {@code true} if the specified subregion of this string
1326      *          matches the specified subregion of the string argument;
1327      *          {@code false} otherwise. Whether the matching is exact
1328      *          or case insensitive depends on the {@code ignoreCase}
1329      *          argument.
1330      */
1331     public boolean regionMatches(boolean ignoreCase, int toffset,
1332             String other, int ooffset, int len) {
1333         char ta[] = value;
1334         int to = toffset;
1335         char pa[] = other.value;
1336         int po = ooffset;
1337         // Note: toffset, ooffset, or len might be near -1>>>1.
1338         if ((ooffset < 0) || (toffset < 0)
1339                 || (toffset > (long)value.length - len)
1340                 || (ooffset > (long)other.value.length - len)) {
1341             return false;
1342         }
1343         while (len-- > 0) {
1344             char c1 = ta[to++];
1345             char c2 = pa[po++];
1346             if (c1 == c2) {
1347                 continue;
1348             }
1349             if (ignoreCase) {
1350                 // If characters don't match but case may be ignored,
1351                 // try converting both characters to uppercase.
1352                 // If the results match, then the comparison scan should
1353                 // continue.
1354                 char u1 = Character.toUpperCase(c1);
1355                 char u2 = Character.toUpperCase(c2);
1356                 if (u1 == u2) {
1357                     continue;
1358                 }
1359                 // Unfortunately, conversion to uppercase does not work properly
1360                 // for the Georgian alphabet, which has strange rules about case
1361                 // conversion.  So we need to make one last check before
1362                 // exiting.
1363                 if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
1364                     continue;
1365                 }
1366             }
1367             return false;
1368         }
1369         return true;
1370     }
1371 
1372     /**
1373      * Tests if the substring of this string beginning at the
1374      * specified index starts with the specified prefix.
1375      *
1376      * @param   prefix    the prefix.
1377      * @param   toffset   where to begin looking in this string.
1378      * @return  {@code true} if the character sequence represented by the
1379      *          argument is a prefix of the substring of this object starting
1380      *          at index {@code toffset}; {@code false} otherwise.
1381      *          The result is {@code false} if {@code toffset} is
1382      *          negative or greater than the length of this
1383      *          {@code String} object; otherwise the result is the same
1384      *          as the result of the expression
1385      *          <pre>
1386      *          this.substring(toffset).startsWith(prefix)
1387      *          </pre>
1388      */
1389     public boolean startsWith(String prefix, int toffset) {
1390         char ta[] = value;
1391         int to = toffset;
1392         char pa[] = prefix.value;
1393         int po = 0;
1394         int pc = prefix.value.length;
1395         // Note: toffset might be near -1>>>1.
1396         if ((toffset < 0) || (toffset > value.length - pc)) {
1397             return false;
1398         }
1399         while (--pc >= 0) {
1400             if (ta[to++] != pa[po++]) {
1401                 return false;
1402             }
1403         }
1404         return true;
1405     }
1406 
1407     /**
1408      * Tests if this string starts with the specified prefix.
1409      *
1410      * @param   prefix   the prefix.
1411      * @return  {@code true} if the character sequence represented by the
1412      *          argument is a prefix of the character sequence represented by
1413      *          this string; {@code false} otherwise.
1414      *          Note also that {@code true} will be returned if the
1415      *          argument is an empty string or is equal to this
1416      *          {@code String} object as determined by the
1417      *          {@link #equals(Object)} method.
1418      * @since   1. 0
1419      */
1420     public boolean startsWith(String prefix) {
1421         return startsWith(prefix, 0);
1422     }
1423 
1424     /**
1425      * Tests if this string ends with the specified suffix.
1426      *
1427      * @param   suffix   the suffix.
1428      * @return  {@code true} if the character sequence represented by the
1429      *          argument is a suffix of the character sequence represented by
1430      *          this object; {@code false} otherwise. Note that the
1431      *          result will be {@code true} if the argument is the
1432      *          empty string or is equal to this {@code String} object
1433      *          as determined by the {@link #equals(Object)} method.
1434      */
1435     public boolean endsWith(String suffix) {
1436         return startsWith(suffix, value.length - suffix.value.length);
1437     }
1438 
1439     /**
1440      * Returns a hash code for this string. The hash code for a
1441      * {@code String} object is computed as
1442      * <blockquote><pre>
1443      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
1444      * </pre></blockquote>
1445      * using {@code int} arithmetic, where {@code s[i]} is the
1446      * <i>i</i>th character of the string, {@code n} is the length of
1447      * the string, and {@code ^} indicates exponentiation.
1448      * (The hash value of the empty string is zero.)
1449      *
1450      * @return  a hash code value for this object.
1451      */
1452     public int hashCode() {
1453         int h = hash;
1454         if (h == 0 && value.length > 0) {
1455             char val[] = value;
1456 
1457             for (int i = 0; i < value.length; i++) {
1458                 h = 31 * h + val[i];
1459             }
1460             hash = h;
1461         }
1462         return h;
1463     }
1464 
1465     /**
1466      * Returns the index within this string of the first occurrence of
1467      * the specified character. If a character with value
1468      * {@code ch} occurs in the character sequence represented by
1469      * this {@code String} object, then the index (in Unicode
1470      * code units) of the first such occurrence is returned. For
1471      * values of {@code ch} in the range from 0 to 0xFFFF
1472      * (inclusive), this is the smallest value <i>k</i> such that:
1473      * <blockquote><pre>
1474      * this.charAt(<i>k</i>) == ch
1475      * </pre></blockquote>
1476      * is true. For other values of {@code ch}, it is the
1477      * smallest value <i>k</i> such that:
1478      * <blockquote><pre>
1479      * this.codePointAt(<i>k</i>) == ch
1480      * </pre></blockquote>
1481      * is true. In either case, if no such character occurs in this
1482      * string, then {@code -1} is returned.
1483      *
1484      * @param   ch   a character (Unicode code point).
1485      * @return  the index of the first occurrence of the character in the
1486      *          character sequence represented by this object, or
1487      *          {@code -1} if the character does not occur.
1488      */
1489     public int indexOf(int ch) {
1490         return indexOf(ch, 0);
1491     }
1492 
1493     /**
1494      * Returns the index within this string of the first occurrence of the
1495      * specified character, starting the search at the specified index.
1496      * <p>
1497      * If a character with value {@code ch} occurs in the
1498      * character sequence represented by this {@code String}
1499      * object at an index no smaller than {@code fromIndex}, then
1500      * the index of the first such occurrence is returned. For values
1501      * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
1502      * this is the smallest value <i>k</i> such that:
1503      * <blockquote><pre>
1504      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1505      * </pre></blockquote>
1506      * is true. For other values of {@code ch}, it is the
1507      * smallest value <i>k</i> such that:
1508      * <blockquote><pre>
1509      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
1510      * </pre></blockquote>
1511      * is true. In either case, if no such character occurs in this
1512      * string at or after position {@code fromIndex}, then
1513      * {@code -1} is returned.
1514      *
1515      * <p>
1516      * There is no restriction on the value of {@code fromIndex}. If it
1517      * is negative, it has the same effect as if it were zero: this entire
1518      * string may be searched. If it is greater than the length of this
1519      * string, it has the same effect as if it were equal to the length of
1520      * this string: {@code -1} is returned.
1521      *
1522      * <p>All indices are specified in {@code char} values
1523      * (Unicode code units).
1524      *
1525      * @param   ch          a character (Unicode code point).
1526      * @param   fromIndex   the index to start the search from.
1527      * @return  the index of the first occurrence of the character in the
1528      *          character sequence represented by this object that is greater
1529      *          than or equal to {@code fromIndex}, or {@code -1}
1530      *          if the character does not occur.
1531      */
1532     public int indexOf(int ch, int fromIndex) {
1533         final int max = value.length;
1534         if (fromIndex < 0) {
1535             fromIndex = 0;
1536         } else if (fromIndex >= max) {
1537             // Note: fromIndex might be near -1>>>1.
1538             return -1;
1539         }
1540 
1541         if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
1542             // handle most cases here (ch is a BMP code point or a
1543             // negative value (invalid code point))
1544             final char[] value = this.value;
1545             for (int i = fromIndex; i < max; i++) {
1546                 if (value[i] == ch) {
1547                     return i;
1548                 }
1549             }
1550             return -1;
1551         } else {
1552             return indexOfSupplementary(ch, fromIndex);
1553         }
1554     }
1555 
1556     /**
1557      * Handles (rare) calls of indexOf with a supplementary character.
