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    1   /*
    2    * Copyright (c) 1994, 2010, 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
  682        * {@code byte}.
  683        */
  684       public byte byteValue() {
  685           return (byte)value;
  686       }
  687   
  688       /**
  689        * Returns the value of this {@code Integer} as a
  690        * {@code short}.
  691        */
  692       public short shortValue() {
  693           return (short)value;
  694       }
  695   
  696       /**
  697        * Returns the value of this {@code Integer} as an
  698        * {@code int}.
  699        */
  700       public int intValue() {
  701           return value;
  702       }
  703   
  704       /**
  705        * Returns the value of this {@code Integer} as a
  706        * {@code long}.
  707        */
  708       public long longValue() {
  709           return (long)value;
  710       }
  711   
  712       /**
  713        * Returns the value of this {@code Integer} as a
  714        * {@code float}.
  715        */
  716       public float floatValue() {
  717           return (float)value;
  718       }
  719   
  720       /**
  721        * Returns the value of this {@code Integer} as a
  722        * {@code double}.
  723        */
  724       public double doubleValue() {
  725           return (double)value;
  726       }
  727   
  728       /**
  729        * Returns a {@code String} object representing this
  730        * {@code Integer}'s value. The value is converted to signed
  731        * decimal representation and returned as a string, exactly as if
  732        * the integer value were given as an argument to the {@link
  733        * java.lang.Integer#toString(int)} method.
  734        *
  735        * @return  a string representation of the value of this object in
  736        *          base&nbsp;10.
  737        */
  738       public String toString() {
  739           return toString(value);
  740       }
  741   
  742       /**
  743        * Returns a hash code for this {@code Integer}.
  744        *
  745        * @return  a hash code value for this object, equal to the
  746        *          primitive {@code int} value represented by this
  747        *          {@code Integer} object.
  748        */
  749       public int hashCode() {
  750           return value;
  751       }
  752   
  753       /**
  754        * Compares this object to the specified object.  The result is
  755        * {@code true} if and only if the argument is not
  756        * {@code null} and is an {@code Integer} object that
  757        * contains the same {@code int} value as this object.
  758        *
  759        * @param   obj   the object to compare with.
  760        * @return  {@code true} if the objects are the same;
  761        *          {@code false} otherwise.
  762        */
  763       public boolean equals(Object obj) {
  764           if (obj instanceof Integer) {
  765               return value == ((Integer)obj).intValue();
  766           }
  767           return false;
  768       }
  769   
  770       /**
  771        * Determines the integer value of the system property with the
  772        * specified name.
  773        *
  774        * <p>The first argument is treated as the name of a system property.
  775        * System properties are accessible through the
  776        * {@link java.lang.System#getProperty(java.lang.String)} method. The
  777        * string value of this property is then interpreted as an integer
  778        * value and an {@code Integer} object representing this value is
  779        * returned. Details of possible numeric formats can be found with
  780        * the definition of {@code getProperty}.
  781        *
  782        * <p>If there is no property with the specified name, if the specified name
  783        * is empty or {@code null}, or if the property does not have
  784        * the correct numeric format, then {@code null} is returned.
  785        *
  786        * <p>In other words, this method returns an {@code Integer}
  787        * object equal to the value of:
  788        *
  789        * <blockquote>
  790        *  {@code getInteger(nm, null)}
  791        * </blockquote>
  792        *
  793        * @param   nm   property name.
  794        * @return  the {@code Integer} value of the property.
  795        * @see     java.lang.System#getProperty(java.lang.String)
  796        * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
  797        */
  798       public static Integer getInteger(String nm) {
  799           return getInteger(nm, null);
  800       }
  801   
  802       /**
  803        * Determines the integer value of the system property with the
  804        * specified name.
  805        *
  806        * <p>The first argument is treated as the name of a system property.
  807        * System properties are accessible through the {@link
  808        * java.lang.System#getProperty(java.lang.String)} method. The
  809        * string value of this property is then interpreted as an integer
  810        * value and an {@code Integer} object representing this value is
  811        * returned. Details of possible numeric formats can be found with
  812        * the definition of {@code getProperty}.
  813        *
  814        * <p>The second argument is the default value. An {@code Integer} object
  815        * that represents the value of the second argument is returned if there
  816        * is no property of the specified name, if the property does not have
  817        * the correct numeric format, or if the specified name is empty or
  818        * {@code null}.
