Source Code of Java - Integer

/*
* %W% %E%
*
* Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/

package java.lang;

import java.util.Properties;

/**
* The <code>Integer</code> class wraps a value of the primitive type
* <code>int</code> in an object. An object of type
* <code>Integer</code> contains a single field whose type is
* <code>int</code>.
*
*  <p>
*
* In addition, this class provides several methods for converting an
* <code>int</code> to a <code>String</code> and a <code>String</code>
* to an <code>int</code>, as well as other constants and methods
* useful when dealing with an <code>int</code>.
*
* <p>Implementation note: The implementations of the "bit twiddling"
* methods (such as {@link #highestOneBit(int) highestOneBit} and
* {@link #numberOfTrailingZeros(int) numberOfTrailingZeros}) are
* based on material from Henry S. Warren, Jr.'s <i>Hacker's
* Delight</i>, (Addison Wesley, 2002).
*
* @author  Lee Boynton
* @author  Arthur van Hoff
* @author  Josh Bloch
* @version %I%, %G%
* @since JDK1.0
*/
public final class Integer extends Number implements Comparable<Integer> {
/**
* A constant holding the minimum value an <code>int</code> can
* have, -2<sup>31</sup>.
*/
public static final int   MIN_VALUE = 0x80000000;

/**
* A constant holding the maximum value an <code>int</code> can
* have, 2<sup>31</sup>-1.
*/
public static final int   MAX_VALUE = 0x7fffffff;

/**
* The <code>Class</code> instance representing the primitive type
* <code>int</code>.
*
* @since   JDK1.1
*/
public static final Class<Integer>  TYPE = (Class<Integer>) Class.getPrimitiveClass("int");

/**
* All possible chars for representing a number as a String
*/
final static char[] digits = {
'0' , '1' , '2' , '3' , '4' , '5' ,
'6' , '7' , '8' , '9' , 'a' , 'b' ,
'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
'o' , 'p' , 'q' , 'r' , 's' , 't' ,
'u' , 'v' , 'w' , 'x' , 'y' , 'z'
};

/**
* Returns a string representation of the first argument in the
* radix specified by the second argument.
* <p>
* If the radix is smaller than <code>Character.MIN_RADIX</code>
* or larger than <code>Character.MAX_RADIX</code>, then the radix
* <code>10</code> is used instead.
* <p>
* If the first argument is negative, the first element of the
* result is the ASCII minus character <code>'-'</code>
* (<code>'\u002D'</code>). If the first argument is not
* negative, no sign character appears in the result.
* <p>
* The remaining characters of the result represent the magnitude
* of the first argument. If the magnitude is zero, it is
* represented by a single zero character <code>'0'</code>
* (<code>'\u0030'</code>); otherwise, the first character of
* the representation of the magnitude will not be the zero
* character.  The following ASCII characters are used as digits:
* <blockquote><pre>
*   0123456789abcdefghijklmnopqrstuvwxyz
* </pre></blockquote>
* These are <code>'\u0030'</code> through
* <code>'\u0039'</code> and <code>'\u0061'</code> through
* <code>'\u007A'</code>. If <code>radix</code> is
* <var>N</var>, then the first <var>N</var> of these characters
* are used as radix-<var>N</var> digits in the order shown. Thus,
* the digits for hexadecimal (radix 16) are
* <code>0123456789abcdef</code>. If uppercase letters are
* desired, the {@link java.lang.String#toUpperCase()} method may
* be called on the result:
* <blockquote><pre>
* Integer.toString(n, 16).toUpperCase()
* </pre></blockquote>
*
* @param   i       an integer to be converted to a string.
* @param   radix   the radix to use in the string representation.
* @return  a string representation of the argument in the specified radix.
* @see     java.lang.Character#MAX_RADIX
* @see     java.lang.Character#MIN_RADIX
*/
public static String toString(int i, int radix) {

if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
radix = 10;