1558      */
1559     private int indexOfSupplementary(int ch, int fromIndex) {
1560         if (Character.isValidCodePoint(ch)) {
1561             final char[] value = this.value;
1562             final char hi = Character.highSurrogate(ch);
1563             final char lo = Character.lowSurrogate(ch);
1564             final int max = value.length - 1;
1565             for (int i = fromIndex; i < max; i++) {
1566                 if (value[i] == hi && value[i + 1] == lo) {
1567                     return i;
1568                 }
1569             }
1570         }
1571         return -1;
1572     }
1573 
1574     /**
1575      * Returns the index within this string of the last occurrence of
1576      * the specified character. For values of {@code ch} in the
1577      * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
1578      * units) returned is the largest value <i>k</i> such that:
1579      * <blockquote><pre>
1580      * this.charAt(<i>k</i>) == ch
1581      * </pre></blockquote>
1582      * is true. For other values of {@code ch}, it is the
1583      * largest value <i>k</i> such that:
1584      * <blockquote><pre>
1585      * this.codePointAt(<i>k</i>) == ch
1586      * </pre></blockquote>
1587      * is true.  In either case, if no such character occurs in this
1588      * string, then {@code -1} is returned.  The
1589      * {@code String} is searched backwards starting at the last
1590      * character.
1591      *
1592      * @param   ch   a character (Unicode code point).
1593      * @return  the index of the last occurrence of the character in the
1594      *          character sequence represented by this object, or
1595      *          {@code -1} if the character does not occur.
1596      */
1597     public int lastIndexOf(int ch) {
1598         return lastIndexOf(ch, value.length - 1);
1599     }
1600 
1601     /**
1602      * Returns the index within this string of the last occurrence of
1603      * the specified character, searching backward starting at the
1604      * specified index. For values of {@code ch} in the range
1605      * from 0 to 0xFFFF (inclusive), the index returned is the largest
1606      * value <i>k</i> such that:
1607      * <blockquote><pre>
1608      * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1609      * </pre></blockquote>
1610      * is true. For other values of {@code ch}, it is the
1611      * largest value <i>k</i> such that:
1612      * <blockquote><pre>
1613      * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
1614      * </pre></blockquote>
1615      * is true. In either case, if no such character occurs in this
1616      * string at or before position {@code fromIndex}, then
1617      * {@code -1} is returned.
1618      *
1619      * <p>All indices are specified in {@code char} values
1620      * (Unicode code units).
1621      *
1622      * @param   ch          a character (Unicode code point).
1623      * @param   fromIndex   the index to start the search from. There is no
1624      *          restriction on the value of {@code fromIndex}. If it is
1625      *          greater than or equal to the length of this string, it has
1626      *          the same effect as if it were equal to one less than the
1627      *          length of this string: this entire string may be searched.
1628      *          If it is negative, it has the same effect as if it were -1:
1629      *          -1 is returned.
1630      * @return  the index of the last occurrence of the character in the
1631      *          character sequence represented by this object that is less
1632      *          than or equal to {@code fromIndex}, or {@code -1}
1633      *          if the character does not occur before that point.
1634      */
1635     public int lastIndexOf(int ch, int fromIndex) {
1636         if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
1637             // handle most cases here (ch is a BMP code point or a
1638             // negative value (invalid code point))
1639             final char[] value = this.value;
1640             int i = Math.min(fromIndex, value.length - 1);
1641             for (; i >= 0; i--) {
1642                 if (value[i] == ch) {
1643                     return i;
1644                 }
1645             }
1646             return -1;
1647         } else {
1648             return lastIndexOfSupplementary(ch, fromIndex);
1649         }
1650     }
1651 
1652     /**
1653      * Handles (rare) calls of lastIndexOf with a supplementary character.
1654      */
1655     private int lastIndexOfSupplementary(int ch, int fromIndex) {
1656         if (Character.isValidCodePoint(ch)) {
1657             final char[] value = this.value;
1658             char hi = Character.highSurrogate(ch);
1659             char lo = Character.lowSurrogate(ch);
1660             int i = Math.min(fromIndex, value.length - 2);
1661             for (; i >= 0; i--) {
1662                 if (value[i] == hi && value[i + 1] == lo) {
1663                     return i;
1664                 }
1665             }
1666         }
1667         return -1;
1668     }
1669 
1670     /**
1671      * Returns the index within this string of the first occurrence of the
1672      * specified substring.
1673      *
1674      * <p>The returned index is the smallest value <i>k</i> for which:
1675      * <blockquote><pre>
1676      * this.startsWith(str, <i>k</i>)
1677      * </pre></blockquote>
1678      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1679      *
1680      * @param   str   the substring to search for.
1681      * @return  the index of the first occurrence of the specified substring,
1682      *          or {@code -1} if there is no such occurrence.
1683      */
1684     public int indexOf(String str) {
1685         return indexOf(str, 0);
1686     }
1687 
1688     /**
1689      * Returns the index within this string of the first occurrence of the
1690      * specified substring, starting at the specified index.
1691      *
1692      * <p>The returned index is the smallest value <i>k</i> for which:
1693      * <blockquote><pre>
1694      * <i>k</i> &gt;= fromIndex {@code &&} this.startsWith(str, <i>k</i>)
1695      * </pre></blockquote>
1696      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1697      *
1698      * @param   str         the substring to search for.
1699      * @param   fromIndex   the index from which to start the search.
1700      * @return  the index of the first occurrence of the specified substring,
1701      *          starting at the specified index,
1702      *          or {@code -1} if there is no such occurrence.
1703      */
1704     public int indexOf(String str, int fromIndex) {
1705         return indexOf(value, 0, value.length,
1706                 str.value, 0, str.value.length, fromIndex);
1707     }
1708 
1709     /**
1710      * Code shared by String and AbstractStringBuilder to do searches. The
1711      * source is the character array being searched, and the target
1712      * is the string being searched for.
1713      *
1714      * @param   source       the characters being searched.
1715      * @param   sourceOffset offset of the source string.
1716      * @param   sourceCount  count of the source string.
1717      * @param   target       the characters being searched for.
1718      * @param   fromIndex    the index to begin searching from.
1719      */
1720     static int indexOf(char[] source, int sourceOffset, int sourceCount,
1721             String target, int fromIndex) {
1722         return indexOf(source, sourceOffset, sourceCount,
1723                        target.value, 0, target.value.length,
1724                        fromIndex);
1725     }
1726 
1727     /**
1728      * Code shared by String and StringBuffer to do searches. The
1729      * source is the character array being searched, and the target
1730      * is the string being searched for.
1731      *
1732      * @param   source       the characters being searched.
1733      * @param   sourceOffset offset of the source string.
1734      * @param   sourceCount  count of the source string.
1735      * @param   target       the characters being searched for.
1736      * @param   targetOffset offset of the target string.
1737      * @param   targetCount  count of the target string.
1738      * @param   fromIndex    the index to begin searching from.
1739      */
1740     static int indexOf(char[] source, int sourceOffset, int sourceCount,
1741             char[] target, int targetOffset, int targetCount,
1742             int fromIndex) {
1743         if (fromIndex >= sourceCount) {
1744             return (targetCount == 0 ? sourceCount : -1);
1745         }
1746         if (fromIndex < 0) {
1747             fromIndex = 0;
1748         }
1749         if (targetCount == 0) {
1750             return fromIndex;
1751         }
1752 
1753         char first = target[targetOffset];
1754         int max = sourceOffset + (sourceCount - targetCount);
1755 
1756         for (int i = sourceOffset + fromIndex; i <= max; i++) {
1757             /* Look for first character. */
1758             if (source[i] != first) {
1759                 while (++i <= max && source[i] != first);
1760             }
1761 
1762             /* Found first character, now look at the rest of v2 */
1763             if (i <= max) {
1764                 int j = i + 1;
1765                 int end = j + targetCount - 1;
1766                 for (int k = targetOffset + 1; j < end && source[j]
1767                         == target[k]; j++, k++);
1768 
1769                 if (j == end) {
1770                     /* Found whole string. */
1771                     return i - sourceOffset;
1772                 }
1773             }
1774         }
1775         return -1;
1776     }
1777 
1778     /**
1779      * Returns the index within this string of the last occurrence of the
1780      * specified substring.  The last occurrence of the empty string ""
1781      * is considered to occur at the index value {@code this.length()}.
