1 /*
   2  * Copyright (c) 1994, 2011, 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.util.Properties;
  29 
  30 /**
  31  * The {@code Integer} class wraps a value of the primitive type
  32  * {@code int} in an object. An object of type {@code Integer}
  33  * contains a single field whose type is {@code int}.
  34  *
  35  * <p>In addition, this class provides several methods for converting
  36  * an {@code int} to a {@code String} and a {@code String} to an
  37  * {@code int}, as well as other constants and methods useful when
  38  * dealing with an {@code int}.
  39  *
  40  * <p>Implementation note: The implementations of the "bit twiddling"
  41  * methods (such as {@link #highestOneBit(int) highestOneBit} and
  42  * {@link #numberOfTrailingZeros(int) numberOfTrailingZeros}) are
  43  * based on material from Henry S. Warren, Jr.'s <i>Hacker's
  44  * Delight</i>, (Addison Wesley, 2002).
  45  *
  46  * @author  Lee Boynton
  47  * @author  Arthur van Hoff
  48  * @author  Josh Bloch
  49  * @author  Joseph D. Darcy
  50  * @since JDK1.0
  51  */
  52 public final class Integer extends Number implements Comparable<Integer> {
  53     /**
  54      * A constant holding the minimum value an {@code int} can
  55      * have, -2<sup>31</sup>.
  56      */
  57     public static final int   MIN_VALUE = 0x80000000;
  58 
  59     /**
  60      * A constant holding the maximum value an {@code int} can
  61      * have, 2<sup>31</sup>-1.
  62      */
  63     public static final int   MAX_VALUE = 0x7fffffff;
  64 
  65     /**
  66      * The {@code Class} instance representing the primitive type
  67      * {@code int}.
  68      *
  69      * @since   JDK1.1
  70      */
  71     public static final Class<Integer>  TYPE = (Class<Integer>) Class.getPrimitiveClass("int");
  72 
  73     /**
  74      * All possible chars for representing a number as a String
  75      */
  76     final static char[] digits = {
  77         '0' , '1' , '2' , '3' , '4' , '5' ,
  78         '6' , '7' , '8' , '9' , 'a' , 'b' ,
  79         'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
  80         'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
  81         'o' , 'p' , 'q' , 'r' , 's' , 't' ,
  82         'u' , 'v' , 'w' , 'x' , 'y' , 'z'
  83     };
  84 
  85     /**
  86      * Returns a string representation of the first argument in the
  87      * radix specified by the second argument.
  88      *
  89      * <p>If the radix is smaller than {@code Character.MIN_RADIX}
  90      * or larger than {@code Character.MAX_RADIX}, then the radix
  91      * {@code 10} is used instead.
  92      *
  93      * <p>If the first argument is negative, the first element of the
  94      * result is the ASCII minus character {@code '-'}
  95      * (<code>'&#92;u002D'</code>). If the first argument is not
  96      * negative, no sign character appears in the result.
  97      *
  98      * <p>The remaining characters of the result represent the magnitude
  99      * of the first argument. If the magnitude is zero, it is
 100      * represented by a single zero character {@code '0'}
 101      * (<code>'&#92;u0030'</code>); otherwise, the first character of
 102      * the representation of the magnitude will not be the zero
 103      * character.  The following ASCII characters are used as digits:
 104      *
 105      * <blockquote>
 106      *   {@code 0123456789abcdefghijklmnopqrstuvwxyz}
 107      * </blockquote>
 108      *
 109      * These are <code>'&#92;u0030'</code> through
 110      * <code>'&#92;u0039'</code> and <code>'&#92;u0061'</code> through
 111      * <code>'&#92;u007A'</code>. If {@code radix} is
 112      * <var>N</var>, then the first <var>N</var> of these characters
 113      * are used as radix-<var>N</var> digits in the order shown. Thus,
 114      * the digits for hexadecimal (radix 16) are
 115      * {@code 0123456789abcdef}. If uppercase letters are
 116      * desired, the {@link java.lang.String#toUpperCase()} method may
 117      * be called on the result:
 118      *
 119      * <blockquote>
 120      *  {@code Integer.toString(n, 16).toUpperCase()}
 121      * </blockquote>
 122      *
 123      * @param   i       an integer to be converted to a string.
 124      * @param   radix   the radix to use in the string representation.
 125      * @return  a string representation of the argument in the specified radix.
 126      * @see     java.lang.Character#MAX_RADIX
 127      * @see     java.lang.Character#MIN_RADIX
 128      */
 129     public static String toString(int i, int radix) {
 130 
 131         if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
 132             radix = 10;
 133 
 134         /* Use the faster version */
 135         if (radix == 10) {
 136             return toString(i);
 137         }
 138 
 139         char buf[] = new char[33];
 140         boolean negative = (i < 0);
 141         int charPos = 32;
 142 
 143         if (!negative) {
 144             i = -i;
 145         }
 146 
 147         while (i <= -radix) {
 148             buf[charPos--] = digits[-(i % radix)];
 149             i = i / radix;
 150         }
 151         buf[charPos] = digits[-i];
 152 
 153         if (negative) {
 154             buf[--charPos] = '-';
 155         }
 156 
 157         return new String(buf, charPos, (33 - charPos));
 158     }
 159 
 160     /**
 161      * Returns a string representation of the integer argument as an
 162      * unsigned integer in base&nbsp;16.