  819        *
  820        * <p>In other words, this method returns an {@code Integer} object
  821        * equal to the value of:
  822        *
  823        * <blockquote>
  824        *  {@code getInteger(nm, new Integer(val))}
  825        * </blockquote>
  826        *
  827        * but in practice it may be implemented in a manner such as:
  828        *
  829        * <blockquote><pre>
  830        * Integer result = getInteger(nm, null);
  831        * return (result == null) ? new Integer(val) : result;
  832        * </pre></blockquote>
  833        *
  834        * to avoid the unnecessary allocation of an {@code Integer}
  835        * object when the default value is not needed.
  836        *
  837        * @param   nm   property name.
  838        * @param   val   default value.
  839        * @return  the {@code Integer} value of the property.
  840        * @see     java.lang.System#getProperty(java.lang.String)
  841        * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
  842        */
  843       public static Integer getInteger(String nm, int val) {
  844           Integer result = getInteger(nm, null);
  845           return (result == null) ? Integer.valueOf(val) : result;
  846       }
  847   
  848       /**
  849        * Returns the integer value of the system property with the
  850        * specified name.  The first argument is treated as the name of a
  851        * system property.  System properties are accessible through the
  852        * {@link java.lang.System#getProperty(java.lang.String)} method.
  853        * The string value of this property is then interpreted as an
  854        * integer value, as per the {@code Integer.decode} method,
  855        * and an {@code Integer} object representing this value is
  856        * returned.
  857        *
  858        * <ul><li>If the property value begins with the two ASCII characters
  859        *         {@code 0x} or the ASCII character {@code #}, not
  860        *      followed by a minus sign, then the rest of it is parsed as a
  861        *      hexadecimal integer exactly as by the method
  862        *      {@link #valueOf(java.lang.String, int)} with radix 16.
  863        * <li>If the property value begins with the ASCII character
  864        *     {@code 0} followed by another character, it is parsed as an
  865        *     octal integer exactly as by the method
  866        *     {@link #valueOf(java.lang.String, int)} with radix 8.
  867        * <li>Otherwise, the property value is parsed as a decimal integer
  868        * exactly as by the method {@link #valueOf(java.lang.String, int)}
  869        * with radix 10.
  870        * </ul>
  871        *
  872        * <p>The second argument is the default value. The default value is
  873        * returned if there is no property of the specified name, if the
  874        * property does not have the correct numeric format, or if the
  875        * specified name is empty or {@code null}.
  876        *
  877        * @param   nm   property name.
  878        * @param   val   default value.
  879        * @return  the {@code Integer} value of the property.
  880        * @see     java.lang.System#getProperty(java.lang.String)
  881        * @see java.lang.System#getProperty(java.lang.String, java.lang.String)
  882        * @see java.lang.Integer#decode
  883        */
  884       public static Integer getInteger(String nm, Integer val) {
  885           String v = null;
  886           try {
  887               v = System.getProperty(nm);
  888           } catch (IllegalArgumentException e) {
  889           } catch (NullPointerException e) {
  890           }
  891           if (v != null) {
  892               try {
  893                   return Integer.decode(v);
  894               } catch (NumberFormatException e) {
  895               }
  896           }
  897           return val;
  898       }
  899   
  900       /**
  901        * Decodes a {@code String} into an {@code Integer}.
  902        * Accepts decimal, hexadecimal, and octal numbers given
  903        * by the following grammar:
  904        *
  905        * <blockquote>
  906        * <dl>
  907        * <dt><i>DecodableString:</i>
  908        * <dd><i>Sign<sub>opt</sub> DecimalNumeral</i>
  909        * <dd><i>Sign<sub>opt</sub></i> {@code 0x} <i>HexDigits</i>
  910        * <dd><i>Sign<sub>opt</sub></i> {@code 0X} <i>HexDigits</i>
  911        * <dd><i>Sign<sub>opt</sub></i> {@code #} <i>HexDigits</i>
  912        * <dd><i>Sign<sub>opt</sub></i> {@code 0} <i>OctalDigits</i>
  913        * <p>
  914        * <dt><i>Sign:</i>
  915        * <dd>{@code -}
  916        * <dd>{@code +}
  917        * </dl>
  918        * </blockquote>
  919        *
  920        * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
  921        * are as defined in section 3.10.1 of
  922        * <cite>The Java&trade; Language Specification</cite>,
  923        * except that underscores are not accepted between digits.