1782      *
1783      * <p>The returned index is the largest value <i>k</i> for which:
1784      * <blockquote><pre>
1785      * this.startsWith(str, <i>k</i>)
1786      * </pre></blockquote>
1787      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1788      *
1789      * @param   str   the substring to search for.
1790      * @return  the index of the last occurrence of the specified substring,
1791      *          or {@code -1} if there is no such occurrence.
1792      */
1793     public int lastIndexOf(String str) {
1794         return lastIndexOf(str, value.length);
1795     }
1796 
1797     /**
1798      * Returns the index within this string of the last occurrence of the
1799      * specified substring, searching backward starting at the specified index.
1800      *
1801      * <p>The returned index is the largest value <i>k</i> for which:
1802      * <blockquote><pre>
1803      * <i>k</i> {@code <=} fromIndex {@code &&} this.startsWith(str, <i>k</i>)
1804      * </pre></blockquote>
1805      * If no such value of <i>k</i> exists, then {@code -1} is returned.
1806      *
1807      * @param   str         the substring to search for.
1808      * @param   fromIndex   the index to start the search from.
1809      * @return  the index of the last occurrence of the specified substring,
1810      *          searching backward from the specified index,
1811      *          or {@code -1} if there is no such occurrence.
1812      */
1813     public int lastIndexOf(String str, int fromIndex) {
1814         return lastIndexOf(value, 0, value.length,
1815                 str.value, 0, str.value.length, fromIndex);
1816     }
1817 
1818     /**
1819      * Code shared by String and AbstractStringBuilder to do searches. The
1820      * source is the character array being searched, and the target
1821      * is the string being searched for.
1822      *
1823      * @param   source       the characters being searched.
1824      * @param   sourceOffset offset of the source string.
1825      * @param   sourceCount  count of the source string.
1826      * @param   target       the characters being searched for.
1827      * @param   fromIndex    the index to begin searching from.
1828      */
1829     static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
1830             String target, int fromIndex) {
1831         return lastIndexOf(source, sourceOffset, sourceCount,
1832                        target.value, 0, target.value.length,
1833                        fromIndex);
1834     }
1835 
1836     /**
1837      * Code shared by String and StringBuffer to do searches. The
1838      * source is the character array being searched, and the target
1839      * is the string being searched for.
1840      *
1841      * @param   source       the characters being searched.
1842      * @param   sourceOffset offset of the source string.
1843      * @param   sourceCount  count of the source string.
1844      * @param   target       the characters being searched for.
1845      * @param   targetOffset offset of the target string.
1846      * @param   targetCount  count of the target string.
1847      * @param   fromIndex    the index to begin searching from.
1848      */
1849     static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
1850             char[] target, int targetOffset, int targetCount,
1851             int fromIndex) {
1852         /*
1853          * Check arguments; return immediately where possible. For
1854          * consistency, don't check for null str.
1855          */
1856         int rightIndex = sourceCount - targetCount;
1857         if (fromIndex < 0) {
1858             return -1;
1859         }
1860         if (fromIndex > rightIndex) {
1861             fromIndex = rightIndex;
1862         }
1863         /* Empty string always matches. */
1864         if (targetCount == 0) {
1865             return fromIndex;
1866         }
1867 
1868         int strLastIndex = targetOffset + targetCount - 1;
1869         char strLastChar = target[strLastIndex];
1870         int min = sourceOffset + targetCount - 1;
1871         int i = min + fromIndex;
1872 
1873     startSearchForLastChar:
1874         while (true) {
1875             while (i >= min && source[i] != strLastChar) {
1876                 i--;
1877             }
1878             if (i < min) {
1879                 return -1;
1880             }
1881             int j = i - 1;
1882             int start = j - (targetCount - 1);
1883             int k = strLastIndex - 1;
1884 
1885             while (j > start) {
1886                 if (source[j--] != target[k--]) {
1887                     i--;
1888                     continue startSearchForLastChar;
1889                 }
1890             }
1891             return start - sourceOffset + 1;
1892         }
1893     }
1894 
1895     /**
1896      * Returns a new string that is a substring of this string. The
1897      * substring begins with the character at the specified index and
1898      * extends to the end of this string. <p>
1899      * Examples:
1900      * <blockquote><pre>
1901      * "unhappy".substring(2) returns "happy"
1902      * "Harbison".substring(3) returns "bison"
1903      * "emptiness".substring(9) returns "" (an empty string)
1904      * </pre></blockquote>
1905      *
1906      * @param      beginIndex   the beginning index, inclusive.
1907      * @return     the specified substring.
1908      * @exception  IndexOutOfBoundsException  if
1909      *             {@code beginIndex} is negative or larger than the
1910      *             length of this {@code String} object.
1911      */
1912     public String substring(int beginIndex) {
1913         if (beginIndex < 0) {
1914             throw new StringIndexOutOfBoundsException(beginIndex);
1915         }
1916         int subLen = value.length - beginIndex;
1917         if (subLen < 0) {
1918             throw new StringIndexOutOfBoundsException(subLen);
1919         }
1920         return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
1921     }
1922 
1923     /**
1924      * Returns a new string that is a substring of this string. The
1925      * substring begins at the specified {@code beginIndex} and
1926      * extends to the character at index {@code endIndex - 1}.
1927      * Thus the length of the substring is {@code endIndex-beginIndex}.
1928      * <p>
1929      * Examples:
1930      * <blockquote><pre>
1931      * "hamburger".substring(4, 8) returns "urge"
1932      * "smiles".substring(1, 5) returns "mile"
1933      * </pre></blockquote>
1934      *
1935      * @param      beginIndex   the beginning index, inclusive.
1936      * @param      endIndex     the ending index, exclusive.
1937      * @return     the specified substring.
1938      * @exception  IndexOutOfBoundsException  if the
1939      *             {@code beginIndex} is negative, or
1940      *             {@code endIndex} is larger than the length of
1941      *             this {@code String} object, or
1942      *             {@code beginIndex} is larger than
1943      *             {@code endIndex}.
1944      */
1945     public String substring(int beginIndex, int endIndex) {
1946         if (beginIndex < 0) {
1947             throw new StringIndexOutOfBoundsException(beginIndex);
1948         }
1949         if (endIndex > value.length) {
1950             throw new StringIndexOutOfBoundsException(endIndex);
1951         }
1952         int subLen = endIndex - beginIndex;
1953         if (subLen < 0) {
1954             throw new StringIndexOutOfBoundsException(subLen);
1955         }
1956         return ((beginIndex == 0) && (endIndex == value.length)) ? this
1957                 : new String(value, beginIndex, subLen);
1958     }
1959 
1960     /**
1961      * Returns a new character sequence that is a subsequence of this sequence.
1962      *
1963      * <p> An invocation of this method of the form
1964      *
1965      * <blockquote><pre>
1966      * str.subSequence(begin,&nbsp;end)</pre></blockquote>
1967      *
1968      * behaves in exactly the same way as the invocation
1969      *
1970      * <blockquote><pre>
1971      * str.substring(begin,&nbsp;end)</pre></blockquote>
1972      *
1973      * This method is defined so that the {@code String} class can implement
1974      * the {@link CharSequence} interface.
1975      *
1976      * @param   beginIndex   the begin index, inclusive.
1977      * @param   endIndex     the end index, exclusive.
1978      * @return  the specified subsequence.
1979      *
1980      * @throws  IndexOutOfBoundsException
1981      *          if {@code beginIndex} or {@code endIndex} is negative,
1982      *          if {@code endIndex} is greater than {@code length()},
1983      *          or if {@code beginIndex} is greater than {@code endIndex}
1984      *
1985      * @since 1.4
1986      * @spec JSR-51
1987      */
1988     public CharSequence subSequence(int beginIndex, int endIndex) {
1989         return this.substring(beginIndex, endIndex);
1990     }
1991 
1992     /**
1993      * Concatenates the specified string to the end of this string.
1994      * <p>
1995      * If the length of the argument string is {@code 0}, then this
1996      * {@code String} object is returned. Otherwise, a new
1997      * {@code String} object is created, representing a character
1998      * sequence that is the concatenation of the character sequence
1999      * represented by this {@code String} object and the character
2000      * sequence represented by the argument string.<p>
2001      * Examples:
2002      * <blockquote><pre>
2003      * "cares".concat("s") returns "caress"
2004      * "to".concat("get").concat("her") returns "together"
2005      * </pre></blockquote>
2006      *
2007      * @param   str   the {@code String} that is concatenated to the end
2008      *                of this {@code String}.