 163      *
 164      * <p>The unsigned integer value is the argument plus 2<sup>32</sup>
 165      * if the argument is negative; otherwise, it is equal to the
 166      * argument.  This value is converted to a string of ASCII digits
 167      * in hexadecimal (base&nbsp;16) with no extra leading
 168      * {@code 0}s. If the unsigned magnitude is zero, it is
 169      * represented by a single zero character {@code '0'}
 170      * (<code>'&#92;u0030'</code>); otherwise, the first character of
 171      * the representation of the unsigned magnitude will not be the
 172      * zero character. The following characters are used as
 173      * hexadecimal digits:
 174      *
 175      * <blockquote>
 176      *  {@code 0123456789abcdef}
 177      * </blockquote>
 178      *
 179      * These are the characters <code>'&#92;u0030'</code> through
 180      * <code>'&#92;u0039'</code> and <code>'&#92;u0061'</code> through
 181      * <code>'&#92;u0066'</code>. If uppercase letters are
 182      * desired, the {@link java.lang.String#toUpperCase()} method may
 183      * be called on the result:
 184      *
 185      * <blockquote>
 186      *  {@code Integer.toHexString(n).toUpperCase()}
 187      * </blockquote>
 188      *
 189      * @param   i   an integer to be converted to a string.
 190      * @return  the string representation of the unsigned integer value
 191      *          represented by the argument in hexadecimal (base&nbsp;16).
 192      * @since   JDK1.0.2
 193      */
 194     public static String toHexString(int i) {
 195         return toUnsignedString(i, 4);
 196     }
 197 
 198     /**
 199      * Returns a string representation of the integer argument as an
 200      * unsigned integer in base&nbsp;8.
 201      *
 202      * <p>The unsigned integer value is the argument plus 2<sup>32</sup>
 203      * if the argument is negative; otherwise, it is equal to the
 204      * argument.  This value is converted to a string of ASCII digits
 205      * in octal (base&nbsp;8) with no extra leading {@code 0}s.
 206      *
 207      * <p>If the unsigned magnitude is zero, it is represented by a
 208      * single zero character {@code '0'}
 209      * (<code>'&#92;u0030'</code>); otherwise, the first character of
 210      * the representation of the unsigned magnitude will not be the
 211      * zero character. The following characters are used as octal
 212      * digits:
 213      *
 214      * <blockquote>
 215      * {@code 01234567}
 216      * </blockquote>
 217      *
 218      * These are the characters <code>'&#92;u0030'</code> through
 219      * <code>'&#92;u0037'</code>.
 220      *
 221      * @param   i   an integer to be converted to a string.
 222      * @return  the string representation of the unsigned integer value
 223      *          represented by the argument in octal (base&nbsp;8).
 224      * @since   JDK1.0.2
 225      */
 226     public static String toOctalString(int i) {
 227         return toUnsignedString(i, 3);
 228     }
 229 
 230     /**
 231      * Returns a string representation of the integer argument as an
 232      * unsigned integer in base&nbsp;2.
 233      *
 234      * <p>The unsigned integer value is the argument plus 2<sup>32</sup>
 235      * if the argument is negative; otherwise it is equal to the
 236      * argument.  This value is converted to a string of ASCII digits
 237      * in binary (base&nbsp;2) with no extra leading {@code 0}s.
 238      * If the unsigned magnitude is zero, it is represented by a
 239      * single zero character {@code '0'}
 240      * (<code>'&#92;u0030'</code>); otherwise, the first character of
 241      * the representation of the unsigned magnitude will not be the
 242      * zero character. The characters {@code '0'}
 243      * (<code>'&#92;u0030'</code>) and {@code '1'}
 244      * (<code>'&#92;u0031'</code>) are used as binary digits.
 245      *
 246      * @param   i   an integer to be converted to a string.
 247      * @return  the string representation of the unsigned integer value
 248      *          represented by the argument in binary (base&nbsp;2).
 249      * @since   JDK1.0.2
 250      */
 251     public static String toBinaryString(int i) {
 252         return toUnsignedString(i, 1);
 253     }
 254 
 255     /**
 256      * Convert the integer to an unsigned number.
 257      */
 258     private static String toUnsignedString(int i, int shift) {
 259         char[] buf = new char[32];
 260         int charPos = 32;
 261         int radix = 1 << shift;
 262         int mask = radix - 1;
 263         do {
 264             buf[--charPos] = digits[i & mask];
 265             i >>>= shift;
 266         } while (i != 0);
 267 
 268         return new String(buf, charPos, (32 - charPos));
 269     }
 270 
 271 
 272     final static char [] DigitTens = {
 273         '0', '0', '0', '0', '0', '0', '0', '0', '0', '0',
 274         '1', '1', '1', '1', '1', '1', '1', '1', '1', '1',
 275         '2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
 276         '3', '3', '3', '3', '3', '3', '3', '3', '3', '3',
 277         '4', '4', '4', '4', '4', '4', '4', '4', '4', '4',
 278         '5', '5', '5', '5', '5', '5', '5', '5', '5', '5',
 279         '6', '6', '6', '6', '6', '6', '6', '6', '6', '6',
 280         '7', '7', '7', '7', '7', '7', '7', '7', '7', '7',
 281         '8', '8', '8', '8', '8', '8', '8', '8', '8', '8',
 282         '9', '9', '9', '9', '9', '9', '9', '9', '9', '9',
 283         } ;
 284 
 285     final static char [] DigitOnes = {
 286         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 287         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 288         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 289         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 290         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 291         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 292         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 293         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 294         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 295         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 296         } ;
 297 
 298         // I use the "invariant division by multiplication" trick to
 299         // accelerate Integer.toString.  In particular we want to
 300         // avoid division by 10.
 301         //
 302         // The "trick" has roughly the same performance characteristics
 303         // as the "classic" Integer.toString code on a non-JIT VM.
 304         // The trick avoids .rem and .div calls but has a longer code
 305         // path and is thus dominated by dispatch overhead.  In the
 306         // JIT case the dispatch overhead doesn't exist and the
 307         // "trick" is considerably faster than the classic code.
 308         //
 309         // TODO-FIXME: convert (x * 52429) into the equiv shift-add
 310         // sequence.
 311         //
 312         // RE:  Division by Invariant Integers using Multiplication
 313         //      T Gralund, P Montgomery
 314         //      ACM PLDI 1994
 315         //
 316 
 317     /**
 318      * Returns a {@code String} object representing the
 319      * specified integer. The argument is converted to signed decimal
 320      * representation and returned as a string, exactly as if the
 321      * argument and radix 10 were given as arguments to the {@link
 322      * #toString(int, int)} method.