/* Use the faster version */
if (radix == 10) {
return toString(i);
}

char buf[] = new char[33];
boolean negative = (i < 0);
int charPos = 32;

if (!negative) {
i = -i;
}

while (i <= -radix) {
buf[charPos--] = digits[-(i % radix)];
i = i / radix;
}
buf[charPos] = digits[-i];

if (negative) {
buf[--charPos] = '-';
}

return new String(buf, charPos, (33 - charPos));
}

/**
* Returns a string representation of the integer argument as an
* unsigned integer in base 16.
* <p>
* The unsigned integer value is the argument plus 2<sup>32</sup>
* if the argument is negative; otherwise, it is equal to the
* argument.  This value is converted to a string of ASCII digits
* in hexadecimal (base 16) with no extra leading
* <code>0</code>s. If the unsigned magnitude is zero, it is
* represented by a single zero character <code>'0'</code>
* (<code>'\u0030'</code>); otherwise, the first character of
* the representation of the unsigned magnitude will not be the
* zero character. The following characters are used as
* hexadecimal digits:
* <blockquote><pre>
* 0123456789abcdef
* </pre></blockquote>
* These are the characters <code>'\u0030'</code> through
* <code>'\u0039'</code> and <code>'\u0061'</code> through
* <code>'\u0066'</code>. If uppercase letters are
* desired, the {@link java.lang.String#toUpperCase()} method may
* be called on the result:
* <blockquote><pre>
* Integer.toHexString(n).toUpperCase()
* </pre></blockquote>
*
* @param   i   an integer to be converted to a string.
* @return  the string representation of the unsigned integer value
*          represented by the argument in hexadecimal (base 16).
* @since   JDK1.0.2
*/
public static String toHexString(int i) {
return toUnsignedString(i, 4);
}

/**
* Returns a string representation of the integer argument as an
* unsigned integer in base 8.
* <p>
* The unsigned integer value is the argument plus 2<sup>32</sup>
* if the argument is negative; otherwise, it is equal to the
* argument.  This value is converted to a string of ASCII digits
* in octal (base 8) with no extra leading <code>0</code>s.
* <p>
* If the unsigned magnitude is zero, it is represented by a
* single zero character <code>'0'</code>
* (<code>'\u0030'</code>); otherwise, the first character of
* the representation of the unsigned magnitude will not be the
* zero character. The following characters are used as octal
* digits:
* <blockquote><pre>
* 01234567
* </pre></blockquote>
* These are the characters <code>'\u0030'</code> through
* <code>'\u0037'</code>.
*
* @param   i   an integer to be converted to a string.
* @return  the string representation of the unsigned integer value
*          represented by the argument in octal (base 8).
* @since   JDK1.0.2
*/
public static String toOctalString(int i) {
return toUnsignedString(i, 3);
}

/**
* Returns a string representation of the integer argument as an
* unsigned integer in base 2.
* <p>
* The unsigned integer value is the argument plus 2<sup>32</sup>
* if the argument is negative; otherwise it is equal to the
* argument.  This value is converted to a string of ASCII digits
* in binary (base 2) with no extra leading <code>0</code>s.
* If the unsigned magnitude is zero, it is represented by a
* single zero character <code>'0'</code>
* (<code>'\u0030'</code>); otherwise, the first character of
* the representation of the unsigned magnitude will not be the
* zero character. The characters <code>'0'</code>
* (<code>'\u0030'</code>) and <code>'1'</code>
* (<code>'\u0031'</code>) are used as binary digits.
*
* @param   i   an integer to be converted to a string.
* @return  the string representation of the unsigned integer value
*          represented by the argument in binary (base 2).
* @since   JDK1.0.2
*/
public static String toBinaryString(int i) {
return toUnsignedString(i, 1);
}

/**
* Convert the integer to an unsigned number.
*/
private static String toUnsignedString(int i, int shift) {
char[] buf = new char[32];
int charPos = 32;
int radix = 1 << shift;
int mask = radix - 1;
do {
buf[--charPos] = digits[i & mask];
i >>>= shift;
} while (i != 0);

return new String(buf, charPos, (32 - charPos));
}

final static char [] DigitTens = {
'0', '0', '0', '0', '0', '0', '0', '0', '0', '0',
'1', '1', '1', '1', '1', '1', '1', '1', '1', '1',
'2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
'3', '3', '3', '3', '3', '3', '3', '3', '3', '3',
'4', '4', '4', '4', '4', '4', '4', '4', '4', '4',
'5', '5', '5', '5', '5', '5', '5', '5', '5', '5',
'6', '6', '6', '6', '6', '6', '6', '6', '6', '6',
'7', '7', '7', '7', '7', '7', '7', '7', '7', '7',
'8', '8', '8', '8', '8', '8', '8', '8', '8', '8',
'9', '9', '9', '9', '9', '9', '9', '9', '9', '9',
} ;

final static char [] DigitOnes = {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
} ;