2009      * @return  a string that represents the concatenation of this object's
2010      *          characters followed by the string argument's characters.
2011      */
2012     public String concat(String str) {
2013         int otherLen = str.length();
2014         if (otherLen == 0) {
2015             return this;
2016         }
2017         int len = value.length;
2018         char buf[] = Arrays.copyOf(value, len + otherLen);
2019         str.getChars(buf, len);
2020         return new String(buf, true);
2021     }
2022 
2023     /**
2024      * Returns a new string resulting from replacing all occurrences of
2025      * {@code oldChar} in this string with {@code newChar}.
2026      * <p>
2027      * If the character {@code oldChar} does not occur in the
2028      * character sequence represented by this {@code String} object,
2029      * then a reference to this {@code String} object is returned.
2030      * Otherwise, a new {@code String} object is created that
2031      * represents a character sequence identical to the character sequence
2032      * represented by this {@code String} object, except that every
2033      * occurrence of {@code oldChar} is replaced by an occurrence
2034      * of {@code newChar}.
2035      * <p>
2036      * Examples:
2037      * <blockquote><pre>
2038      * "mesquite in your cellar".replace('e', 'o')
2039      *         returns "mosquito in your collar"
2040      * "the war of baronets".replace('r', 'y')
2041      *         returns "the way of bayonets"
2042      * "sparring with a purple porpoise".replace('p', 't')
2043      *         returns "starring with a turtle tortoise"
2044      * "JonL".replace('q', 'x') returns "JonL" (no change)
2045      * </pre></blockquote>
2046      *
2047      * @param   oldChar   the old character.
2048      * @param   newChar   the new character.
2049      * @return  a string derived from this string by replacing every
2050      *          occurrence of {@code oldChar} with {@code newChar}.
2051      */
2052     public String replace(char oldChar, char newChar) {
2053         if (oldChar != newChar) {
2054             int len = value.length;
2055             int i = -1;
2056             char[] val = value; /* avoid getfield opcode */
2057 
2058             while (++i < len) {
2059                 if (val[i] == oldChar) {
2060                     break;
2061                 }
2062             }
2063             if (i < len) {
2064                 char buf[] = new char[len];
2065                 for (int j = 0; j < i; j++) {
2066                     buf[j] = val[j];
2067                 }
2068                 while (i < len) {
2069                     char c = val[i];
2070                     buf[i] = (c == oldChar) ? newChar : c;
2071                     i++;
2072                 }
2073                 return new String(buf, true);
2074             }
2075         }
2076         return this;
2077     }
2078 
2079     /**
2080      * Tells whether or not this string matches the given <a
2081      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2082      *
2083      * <p> An invocation of this method of the form
2084      * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
2085      * same result as the expression
2086      *
2087      * <blockquote>
2088      * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String,CharSequence)
2089      * matches(<i>regex</i>, <i>str</i>)}
2090      * </blockquote>
2091      *
2092      * @param   regex
2093      *          the regular expression to which this string is to be matched
2094      *
2095      * @return  {@code true} if, and only if, this string matches the
2096      *          given regular expression
2097      *
2098      * @throws  PatternSyntaxException
2099      *          if the regular expression's syntax is invalid
2100      *
2101      * @see java.util.regex.Pattern
2102      *
2103      * @since 1.4
2104      * @spec JSR-51
2105      */
2106     public boolean matches(String regex) {
2107         return Pattern.matches(regex, this);
2108     }
2109 
2110     /**
2111      * Returns true if and only if this string contains the specified
2112      * sequence of char values.
2113      *
2114      * @param s the sequence to search for
2115      * @return true if this string contains {@code s}, false otherwise
2116      * @since 1.5
2117      */
2118     public boolean contains(CharSequence s) {
2119         return indexOf(s.toString()) > -1;
2120     }
2121 
2122     /**
2123      * Replaces the first substring of this string that matches the given <a
2124      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2125      * given replacement.
2126      *
2127      * <p> An invocation of this method of the form
2128      * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2129      * yields exactly the same result as the expression
2130      *
2131      * <blockquote>
2132      * <code>
2133      * {@link java.util.regex.Pattern}.{@link
2134      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2135      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2136      * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
2137      * </code>
2138      * </blockquote>
2139      *
2140      *<p>
2141      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2142      * replacement string may cause the results to be different than if it were
2143      * being treated as a literal replacement string; see
2144      * {@link java.util.regex.Matcher#replaceFirst}.
2145      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2146      * meaning of these characters, if desired.
2147      *
2148      * @param   regex
2149      *          the regular expression to which this string is to be matched
2150      * @param   replacement
2151      *          the string to be substituted for the first match
2152      *
2153      * @return  The resulting {@code String}
2154      *
2155      * @throws  PatternSyntaxException
2156      *          if the regular expression's syntax is invalid
2157      *
2158      * @see java.util.regex.Pattern
2159      *
2160      * @since 1.4
2161      * @spec JSR-51
2162      */
2163     public String replaceFirst(String regex, String replacement) {
2164         return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
2165     }
2166 
2167     /**
2168      * Replaces each substring of this string that matches the given <a
2169      * href="../util/regex/Pattern.html#sum">regular expression</a> with the
2170      * given replacement.
2171      *
2172      * <p> An invocation of this method of the form
2173      * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
2174      * yields exactly the same result as the expression
2175      *
2176      * <blockquote>
2177      * <code>
2178      * {@link java.util.regex.Pattern}.{@link
2179      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2180      * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
2181      * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
2182      * </code>
2183      * </blockquote>
2184      *
2185      *<p>
2186      * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
2187      * replacement string may cause the results to be different than if it were
2188      * being treated as a literal replacement string; see
2189      * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
2190      * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
2191      * meaning of these characters, if desired.
2192      *
2193      * @param   regex
2194      *          the regular expression to which this string is to be matched
2195      * @param   replacement
2196      *          the string to be substituted for each match
2197      *
2198      * @return  The resulting {@code String}
2199      *
2200      * @throws  PatternSyntaxException
2201      *          if the regular expression's syntax is invalid
2202      *
2203      * @see java.util.regex.Pattern
2204      *
2205      * @since 1.4
2206      * @spec JSR-51
2207      */
2208     public String replaceAll(String regex, String replacement) {
2209         return Pattern.compile(regex).matcher(this).replaceAll(replacement);
2210     }
2211 
2212     /**
2213      * Replaces each substring of this string that matches the literal target
2214      * sequence with the specified literal replacement sequence. The
2215      * replacement proceeds from the beginning of the string to the end, for
2216      * example, replacing "aa" with "b" in the string "aaa" will result in
2217      * "ba" rather than "ab".
2218      *
2219      * @param  target The sequence of char values to be replaced
2220      * @param  replacement The replacement sequence of char values
2221      * @return  The resulting string
2222      * @since 1.5
2223      */
2224     public String replace(CharSequence target, CharSequence replacement) {
2225         return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(
2226                 this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
2227     }
2228 
2229     /**
2230      * Splits this string around matches of the given
2231      * <a href="../util/regex/Pattern.html#sum">regular expression</a>.
2232      *
2233      * <p> The array returned by this method contains each substring of this
2234      * string that is terminated by another substring that matches the given
2235      * expression or is terminated by the end of the string.  The substrings in
2236      * the array are in the order in which they occur in this string.  If the
2237      * expression does not match any part of the input then the resulting array
2238      * has just one element, namely this string.
2239      *
2240      * <p> The {@code limit} parameter controls the number of times the
2241      * pattern is applied and therefore affects the length of the resulting
2242      * array.  If the limit <i>n</i> is greater than zero then the pattern
2243      * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
2244      * length will be no greater than <i>n</i>, and the array's last entry
2245      * will contain all input beyond the last matched delimiter.  If <i>n</i>
2246      * is non-positive then the pattern will be applied as many times as
2247      * possible and the array can have any length.  If <i>n</i> is zero then
2248      * the pattern will be applied as many times as possible, the array can
2249      * have any length, and trailing empty strings will be discarded.
