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. Http://youtube.com
53. public final class Integer extends Number implements Comparable<Integer> {
54.     /**
55.      * A constant holding the minimum value an {@code int} can
56.      * have, -2³¹.
57.      */
58.     public static final int   MIN_VALUE = 0x80000000;
59.  
60.     /**
61.      * A constant holding the maximum value an {@code int} can
62.      * have, 2³¹-1.
63.      */
64.     public static final int   MAX_VALUE = 0x7fffffff;
65.  
66.     /**
67.      * The {@code Class} instance representing the primitive type
68.      * {@code int}.
69.      *
70.      * @since   JDK1.1
71.      */
72.     public static final Class<Integer>  TYPE = (Class<Integer>) Class.getPrimitiveClass("int");
73.  
74.     /**
75.      * All possible chars for representing a number as a String
76.      */
77.     final static char[] digits = {
78.         '0' , '1' , '2' , '3' , '4' , '5' ,
79.         '6' , '7' , '8' , '9' , 'a' , 'b' ,
80.         'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
81.         'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
82.         'o' , 'p' , 'q' , 'r' , 's' , 't' ,
83.         'u' , 'v' , 'w' , 'x' , 'y' , 'z'
84.     };
85.  
86.     /**
87.      * Returns a string representation of the first argument in the
88.      * radix specified by the second argument.
89.      *
90.      * <p>If the radix is smaller than {@code Character.MIN_RADIX}
91.      * or larger than {@code Character.MAX_RADIX}, then the radix
92.      * {@code 10} is used instead.
93.      *
94.      * <p>If the first argument is negative, the first element of the
95.      * result is the ASCII minus character {@code '-'}
96.      * (<code>'&#92;u002D'</code>). If the first argument is not
97.      * negative, no sign character appears in the result.
98.      *
99.      * <p>The remaining characters of the result represent the magnitude
100.      * of the first argument. If the magnitude is zero, it is
101.      * represented by a single zero character {@code '0'}
102.      * (<code>'&#92;u0030'</code>); otherwise, the first character of
103.      * the representation of the magnitude will not be the zero
104.      * character.  The following ASCII characters are used as digits:
105.      *
106.      * <blockquote>
107.      *   {@code 0123456789abcdefghijklmnopqrstuvwxyz}
108.      * </blockquote>
109.      *
110.      * These are <code>'&#92;u0030'</code> through
111.      * <code>'&#92;u0039'</code> and <code>'&#92;u0061'</code> through
112.      * <code>'&#92;u007A'</code>. If {@code radix} is
113.      * <var>N</var>, then the first <var>N</var> of these characters
114.      * are used as radix-<var>N</var> digits in the order shown. Thus,
115.      * the digits for hexadecimal (radix 16) are
116.      * {@code 0123456789abcdef}. If uppercase letters are
117.      * desired, the {@link java.lang.String#toUpperCase()} method may
118.      * be called on the result:
119.      *
120.      * <blockquote>
121.      *  {@code Integer.toString(n, 16).toUpperCase()}
122.      * </blockquote>
123.      *
124.      * @param   i       an integer to be converted to a string.
125.      * @param   radix   the radix to use in the string representation.
126.      * @return  a string representation of the argument in the specified radix.
127.      * @see     java.lang.Character#MAX_RADIX
128.      * @see     java.lang.Character#MIN_RADIX
129.      */
130.     public static String toString(int i, int radix) {
131.  
132.         if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
133.             radix = 10;
134.  
135.         /* Use the faster version */
136.         if (radix == 10) {
137.             return toString(i);
138.         }
139.  
140.         char buf[] = new char[33];
141.         boolean negative = (i < 0);
142.         int charPos = 32;
143.  
144.         if (!negative) {
145.             i = -i;
146.         }
147.  
148.         while (i <= -radix) {
149.             buf[charPos--] = digits[-(i % radix)];
150.             i = i / radix;
151.         }
152.         buf[charPos] = digits[-i];
153.  
154.         if (negative) {
155.             buf[--charPos] = '-';
156.         }
157.  
158.         return new String(buf, charPos, (33 - charPos));
159.     }
160.  
161.     /**
162.      * Returns a string representation of the integer argument as an
163.      * unsigned integer in base&nbsp;16.
164.      *
165.      * <p>The unsigned integer value is the argument plus 2³²
166.      * if the argument is negative; otherwise, it is equal to the
167.      * argument.  This value is converted to a string of ASCII digits
168.      * in hexadecimal (base&nbsp;16) with no extra leading
169.      * {@code 0}s. If the unsigned magnitude is zero, it is
170.      * represented by a single zero character {@code '0'}
171.      * (<code>'&#92;u0030'</code>); otherwise, the first character of
172.      * the representation of the unsigned magnitude will not be the
173.      * zero character. The following characters are used as
174.      * hexadecimal digits:
175.      *
176.      * <blockquote>
177.      *  {@code 0123456789abcdef}
178.      * </blockquote>
179.      *
180.      * These are the characters <code>'&#92;u0030'</code> through
181.      * <code>'&#92;u0039'</code> and <code>'&#92;u0061'</code> through
182.      * <code>'&#92;u0066'</code>. If uppercase letters are
183.      * desired, the {@link java.lang.String#toUpperCase()} method may
184.      * be called on the result:
185.      *
186.      * <blockquote>
187.      *  {@code Integer.toHexString(n).toUpperCase()}
188.      * </blockquote>
189.      *
190.      * @param   i   an integer to be converted to a string.
191.      * @return  the string representation of the unsigned integer value
192.      *          represented by the argument in hexadecimal (base&nbsp;16).
193.      * @since   JDK1.0.2
194.      */
195.     public static String toHexString(int i) {
196.         return toUnsignedString(i, 4);
197.     }
198.  