 323      *
 324      * @param   i   an integer to be converted.
 325      * @return  a string representation of the argument in base&nbsp;10.
 326      */
 327     public static String toString(int i) {
 328         if (i == Integer.MIN_VALUE)
 329             return "-2147483648";
 330         int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
 331         char[] buf = new char[size];
 332         getChars(i, size, buf);
 333         return new String(0, size, buf);
 334     }
 335 
 336     /**
 337      * Places characters representing the integer i into the
 338      * character array buf. The characters are placed into
 339      * the buffer backwards starting with the least significant
 340      * digit at the specified index (exclusive), and working
 341      * backwards from there.
 342      *
 343      * Will fail if i == Integer.MIN_VALUE
 344      */
 345     static void getChars(int i, int index, char[] buf) {
 346         int q, r;
 347         int charPos = index;
 348         char sign = 0;
 349 
 350         if (i < 0) {
 351             sign = '-';
 352             i = -i;
 353         }
 354 
 355         // Generate two digits per iteration
 356         while (i >= 65536) {
 357             q = i / 100;
 358         // really: r = i - (q * 100);
 359             r = i - ((q << 6) + (q << 5) + (q << 2));
 360             i = q;
 361             buf [--charPos] = DigitOnes[r];
 362             buf [--charPos] = DigitTens[r];
 363         }
 364 
 365         // Fall thru to fast mode for smaller numbers
 366         // assert(i <= 65536, i);
 367         for (;;) {
 368             q = (i * 52429) >>> (16+3);
 369             r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
 370             buf [--charPos] = digits [r];
 371             i = q;
 372             if (i == 0) break;
 373         }
 374         if (sign != 0) {
 375             buf [--charPos] = sign;
 376         }
 377     }
 378 
 379     final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
 380                                       99999999, 999999999, Integer.MAX_VALUE };
 381 
 382     // Requires positive x
 383     static int stringSize(int x) {
 384         for (int i=0; ; i++)
 385             if (x <= sizeTable[i])
 386                 return i+1;
 387     }
 388 
 389     /**
 390      * Parses the string argument as a signed integer in the radix
 391      * specified by the second argument. The characters in the string
 392      * must all be digits of the specified radix (as determined by
 393      * whether {@link java.lang.Character#digit(char, int)} returns a
 394      * nonnegative value), except that the first character may be an
 395      * ASCII minus sign {@code '-'} (<code>'&#92;u002D'</code>) to
 396      * indicate a negative value or an ASCII plus sign {@code '+'}
 397      * (<code>'&#92;u002B'</code>) to indicate a positive value. The
 398      * resulting integer value is returned.
 399      *
 400      * <p>An exception of type {@code NumberFormatException} is
 401      * thrown if any of the following situations occurs:
 402      * <ul>
 403      * <li>The first argument is {@code null} or is a string of
 404      * length zero.
 405      *
 406      * <li>The radix is either smaller than
 407      * {@link java.lang.Character#MIN_RADIX} or
 408      * larger than {@link java.lang.Character#MAX_RADIX}.
 409      *
 410      * <li>Any character of the string is not a digit of the specified
 411      * radix, except that the first character may be a minus sign
 412      * {@code '-'} (<code>'&#92;u002D'</code>) or plus sign
 413      * {@code '+'} (<code>'&#92;u002B'</code>) provided that the
 414      * string is longer than length 1.
 415      *
 416      * <li>The value represented by the string is not a value of type
 417      * {@code int}.
 418      * </ul>
 419      *
 420      * <p>Examples:
 421      * <blockquote><pre>
 422      * parseInt("0", 10) returns 0
 423      * parseInt("473", 10) returns 473
 424      * parseInt("+42", 10) returns 42
 425      * parseInt("-0", 10) returns 0
 426      * parseInt("-FF", 16) returns -255
 427      * parseInt("1100110", 2) returns 102
 428      * parseInt("2147483647", 10) returns 2147483647
 429      * parseInt("-2147483648", 10) returns -2147483648
 430      * parseInt("2147483648", 10) throws a NumberFormatException
 431      * parseInt("99", 8) throws a NumberFormatException
 432      * parseInt("Kona", 10) throws a NumberFormatException
 433      * parseInt("Kona", 27) returns 411787
 434      * </pre></blockquote>
 435      *
 436      * @param      s   the {@code String} containing the integer
 437      *                  representation to be parsed
 438      * @param      radix   the radix to be used while parsing {@code s}.
 439      * @return     the integer represented by the string argument in the
 440      *             specified radix.
 441      * @exception  NumberFormatException if the {@code String}
 442      *             does not contain a parsable {@code int}.
 443      */
 444     public static int parseInt(String s, int radix)
 445                 throws NumberFormatException
 446     {
 447         /*
 448          * WARNING: This method may be invoked early during VM initialization
 449          * before IntegerCache is initialized. Care must be taken to not use
 450          * the valueOf method.