2250      *
2251      * <p> The string {@code "boo:and:foo"}, for example, yields the
2252      * following results with these parameters:
2253      *
2254      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and result">
2255      * <tr>
2256      *     <th>Regex</th>
2257      *     <th>Limit</th>
2258      *     <th>Result</th>
2259      * </tr>
2260      * <tr><td align=center>:</td>
2261      *     <td align=center>2</td>
2262      *     <td>{@code { "boo", "and:foo" }}</td></tr>
2263      * <tr><td align=center>:</td>
2264      *     <td align=center>5</td>
2265      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2266      * <tr><td align=center>:</td>
2267      *     <td align=center>-2</td>
2268      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2269      * <tr><td align=center>o</td>
2270      *     <td align=center>5</td>
2271      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2272      * <tr><td align=center>o</td>
2273      *     <td align=center>-2</td>
2274      *     <td>{@code { "b", "", ":and:f", "", "" }}</td></tr>
2275      * <tr><td align=center>o</td>
2276      *     <td align=center>0</td>
2277      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2278      * </table></blockquote>
2279      *
2280      * <p> An invocation of this method of the form
2281      * <i>str.</i>{@code split(}<i>regex</i>{@code ,}&nbsp;<i>n</i>{@code )}
2282      * yields the same result as the expression
2283      *
2284      * <blockquote>
2285      * <code>
2286      * {@link java.util.regex.Pattern}.{@link
2287      * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
2288      * java.util.regex.Pattern#split(java.lang.CharSequence,int) split}(<i>str</i>,&nbsp;<i>n</i>)
2289      * </code>
2290      * </blockquote>
2291      *
2292      *
2293      * @param  regex
2294      *         the delimiting regular expression
2295      *
2296      * @param  limit
2297      *         the result threshold, as described above
2298      *
2299      * @return  the array of strings computed by splitting this string
2300      *          around matches of the given regular expression
2301      *
2302      * @throws  PatternSyntaxException
2303      *          if the regular expression's syntax is invalid
2304      *
2305      * @see java.util.regex.Pattern
2306      *
2307      * @since 1.4
2308      * @spec JSR-51
2309      */
2310     public String[] split(String regex, int limit) {
2311         /* fastpath if the regex is a
2312          (1)one-char String and this character is not one of the
2313             RegEx's meta characters ".$|()[{^?*+\\", or
2314          (2)two-char String and the first char is the backslash and
2315             the second is not the ascii digit or ascii letter.
2316          */
2317         char ch = 0;
2318         if (((regex.value.length == 1 &&
2319              ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
2320              (regex.length() == 2 &&
2321               regex.charAt(0) == '\\' &&
2322               (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
2323               ((ch-'a')|('z'-ch)) < 0 &&
2324               ((ch-'A')|('Z'-ch)) < 0)) &&
2325             (ch < Character.MIN_HIGH_SURROGATE ||
2326              ch > Character.MAX_LOW_SURROGATE))
2327         {
2328             int off = 0;
2329             int next = 0;
2330             boolean limited = limit > 0;
2331             ArrayList<String> list = new ArrayList<>();
2332             while ((next = indexOf(ch, off)) != -1) {
2333                 if (!limited || list.size() < limit - 1) {
2334                     list.add(substring(off, next));
2335                     off = next + 1;
2336                 } else {    // last one
2337                     //assert (list.size() == limit - 1);
2338                     list.add(substring(off, value.length));
2339                     off = value.length;
2340                     break;
2341                 }
2342             }
2343             // If no match was found, return this
2344             if (off == 0)
2345                 return new String[]{this};
2346 
2347             // Add remaining segment
2348             if (!limited || list.size() < limit)
2349                 list.add(substring(off, value.length));
2350 
2351             // Construct result
2352             int resultSize = list.size();
2353             if (limit == 0) {
2354                 while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
2355                     resultSize--;
2356                 }
2357             }
2358             String[] result = new String[resultSize];
2359             return list.subList(0, resultSize).toArray(result);
2360         }
2361         return Pattern.compile(regex).split(this, limit);
2362     }
2363 
2364     /**
2365      * Splits this string around matches of the given <a
2366      * href="../util/regex/Pattern.html#sum">regular expression</a>.
2367      *
2368      * <p> This method works as if by invoking the two-argument {@link
2369      * #split(String, int) split} method with the given expression and a limit
2370      * argument of zero.  Trailing empty strings are therefore not included in
2371      * the resulting array.
2372      *
2373      * <p> The string {@code "boo:and:foo"}, for example, yields the following
2374      * results with these expressions:
2375      *
2376      * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and result">
2377      * <tr>
2378      *  <th>Regex</th>
2379      *  <th>Result</th>
2380      * </tr>
2381      * <tr><td align=center>:</td>
2382      *     <td>{@code { "boo", "and", "foo" }}</td></tr>
2383      * <tr><td align=center>o</td>
2384      *     <td>{@code { "b", "", ":and:f" }}</td></tr>
2385      * </table></blockquote>
2386      *
2387      *
2388      * @param  regex
2389      *         the delimiting regular expression
2390      *
2391      * @return  the array of strings computed by splitting this string
2392      *          around matches of the given regular expression
2393      *
2394      * @throws  PatternSyntaxException
2395      *          if the regular expression's syntax is invalid
2396      *
2397      * @see java.util.regex.Pattern
2398      *
2399      * @since 1.4
2400      * @spec JSR-51
2401      */
2402     public String[] split(String regex) {
2403         return split(regex, 0);
2404     }
2405 
2406     /**
2407      * Returns a new String composed of copies of the
2408      * {@code CharSequence elements} joined together with a copy of
2409      * the specified {@code delimiter}.
2410      *
2411      * <blockquote>For example,
2412      * <pre>{@code
2413      *     String message = String.join("-", "Java", "is", "cool");
2414      *     // message returned is: "Java-is-cool"
2415      * }</pre></blockquote>
2416      *
2417      * Note that if an element is null, then {@code "null"} is added.
2418      *
2419      * @param  delimiter the delimiter that separates each element
2420      * @param  elements the elements to join together.
2421      *
2422      * @return a new {@code String} that is composed of the {@code elements}
2423      *         separated by the {@code delimiter}
2424      *
2425      * @throws NullPointerException If {@code delimiter} or {@code elements}
2426      *         is {@code null}
2427      *
2428      * @see java.util.StringJoiner
2429      * @since 1.8
2430      */
2431     public static String join(CharSequence delimiter, CharSequence... elements) {
2432         Objects.requireNonNull(delimiter);
2433         Objects.requireNonNull(elements);
2434         // Number of elements not likely worth Arrays.stream overhead.
2435         StringJoiner joiner = new StringJoiner(delimiter);
2436         for (CharSequence cs: elements) {
2437             joiner.add(cs);
2438         }
2439         return joiner.toString();
2440     }
2441 
2442     /**
2443      * Returns a new {@code String} composed of copies of the
2444      * {@code CharSequence elements} joined together with a copy of the
2445      * specified {@code delimiter}.
2446      *
2447      * <blockquote>For example,
2448      * <pre>{@code
2449      *     List<String> strings = new LinkedList<>();
2450      *     strings.add("Java");strings.add("is");
2451      *     strings.add("cool");
2452      *     String message = String.join(" ", strings);
2453      *     //message returned is: "Java is cool"
2454      *
2455      *     Set<String> strings = new LinkedHashSet<>();
2456      *     strings.add("Java"); strings.add("is");
2457      *     strings.add("very"); strings.add("cool");
2458      *     String message = String.join("-", strings);
2459      *     //message returned is: "Java-is-very-cool"
2460      * }</pre></blockquote>
2461      *
2462      * Note that if an individual element is {@code null}, then {@code "null"} is added.
2463      *
2464      * @param  delimiter a sequence of characters that is used to separate each
2465      *         of the {@code elements} in the resulting {@code String}
2466      * @param  elements an {@code Iterable} that will have its {@code elements}
2467      *         joined together.
2468      *
2469      * @return a new {@code String} that is composed from the {@code elements}
2470      *         argument
2471      *
2472      * @throws NullPointerException If {@code delimiter} or {@code elements}
2473      *         is {@code null}
2474      *
2475      * @see    #join(CharSequence,CharSequence...)