199.     /**
200.      * Returns a string representation of the integer argument as an
201.      * unsigned integer in base&nbsp;8.
202.      *
203.      * <p>The unsigned integer value is the argument plus 2³²
204.      * if the argument is negative; otherwise, it is equal to the
205.      * argument.  This value is converted to a string of ASCII digits
206.      * in octal (base&nbsp;8) with no extra leading {@code 0}s.
207.      *
208.      * <p>If the unsigned magnitude is zero, it is represented by a
209.      * single zero character {@code '0'}
210.      * (<code>'&#92;u0030'</code>); otherwise, the first character of
211.      * the representation of the unsigned magnitude will not be the
212.      * zero character. The following characters are used as octal
213.      * digits:
214.      *
215.      * <blockquote>
216.      * {@code 01234567}
217.      * </blockquote>
218.      *
219.      * These are the characters <code>'&#92;u0030'</code> through
220.      * <code>'&#92;u0037'</code>.
221.      *
222.      * @param   i   an integer to be converted to a string.
223.      * @return  the string representation of the unsigned integer value
224.      *          represented by the argument in octal (base&nbsp;8).
225.      * @since   JDK1.0.2
226.      */
227.     public static String toOctalString(int i) {
228.         return toUnsignedString(i, 3);
229.     }
230.  
231.     /**
232.      * Returns a string representation of the integer argument as an
233.      * unsigned integer in base&nbsp;2.
234.      *
235.      * <p>The unsigned integer value is the argument plus 2³²
236.      * if the argument is negative; otherwise it is equal to the
237.      * argument.  This value is converted to a string of ASCII digits
238.      * in binary (base&nbsp;2) with no extra leading {@code 0}s.
239.      * If the unsigned magnitude is zero, it is represented by a
240.      * single zero character {@code '0'}
241.      * (<code>'&#92;u0030'</code>); otherwise, the first character of
242.      * the representation of the unsigned magnitude will not be the
243.      * zero character. The characters {@code '0'}
244.      * (<code>'&#92;u0030'</code>) and {@code '1'}
245.      * (<code>'&#92;u0031'</code>) are used as binary digits.
246.      *
247.      * @param   i   an integer to be converted to a string.
248.      * @return  the string representation of the unsigned integer value
249.      *          represented by the argument in binary (base&nbsp;2).
250.      * @since   JDK1.0.2
251.      */
252.     public static String toBinaryString(int i) {
253.         return toUnsignedString(i, 1);
254.     }
255.  
256.     /**
257.      * Convert the integer to an unsigned number.
258.      */
259.     private static String toUnsignedString(int i, int shift) {
260.         char[] buf = new char[32];
261.         int charPos = 32;
262.         int radix = 1 << shift;
263.         int mask = radix - 1;
264.         do {
265.             buf[--charPos] = digits[i & mask];
266.             i >>>= shift;
267.         } while (i != 0);
268.  
269.         return new String(buf, charPos, (32 - charPos));
270.     }
271.  
272.  
273.     final static char [] DigitTens = {
274.         '0', '0', '0', '0', '0', '0', '0', '0', '0', '0',
275.         '1', '1', '1', '1', '1', '1', '1', '1', '1', '1',
276.         '2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
277.         '3', '3', '3', '3', '3', '3', '3', '3', '3', '3',
278.         '4', '4', '4', '4', '4', '4', '4', '4', '4', '4',
279.         '5', '5', '5', '5', '5', '5', '5', '5', '5', '5',
280.         '6', '6', '6', '6', '6', '6', '6', '6', '6', '6',
281.         '7', '7', '7', '7', '7', '7', '7', '7', '7', '7',
282.         '8', '8', '8', '8', '8', '8', '8', '8', '8', '8',
283.         '9', '9', '9', '9', '9', '9', '9', '9', '9', '9',
284.         } ;
285.  
286.     final static char [] DigitOnes = {
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.         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
297.         } ;
298.  
299.         // I use the "invariant division by multiplication" trick to
300.         // accelerate Integer.toString.  In particular we want to
301.         // avoid division by 10.
302.         //
303.         // The "trick" has roughly the same performance characteristics
304.         // as the "classic" Integer.toString code on a non-JIT VM.
305.         // The trick avoids .rem and .div calls but has a longer code
306.         // path and is thus dominated by dispatch overhead.  In the
307.         // JIT case the dispatch overhead doesn't exist and the
308.         // "trick" is considerably faster than the classic code.
309.         //
310.         // TODO-FIXME: convert (x * 52429) into the equiv shift-add
311.         // sequence.
312.         //
313.         // RE:  Division by Invariant Integers using Multiplication
314.         //      T Gralund, P Montgomery
315.         //      ACM PLDI 1994
316.         //
317.  
318.     /**
319.      * Returns a {@code String} object representing the
320.      * specified integer. The argument is converted to signed decimal
321.      * representation and returned as a string, exactly as if the
322.      * argument and radix 10 were given as arguments to the {@link
323.      * #toString(int, int)} method.
324.      *
325.      * @param   i   an integer to be converted.
326.      * @return  a string representation of the argument in base&nbsp;10.
327.      */
328.     public static String toString(int i) {
329.         if (i == Integer.MIN_VALUE)
330.             return "-2147483648";
331.         int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
332.         char[] buf = new char[size];
333.         getChars(i, size, buf);
334.         return new String(buf, true);
335.     }
336.  
337.     /**
338.      * Places characters representing the integer i into the
339.      * character array buf. The characters are placed into
340.      * the buffer backwards starting with the least significant
341.      * digit at the specified index (exclusive), and working
342.      * backwards from there.
343.      *
344.      * Will fail if i == Integer.MIN_VALUE
345.      */
346.     static void getChars(int i, int index, char[] buf) {
347.         int q, r;
348.         int charPos = index;
349.         char sign = 0;
350.  