// I use the "invariant division by multiplication" trick to
// accelerate Integer.toString.  In particular we want to
// avoid division by 10.
//
// The "trick" has roughly the same performance characteristics
// as the "classic" Integer.toString code on a non-JIT VM.
// The trick avoids .rem and .div calls but has a longer code
// path and is thus dominated by dispatch overhead.  In the
// JIT case the dispatch overhead doesn't exist and the
// "trick" is considerably faster than the classic code.
//
// TODO-FIXME: convert (x * 52429) into the equiv shift-add
// sequence.
//
// RE:  Division by Invariant Integers using Multiplication
//      T Gralund, P Montgomery
//      ACM PLDI 1994
//

/**
* Returns a <code>String</code> object representing the
* specified integer. The argument is converted to signed decimal
* representation and returned as a string, exactly as if the
* argument and radix 10 were given as arguments to the {@link
* #toString(int, int)} method.
*
* @param   i   an integer to be converted.
* @return  a string representation of the argument in base 10.
*/
public static String toString(int i) {
if (i == Integer.MIN_VALUE)
return "-2147483648";
int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
char[] buf = new char[size];
getChars(i, size, buf);
return new String(0, size, buf);
}

/**
* Places characters representing the integer i into the
* character array buf. The characters are placed into
* the buffer backwards starting with the least significant
* digit at the specified index (exclusive), and working
* backwards from there.
*
* Will fail if i == Integer.MIN_VALUE
*/
static void getChars(int i, int index, char[] buf) {
int q, r;
int charPos = index;
char sign = 0;

if (i < 0) {
sign = '-';
i = -i;
}

// Generate two digits per iteration
while (i >= 65536) {
q = i / 100;
// really: r = i - (q * 100);
r = i - ((q << 6) + (q << 5) + (q << 2));
i = q;
buf [--charPos] = DigitOnes[r];
buf [--charPos] = DigitTens[r];
}

// Fall thru to fast mode for smaller numbers
// assert(i <= 65536, i);
for (;;) {
q = (i * 52429) >>> (16+3);
r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
buf [--charPos] = digits [r];
i = q;
if (i == 0) break;
}
if (sign != 0) {
buf [--charPos] = sign;
}
}

final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
99999999, 999999999, Integer.MAX_VALUE };

// Requires positive x
static int stringSize(int x) {
for (int i=0; ; i++)
if (x <= sizeTable[i])
return i+1;
}

/**
* Parses the string argument as a signed integer in the radix
* specified by the second argument. The characters in the string
* must all be digits of the specified radix (as determined by
* whether {@link java.lang.Character#digit(char, int)} returns a
* nonnegative value), except that the first character may be an
* ASCII minus sign <code>'-'</code> (<code>'\u002D'</code>) to
* indicate a negative value. The resulting integer value is returned.
* <p>
* An exception of type <code>NumberFormatException</code> is
* thrown if any of the following situations occurs:
* <ul>
* <li>The first argument is <code>null</code> or is a string of
* length zero.
* <li>The radix is either smaller than
* {@link java.lang.Character#MIN_RADIX} or
* larger than {@link java.lang.Character#MAX_RADIX}.
* <li>Any character of the string is not a digit of the specified
* radix, except that the first character may be a minus sign
* <code>'-'</code> (<code>'\u002D'</code>) provided that the
* string is longer than length 1.
* <li>The value represented by the string is not a value of type
* <code>int</code>.
* </ul><p>
* Examples:
* <blockquote><pre>
* parseInt("0", 10) returns 0
* parseInt("473", 10) returns 473
* parseInt("-0", 10) returns 0
* parseInt("-FF", 16) returns -255
* parseInt("1100110", 2) returns 102
* parseInt("2147483647", 10) returns 2147483647
* parseInt("-2147483648", 10) returns -2147483648
* parseInt("2147483648", 10) throws a NumberFormatException
* parseInt("99", 8) throws a NumberFormatException
* parseInt("Kona", 10) throws a NumberFormatException
* parseInt("Kona", 27) returns 411787
* </pre></blockquote>
*
* @param      s   the <code>String</code> containing the integer
*          representation to be parsed
* @param      radix   the radix to be used while parsing <code>s</code>.
* @return     the integer represented by the string argument in the
*             specified radix.
* @exception  NumberFormatException if the <code>String</code>
*         does not contain a parsable <code>int</code>.
*/
public static int parseInt(String s, int radix)
throws NumberFormatException
{
if (s == null) {
throw new NumberFormatException("null");
}