 451          */
 452 
 453         if (s == null) {
 454             throw new NumberFormatException("null");
 455         }
 456 
 457         if (radix < Character.MIN_RADIX) {
 458             throw new NumberFormatException("radix " + radix +
 459                                             " less than Character.MIN_RADIX");
 460         }
 461 
 462         if (radix > Character.MAX_RADIX) {
 463             throw new NumberFormatException("radix " + radix +
 464                                             " greater than Character.MAX_RADIX");
 465         }
 466 
 467         int result = 0;
 468         boolean negative = false;
 469         int i = 0, len = s.length();
 470         int limit = -Integer.MAX_VALUE;
 471         int multmin;
 472         int digit;
 473 
 474         if (len > 0) {
 475             char firstChar = s.charAt(0);
 476             if (firstChar < '0') { // Possible leading "+" or "-"
 477                 if (firstChar == '-') {
 478                     negative = true;
 479                     limit = Integer.MIN_VALUE;
 480                 } else if (firstChar != '+')
 481                     throw NumberFormatException.forInputString(s);
 482 
 483                 if (len == 1) // Cannot have lone "+" or "-"
 484                     throw NumberFormatException.forInputString(s);
 485                 i++;
 486             }
 487             multmin = limit / radix;
 488             while (i < len) {
 489                 // Accumulating negatively avoids surprises near MAX_VALUE
 490                 digit = Character.digit(s.charAt(i++),radix);
 491                 if (digit < 0) {
 492                     throw NumberFormatException.forInputString(s);
 493                 }
 494                 if (result < multmin) {
 495                     throw NumberFormatException.forInputString(s);
 496                 }
 497                 result *= radix;
 498                 if (result < limit + digit) {
 499                     throw NumberFormatException.forInputString(s);
 500                 }
 501                 result -= digit;
 502             }
 503         } else {
 504             throw NumberFormatException.forInputString(s);
 505         }
 506         return negative ? result : -result;
 507     }
 508 
 509     /**
 510      * Parses the string argument as a signed decimal integer. The
 511      * characters in the string must all be decimal digits, except
 512      * that the first character may be an ASCII minus sign {@code '-'}
 513      * (<code>'&#92;u002D'</code>) to indicate a negative value or an
 514      * ASCII plus sign {@code '+'} (<code>'&#92;u002B'</code>) to
 515      * indicate a positive value. The resulting integer value is
 516      * returned, exactly as if the argument and the radix 10 were
 517      * given as arguments to the {@link #parseInt(java.lang.String,
 518      * int)} method.
 519      *
 520      * @param s    a {@code String} containing the {@code int}
 521      *             representation to be parsed
 522      * @return     the integer value represented by the argument in decimal.
 523      * @exception  NumberFormatException  if the string does not contain a
 524      *               parsable integer.
 525      */
 526     public static int parseInt(String s) throws NumberFormatException {
 527         return parseInt(s,10);
 528     }
 529 
 530     /**
 531      * Returns an {@code Integer} object holding the value
 532      * extracted from the specified {@code String} when parsed
 533      * with the radix given by the second argument. The first argument
 534      * is interpreted as representing a signed integer in the radix
 535      * specified by the second argument, exactly as if the arguments
 536      * were given to the {@link #parseInt(java.lang.String, int)}
 537      * method. The result is an {@code Integer} object that
 538      * represents the integer value specified by the string.
 539      *
 540      * <p>In other words, this method returns an {@code Integer}
 541      * object equal to the value of:
 542      *
 543      * <blockquote>
 544      *  {@code new Integer(Integer.parseInt(s, radix))}
 545      * </blockquote>
 546      *
 547      * @param      s   the string to be parsed.
 548      * @param      radix the radix to be used in interpreting {@code s}
 549      * @return     an {@code Integer} object holding the value
 550      *             represented by the string argument in the specified
 551      *             radix.
 552      * @exception NumberFormatException if the {@code String}
 553      *            does not contain a parsable {@code int}.
 554      */
 555     public static Integer valueOf(String s, int radix) throws NumberFormatException {
 556         return Integer.valueOf(parseInt(s,radix));
 557     }
 558 
 559     /**
 560      * Returns an {@code Integer} object holding the
 561      * value of the specified {@code String}. The argument is
 562      * interpreted as representing a signed decimal integer, exactly
 563      * as if the argument were given to the {@link
 564      * #parseInt(java.lang.String)} method. The result is an
 565      * {@code Integer} object that represents the integer value
 566      * specified by the string.
 567      *
 568      * <p>In other words, this method returns an {@code Integer}
 569      * object equal to the value of:
 570      *
 571      * <blockquote>
 572      *  {@code new Integer(Integer.parseInt(s))}
 573      * </blockquote>
 574      *
 575      * @param      s   the string to be parsed.
 576      * @return     an {@code Integer} object holding the value
 577      *             represented by the string argument.
 578      * @exception  NumberFormatException  if the string cannot be parsed
 579      *             as an integer.
 580      */
 581     public static Integer valueOf(String s) throws NumberFormatException {
 582         return Integer.valueOf(parseInt(s, 10));
 583     }
 584 
 585     /**
 586      * Cache to support the object identity semantics of autoboxing for values between
 587      * -128 and 127 (inclusive) as required by JLS.
 588      *
 589      * The cache is initialized on first usage.  The size of the cache
 590      * may be controlled by the -XX:AutoBoxCacheMax=<size> option.
 591      * During VM initialization, java.lang.Integer.IntegerCache.high property
 592      * may be set and saved in the private system properties in the
 593      * sun.misc.VM class.
 594      */
 595 
 596     private static class IntegerCache {
 597         static final int low = -128;
 598         static final int high;
 599         static final Integer cache[];
 600 
 601         static {
 602             // high value may be configured by property
 603             int h = 127;
 604             String integerCacheHighPropValue =
 605                 sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
 606             if (integerCacheHighPropValue != null) {
 607                 int i = parseInt(integerCacheHighPropValue);
 608                 i = Math.max(i, 127);
 609                 // Maximum array size is Integer.MAX_VALUE
 610                 h = Math.min(i, Integer.MAX_VALUE - (-low));
 611             }
 612             high = h;
 613 
 614             cache = new Integer[(high - low) + 1];
 615             int j = low;
 616             for(int k = 0; k < cache.length; k++)
 617                 cache[k] = new Integer(j++);
 618         }
 619 
 620         private IntegerCache() {}
 621     }
 622 
 623     /**
 624      * Returns an {@code Integer} instance representing the specified
 625      * {@code int} value.  If a new {@code Integer} instance is not
 626      * required, this method should generally be used in preference to
 627      * the constructor {@link #Integer(int)}, as this method is likely
 628      * to yield significantly better space and time performance by
 629      * caching frequently requested values.
 630      *
 631      * This method will always cache values in the range -128 to 127,
 632      * inclusive, and may cache other values outside of this range.
 633      *
 634      * @param  i an {@code int} value.