  924        *
  925        * <p>The sequence of characters following an optional
  926        * sign and/or radix specifier ("{@code 0x}", "{@code 0X}",
  927        * "{@code #}", or leading zero) is parsed as by the {@code
  928        * Integer.parseInt} method with the indicated radix (10, 16, or
  929        * 8).  This sequence of characters must represent a positive
  930        * value or a {@link NumberFormatException} will be thrown.  The
  931        * result is negated if first character of the specified {@code
  932        * String} is the minus sign.  No whitespace characters are
  933        * permitted in the {@code String}.
  934        *
  935        * @param     nm the {@code String} to decode.
  936        * @return    an {@code Integer} object holding the {@code int}
  937        *             value represented by {@code nm}
  938        * @exception NumberFormatException  if the {@code String} does not
  939        *            contain a parsable integer.
  940        * @see java.lang.Integer#parseInt(java.lang.String, int)
  941        */
  942       public static Integer decode(String nm) throws NumberFormatException {
  943           int radix = 10;
  944           int index = 0;
  945           boolean negative = false;
  946           Integer result;
  947   
  948           if (nm.length() == 0)
  949               throw new NumberFormatException("Zero length string");
  950           char firstChar = nm.charAt(0);
  951           // Handle sign, if present
  952           if (firstChar == '-') {
  953               negative = true;
  954               index++;
  955           } else if (firstChar == '+')
  956               index++;
  957   
  958           // Handle radix specifier, if present
  959           if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
  960               index += 2;
  961               radix = 16;
  962           }
  963           else if (nm.startsWith("#", index)) {
  964               index ++;
  965               radix = 16;
  966           }
  967           else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
  968               index ++;
  969               radix = 8;
  970           }
  971   
  972           if (nm.startsWith("-", index) || nm.startsWith("+", index))
  973               throw new NumberFormatException("Sign character in wrong position");
  974   
  975           try {
  976               result = Integer.valueOf(nm.substring(index), radix);
  977               result = negative ? Integer.valueOf(-result.intValue()) : result;
  978           } catch (NumberFormatException e) {
  979               // If number is Integer.MIN_VALUE, we'll end up here. The next line
  980               // handles this case, and causes any genuine format error to be
  981               // rethrown.
  982               String constant = negative ? ("-" + nm.substring(index))
  983                                          : nm.substring(index);
  984               result = Integer.valueOf(constant, radix);
  985           }
  986           return result;
  987       }
  988   
  989       /**
  990        * Compares two {@code Integer} objects numerically.
  991        *
  992        * @param   anotherInteger   the {@code Integer} to be compared.
  993        * @return  the value {@code 0} if this {@code Integer} is
  994        *          equal to the argument {@code Integer}; a value less than
  995        *          {@code 0} if this {@code Integer} is numerically less
  996        *          than the argument {@code Integer}; and a value greater
  997        *          than {@code 0} if this {@code Integer} is numerically
  998        *           greater than the argument {@code Integer} (signed
  999        *           comparison).
 1000        * @since   1.2
 1001        */
 1002       public int compareTo(Integer anotherInteger) {
 1003           return compare(this.value, anotherInteger.value);
 1004       }
 1005   
 1006       /**
 1007        * Compares two {@code int} values numerically.
 1008        * The value returned is identical to what would be returned by:
 1009        * <pre>
 1010        *    Integer.valueOf(x).compareTo(Integer.valueOf(y))
 1011        * </pre>
 1012        *
 1013        * @param  x the first {@code int} to compare
 1014        * @param  y the second {@code int} to compare
 1015        * @return the value {@code 0} if {@code x == y};
 1016        *         a value less than {@code 0} if {@code x < y}; and
 1017        *         a value greater than {@code 0} if {@code x > y}
 1018        * @since 1.7
 1019        */
 1020       public static int compare(int x, int y) {
 1021           return (x < y) ? -1 : ((x == y) ? 0 : 1);
 1022       }
 1023   
 1024   
 1025       // Bit twiddling
 1026   
 1027       /**
 1028        * The number of bits used to represent an {@code int} value in two's
 1029        * complement binary form.
 1030        *
 1031        * @since 1.5
 1032        */
 1033       public static final int SIZE = 32;
 1034   
 1035       /**
 1036        * Returns an {@code int} value with at most a single one-bit, in the
 1037        * position of the highest-order ("leftmost") one-bit in the specified
 1038        * {@code int} value.  Returns zero if the specified value has no
 1039        * one-bits in its two's complement binary representation, that is, if it
 1040        * is equal to zero.