if (radix < Character.MIN_RADIX) {
throw new NumberFormatException("radix " + radix +
" less than Character.MIN_RADIX");
}

if (radix > Character.MAX_RADIX) {
throw new NumberFormatException("radix " + radix +
" greater than Character.MAX_RADIX");
}

int result = 0;
boolean negative = false;
int i = 0, max = s.length();
int limit;
int multmin;
int digit;

if (max > 0) {
if (s.charAt(0) == '-') {
negative = true;
limit = Integer.MIN_VALUE;
i++;
} else {
limit = -Integer.MAX_VALUE;
}
multmin = limit / radix;
if (i < max) {
digit = Character.digit(s.charAt(i++),radix);
if (digit < 0) {
throw NumberFormatException.forInputString(s);
} else {
result = -digit;
}
}
while (i < max) {
// Accumulating negatively avoids surprises near MAX_VALUE
digit = Character.digit(s.charAt(i++),radix);
if (digit < 0) {
throw NumberFormatException.forInputString(s);
}
if (result < multmin) {
throw NumberFormatException.forInputString(s);
}
result *= radix;
if (result < limit + digit) {
throw NumberFormatException.forInputString(s);
}
result -= digit;
}
} else {
throw NumberFormatException.forInputString(s);
}
if (negative) {
if (i > 1) {
return result;
} else {    /* Only got "-" */
throw NumberFormatException.forInputString(s);
}
} else {
return -result;
}
}

/**
* Parses the string argument as a signed decimal integer. The
* characters in the string must all be decimal digits, except that
* the first character may be an ASCII minus sign <code>'-'</code>
* (<code>'\u002D'</code>) to indicate a negative value. The resulting
* integer value is returned, exactly as if the argument and the radix
* 10 were given as arguments to the
* {@link #parseInt(java.lang.String, int)} method.
*
* @param s    a <code>String</code> containing the <code>int</code>
*             representation to be parsed
* @return     the integer value represented by the argument in decimal.
* @exception  NumberFormatException  if the string does not contain a
*               parsable integer.
*/
public static int parseInt(String s) throws NumberFormatException {
return parseInt(s,10);
}

/**
* Returns an <code>Integer</code> object holding the value
* extracted from the specified <code>String</code> when parsed
* with the radix given by the second argument. The first argument
* is interpreted as representing a signed integer in the radix
* specified by the second argument, exactly as if the arguments
* were given to the {@link #parseInt(java.lang.String, int)}
* method. The result is an <code>Integer</code> object that
* represents the integer value specified by the string.
* <p>
* In other words, this method returns an <code>Integer</code>
* object equal to the value of:
*
* <blockquote><code>
* new Integer(Integer.parseInt(s, radix))
* </code></blockquote>
*
* @param      s   the string to be parsed.
* @param      radix the radix to be used in interpreting <code>s</code>
* @return     an <code>Integer</code> object holding the value
*             represented by the string argument in the specified
*             radix.
* @exception NumberFormatException if the <code>String</code>
*        does not contain a parsable <code>int</code>.
*/
public static Integer valueOf(String s, int radix) throws NumberFormatException {
return Integer.valueOf(parseInt(s,radix));
}

/**
* Returns an <code>Integer</code> object holding the
* value of the specified <code>String</code>. The argument is
* interpreted as representing a signed decimal integer, exactly
* as if the argument were given to the {@link
* #parseInt(java.lang.String)} method. The result is an
* <code>Integer</code> object that represents the integer value
* specified by the string.
* <p>
* In other words, this method returns an <code>Integer</code>
* object equal to the value of:
*
* <blockquote><code>
* new Integer(Integer.parseInt(s))
* </code></blockquote>
*
* @param      s   the string to be parsed.
* @return     an <code>Integer</code> object holding the value
*             represented by the string argument.
* @exception  NumberFormatException  if the string cannot be parsed
*             as an integer.
*/
public static Integer valueOf(String s) throws NumberFormatException {
return Integer.valueOf(parseInt(s, 10));
}

/**
* Cache to support the object identity semantics of autoboxing for values between
* -128 and 127 (inclusive) as required by JLS.
*
* The cache is initialized on first usage. During VM initialization the
* getAndRemoveCacheProperties method may be used to get and remove any system
* properites that configure the cache size. At this time, the size of the
* cache may be controlled by the vm option -XX:AutoBoxCacheMax=<size>.
*/