351.         if (i < 0) {
352.             sign = '-';
353.             i = -i;
354.         }
355.  
356.         // Generate two digits per iteration
357.         while (i >= 65536) {
358.             q = i / 100;
359.         // really: r = i - (q * 100);
360.             r = i - ((q << 6) + (q << 5) + (q << 2));
361.             i = q;
362.             buf [--charPos] = DigitOnes[r];
363.             buf [--charPos] = DigitTens[r];
364.         }
365.  
366.         // Fall thru to fast mode for smaller numbers
367.         // assert(i <= 65536, i);
368.         for (;;) {
369.             q = (i * 52429) >>> (16+3);
370.             r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
371.             buf [--charPos] = digits [r];
372.             i = q;
373.             if (i == 0) break;
374.         }
375.         if (sign != 0) {
376.             buf [--charPos] = sign;
377.         }
378.     }
379.  
380.     final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
381.                                       99999999, 999999999, Integer.MAX_VALUE };
382.  
383.     // Requires positive x
384.     static int stringSize(int x) {
385.         for (int i=0; ; i++)
386.             if (x <= sizeTable[i])
387.                 return i+1;
388.     }
389.  
390.     /**
391.      * Parses the string argument as a signed integer in the radix
392.      * specified by the second argument. The characters in the string
393.      * must all be digits of the specified radix (as determined by
394.      * whether {@link java.lang.Character#digit(char, int)} returns a
395.      * nonnegative value), except that the first character may be an
396.      * ASCII minus sign {@code '-'} (<code>'&#92;u002D'</code>) to
397.      * indicate a negative value or an ASCII plus sign {@code '+'}
398.      * (<code>'&#92;u002B'</code>) to indicate a positive value. The
399.      * resulting integer value is returned.
400.      *
401.      * <p>An exception of type {@code NumberFormatException} is
402.      * thrown if any of the following situations occurs:
403.      * <ul>
404.      * <li>The first argument is {@code null} or is a string of
405.      * length zero.
406.      *
407.      * <li>The radix is either smaller than
408.      * {@link java.lang.Character#MIN_RADIX} or
409.      * larger than {@link java.lang.Character#MAX_RADIX}.
410.      *
411.      * <li>Any character of the string is not a digit of the specified
412.      * radix, except that the first character may be a minus sign
413.      * {@code '-'} (<code>'&#92;u002D'</code>) or plus sign
414.      * {@code '+'} (<code>'&#92;u002B'</code>) provided that the
415.      * string is longer than length 1.
416.      *
417.      * <li>The value represented by the string is not a value of type
418.      * {@code int}.
419.      * </ul>
420.      *
421.      * <p>Examples:
422.      * <blockquote><pre>
423.      * parseInt("0", 10) returns 0
424.      * parseInt("473", 10) returns 473
425.      * parseInt("+42", 10) returns 42
426.      * parseInt("-0", 10) returns 0
427.      * parseInt("-FF", 16) returns -255
428.      * parseInt("1100110", 2) returns 102
429.      * parseInt("2147483647", 10) returns 2147483647
430.      * parseInt("-2147483648", 10) returns -2147483648
431.      * parseInt("2147483648", 10) throws a NumberFormatException
432.      * parseInt("99", 8) throws a NumberFormatException
433.      * parseInt("Kona", 10) throws a NumberFormatException
434.      * parseInt("Kona", 27) returns 411787
435.      * </pre></blockquote>
436.      *
437.      * @param      s   the {@code String} containing the integer
438.      *                  representation to be parsed
439.      * @param      radix   the radix to be used while parsing {@code s}.
440.      * @return     the integer represented by the string argument in the
441.      *             specified radix.
442.      * @exception  NumberFormatException if the {@code String}
443.      *             does not contain a parsable {@code int}.
444.      */
445.     public static int parseInt(String s, int radix)
446.                 throws NumberFormatException
447.     {
448.         /*
449.          * WARNING: This method may be invoked early during VM initialization
450.          * before IntegerCache is initialized. Care must be taken to not use
451.          * the valueOf method.
452.          */
453.  
454.         if (s == null) {
455.             throw new NumberFormatException("null");
456.         }
457.  
458.         if (radix < Character.MIN_RADIX) {
459.             throw new NumberFormatException("radix " + radix +
460.                                             " less than Character.MIN_RADIX");
461.         }
462.  
463.         if (radix > Character.MAX_RADIX) {
464.             throw new NumberFormatException("radix " + radix +
465.                                             " greater than Character.MAX_RADIX");
466.         }
467.  
468.         int result = 0;
469.         boolean negative = false;
470.         int i = 0, len = s.length();
471.         int limit = -Integer.MAX_VALUE;
472.         int multmin;
473.         int digit;
474.  
475.         if (len > 0) {
476.             char firstChar = s.charAt(0);
477.             if (firstChar < '0') { // Possible leading "+" or "-"
478.                 if (firstChar == '-') {
479.                     negative = true;
480.                     limit = Integer.MIN_VALUE;
481.                 } else if (firstChar != '+')
482.                     throw NumberFormatException.forInputString(s);
483.  
484.                 if (len == 1) // Cannot have lone "+" or "-"
485.                     throw NumberFormatException.forInputString(s);
486.                 i++;
487.             }
488.             multmin = limit / radix;
489.             while (i < len) {
490.                 // Accumulating negatively avoids surprises near MAX_VALUE
491.                 digit = Character.digit(s.charAt(i++),radix);
492.                 if (digit < 0) {
493.                     throw NumberFormatException.forInputString(s);
494.                 }
495.                 if (result < multmin) {
496.                     throw NumberFormatException.forInputString(s);
497.                 }
498.                 result *= radix;
499.                 if (result < limit + digit) {
500.                     throw NumberFormatException.forInputString(s);
501.                 }
502.                 result -= digit;
503.             }
504.         } else {
505.             throw NumberFormatException.forInputString(s);
506.         }
507.         return negative ? result : -result;
508.     }
509.  