 635      * @return an {@code Integer} instance representing {@code i}.
 636      * @since  1.5
 637      */
 638     public static Integer valueOf(int i) {
 639         assert IntegerCache.high >= 127;
 640         if (i >= IntegerCache.low && i <= IntegerCache.high)
 641             return IntegerCache.cache[i + (-IntegerCache.low)];
 642         return new Integer(i);
 643     }
 644 
 645     /**
 646      * The value of the {@code Integer}.
 647      *
 648      * @serial
 649      */
 650     private final int value;
 651 
 652     /**
 653      * Constructs a newly allocated {@code Integer} object that
 654      * represents the specified {@code int} value.
 655      *
 656      * @param   value   the value to be represented by the
 657      *                  {@code Integer} object.
 658      */
 659     public Integer(int value) {
 660         this.value = value;
 661     }
 662 
 663     /**
 664      * Constructs a newly allocated {@code Integer} object that
 665      * represents the {@code int} value indicated by the
 666      * {@code String} parameter. The string is converted to an
 667      * {@code int} value in exactly the manner used by the
 668      * {@code parseInt} method for radix 10.
 669      *
 670      * @param      s   the {@code String} to be converted to an
 671      *                 {@code Integer}.
 672      * @exception  NumberFormatException  if the {@code String} does not
 673      *               contain a parsable integer.
 674      * @see        java.lang.Integer#parseInt(java.lang.String, int)
 675      */
 676     public Integer(String s) throws NumberFormatException {
 677         this.value = parseInt(s, 10);
 678     }
 679 
 680     /**
 681      * Returns the value of this {@code Integer} as a {@code byte}
 682      * after a narrowing primitive conversion.
 683      * @jls 5.1.3 Narrowing Primitive Conversions
 684      */
 685     public byte byteValue() {
 686         return (byte)value;
 687     }
 688 
 689     /**
 690      * Returns the value of this {@code Integer} as a {@code short}
 691      * after a narrowing primitive conversion.
 692      * @jls 5.1.3 Narrowing Primitive Conversions
 693      */
 694     public short shortValue() {
 695         return (short)value;
 696     }
 697 
 698     /**
 699      * Returns the value of this {@code Integer} as an
 700      * {@code int}.
 701      */
 702     public int intValue() {
 703         return value;
 704     }
 705 
 706     /**
 707      * Returns the value of this {@code Integer} as a {@code long}
 708      * after a widening primitive conversion.
 709      * @jls 5.1.2 Widening Primitive Conversions
 710      */
 711     public long longValue() {
 712         return (long)value;
 713     }
 714 
 715     /**
 716      * Returns the value of this {@code Integer} as a {@code float}
 717      * after a widening primitive conversion.
 718      * @jls 5.1.2 Widening Primitive Conversions
 719      */
 720     public float floatValue() {
 721         return (float)value;
 722     }
 723 
 724     /**
 725      * Returns the value of this {@code Integer} as a {@code double}
 726      * after a widening primitive conversion.
 727      * @jls 5.1.2 Widening Primitive Conversions
 728      */
 729     public double doubleValue() {
 730         return (double)value;
 731     }
 732 
 733     /**
 734      * Returns a {@code String} object representing this
 735      * {@code Integer}'s value. The value is converted to signed
 736      * decimal representation and returned as a string, exactly as if
 737      * the integer value were given as an argument to the {@link
 738      * java.lang.Integer#toString(int)} method.
 739      *
 740      * @return  a string representation of the value of this object in
 741      *          base&nbsp;10.
 742      */
 743     public String toString() {
 744         return toString(value);
 745     }
 746 
 747     /**
 748      * Returns a hash code for this {@code Integer}.
 749      *
 750      * @return  a hash code value for this object, equal to the
 751      *          primitive {@code int} value represented by this
 752      *          {@code Integer} object.
 753      */
 754     public int hashCode() {
 755         return value;
 756     }
 757 
 758     /**
 759      * Compares this object to the specified object.  The result is
 760      * {@code true} if and only if the argument is not
 761      * {@code null} and is an {@code Integer} object that
 762      * contains the same {@code int} value as this object.
 763      *
 764      * @param   obj   the object to compare with.
 765      * @return  {@code true} if the objects are the same;
 766      *          {@code false} otherwise.
 767      */
 768     public boolean equals(Object obj) {
 769         if (obj instanceof Integer) {
 770             return value == ((Integer)obj).intValue();
 771         }
 772         return false;
 773     }
 774 
 775     /**
 776      * Determines the integer value of the system property with the
 777      * specified name.
 778      *
 779      * <p>The first argument is treated as the name of a system
 780      * property.  System properties are accessible through the {@link
 781      * java.lang.System#getProperty(java.lang.String)} method. The
 782      * string value of this property is then interpreted as an integer
 783      * value using the grammar supported by {@link Integer#decode decode} and
 784      * an {@code Integer} object representing this value is returned.
 785      *
 786      * <p>If there is no property with the specified name, if the
 787      * specified name is empty or {@code null}, or if the property
 788      * does not have the correct numeric format, then {@code null} is
 789      * returned.
 790      *
 791      * <p>In other words, this method returns an {@code Integer}
 792      * object equal to the value of:
 793      *
 794      * <blockquote>
 795      *  {@code getInteger(nm, null)}
 796      * </blockquote>
 797      *
 798      * @param   nm   property name.
 799      * @return  the {@code Integer} value of the property.
 800      * @throws  SecurityException for the same reasons as
 801      *          {@link System#getProperty(String) System.getProperty}
 802      * @see     java.lang.System#getProperty(java.lang.String)
 803      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
 804      */
 805     public static Integer getInteger(String nm) {
 806         return getInteger(nm, null);
 807     }
 808 
 809     /**
 810      * Determines the integer value of the system property with the
 811      * specified name.