2476      * @see    java.util.StringJoiner
2477      * @since 1.8
2478      */
2479     public static String join(CharSequence delimiter,
2480             Iterable<? extends CharSequence> elements) {
2481         Objects.requireNonNull(delimiter);
2482         Objects.requireNonNull(elements);
2483         StringJoiner joiner = new StringJoiner(delimiter);
2484         for (CharSequence cs: elements) {
2485             joiner.add(cs);
2486         }
2487         return joiner.toString();
2488     }
2489 
2490     /**
2491      * Converts all of the characters in this {@code String} to lower
2492      * case using the rules of the given {@code Locale}.  Case mapping is based
2493      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2494      * class. Since case mappings are not always 1:1 char mappings, the resulting
2495      * {@code String} may be a different length than the original {@code String}.
2496      * <p>
2497      * Examples of lowercase  mappings are in the following table:
2498      * <table border="1" summary="Lowercase mapping examples showing language code of locale, upper case, lower case, and description">
2499      * <tr>
2500      *   <th>Language Code of Locale</th>
2501      *   <th>Upper Case</th>
2502      *   <th>Lower Case</th>
2503      *   <th>Description</th>
2504      * </tr>
2505      * <tr>
2506      *   <td>tr (Turkish)</td>
2507      *   <td>&#92;u0130</td>
2508      *   <td>&#92;u0069</td>
2509      *   <td>capital letter I with dot above -&gt; small letter i</td>
2510      * </tr>
2511      * <tr>
2512      *   <td>tr (Turkish)</td>
2513      *   <td>&#92;u0049</td>
2514      *   <td>&#92;u0131</td>
2515      *   <td>capital letter I -&gt; small letter dotless i </td>
2516      * </tr>
2517      * <tr>
2518      *   <td>(all)</td>
2519      *   <td>French Fries</td>
2520      *   <td>french fries</td>
2521      *   <td>lowercased all chars in String</td>
2522      * </tr>
2523      * <tr>
2524      *   <td>(all)</td>
2525      *   <td><img src="doc-files/capiota.gif" alt="capiota"><img src="doc-files/capchi.gif" alt="capchi">
2526      *       <img src="doc-files/captheta.gif" alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil">
2527      *       <img src="doc-files/capsigma.gif" alt="capsigma"></td>
2528      *   <td><img src="doc-files/iota.gif" alt="iota"><img src="doc-files/chi.gif" alt="chi">
2529      *       <img src="doc-files/theta.gif" alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon">
2530      *       <img src="doc-files/sigma1.gif" alt="sigma"></td>
2531      *   <td>lowercased all chars in String</td>
2532      * </tr>
2533      * </table>
2534      *
2535      * @param locale use the case transformation rules for this locale
2536      * @return the {@code String}, converted to lowercase.
2537      * @see     java.lang.String#toLowerCase()
2538      * @see     java.lang.String#toUpperCase()
2539      * @see     java.lang.String#toUpperCase(Locale)
2540      * @since   1.1
2541      */
2542     public String toLowerCase(Locale locale) {
2543         if (locale == null) {
2544             throw new NullPointerException();
2545         }
2546 
2547         int firstUpper;
2548         final int len = value.length;
2549 
2550         /* Now check if there are any characters that need to be changed. */
2551         scan: {
2552             for (firstUpper = 0 ; firstUpper < len; ) {
2553                 char c = value[firstUpper];
2554                 if ((c >= Character.MIN_HIGH_SURROGATE)
2555                         && (c <= Character.MAX_HIGH_SURROGATE)) {
2556                     int supplChar = codePointAt(firstUpper);
2557                     if (supplChar != Character.toLowerCase(supplChar)) {
2558                         break scan;
2559                     }
2560                     firstUpper += Character.charCount(supplChar);
2561                 } else {
2562                     if (c != Character.toLowerCase(c)) {
2563                         break scan;
2564                     }
2565                     firstUpper++;
2566                 }
2567             }
2568             return this;
2569         }
2570 
2571         char[] result = new char[len];
2572         int resultOffset = 0;  /* result may grow, so i+resultOffset
2573                                 * is the write location in result */
2574 
2575         /* Just copy the first few lowerCase characters. */
2576         System.arraycopy(value, 0, result, 0, firstUpper);
2577 
2578         String lang = locale.getLanguage();
2579         boolean localeDependent =
2580                 (lang == "tr" || lang == "az" || lang == "lt");
2581         char[] lowerCharArray;
2582         int lowerChar;
2583         int srcChar;
2584         int srcCount;
2585         for (int i = firstUpper; i < len; i += srcCount) {
2586             srcChar = (int)value[i];
2587             if ((char)srcChar >= Character.MIN_HIGH_SURROGATE
2588                     && (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
2589                 srcChar = codePointAt(i);
2590                 srcCount = Character.charCount(srcChar);
2591             } else {
2592                 srcCount = 1;
2593             }
2594             if (localeDependent || srcChar == '\u03A3') { // GREEK CAPITAL LETTER SIGMA
2595                 lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
2596             } else {
2597                 lowerChar = Character.toLowerCase(srcChar);
2598             }
2599             if ((lowerChar == Character.ERROR)
2600                     || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
2601                 if (lowerChar == Character.ERROR) {
2602                     lowerCharArray =
2603                             ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
2604                 } else if (srcCount == 2) {
2605                     resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
2606                     continue;
2607                 } else {
2608                     lowerCharArray = Character.toChars(lowerChar);
2609                 }
2610 
2611                 /* Grow result if needed */
2612                 int mapLen = lowerCharArray.length;
2613                 if (mapLen > srcCount) {
2614                     char[] result2 = new char[result.length + mapLen - srcCount];
2615                     System.arraycopy(result, 0, result2, 0, i + resultOffset);
2616                     result = result2;
2617                 }
2618                 for (int x = 0; x < mapLen; ++x) {
2619                     result[i + resultOffset + x] = lowerCharArray[x];
2620                 }
2621                 resultOffset += (mapLen - srcCount);
2622             } else {
2623                 result[i + resultOffset] = (char)lowerChar;
2624             }
2625         }
2626         return new String(result, 0, len + resultOffset);
2627     }
2628 
2629     /**
2630      * Converts all of the characters in this {@code String} to lower
2631      * case using the rules of the default locale. This is equivalent to calling
2632      * {@code toLowerCase(Locale.getDefault())}.
2633      * <p>
2634      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2635      * results if used for strings that are intended to be interpreted locale
2636      * independently.
2637      * Examples are programming language identifiers, protocol keys, and HTML
2638      * tags.
2639      * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
2640      * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
2641      * LATIN SMALL LETTER DOTLESS I character.
2642      * To obtain correct results for locale insensitive strings, use
2643      * {@code toLowerCase(Locale.ROOT)}.
2644      * <p>
2645      * @return  the {@code String}, converted to lowercase.
2646      * @see     java.lang.String#toLowerCase(Locale)
2647      */
2648     public String toLowerCase() {
2649         return toLowerCase(Locale.getDefault());
2650     }
2651 
2652     /**
2653      * Converts all of the characters in this {@code String} to upper
2654      * case using the rules of the given {@code Locale}. Case mapping is based
2655      * on the Unicode Standard version specified by the {@link java.lang.Character Character}
2656      * class. Since case mappings are not always 1:1 char mappings, the resulting
2657      * {@code String} may be a different length than the original {@code String}.
2658      * <p>
2659      * Examples of locale-sensitive and 1:M case mappings are in the following table.
2660      *
2661      * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.">
2662      * <tr>
2663      *   <th>Language Code of Locale</th>
2664      *   <th>Lower Case</th>
2665      *   <th>Upper Case</th>
2666      *   <th>Description</th>
2667      * </tr>
2668      * <tr>
2669      *   <td>tr (Turkish)</td>
2670      *   <td>&#92;u0069</td>
2671      *   <td>&#92;u0130</td>
2672      *   <td>small letter i -&gt; capital letter I with dot above</td>
2673      * </tr>
2674      * <tr>
2675      *   <td>tr (Turkish)</td>
2676      *   <td>&#92;u0131</td>
2677      *   <td>&#92;u0049</td>
2678      *   <td>small letter dotless i -&gt; capital letter I</td>
2679      * </tr>
2680      * <tr>
2681      *   <td>(all)</td>
2682      *   <td>&#92;u00df</td>
2683      *   <td>&#92;u0053 &#92;u0053</td>
2684      *   <td>small letter sharp s -&gt; two letters: SS</td>
2685      * </tr>
2686      * <tr>
2687      *   <td>(all)</td>
2688      *   <td>Fahrvergn&uuml;gen</td>
2689      *   <td>FAHRVERGN&Uuml;GEN</td>
2690      *   <td></td>
2691      * </tr>
2692      * </table>
2693      * @param locale use the case transformation rules for this locale
2694      * @return the {@code String}, converted to uppercase.