510.     /**
511.      * Parses the string argument as a signed decimal integer. The
512.      * characters in the string must all be decimal digits, except
513.      * that the first character may be an ASCII minus sign {@code '-'}
514.      * (<code>'&#92;u002D'</code>) to indicate a negative value or an
515.      * ASCII plus sign {@code '+'} (<code>'&#92;u002B'</code>) to
516.      * indicate a positive value. The resulting integer value is
517.      * returned, exactly as if the argument and the radix 10 were
518.      * given as arguments to the {@link #parseInt(java.lang.String,
519.      * int)} method.
520.      *
521.      * @param s    a {@code String} containing the {@code int}
522.      *             representation to be parsed
523.      * @return     the integer value represented by the argument in decimal.
524.      * @exception  NumberFormatException  if the string does not contain a
525.      *               parsable integer.
526.      */
527.     public static int parseInt(String s) throws NumberFormatException {
528.         return parseInt(s,10);
529.     }
530.  
531.     /**
532.      * Returns an {@code Integer} object holding the value
533.      * extracted from the specified {@code String} when parsed
534.      * with the radix given by the second argument. The first argument
535.      * is interpreted as representing a signed integer in the radix
536.      * specified by the second argument, exactly as if the arguments
537.      * were given to the {@link #parseInt(java.lang.String, int)}
538.      * method. The result is an {@code Integer} object that
539.      * represents the integer value specified by the string.
540.      *
541.      * <p>In other words, this method returns an {@code Integer}
542.      * object equal to the value of:
543.      *
544.      * <blockquote>
545.      *  {@code new Integer(Integer.parseInt(s, radix))}
546.      * </blockquote>
547.      *
548.      * @param      s   the string to be parsed.
549.      * @param      radix the radix to be used in interpreting {@code s}
550.      * @return     an {@code Integer} object holding the value
551.      *             represented by the string argument in the specified
552.      *             radix.
553.      * @exception NumberFormatException if the {@code String}
554.      *            does not contain a parsable {@code int}.
555.      */
556.     public static Integer valueOf(String s, int radix) throws NumberFormatException {
557.         return Integer.valueOf(parseInt(s,radix));
558.     }
559.  
560.     /**
561.      * Returns an {@code Integer} object holding the
562.      * value of the specified {@code String}. The argument is
563.      * interpreted as representing a signed decimal integer, exactly
564.      * as if the argument were given to the {@link
565.      * #parseInt(java.lang.String)} method. The result is an
566.      * {@code Integer} object that represents the integer value
567.      * specified by the string.
568.      *
569.      * <p>In other words, this method returns an {@code Integer}
570.      * object equal to the value of:
571.      *
572.      * <blockquote>
573.      *  {@code new Integer(Integer.parseInt(s))}
574.      * </blockquote>
575.      *
576.      * @param      s   the string to be parsed.
577.      * @return     an {@code Integer} object holding the value
578.      *             represented by the string argument.
579.      * @exception  NumberFormatException  if the string cannot be parsed
580.      *             as an integer.
581.      */
582.     public static Integer valueOf(String s) throws NumberFormatException {
583.         return Integer.valueOf(parseInt(s, 10));
584.     }
585.  
586.     /**
587.      * Cache to support the object identity semantics of autoboxing for values between
588.      * -128 and 127 (inclusive) as required by JLS.
589.      *
590.      * The cache is initialized on first usage.  The size of the cache
591.      * may be controlled by the -XX:AutoBoxCacheMax=<size> option.
592.      * During VM initialization, java.lang.Integer.IntegerCache.high property
593.      * may be set and saved in the private system properties in the
594.      * sun.misc.VM class.
595.      */
596.  
597.     private static class IntegerCache {
598.         static final int low = -128;
599.         static final int high;
600.         static final Integer cache[];
601.  
602.         static {
603.             // high value may be configured by property
604.             int h = 127;
605.             String integerCacheHighPropValue =
606.                 sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
607.             if (integerCacheHighPropValue != null) {
608.                 int i = parseInt(integerCacheHighPropValue);
609.                 i = Math.max(i, 127);
610.                 // Maximum array size is Integer.MAX_VALUE
611.                 h = Math.min(i, Integer.MAX_VALUE - (-low));
612.             }
613.             high = h;
614.  
615.             cache = new Integer[(high - low) + 1];
616.             int j = low;
617.             for(int k = 0; k < cache.length; k++)
618.                 cache[k] = new Integer(j++);
619.         }
620.  
621.         private IntegerCache() {}
622.     }
623.  
624.     /**
625.      * Returns an {@code Integer} instance representing the specified
626.      * {@code int} value.  If a new {@code Integer} instance is not
627.      * required, this method should generally be used in preference to
628.      * the constructor {@link #Integer(int)}, as this method is likely
629.      * to yield significantly better space and time performance by
630.      * caching frequently requested values.
631.      *
632.      * This method will always cache values in the range -128 to 127,
633.      * inclusive, and may cache other values outside of this range.
634.      *
635.      * @param  i an {@code int} value.
636.      * @return an {@code Integer} instance representing {@code i}.
637.      * @since  1.5
638.      */
639.     public static Integer valueOf(int i) {
640.         assert IntegerCache.high >= 127;
641.         if (i >= IntegerCache.low && i <= IntegerCache.high)
642.             return IntegerCache.cache[i + (-IntegerCache.low)];
643.         return new Integer(i);
644.     }
645.  
646.     /**
647.      * The value of the {@code Integer}.
648.      *
649.      * @serial
650.      */
651.     private final int value;
652.  