 1041        *
 1042        * @return an {@code int} value with a single one-bit, in the position
 1043        *     of the highest-order one-bit in the specified value, or zero if
 1044        *     the specified value is itself equal to zero.
 1045        * @since 1.5
 1046        */
 1047       public static int highestOneBit(int i) {
 1048           // HD, Figure 3-1
 1049           i |= (i >>  1);
 1050           i |= (i >>  2);
 1051           i |= (i >>  4);
 1052           i |= (i >>  8);
 1053           i |= (i >> 16);
 1054           return i - (i >>> 1);
 1055       }
 1056   
 1057       /**
 1058        * Returns an {@code int} value with at most a single one-bit, in the
 1059        * position of the lowest-order ("rightmost") one-bit in the specified
 1060        * {@code int} value.  Returns zero if the specified value has no
 1061        * one-bits in its two's complement binary representation, that is, if it
 1062        * is equal to zero.
 1063        *
 1064        * @return an {@code int} value with a single one-bit, in the position
 1065        *     of the lowest-order one-bit in the specified value, or zero if
 1066        *     the specified value is itself equal to zero.
 1067        * @since 1.5
 1068        */
 1069       public static int lowestOneBit(int i) {
 1070           // HD, Section 2-1
 1071           return i & -i;
 1072       }
 1073   
 1074       /**
 1075        * Returns the number of zero bits preceding the highest-order
 1076        * ("leftmost") one-bit in the two's complement binary representation
 1077        * of the specified {@code int} value.  Returns 32 if the
 1078        * specified value has no one-bits in its two's complement representation,
 1079        * in other words if it is equal to zero.
 1080        *
 1081        * <p>Note that this method is closely related to the logarithm base 2.
 1082        * For all positive {@code int} values x:
 1083        * <ul>
 1084        * <li>floor(log<sub>2</sub>(x)) = {@code 31 - numberOfLeadingZeros(x)}
 1085        * <li>ceil(log<sub>2</sub>(x)) = {@code 32 - numberOfLeadingZeros(x - 1)}
 1086        * </ul>
 1087        *
 1088        * @return the number of zero bits preceding the highest-order
 1089        *     ("leftmost") one-bit in the two's complement binary representation
 1090        *     of the specified {@code int} value, or 32 if the value
 1091        *     is equal to zero.
 1092        * @since 1.5
 1093        */
 1094       public static int numberOfLeadingZeros(int i) {
 1095           // HD, Figure 5-6
 1096           if (i == 0)
 1097               return 32;
 1098           int n = 1;
 1099           if (i >>> 16 == 0) { n += 16; i <<= 16; }
 1100           if (i >>> 24 == 0) { n +=  8; i <<=  8; }
 1101           if (i >>> 28 == 0) { n +=  4; i <<=  4; }
 1102           if (i >>> 30 == 0) { n +=  2; i <<=  2; }
 1103           n -= i >>> 31;
 1104           return n;
 1105       }
 1106   
 1107       /**
 1108        * Returns the number of zero bits following the lowest-order ("rightmost")
 1109        * one-bit in the two's complement binary representation of the specified
 1110        * {@code int} value.  Returns 32 if the specified value has no
 1111        * one-bits in its two's complement representation, in other words if it is
 1112        * equal to zero.
 1113        *
 1114        * @return the number of zero bits following the lowest-order ("rightmost")
 1115        *     one-bit in the two's complement binary representation of the
 1116        *     specified {@code int} value, or 32 if the value is equal
 1117        *     to zero.
 1118        * @since 1.5
 1119        */
 1120       public static int numberOfTrailingZeros(int i) {
 1121           // HD, Figure 5-14
 1122           int y;
 1123           if (i == 0) return 32;
 1124           int n = 31;
 1125           y = i <<16; if (y != 0) { n = n -16; i = y; }
 1126           y = i << 8; if (y != 0) { n = n - 8; i = y; }
 1127           y = i << 4; if (y != 0) { n = n - 4; i = y; }
 1128           y = i << 2; if (y != 0) { n = n - 2; i = y; }
 1129           return n - ((i << 1) >>> 31);
 1130       }
 1131   
 1132       /**
 1133        * Returns the number of one-bits in the two's complement binary
 1134        * representation of the specified {@code int} value.  This function is
 1135        * sometimes referred to as the <i>population count</i>.
 1136        *
 1137        * @return the number of one-bits in the two's complement binary
 1138        *     representation of the specified {@code int} value.