 812      *
 813      * <p>The first argument is treated as the name of a system
 814      * property.  System properties are accessible through the {@link
 815      * java.lang.System#getProperty(java.lang.String)} method. The
 816      * string value of this property is then interpreted as an integer
 817      * value using the grammar supported by {@link Integer#decode decode} and
 818      * an {@code Integer} object representing this value is returned.
 819      *
 820      * <p>The second argument is the default value. An {@code Integer} object
 821      * that represents the value of the second argument is returned if there
 822      * is no property of the specified name, if the property does not have
 823      * the correct numeric format, or if the specified name is empty or
 824      * {@code null}.
 825      *
 826      * <p>In other words, this method returns an {@code Integer} object
 827      * equal to the value of:
 828      *
 829      * <blockquote>
 830      *  {@code getInteger(nm, new Integer(val))}
 831      * </blockquote>
 832      *
 833      * but in practice it may be implemented in a manner such as:
 834      *
 835      * <blockquote><pre>
 836      * Integer result = getInteger(nm, null);
 837      * return (result == null) ? new Integer(val) : result;
 838      * </pre></blockquote>
 839      *
 840      * to avoid the unnecessary allocation of an {@code Integer}
 841      * object when the default value is not needed.
 842      *
 843      * @param   nm   property name.
 844      * @param   val   default value.
 845      * @return  the {@code Integer} value of the property.
 846      * @throws  SecurityException for the same reasons as
 847      *          {@link System#getProperty(String) System.getProperty}
 848      * @see     java.lang.System#getProperty(java.lang.String)
 849      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
 850      */
 851     public static Integer getInteger(String nm, int val) {
 852         Integer result = getInteger(nm, null);
 853         return (result == null) ? Integer.valueOf(val) : result;
 854     }
 855 
 856     /**
 857      * Returns the integer value of the system property with the
 858      * specified name.  The first argument is treated as the name of a
 859      * system property.  System properties are accessible through the
 860      * {@link java.lang.System#getProperty(java.lang.String)} method.
 861      * The string value of this property is then interpreted as an
 862      * integer value, as per the {@link Integer#decode decode} method,
 863      * and an {@code Integer} object representing this value is
 864      * returned; in summary:
 865      *
 866      * <ul><li>If the property value begins with the two ASCII characters
 867      *         {@code 0x} or the ASCII character {@code #}, not
 868      *      followed by a minus sign, then the rest of it is parsed as a
 869      *      hexadecimal integer exactly as by the method
 870      *      {@link #valueOf(java.lang.String, int)} with radix 16.
 871      * <li>If the property value begins with the ASCII character
 872      *     {@code 0} followed by another character, it is parsed as an
 873      *     octal integer exactly as by the method
 874      *     {@link #valueOf(java.lang.String, int)} with radix 8.
 875      * <li>Otherwise, the property value is parsed as a decimal integer
 876      * exactly as by the method {@link #valueOf(java.lang.String, int)}
 877      * with radix 10.
 878      * </ul>
 879      *
 880      * <p>The second argument is the default value. The default value is
 881      * returned if there is no property of the specified name, if the
 882      * property does not have the correct numeric format, or if the
 883      * specified name is empty or {@code null}.
 884      *
 885      * @param   nm   property name.
 886      * @param   val   default value.
 887      * @return  the {@code Integer} value of the property.
 888      * @throws  SecurityException for the same reasons as
 889      *          {@link System#getProperty(String) System.getProperty}
 890      * @see     System#getProperty(java.lang.String)
 891      * @see     System#getProperty(java.lang.String, java.lang.String)
 892      */
 893     public static Integer getInteger(String nm, Integer val) {
 894         String v = null;
 895         try {
 896             v = System.getProperty(nm);
 897         } catch (IllegalArgumentException | NullPointerException e) {
 898         }
 899         if (v != null) {
 900             try {
 901                 return Integer.decode(v);
 902             } catch (NumberFormatException e) {
 903             }
 904         }
 905         return val;
 906     }
 907 
 908     /**
 909      * Decodes a {@code String} into an {@code Integer}.
 910      * Accepts decimal, hexadecimal, and octal numbers given
 911      * by the following grammar:
 912      *
 913      * <blockquote>
 914      * <dl>
 915      * <dt><i>DecodableString:</i>
 916      * <dd><i>Sign<sub>opt</sub> DecimalNumeral</i>
 917      * <dd><i>Sign<sub>opt</sub></i> {@code 0x} <i>HexDigits</i>
 918      * <dd><i>Sign<sub>opt</sub></i> {@code 0X} <i>HexDigits</i>
 919      * <dd><i>Sign<sub>opt</sub></i> {@code #} <i>HexDigits</i>
 920      * <dd><i>Sign<sub>opt</sub></i> {@code 0} <i>OctalDigits</i>
 921      * <p>
 922      * <dt><i>Sign:</i>
 923      * <dd>{@code -}
 924      * <dd>{@code +}
 925      * </dl>
 926      * </blockquote>
 927      *
 928      * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
 929      * are as defined in section 3.10.1 of
 930      * <cite>The Java&trade; Language Specification</cite>,
 931      * except that underscores are not accepted between digits.
 932      *
 933      * <p>The sequence of characters following an optional
 934      * sign and/or radix specifier ("{@code 0x}", "{@code 0X}",
 935      * "{@code #}", or leading zero) is parsed as by the {@code
 936      * Integer.parseInt} method with the indicated radix (10, 16, or
 937      * 8).  This sequence of characters must represent a positive
 938      * value or a {@link NumberFormatException} will be thrown.  The
 939      * result is negated if first character of the specified {@code
 940      * String} is the minus sign.  No whitespace characters are
 941      * permitted in the {@code String}.
 942      *
 943      * @param     nm the {@code String} to decode.
 944      * @return    an {@code Integer} object holding the {@code int}
 945      *             value represented by {@code nm}
 946      * @exception NumberFormatException  if the {@code String} does not
 947      *            contain a parsable integer.