653.     /**
654.      * Constructs a newly allocated {@code Integer} object that
655.      * represents the specified {@code int} value.
656.      *
657.      * @param   value   the value to be represented by the
658.      *                  {@code Integer} object.
659.      */
660.     public Integer(int value) {
661.         this.value = value;
662.     }
663.  
664.     /**
665.      * Constructs a newly allocated {@code Integer} object that
666.      * represents the {@code int} value indicated by the
667.      * {@code String} parameter. The string is converted to an
668.      * {@code int} value in exactly the manner used by the
669.      * {@code parseInt} method for radix 10.
670.      *
671.      * @param      s   the {@code String} to be converted to an
672.      *                 {@code Integer}.
673.      * @exception  NumberFormatException  if the {@code String} does not
674.      *               contain a parsable integer.
675.      * @see        java.lang.Integer#parseInt(java.lang.String, int)
676.      */
677.     public Integer(String s) throws NumberFormatException {
678.         this.value = parseInt(s, 10);
679.     }
680.  
681.     /**
682.      * Returns the value of this {@code Integer} as a
683.      * {@code byte}.
684.      */
685.     public byte byteValue() {
686.         return (byte)value;
687.     }
688.  
689.     /**
690.      * Returns the value of this {@code Integer} as a
691.      * {@code short}.
692.      */
693.     public short shortValue() {
694.         return (short)value;
695.     }
696.  
697.     /**
698.      * Returns the value of this {@code Integer} as an
699.      * {@code int}.
700.      */
701.     public int intValue() {
702.         return value;
703.     }
704.  
705.     /**
706.      * Returns the value of this {@code Integer} as a
707.      * {@code long}.
708.      */
709.     public long longValue() {
710.         return (long)value;
711.     }
712.  
713.     /**
714.      * Returns the value of this {@code Integer} as a
715.      * {@code float}.
716.      */
717.     public float floatValue() {
718.         return (float)value;
719.     }
720.  
721.     /**
722.      * Returns the value of this {@code Integer} as a
723.      * {@code double}.
724.      */
725.     public double doubleValue() {
726.         return (double)value;
727.     }
728.  
729.     /**
730.      * Returns a {@code String} object representing this
731.      * {@code Integer}'s value. The value is converted to signed
732.      * decimal representation and returned as a string, exactly as if
733.      * the integer value were given as an argument to the {@link
734.      * java.lang.Integer#toString(int)} method.
735.      *
736.      * @return  a string representation of the value of this object in
737.      *          base&nbsp;10.
738.      */
739.     public String toString() {
740.         return toString(value);
741.     }
742.  
743.     /**
744.      * Returns a hash code for this {@code Integer}.
745.      *
746.      * @return  a hash code value for this object, equal to the
747.      *          primitive {@code int} value represented by this
748.      *          {@code Integer} object.
749.      */
750.     public int hashCode() {
751.         return value;
752.     }
753.  
754.     /**
755.      * Compares this object to the specified object.  The result is
756.      * {@code true} if and only if the argument is not
757.      * {@code null} and is an {@code Integer} object that
758.      * contains the same {@code int} value as this object.
759.      *
760.      * @param   obj   the object to compare with.
761.      * @return  {@code true} if the objects are the same;
762.      *          {@code false} otherwise.
763.      */
764.     public boolean equals(Object obj) {
765.         if (obj instanceof Integer) {
766.             return value == ((Integer)obj).intValue();
767.         }
768.         return false;
769.     }
770.  
771.     /**
772.      * Determines the integer value of the system property with the
773.      * specified name.
774.      *
775.      * <p>The first argument is treated as the name of a system property.
776.      * System properties are accessible through the
777.      * {@link java.lang.System#getProperty(java.lang.String)} method. The
778.      * string value of this property is then interpreted as an integer
779.      * value and an {@code Integer} object representing this value is
780.      * returned. Details of possible numeric formats can be found with
781.      * the definition of {@code getProperty}.
782.      *
783.      * <p>If there is no property with the specified name, if the specified name
784.      * is empty or {@code null}, or if the property does not have
785.      * the correct numeric format, then {@code null} is returned.
786.      *
787.      * <p>In other words, this method returns an {@code Integer}
788.      * object equal to the value of:
789.      *
790.      * <blockquote>
791.      *  {@code getInteger(nm, null)}
792.      * </blockquote>
793.      *
794.      * @param   nm   property name.
795.      * @return  the {@code Integer} value of the property.
796.      * @see     java.lang.System#getProperty(java.lang.String)
797.      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
798.      */
799.     public static Integer getInteger(String nm) {
800.         return getInteger(nm, null);
801.     }
802.  
803.     /**
804.      * Determines the integer value of the system property with the
805.      * specified name.
806.      *
807.      * <p>The first argument is treated as the name of a system property.
808.      * System properties are accessible through the {@link
809.      * java.lang.System#getProperty(java.lang.String)} method. The
810.      * string value of this property is then interpreted as an integer
811.      * value and an {@code Integer} object representing this value is
812.      * returned. Details of possible numeric formats can be found with
813.      * the definition of {@code getProperty}.
814.      *
815.      * <p>The second argument is the default value. An {@code Integer} object
816.      * that represents the value of the second argument is returned if there
817.      * is no property of the specified name, if the property does not have
818.      * the correct numeric format, or if the specified name is empty or
819.      * {@code null}.
820.      *
821.      * <p>In other words, this method returns an {@code Integer} object
822.      * equal to the value of:
823.      *
824.      * <blockquote>
825.      *  {@code getInteger(nm, new Integer(val))}
826.      * </blockquote>
827.      *
828.      * but in practice it may be implemented in a manner such as:
829.      *
830.      * <blockquote><pre>
831.      * Integer result = getInteger(nm, null);
832.      * return (result == null) ? new Integer(val) : result;
833.      * </pre></blockquote>
834.      *
835.      * to avoid the unnecessary allocation of an {@code Integer}
836.      * object when the default value is not needed.