// value of java.lang.Integer.IntegerCache.high property (obtained during VM init)
private static String integerCacheHighPropValue;

static void getAndRemoveCacheProperties() {
if (!sun.misc.VM.isBooted()) {
Properties props = System.getProperties();
integerCacheHighPropValue =
(String)props.remove("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null)
System.setProperties(props);  // remove from system props
}
}

private static class IntegerCache {
static final int high;
static final Integer cache[];

static {
final int low = -128;

// high value may be configured by property
int h = 127;
if (integerCacheHighPropValue != null) {
// Use Long.decode here to avoid invoking methods that
// require Integer's autoboxing cache to be initialized
int i = Long.decode(integerCacheHighPropValue).intValue();
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - -low);
}
high = h;

cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
}

private IntegerCache() {}
}

/**
* Returns a <tt>Integer</tt> instance representing the specified
* <tt>int</tt> value.
* If a new <tt>Integer</tt> instance is not required, this method
* should generally be used in preference to the constructor
* {@link #Integer(int)}, as this method is likely to yield
* significantly better space and time performance by caching
* frequently requested values.
*
* @param  i an <code>int</code> value.
* @return a <tt>Integer</tt> instance representing <tt>i</tt>.
* @since  1.5
*/
public static Integer valueOf(int i) {
if(i >= -128 && i <= IntegerCache.high)
return IntegerCache.cache[i + 128];
else
return new Integer(i);
}

/**
* The value of the <code>Integer</code>.
*
* @serial
*/
private final int value;

/**
* Constructs a newly allocated <code>Integer</code> object that
* represents the specified <code>int</code> value.
*
* @param   value   the value to be represented by the
*          <code>Integer</code> object.
*/
public Integer(int value) {
this.value = value;
}

/**
* Constructs a newly allocated <code>Integer</code> object that
* represents the <code>int</code> value indicated by the
* <code>String</code> parameter. The string is converted to an
* <code>int</code> value in exactly the manner used by the
* <code>parseInt</code> method for radix 10.
*
* @param      s   the <code>String</code> to be converted to an
*                 <code>Integer</code>.
* @exception  NumberFormatException  if the <code>String</code> does not
*               contain a parsable integer.
* @see        java.lang.Integer#parseInt(java.lang.String, int)
*/
public Integer(String s) throws NumberFormatException {
this.value = parseInt(s, 10);
}

/**
* Returns the value of this <code>Integer</code> as a
* <code>byte</code>.
*/
public byte byteValue() {
return (byte)value;
}

/**
* Returns the value of this <code>Integer</code> as a
* <code>short</code>.
*/
public short shortValue() {
return (short)value;
}

/**
* Returns the value of this <code>Integer</code> as an
* <code>int</code>.
*/
public int intValue() {
return value;
}

/**
* Returns the value of this <code>Integer</code> as a
* <code>long</code>.
*/
public long longValue() {
return (long)value;
}

/**
* Returns the value of this <code>Integer</code> as a
* <code>float</code>.
*/
public float floatValue() {
return (float)value;
}

/**
* Returns the value of this <code>Integer</code> as a
* <code>double</code>.
*/
public double doubleValue() {
return (double)value;
}

/**
* Returns a <code>String</code> object representing this
* <code>Integer</code>'s value. The value is converted to signed
* decimal representation and returned as a string, exactly as if
* the integer value were given as an argument to the {@link
* java.lang.Integer#toString(int)} method.
*
* @return  a string representation of the value of this object in
*          base 10.
*/
public String toString() {
return String.valueOf(value);
}

/**
* Returns a hash code for this <code>Integer</code>.
*
* @return  a hash code value for this object, equal to the
*          primitive <code>int</code> value represented by this
*          <code>Integer</code> object.
*/
public int hashCode() {
return value;
}

/**
* Compares this object to the specified object.  The result is
* <code>true</code> if and only if the argument is not
* <code>null</code> and is an <code>Integer</code> object that
* contains the same <code>int</code> value as this object.
*
* @param   obj   the object to compare with.
* @return  <code>true</code> if the objects are the same;
*          <code>false</code> otherwise.
*/
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}