2695      * @see     java.lang.String#toUpperCase()
2696      * @see     java.lang.String#toLowerCase()
2697      * @see     java.lang.String#toLowerCase(Locale)
2698      * @since   1.1
2699      */
2700     public String toUpperCase(Locale locale) {
2701         if (locale == null) {
2702             throw new NullPointerException();
2703         }
2704 
2705         int firstLower;
2706         final int len = value.length;
2707 
2708         /* Now check if there are any characters that need to be changed. */
2709         scan: {
2710             for (firstLower = 0 ; firstLower < len; ) {
2711                 int c = (int)value[firstLower];
2712                 int srcCount;
2713                 if ((c >= Character.MIN_HIGH_SURROGATE)
2714                         && (c <= Character.MAX_HIGH_SURROGATE)) {
2715                     c = codePointAt(firstLower);
2716                     srcCount = Character.charCount(c);
2717                 } else {
2718                     srcCount = 1;
2719                 }
2720                 int upperCaseChar = Character.toUpperCaseEx(c);
2721                 if ((upperCaseChar == Character.ERROR)
2722                         || (c != upperCaseChar)) {
2723                     break scan;
2724                 }
2725                 firstLower += srcCount;
2726             }
2727             return this;
2728         }
2729 
2730         /* result may grow, so i+resultOffset is the write location in result */
2731         int resultOffset = 0;
2732         char[] result = new char[len]; /* may grow */
2733 
2734         /* Just copy the first few upperCase characters. */
2735         System.arraycopy(value, 0, result, 0, firstLower);
2736 
2737         String lang = locale.getLanguage();
2738         boolean localeDependent =
2739                 (lang == "tr" || lang == "az" || lang == "lt");
2740         char[] upperCharArray;
2741         int upperChar;
2742         int srcChar;
2743         int srcCount;
2744         for (int i = firstLower; i < len; i += srcCount) {
2745             srcChar = (int)value[i];
2746             if ((char)srcChar >= Character.MIN_HIGH_SURROGATE &&
2747                 (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
2748                 srcChar = codePointAt(i);
2749                 srcCount = Character.charCount(srcChar);
2750             } else {
2751                 srcCount = 1;
2752             }
2753             if (localeDependent) {
2754                 upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);
2755             } else {
2756                 upperChar = Character.toUpperCaseEx(srcChar);
2757             }
2758             if ((upperChar == Character.ERROR)
2759                     || (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
2760                 if (upperChar == Character.ERROR) {
2761                     if (localeDependent) {
2762                         upperCharArray =
2763                                 ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);
2764                     } else {
2765                         upperCharArray = Character.toUpperCaseCharArray(srcChar);
2766                     }
2767                 } else if (srcCount == 2) {
2768                     resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;
2769                     continue;
2770                 } else {
2771                     upperCharArray = Character.toChars(upperChar);
2772                 }
2773 
2774                 /* Grow result if needed */
2775                 int mapLen = upperCharArray.length;
2776                 if (mapLen > srcCount) {
2777                     char[] result2 = new char[result.length + mapLen - srcCount];
2778                     System.arraycopy(result, 0, result2, 0, i + resultOffset);
2779                     result = result2;
2780                 }
2781                 for (int x = 0; x < mapLen; ++x) {
2782                     result[i + resultOffset + x] = upperCharArray[x];
2783                 }
2784                 resultOffset += (mapLen - srcCount);
2785             } else {
2786                 result[i + resultOffset] = (char)upperChar;
2787             }
2788         }
2789         return new String(result, 0, len + resultOffset);
2790     }
2791 
2792     /**
2793      * Converts all of the characters in this {@code String} to upper
2794      * case using the rules of the default locale. This method is equivalent to
2795      * {@code toUpperCase(Locale.getDefault())}.
2796      * <p>
2797      * <b>Note:</b> This method is locale sensitive, and may produce unexpected
2798      * results if used for strings that are intended to be interpreted locale
2799      * independently.
2800      * Examples are programming language identifiers, protocol keys, and HTML
2801      * tags.
2802      * For instance, {@code "title".toUpperCase()} in a Turkish locale
2803      * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
2804      * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
2805      * To obtain correct results for locale insensitive strings, use
2806      * {@code toUpperCase(Locale.ROOT)}.
2807      * <p>
2808      * @return  the {@code String}, converted to uppercase.
2809      * @see     java.lang.String#toUpperCase(Locale)
2810      */
2811     public String toUpperCase() {
2812         return toUpperCase(Locale.getDefault());
2813     }
2814 
2815     /**
2816      * Returns a copy of the string, with leading and trailing whitespace
2817      * omitted.
2818      * <p>
2819      * If this {@code String} object represents an empty character
2820      * sequence, or the first and last characters of character sequence
2821      * represented by this {@code String} object both have codes
2822      * greater than {@code '\u005Cu0020'} (the space character), then a
2823      * reference to this {@code String} object is returned.
2824      * <p>
2825      * Otherwise, if there is no character with a code greater than
2826      * {@code '\u005Cu0020'} in the string, then a new
2827      * {@code String} object representing an empty string is created
2828      * and returned.
2829      * <p>
2830      * Otherwise, let <i>k</i> be the index of the first character in the
2831      * string whose code is greater than {@code '\u005Cu0020'}, and let
2832      * <i>m</i> be the index of the last character in the string whose code
2833      * is greater than {@code '\u005Cu0020'}. A new {@code String}
2834      * object is created, representing the substring of this string that
2835      * begins with the character at index <i>k</i> and ends with the
2836      * character at index <i>m</i>-that is, the result of
2837      * {@code this.substring(k, m + 1)}.
2838      * <p>
2839      * This method may be used to trim whitespace (as defined above) from
2840      * the beginning and end of a string.
2841      *
2842      * @return  A copy of this string with leading and trailing white
2843      *          space removed, or this string if it has no leading or
2844      *          trailing white space.
2845      */
2846     public String trim() {
2847         int len = value.length;
2848         int st = 0;
2849         char[] val = value;    /* avoid getfield opcode */
2850 
2851         while ((st < len) && (val[st] <= ' ')) {
2852             st++;
2853         }
2854         while ((st < len) && (val[len - 1] <= ' ')) {
2855             len--;
2856         }
2857         return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
2858     }
2859 
2860     /**
2861      * This object (which is already a string!) is itself returned.
2862      *
2863      * @return  the string itself.
2864      */
2865     public String toString() {
2866         return this;
2867     }
2868 
2869     /**
2870      * Converts this string to a new character array.
2871      *
2872      * @return  a newly allocated character array whose length is the length
2873      *          of this string and whose contents are initialized to contain
2874      *          the character sequence represented by this string.
2875      */
2876     public char[] toCharArray() {
2877         // Cannot use Arrays.copyOf because of class initialization order issues
2878         char result[] = new char[value.length];
2879         System.arraycopy(value, 0, result, 0, value.length);
2880         return result;
2881     }
2882 
2883     /**
2884      * Returns a formatted string using the specified format string and
2885      * arguments.
2886      *
2887      * <p> The locale always used is the one returned by {@link
2888      * java.util.Locale#getDefault() Locale.getDefault()}.
2889      *
2890      * @param  format
2891      *         A <a href="../util/Formatter.html#syntax">format string</a>
2892      *
2893      * @param  args
2894      *         Arguments referenced by the format specifiers in the format
2895      *         string.  If there are more arguments than format specifiers, the
2896      *         extra arguments are ignored.  The number of arguments is
2897      *         variable and may be zero.  The maximum number of arguments is
2898      *         limited by the maximum dimension of a Java array as defined by
2899      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2900      *         The behaviour on a
2901      *         {@code null} argument depends on the <a
2902      *         href="../util/Formatter.html#syntax">conversion</a>.
2903      *
2904      * @throws  java.util.IllegalFormatException
2905      *          If a format string contains an illegal syntax, a format
2906      *          specifier that is incompatible with the given arguments,
2907      *          insufficient arguments given the format string, or other
2908      *          illegal conditions.  For specification of all possible
2909      *          formatting errors, see the <a
2910      *          href="../util/Formatter.html#detail">Details</a> section of the
2911      *          formatter class specification.