837.      *
838.      * @param   nm   property name.
839.      * @param   val   default value.
840.      * @return  the {@code Integer} value of the property.
841.      * @see     java.lang.System#getProperty(java.lang.String)
842.      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
843.      */
844.     public static Integer getInteger(String nm, int val) {
845.         Integer result = getInteger(nm, null);
846.         return (result == null) ? Integer.valueOf(val) : result;
847.     }
848.  
849.     /**
850.      * Returns the integer value of the system property with the
851.      * specified name.  The first argument is treated as the name of a
852.      * system property.  System properties are accessible through the
853.      * {@link java.lang.System#getProperty(java.lang.String)} method.
854.      * The string value of this property is then interpreted as an
855.      * integer value, as per the {@code Integer.decode} method,
856.      * and an {@code Integer} object representing this value is
857.      * returned.
858.      *
859.      * <ul><li>If the property value begins with the two ASCII characters
860.      *         {@code 0x} or the ASCII character {@code #}, not
861.      *      followed by a minus sign, then the rest of it is parsed as a
862.      *      hexadecimal integer exactly as by the method
863.      *      {@link #valueOf(java.lang.String, int)} with radix 16.
864.      * <li>If the property value begins with the ASCII character
865.      *     {@code 0} followed by another character, it is parsed as an
866.      *     octal integer exactly as by the method
867.      *     {@link #valueOf(java.lang.String, int)} with radix 8.
868.      * <li>Otherwise, the property value is parsed as a decimal integer
869.      * exactly as by the method {@link #valueOf(java.lang.String, int)}
870.      * with radix 10.
871.      * </ul>
872.      *
873.      * <p>The second argument is the default value. The default value is
874.      * returned if there is no property of the specified name, if the
875.      * property does not have the correct numeric format, or if the
876.      * specified name is empty or {@code null}.
877.      *
878.      * @param   nm   property name.
879.      * @param   val   default value.
880.      * @return  the {@code Integer} value of the property.
881.      * @see     java.lang.System#getProperty(java.lang.String)
882.      * @see java.lang.System#getProperty(java.lang.String, java.lang.String)
883.      * @see java.lang.Integer#decode
884.      */
885.     public static Integer getInteger(String nm, Integer val) {
886.         String v = null;
887.         try {
888.             v = System.getProperty(nm);
889.         } catch (IllegalArgumentException e) {
890.         } catch (NullPointerException e) {
891.         }
892.         if (v != null) {
893.             try {
894.                 return Integer.decode(v);
895.             } catch (NumberFormatException e) {
896.             }
897.         }
898.         return val;
899.     }
900.  
901.     /**
902.      * Decodes a {@code String} into an {@code Integer}.
903.      * Accepts decimal, hexadecimal, and octal numbers given
904.      * by the following grammar:
905.      *
906.      * <blockquote>
907.      * <dl>
908.      * <dt><i>DecodableString:</i>
909.      * <dd><i>Sign_opt DecimalNumeral</i>
910.      * <dd><i>Sign_opt</i> {@code 0x} <i>HexDigits</i>
911.      * <dd><i>Sign_opt</i> {@code 0X} <i>HexDigits</i>
912.      * <dd><i>Sign_opt</i> {@code #} <i>HexDigits</i>
913.      * <dd><i>Sign_opt</i> {@code 0} <i>OctalDigits</i>
914.      * <p>
915.      * <dt><i>Sign:</i>
916.      * <dd>{@code -}
917.      * <dd>{@code +}
918.      * </dl>
919.      * </blockquote>
920.      *
921.      * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
922.      * are as defined in section 3.10.1 of
923.      * <cite>The Java&trade; Language Specification</cite>,
924.      * except that underscores are not accepted between digits.
925.      *
926.      * <p>The sequence of characters following an optional
927.      * sign and/or radix specifier ("{@code 0x}", "{@code 0X}",
928.      * "{@code #}", or leading zero) is parsed as by the {@code
929.      * Integer.parseInt} method with the indicated radix (10, 16, or
930.      * 8).  This sequence of characters must represent a positive
931.      * value or a {@link NumberFormatException} will be thrown.  The
932.      * result is negated if first character of the specified {@code
933.      * String} is the minus sign.  No whitespace characters are
934.      * permitted in the {@code String}.
935.      *
936.      * @param     nm the {@code String} to decode.
937.      * @return    an {@code Integer} object holding the {@code int}
938.      *             value represented by {@code nm}
939.      * @exception NumberFormatException  if the {@code String} does not
940.      *            contain a parsable integer.
941.      * @see java.lang.Integer#parseInt(java.lang.String, int)
942.      */
943.     public static Integer decode(String nm) throws NumberFormatException {
944.         int radix = 10;
945.         int index = 0;
946.         boolean negative = false;
947.         Integer result;
948.  
949.         if (nm.length() == 0)
950.             throw new NumberFormatException("Zero length string");
951.         char firstChar = nm.charAt(0);
952.         // Handle sign, if present
953.         if (firstChar == '-') {
954.             negative = true;
955.             index++;
956.         } else if (firstChar == '+')
957.             index++;
958.  
959.         // Handle radix specifier, if present
960.         if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
961.             index += 2;
962.             radix = 16;
963.         }
964.         else if (nm.startsWith("#", index)) {
965.             index ++;
966.             radix = 16;
967.         }
968.         else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
969.             index ++;
970.             radix = 8;
971.         }
972.  
973.         if (nm.startsWith("-", index) || nm.startsWith("+", index))
974.             throw new NumberFormatException("Sign character in wrong position");
975.  