 948      * @see java.lang.Integer#parseInt(java.lang.String, int)
 949      */
 950     public static Integer decode(String nm) throws NumberFormatException {
 951         int radix = 10;
 952         int index = 0;
 953         boolean negative = false;
 954         Integer result;
 955 
 956         if (nm.length() == 0)
 957             throw new NumberFormatException("Zero length string");
 958         char firstChar = nm.charAt(0);
 959         // Handle sign, if present
 960         if (firstChar == '-') {
 961             negative = true;
 962             index++;
 963         } else if (firstChar == '+')
 964             index++;
 965 
 966         // Handle radix specifier, if present
 967         if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
 968             index += 2;
 969             radix = 16;
 970         }
 971         else if (nm.startsWith("#", index)) {
 972             index ++;
 973             radix = 16;
 974         }
 975         else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
 976             index ++;
 977             radix = 8;
 978         }
 979 
 980         if (nm.startsWith("-", index) || nm.startsWith("+", index))
 981             throw new NumberFormatException("Sign character in wrong position");
 982 
 983         try {
 984             result = Integer.valueOf(nm.substring(index), radix);
 985             result = negative ? Integer.valueOf(-result.intValue()) : result;
 986         } catch (NumberFormatException e) {
 987             // If number is Integer.MIN_VALUE, we'll end up here. The next line
 988             // handles this case, and causes any genuine format error to be
 989             // rethrown.
 990             String constant = negative ? ("-" + nm.substring(index))
 991                                        : nm.substring(index);
 992             result = Integer.valueOf(constant, radix);
 993         }
 994         return result;
 995     }
 996 
 997     /**
 998      * Compares two {@code Integer} objects numerically.
 999      *
1000      * @param   anotherInteger   the {@code Integer} to be compared.
1001      * @return  the value {@code 0} if this {@code Integer} is
1002      *          equal to the argument {@code Integer}; a value less than
1003      *          {@code 0} if this {@code Integer} is numerically less
1004      *          than the argument {@code Integer}; and a value greater
1005      *          than {@code 0} if this {@code Integer} is numerically
1006      *           greater than the argument {@code Integer} (signed
1007      *           comparison).
1008      * @since   1.2
1009      */
1010     public int compareTo(Integer anotherInteger) {
1011         return compare(this.value, anotherInteger.value);
1012     }
1013 
1014     /**
1015      * Compares two {@code int} values numerically.
1016      * The value returned is identical to what would be returned by:
1017      * <pre>
1018      *    Integer.valueOf(x).compareTo(Integer.valueOf(y))
1019      * </pre>
1020      *
1021      * @param  x the first {@code int} to compare
1022      * @param  y the second {@code int} to compare
1023      * @return the value {@code 0} if {@code x == y};
1024      *         a value less than {@code 0} if {@code x < y}; and
1025      *         a value greater than {@code 0} if {@code x > y}
1026      * @since 1.7
1027      */
1028     public static int compare(int x, int y) {
1029         return (x < y) ? -1 : ((x == y) ? 0 : 1);
1030     }
1031 
1032 
1033     // Bit twiddling
1034 
1035     /**
1036      * The number of bits used to represent an {@code int} value in two's
1037      * complement binary form.
1038      *
1039      * @since 1.5
1040      */
1041     public static final int SIZE = 32;
1042 
1043     /**
1044      * Returns an {@code int} value with at most a single one-bit, in the
1045      * position of the highest-order ("leftmost") one-bit in the specified
1046      * {@code int} value.  Returns zero if the specified value has no
1047      * one-bits in its two's complement binary representation, that is, if it
1048      * is equal to zero.
1049      *
1050      * @return an {@code int} value with a single one-bit, in the position
1051      *     of the highest-order one-bit in the specified value, or zero if
1052      *     the specified value is itself equal to zero.
1053      * @since 1.5
1054      */
1055     public static int highestOneBit(int i) {
1056         // HD, Figure 3-1
1057         i |= (i >>  1);
1058         i |= (i >>  2);
1059         i |= (i >>  4);
1060         i |= (i >>  8);
1061         i |= (i >> 16);
1062         return i - (i >>> 1);
1063     }
1064 
1065     /**
1066      * Returns an {@code int} value with at most a single one-bit, in the
1067      * position of the lowest-order ("rightmost") one-bit in the specified
1068      * {@code int} value.  Returns zero if the specified value has no
1069      * one-bits in its two's complement binary representation, that is, if it
1070      * is equal to zero.
1071      *
1072      * @return an {@code int} value with a single one-bit, in the position
1073      *     of the lowest-order one-bit in the specified value, or zero if
1074      *     the specified value is itself equal to zero.
1075      * @since 1.5
1076      */
1077     public static int lowestOneBit(int i) {
1078         // HD, Section 2-1
1079         return i & -i;
1080     }
1081 
1082     /**
1083      * Returns the number of zero bits preceding the highest-order
1084      * ("leftmost") one-bit in the two's complement binary representation
1085      * of the specified {@code int} value.  Returns 32 if the
1086      * specified value has no one-bits in its two's complement representation,
1087      * in other words if it is equal to zero.
1088      *
1089      * <p>Note that this method is closely related to the logarithm base 2.
1090      * For all positive {@code int} values x:
1091      * <ul>
1092      * <li>floor(log<sub>2</sub>(x)) = {@code 31 - numberOfLeadingZeros(x)}
1093      * <li>ceil(log<sub>2</sub>(x)) = {@code 32 - numberOfLeadingZeros(x - 1)}
1094      * </ul>
1095      *
1096      * @return the number of zero bits preceding the highest-order
1097      *     ("leftmost") one-bit in the two's complement binary representation
1098      *     of the specified {@code int} value, or 32 if the value
1099      *     is equal to zero.
