1. /*
2.  * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
3.  * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
4.  *
5.  *
6.  *
7.  *
8.  *
9.  *
10.  *
11.  *
12.  *
13.  *
14.  *
15.  *
16.  *
17.  *
18.  *
19.  *
20.  *
21.  *
22.  *
23.  *
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, -2³¹.
56.      */
57.     public static final int   MIN_VALUE = 0x80000000;
58.  
59.     /**
60.      * A constant holding the maximum value an {@code int} can
61.      * have, 2³¹-1.
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 2³²
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 2³²
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 2³²
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(buf, true);
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_opt DecimalNumeral</i>
909.      * <dd><i>Sign_opt</i> {@code 0x} <i>HexDigits</i>
910.      * <dd><i>Sign_opt</i> {@code 0X} <i>HexDigits</i>
911.      * <dd><i>Sign_opt</i> {@code #} <i>HexDigits</i>
912.      * <dd><i>Sign_opt</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(log₂(x)) = {@code 31 - numberOfLeadingZeros(x)}
1085.      * <li>ceil(log₂(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. }
1245.