976.         try {
977.             result = Integer.valueOf(nm.substring(index), radix);
978.             result = negative ? Integer.valueOf(-result.intValue()) : result;
979.         } catch (NumberFormatException e) {
980.             // If number is Integer.MIN_VALUE, we'll end up here. The next line
981.             // handles this case, and causes any genuine format error to be
982.             // rethrown.
983.             String constant = negative ? ("-" + nm.substring(index))
984.                                        : nm.substring(index);
985.             result = Integer.valueOf(constant, radix);
986.         }
987.         return result;
988.     }
989.  
990.     /**
991.      * Compares two {@code Integer} objects numerically.
992.      *
993.      * @param   anotherInteger   the {@code Integer} to be compared.
994.      * @return  the value {@code 0} if this {@code Integer} is
995.      *          equal to the argument {@code Integer}; a value less than
996.      *          {@code 0} if this {@code Integer} is numerically less
997.      *          than the argument {@code Integer}; and a value greater
998.      *          than {@code 0} if this {@code Integer} is numerically
999.      *           greater than the argument {@code Integer} (signed
1000.      *           comparison).
1001.      * @since   1.2
1002.      */
1003.     public int compareTo(Integer anotherInteger) {
1004.         return compare(this.value, anotherInteger.value);
1005.     }
1006.  
1007.     /**
1008.      * Compares two {@code int} values numerically.
1009.      * The value returned is identical to what would be returned by:
1010.      * <pre>
1011.      *    Integer.valueOf(x).compareTo(Integer.valueOf(y))
1012.      * </pre>
1013.      *
1014.      * @param  x the first {@code int} to compare
1015.      * @param  y the second {@code int} to compare
1016.      * @return the value {@code 0} if {@code x == y};
1017.      *         a value less than {@code 0} if {@code x < y}; and
1018.      *         a value greater than {@code 0} if {@code x > y}
1019.      * @since 1.7
1020.      */
1021.     public static int compare(int x, int y) {
1022.         return (x < y) ? -1 : ((x == y) ? 0 : 1);
1023.     }
1024.  
1025.  
1026.     // Bit twiddling
1027.  
1028.     /**
1029.      * The number of bits used to represent an {@code int} value in two's
1030.      * complement binary form.
1031.      *
1032.      * @since 1.5
1033.      */
1034.     public static final int SIZE = 32;
1035.  
1036.     /**
1037.      * Returns an {@code int} value with at most a single one-bit, in the
1038.      * position of the highest-order ("leftmost") one-bit in the specified
1039.      * {@code int} value.  Returns zero if the specified value has no
1040.      * one-bits in its two's complement binary representation, that is, if it
1041.      * is equal to zero.
1042.      *
1043.      * @return an {@code int} value with a single one-bit, in the position
1044.      *     of the highest-order one-bit in the specified value, or zero if
1045.      *     the specified value is itself equal to zero.
1046.      * @since 1.5
1047.      */
1048.     public static int highestOneBit(int i) {
1049.         // HD, Figure 3-1
1050.         i |= (i >>  1);
1051.         i |= (i >>  2);
1052.         i |= (i >>  4);
1053.         i |= (i >>  8);
1054.         i |= (i >> 16);
1055.         return i - (i >>> 1);
1056.     }
1057.  
1058.     /**
1059.      * Returns an {@code int} value with at most a single one-bit, in the
1060.      * position of the lowest-order ("rightmost") one-bit in the specified
1061.      * {@code int} value.  Returns zero if the specified value has no
1062.      * one-bits in its two's complement binary representation, that is, if it
1063.      * is equal to zero.
1064.      *
1065.      * @return an {@code int} value with a single one-bit, in the position
1066.      *     of the lowest-order one-bit in the specified value, or zero if
1067.      *     the specified value is itself equal to zero.
1068.      * @since 1.5
1069.      */
1070.     public static int lowestOneBit(int i) {
1071.         // HD, Section 2-1
1072.         return i & -i;
1073.     }
1074.  
1075.     /**
1076.      * Returns the number of zero bits preceding the highest-order
1077.      * ("leftmost") one-bit in the two's complement binary representation
1078.      * of the specified {@code int} value.  Returns 32 if the
1079.      * specified value has no one-bits in its two's complement representation,
1080.      * in other words if it is equal to zero.
1081.      *
1082.      * <p>Note that this method is closely related to the logarithm base 2.
1083.      * For all positive {@code int} values x:
1084.      * <ul>
1085.      * <li>floor(log₂(x)) = {@code 31 - numberOfLeadingZeros(x)}
1086.      * <li>ceil(log₂(x)) = {@code 32 - numberOfLeadingZeros(x - 1)}
1087.      * </ul>
1088.      *
1089.      * @return the number of zero bits preceding the highest-order
1090.      *     ("leftmost") one-bit in the two's complement binary representation
1091.      *     of the specified {@code int} value, or 32 if the value
1092.      *     is equal to zero.
1093.      * @since 1.5
1094.      */
1095.     public static int numberOfLeadingZeros(int i) {
1096.         // HD, Figure 5-6
1097.         if (i == 0)
1098.             return 32;
1099.         int n = 1;
1100.         if (i >>> 16 == 0) { n += 16; i <<= 16; }
1101.         if (i >>> 24 == 0) { n +=  8; i <<=  8; }
1102.         if (i >>> 28 == 0) { n +=  4; i <<=  4; }
1103.         if (i >>> 30 == 0) { n +=  2; i <<=  2; }
1104.         n -= i >>> 31;
1105.         return n;
1106.     }
1107.  
1108.     /**
1109.      * Returns the number of zero bits following the lowest-order ("rightmost")
1110.      * one-bit in the two's complement binary representation of the specified
1111.      * {@code int} value.  Returns 32 if the specified value has no
1112.      * one-bits in its two's complement representation, in other words if it is
1113.      * equal to zero.