1100      * @since 1.5
1101      */
1102     public static int numberOfLeadingZeros(int i) {
1103         // HD, Figure 5-6
1104         if (i == 0)
1105             return 32;
1106         int n = 1;
1107         if (i >>> 16 == 0) { n += 16; i <<= 16; }
1108         if (i >>> 24 == 0) { n +=  8; i <<=  8; }
1109         if (i >>> 28 == 0) { n +=  4; i <<=  4; }
1110         if (i >>> 30 == 0) { n +=  2; i <<=  2; }
1111         n -= i >>> 31;
1112         return n;
1113     }
1114 
1115     /**
1116      * Returns the number of zero bits following the lowest-order ("rightmost")
1117      * one-bit in the two's complement binary representation of the specified
1118      * {@code int} value.  Returns 32 if the specified value has no
1119      * one-bits in its two's complement representation, in other words if it is
1120      * equal to zero.
1121      *
1122      * @return the number of zero bits following the lowest-order ("rightmost")
1123      *     one-bit in the two's complement binary representation of the
1124      *     specified {@code int} value, or 32 if the value is equal
1125      *     to zero.
1126      * @since 1.5
1127      */
1128     public static int numberOfTrailingZeros(int i) {
1129         // HD, Figure 5-14
1130         int y;
1131         if (i == 0) return 32;
1132         int n = 31;
1133         y = i <<16; if (y != 0) { n = n -16; i = y; }
1134         y = i << 8; if (y != 0) { n = n - 8; i = y; }
1135         y = i << 4; if (y != 0) { n = n - 4; i = y; }
1136         y = i << 2; if (y != 0) { n = n - 2; i = y; }
1137         return n - ((i << 1) >>> 31);
1138     }
1139 
1140     /**
1141      * Returns the number of one-bits in the two's complement binary
1142      * representation of the specified {@code int} value.  This function is
1143      * sometimes referred to as the <i>population count</i>.
1144      *
1145      * @return the number of one-bits in the two's complement binary
1146      *     representation of the specified {@code int} value.
1147      * @since 1.5
1148      */
1149     public static int bitCount(int i) {
1150         // HD, Figure 5-2
1151         i = i - ((i >>> 1) & 0x55555555);
1152         i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
1153         i = (i + (i >>> 4)) & 0x0f0f0f0f;
1154         i = i + (i >>> 8);
1155         i = i + (i >>> 16);
1156         return i & 0x3f;
1157     }
1158 
1159     /**
1160      * Returns the value obtained by rotating the two's complement binary
1161      * representation of the specified {@code int} value left by the
1162      * specified number of bits.  (Bits shifted out of the left hand, or
1163      * high-order, side reenter on the right, or low-order.)
1164      *
1165      * <p>Note that left rotation with a negative distance is equivalent to
1166      * right rotation: {@code rotateLeft(val, -distance) == rotateRight(val,
1167      * distance)}.  Note also that rotation by any multiple of 32 is a
1168      * no-op, so all but the last five bits of the rotation distance can be
1169      * ignored, even if the distance is negative: {@code rotateLeft(val,
1170      * distance) == rotateLeft(val, distance & 0x1F)}.
1171      *
1172      * @return the value obtained by rotating the two's complement binary
1173      *     representation of the specified {@code int} value left by the
1174      *     specified number of bits.
1175      * @since 1.5
1176      */
1177     public static int rotateLeft(int i, int distance) {
1178         return (i << distance) | (i >>> -distance);
1179     }
1180 
1181     /**
1182      * Returns the value obtained by rotating the two's complement binary
1183      * representation of the specified {@code int} value right by the
1184      * specified number of bits.  (Bits shifted out of the right hand, or
1185      * low-order, side reenter on the left, or high-order.)
1186      *
1187      * <p>Note that right rotation with a negative distance is equivalent to
1188      * left rotation: {@code rotateRight(val, -distance) == rotateLeft(val,
1189      * distance)}.  Note also that rotation by any multiple of 32 is a
1190      * no-op, so all but the last five bits of the rotation distance can be
1191      * ignored, even if the distance is negative: {@code rotateRight(val,
1192      * distance) == rotateRight(val, distance & 0x1F)}.
1193      *
1194      * @return the value obtained by rotating the two's complement binary
1195      *     representation of the specified {@code int} value right by the
1196      *     specified number of bits.
1197      * @since 1.5
1198      */
1199     public static int rotateRight(int i, int distance) {
1200         return (i >>> distance) | (i << -distance);
1201     }
1202 
1203     /**
1204      * Returns the value obtained by reversing the order of the bits in the
1205      * two's complement binary representation of the specified {@code int}
1206      * value.
1207      *
1208      * @return the value obtained by reversing order of the bits in the
1209      *     specified {@code int} value.
1210      * @since 1.5
1211      */
1212     public static int reverse(int i) {
1213         // HD, Figure 7-1
1214         i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
1215         i = (i & 0x33333333) << 2 | (i >>> 2) & 0x33333333;
1216         i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
1217         i = (i << 24) | ((i & 0xff00) << 8) |
1218             ((i >>> 8) & 0xff00) | (i >>> 24);
1219         return i;
1220     }
1221 
1222     /**
1223      * Returns the signum function of the specified {@code int} value.  (The
1224      * return value is -1 if the specified value is negative; 0 if the
1225      * specified value is zero; and 1 if the specified value is positive.)
1226      *
1227      * @return the signum function of the specified {@code int} value.
1228      * @since 1.5
1229      */
1230     public static int signum(int i) {
1231         // HD, Section 2-7
1232         return (i >> 31) | (-i >>> 31);
1233     }
1234 
1235     /**
1236      * Returns the value obtained by reversing the order of the bytes in the
1237      * two's complement representation of the specified {@code int} value.
1238      *
1239      * @return the value obtained by reversing the bytes in the specified
1240      *     {@code int} value.
1241      * @since 1.5
1242      */
1243     public static int reverseBytes(int i) {
1244         return ((i >>> 24)           ) |
1245                ((i >>   8) &   0xFF00) |
1246                ((i <<   8) & 0xFF0000) |
1247                ((i << 24));
1248     }
1249 
1250     /** use serialVersionUID from JDK 1.0.2 for interoperability */
1251     private static final long serialVersionUID = 1360826667806852920L;
1252 }