2912      *
2913      * @return  A formatted string
2914      *
2915      * @see  java.util.Formatter
2916      * @since  1.5
2917      */
2918     public static String format(String format, Object... args) {
2919         return new Formatter().format(format, args).toString();
2920     }
2921 
2922     /**
2923      * Returns a formatted string using the specified locale, format string,
2924      * and arguments.
2925      *
2926      * @param  l
2927      *         The {@linkplain java.util.Locale locale} to apply during
2928      *         formatting.  If {@code l} is {@code null} then no localization
2929      *         is applied.
2930      *
2931      * @param  format
2932      *         A <a href="../util/Formatter.html#syntax">format string</a>
2933      *
2934      * @param  args
2935      *         Arguments referenced by the format specifiers in the format
2936      *         string.  If there are more arguments than format specifiers, the
2937      *         extra arguments are ignored.  The number of arguments is
2938      *         variable and may be zero.  The maximum number of arguments is
2939      *         limited by the maximum dimension of a Java array as defined by
2940      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
2941      *         The behaviour on a
2942      *         {@code null} argument depends on the
2943      *         <a href="../util/Formatter.html#syntax">conversion</a>.
2944      *
2945      * @throws  java.util.IllegalFormatException
2946      *          If a format string contains an illegal syntax, a format
2947      *          specifier that is incompatible with the given arguments,
2948      *          insufficient arguments given the format string, or other
2949      *          illegal conditions.  For specification of all possible
2950      *          formatting errors, see the <a
2951      *          href="../util/Formatter.html#detail">Details</a> section of the
2952      *          formatter class specification
2953      *
2954      * @return  A formatted string
2955      *
2956      * @see  java.util.Formatter
2957      * @since  1.5
2958      */
2959     public static String format(Locale l, String format, Object... args) {
2960         return new Formatter(l).format(format, args).toString();
2961     }
2962 
2963     /**
2964      * Returns the string representation of the {@code Object} argument.
2965      *
2966      * @param   obj   an {@code Object}.
2967      * @return  if the argument is {@code null}, then a string equal to
2968      *          {@code "null"}; otherwise, the value of
2969      *          {@code obj.toString()} is returned.
2970      * @see     java.lang.Object#toString()
2971      */
2972     public static String valueOf(Object obj) {
2973         return (obj == null) ? "null" : obj.toString();
2974     }
2975 
2976     /**
2977      * Returns the string representation of the {@code char} array
2978      * argument. The contents of the character array are copied; subsequent
2979      * modification of the character array does not affect the newly
2980      * created string.
2981      *
2982      * @param   data   a {@code char} array.
2983      * @return  a newly allocated string representing the same sequence of
2984      *          characters contained in the character array argument.
2985      */
2986     public static String valueOf(char data[]) {
2987         return new String(data);
2988     }
2989 
2990     /**
2991      * Returns the string representation of a specific subarray of the
2992      * {@code char} array argument.
2993      * <p>
2994      * The {@code offset} argument is the index of the first
2995      * character of the subarray. The {@code count} argument
2996      * specifies the length of the subarray. The contents of the subarray
2997      * are copied; subsequent modification of the character array does not
2998      * affect the newly created string.
2999      *
3000      * @param   data     the character array.
3001      * @param   offset   the initial offset into the value of the
3002      *                  {@code String}.
3003      * @param   count    the length of the value of the {@code String}.
3004      * @return  a string representing the sequence of characters contained
3005      *          in the subarray of the character array argument.
3006      * @exception IndexOutOfBoundsException if {@code offset} is
3007      *          negative, or {@code count} is negative, or
3008      *          {@code offset+count} is larger than
3009      *          {@code data.length}.
3010      */
3011     public static String valueOf(char data[], int offset, int count) {
3012         return new String(data, offset, count);
3013     }
3014 
3015     /**
3016      * Returns a String that represents the character sequence in the
3017      * array specified.
3018      *
3019      * @param   data     the character array.
3020      * @param   offset   initial offset of the subarray.
3021      * @param   count    length of the subarray.
3022      * @return  a {@code String} that contains the characters of the
3023      *          specified subarray of the character array.
3024      */
3025     public static String copyValueOf(char data[], int offset, int count) {
3026         // All public String constructors now copy the data.
3027         return new String(data, offset, count);
3028     }
3029 
3030     /**
3031      * Returns a String that represents the character sequence in the
3032      * array specified.
3033      *
3034      * @param   data   the character array.
3035      * @return  a {@code String} that contains the characters of the
3036      *          character array.
3037      */
3038     public static String copyValueOf(char data[]) {
3039         return new String(data);
3040     }
3041 
3042     /**
3043      * Returns the string representation of the {@code boolean} argument.
3044      *
3045      * @param   b   a {@code boolean}.
3046      * @return  if the argument is {@code true}, a string equal to
3047      *          {@code "true"} is returned; otherwise, a string equal to
3048      *          {@code "false"} is returned.
3049      */
3050     public static String valueOf(boolean b) {
3051         return b ? "true" : "false";
3052     }
3053 
3054     /**
3055      * Returns the string representation of the {@code char}
3056      * argument.
3057      *
3058      * @param   c   a {@code char}.
3059      * @return  a string of length {@code 1} containing
3060      *          as its single character the argument {@code c}.
3061      */
3062     public static String valueOf(char c) {
3063         char data[] = {c};
3064         return new String(data, true);
3065     }
3066 
3067     /**
3068      * Returns the string representation of the {@code int} argument.
3069      * <p>
3070      * The representation is exactly the one returned by the
3071      * {@code Integer.toString} method of one argument.
3072      *
3073      * @param   i   an {@code int}.
3074      * @return  a string representation of the {@code int} argument.
3075      * @see     java.lang.Integer#toString(int, int)
3076      */
3077     public static String valueOf(int i) {
3078         return Integer.toString(i);
3079     }
3080 
3081     /**
3082      * Returns the string representation of the {@code long} argument.
3083      * <p>
3084      * The representation is exactly the one returned by the
3085      * {@code Long.toString} method of one argument.
3086      *
3087      * @param   l   a {@code long}.
3088      * @return  a string representation of the {@code long} argument.
3089      * @see     java.lang.Long#toString(long)
3090      */
3091     public static String valueOf(long l) {
3092         return Long.toString(l);
3093     }
3094 
3095     /**
3096      * Returns the string representation of the {@code float} argument.
3097      * <p>
3098      * The representation is exactly the one returned by the
3099      * {@code Float.toString} method of one argument.
3100      *
3101      * @param   f   a {@code float}.
3102      * @return  a string representation of the {@code float} argument.
3103      * @see     java.lang.Float#toString(float)
3104      */
3105     public static String valueOf(float f) {
3106         return Float.toString(f);
3107     }
3108 
3109     /**
3110      * Returns the string representation of the {@code double} argument.
3111      * <p>
3112      * The representation is exactly the one returned by the
3113      * {@code Double.toString} method of one argument.
3114      *
3115      * @param   d   a {@code double}.
3116      * @return  a  string representation of the {@code double} argument.
3117      * @see     java.lang.Double#toString(double)
3118      */
3119     public static String valueOf(double d) {
3120         return Double.toString(d);
3121     }
3122 
3123     /**
3124      * Returns a canonical representation for the string object.
3125      * <p>
3126      * A pool of strings, initially empty, is maintained privately by the
3127      * class {@code String}.
3128      * <p>
3129      * When the intern method is invoked, if the pool already contains a
3130      * string equal to this {@code String} object as determined by
3131      * the {@link #equals(Object)} method, then the string from the pool is
3132      * returned. Otherwise, this {@code String} object is added to the
3133      * pool and a reference to this {@code String} object is returned.
3134      * <p>
3135      * It follows that for any two strings {@code s} and {@code t},
3136      * {@code s.intern() == t.intern()} is {@code true}
3137      * if and only if {@code s.equals(t)} is {@code true}.
3138      * <p>
3139      * All literal strings and string-valued constant expressions are
3140      * interned. String literals are defined in section 3.10.5 of the
3141      * <cite>The Java&trade; Language Specification</cite>.
3142      *
3143      * @return  a string that has the same contents as this string, but is
3144      *          guaranteed to be from a pool of unique strings.
3145      */
3146     public native String intern();
3147 }