1114.      *
1115.      * @return the number of zero bits following the lowest-order ("rightmost")
1116.      *     one-bit in the two's complement binary representation of the
1117.      *     specified {@code int} value, or 32 if the value is equal
1118.      *     to zero.
1119.      * @since 1.5
1120.      */
1121.     public static int numberOfTrailingZeros(int i) {
1122.         // HD, Figure 5-14
1123.         int y;
1124.         if (i == 0) return 32;
1125.         int n = 31;
1126.         y = i <<16; if (y != 0) { n = n -16; i = y; }
1127.         y = i << 8; if (y != 0) { n = n - 8; i = y; }
1128.         y = i << 4; if (y != 0) { n = n - 4; i = y; }
1129.         y = i << 2; if (y != 0) { n = n - 2; i = y; }
1130.         return n - ((i << 1) >>> 31);
1131.     }
1132.  
1133.     /**
1134.      * Returns the number of one-bits in the two's complement binary
1135.      * representation of the specified {@code int} value.  This function is
1136.      * sometimes referred to as the <i>population count</i>.
1137.      *
1138.      * @return the number of one-bits in the two's complement binary
1139.      *     representation of the specified {@code int} value.
1140.      * @since 1.5
1141.      */
1142.     public static int bitCount(int i) {
1143.         // HD, Figure 5-2
1144.         i = i - ((i >>> 1) & 0x55555555);
1145.         i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
1146.         i = (i + (i >>> 4)) & 0x0f0f0f0f;
1147.         i = i + (i >>> 8);
1148.         i = i + (i >>> 16);
1149.         return i & 0x3f;
1150.     }
1151.  
1152.     /**
1153.      * Returns the value obtained by rotating the two's complement binary
1154.      * representation of the specified {@code int} value left by the
1155.      * specified number of bits.  (Bits shifted out of the left hand, or
1156.      * high-order, side reenter on the right, or low-order.)
1157.      *
1158.      * <p>Note that left rotation with a negative distance is equivalent to
1159.      * right rotation: {@code rotateLeft(val, -distance) == rotateRight(val,
1160.      * distance)}.  Note also that rotation by any multiple of 32 is a
1161.      * no-op, so all but the last five bits of the rotation distance can be
1162.      * ignored, even if the distance is negative: {@code rotateLeft(val,
1163.      * distance) == rotateLeft(val, distance & 0x1F)}.
1164.      *
1165.      * @return the value obtained by rotating the two's complement binary
1166.      *     representation of the specified {@code int} value left by the
1167.      *     specified number of bits.
1168.      * @since 1.5
1169.      */
1170.     public static int rotateLeft(int i, int distance) {
1171.         return (i << distance) | (i >>> -distance);
1172.     }
1173.  
1174.     /**
1175.      * Returns the value obtained by rotating the two's complement binary
1176.      * representation of the specified {@code int} value right by the
1177.      * specified number of bits.  (Bits shifted out of the right hand, or
1178.      * low-order, side reenter on the left, or high-order.)
1179.      *
1180.      * <p>Note that right rotation with a negative distance is equivalent to
1181.      * left rotation: {@code rotateRight(val, -distance) == rotateLeft(val,
1182.      * distance)}.  Note also that rotation by any multiple of 32 is a
1183.      * no-op, so all but the last five bits of the rotation distance can be
1184.      * ignored, even if the distance is negative: {@code rotateRight(val,
1185.      * distance) == rotateRight(val, distance & 0x1F)}.
1186.      *
1187.      * @return the value obtained by rotating the two's complement binary
1188.      *     representation of the specified {@code int} value right by the
1189.      *     specified number of bits.
1190.      * @since 1.5
1191.      */
1192.     public static int rotateRight(int i, int distance) {
1193.         return (i >>> distance) | (i << -distance);
1194.     }
1195.  
1196.     /**
1197.      * Returns the value obtained by reversing the order of the bits in the
1198.      * two's complement binary representation of the specified {@code int}
1199.      * value.
1200.      *
1201.      * @return the value obtained by reversing order of the bits in the
1202.      *     specified {@code int} value.
1203.      * @since 1.5
1204.      */
1205.     public static int reverse(int i) {
1206.         // HD, Figure 7-1
1207.         i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
1208.         i = (i & 0x33333333) << 2 | (i >>> 2) & 0x33333333;
1209.         i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
1210.         i = (i << 24) | ((i & 0xff00) << 8) |
1211.             ((i >>> 8) & 0xff00) | (i >>> 24);
1212.         return i;
1213.     }
1214.  
1215.     /**
1216.      * Returns the signum function of the specified {@code int} value.  (The
1217.      * return value is -1 if the specified value is negative; 0 if the
1218.      * specified value is zero; and 1 if the specified value is positive.)
1219.      *
1220.      * @return the signum function of the specified {@code int} value.
1221.      * @since 1.5
1222.      */
1223.     public static int signum(int i) {
1224.         // HD, Section 2-7
1225.         return (i >> 31) | (-i >>> 31);
1226.     }
1227.  
1228.     /**
1229.      * Returns the value obtained by reversing the order of the bytes in the
1230.      * two's complement representation of the specified {@code int} value.
1231.      *
1232.      * @return the value obtained by reversing the bytes in the specified
1233.      *     {@code int} value.
1234.      * @since 1.5
1235.      */
1236.     public static int reverseBytes(int i) {
1237.         return ((i >>> 24)           ) |
1238.                ((i >>   8) &   0xFF00) |
1239.                ((i <<   8) & 0xFF0000) |
1240.                ((i << 24));
1241.     }
1242.  
1243.     /** use serialVersionUID from JDK 1.0.2 for interoperability */
1244.     private static final long serialVersionUID = 1360826667806852920L;
1245. }
1246.