 1139        * @since 1.5
 1140        */
 1141       public static int bitCount(int i) {
 1142           // HD, Figure 5-2
 1143           i = i - ((i >>> 1) & 0x55555555);
 1144           i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
 1145           i = (i + (i >>> 4)) & 0x0f0f0f0f;
 1146           i = i + (i >>> 8);
 1147           i = i + (i >>> 16);
 1148           return i & 0x3f;
 1149       }
 1150   
 1151       /**
 1152        * Returns the value obtained by rotating the two's complement binary
 1153        * representation of the specified {@code int} value left by the
 1154        * specified number of bits.  (Bits shifted out of the left hand, or
 1155        * high-order, side reenter on the right, or low-order.)
 1156        *
 1157        * <p>Note that left rotation with a negative distance is equivalent to
 1158        * right rotation: {@code rotateLeft(val, -distance) == rotateRight(val,
 1159        * distance)}.  Note also that rotation by any multiple of 32 is a
 1160        * no-op, so all but the last five bits of the rotation distance can be
 1161        * ignored, even if the distance is negative: {@code rotateLeft(val,
 1162        * distance) == rotateLeft(val, distance & 0x1F)}.
 1163        *
 1164        * @return the value obtained by rotating the two's complement binary
 1165        *     representation of the specified {@code int} value left by the
 1166        *     specified number of bits.
 1167        * @since 1.5
 1168        */
 1169       public static int rotateLeft(int i, int distance) {
 1170           return (i << distance) | (i >>> -distance);
 1171       }
 1172   
 1173       /**
 1174        * Returns the value obtained by rotating the two's complement binary
 1175        * representation of the specified {@code int} value right by the
 1176        * specified number of bits.  (Bits shifted out of the right hand, or
 1177        * low-order, side reenter on the left, or high-order.)
 1178        *
 1179        * <p>Note that right rotation with a negative distance is equivalent to
 1180        * left rotation: {@code rotateRight(val, -distance) == rotateLeft(val,
 1181        * distance)}.  Note also that rotation by any multiple of 32 is a
 1182        * no-op, so all but the last five bits of the rotation distance can be
 1183        * ignored, even if the distance is negative: {@code rotateRight(val,
 1184        * distance) == rotateRight(val, distance & 0x1F)}.
 1185        *
 1186        * @return the value obtained by rotating the two's complement binary
 1187        *     representation of the specified {@code int} value right by the
 1188        *     specified number of bits.
 1189        * @since 1.5
 1190        */
 1191       public static int rotateRight(int i, int distance) {
 1192           return (i >>> distance) | (i << -distance);
 1193       }
 1194   
 1195       /**
 1196        * Returns the value obtained by reversing the order of the bits in the
 1197        * two's complement binary representation of the specified {@code int}
 1198        * value.
 1199        *
 1200        * @return the value obtained by reversing order of the bits in the
 1201        *     specified {@code int} value.
 1202        * @since 1.5
 1203        */
 1204       public static int reverse(int i) {
 1205           // HD, Figure 7-1
 1206           i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
 1207           i = (i & 0x33333333) << 2 | (i >>> 2) & 0x33333333;
 1208           i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
 1209           i = (i << 24) | ((i & 0xff00) << 8) |
 1210               ((i >>> 8) & 0xff00) | (i >>> 24);
 1211           return i;
 1212       }
 1213   
 1214       /**
 1215        * Returns the signum function of the specified {@code int} value.  (The
 1216        * return value is -1 if the specified value is negative; 0 if the
 1217        * specified value is zero; and 1 if the specified value is positive.)
 1218        *
 1219        * @return the signum function of the specified {@code int} value.
 1220        * @since 1.5
 1221        */
 1222       public static int signum(int i) {
 1223           // HD, Section 2-7
 1224           return (i >> 31) | (-i >>> 31);
 1225       }
 1226   
 1227       /**
 1228        * Returns the value obtained by reversing the order of the bytes in the
 1229        * two's complement representation of the specified {@code int} value.
 1230        *
 1231        * @return the value obtained by reversing the bytes in the specified
 1232        *     {@code int} value.
 1233        * @since 1.5
 1234        */
 1235       public static int reverseBytes(int i) {
 1236           return ((i >>> 24)           ) |
 1237                  ((i >>   8) &   0xFF00) |
 1238                  ((i <<   8) & 0xFF0000) |
 1239                  ((i << 24));
 1240       }
 1241   
 1242       /** use serialVersionUID from JDK 1.0.2 for interoperability */
 1243       private static final long serialVersionUID = 1360826667806852920L;
 1244   }

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