/**
* Determines the integer value of the system property with the
* specified name.
* <p>
* The first argument is treated as the name of a system property.
* System properties are accessible through the
* {@link java.lang.System#getProperty(java.lang.String)} method. The
* string value of this property is then interpreted as an integer
* value and an <code>Integer</code> object representing this value is
* returned. Details of possible numeric formats can be found with
* the definition of <code>getProperty</code>.
* <p>
* If there is no property with the specified name, if the specified name
* is empty or <code>null</code>, or if the property does not have
* the correct numeric format, then <code>null</code> is returned.
* <p>
* In other words, this method returns an <code>Integer</code>
* object equal to the value of:
*
* <blockquote><code>
* getInteger(nm, null)
* </code></blockquote>
*
* @param   nm   property name.
* @return  the <code>Integer</code> value of the property.
* @see     java.lang.System#getProperty(java.lang.String)
* @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
*/
public static Integer getInteger(String nm) {
return getInteger(nm, null);
}

/**
* Determines the integer value of the system property with the
* specified name.
* <p>
* The first argument is treated as the name of a system property.
* System properties are accessible through the {@link
* java.lang.System#getProperty(java.lang.String)} method. The
* string value of this property is then interpreted as an integer
* value and an <code>Integer</code> object representing this value is
* returned. Details of possible numeric formats can be found with
* the definition of <code>getProperty</code>.
* <p>
* The second argument is the default value. An <code>Integer</code> object
* that represents the value of the second argument is returned if there
* is no property of the specified name, if the property does not have
* the correct numeric format, or if the specified name is empty or
*  <code>null</code>.
* <p>
* In other words, this method returns an <code>Integer</code> object
* equal to the value of:
* <blockquote><code>
* getInteger(nm, new Integer(val))
* </code></blockquote>
* but in practice it may be implemented in a manner such as:
* <blockquote><pre>
* Integer result = getInteger(nm, null);
* return (result == null) ? new Integer(val) : result;
* </pre></blockquote>
* to avoid the unnecessary allocation of an <code>Integer</code>
* object when the default value is not needed.
*
* @param   nm   property name.
* @param   val   default value.
* @return  the <code>Integer</code> value of the property.
* @see     java.lang.System#getProperty(java.lang.String)
* @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
*/
public static Integer getInteger(String nm, int val) {
Integer result = getInteger(nm, null);
return (result == null) ? Integer.valueOf(val) : result;
}

/**
* Returns the integer value of the system property with the
* specified name.  The first argument is treated as the name of a
* system property.  System properties are accessible through the
* {@link java.lang.System#getProperty(java.lang.String)} method.
* The string value of this property is then interpreted as an
* integer value, as per the <code>Integer.decode</code> method,
* and an <code>Integer</code> object representing this value is
* returned.
* <p>
* <ul><li>If the property value begins with the two ASCII characters
*         <code>0x</code> or the ASCII character <code>#</code>, not
*      followed by a minus sign, then the rest of it is parsed as a
*      hexadecimal integer exactly as by the method
*      {@link #valueOf(java.lang.String, int)} with radix 16.
* <li>If the property value begins with the ASCII character
*     <code>0</code> followed by another character, it is parsed as an
*     octal integer exactly as by the method
*     {@link #valueOf(java.lang.String, int)} with radix 8.
* <li>Otherwise, the property value is parsed as a decimal integer
* exactly as by the method {@link #valueOf(java.lang.String, int)}
* with radix 10.
* </ul><p>
* The second argument is the default value. The default value is
* returned if there is no property of the specified name, if the
* property does not have the correct numeric format, or if the
* specified name is empty or <code>null</code>.
*
* @param   nm   property name.
* @param   val   default value.
* @return  the <code>Integer</code> value of the property.
* @see     java.lang.System#getProperty(java.lang.String)
* @see java.lang.System#getProperty(java.lang.String, java.lang.String)
* @see java.lang.Integer#decode
*/
public static Integer getInteger(String nm, Integer val) {
String v = null;
try {
v = System.getProperty(nm);
} catch (IllegalArgumentException e) {
} catch (NullPointerException e) {
}
if (v != null) {
try {
return Integer.decode(v);
} catch (NumberFormatException e) {
}
}
return val;
}

/**
* Decodes a <code>String</code> into an <code>Integer</code>.
* Accepts decimal, hexadecimal, and octal numbers given
* by the following grammar:
*
* <blockquote>
* <dl>
* <dt><i>DecodableString:</i>
* <dd><i>Sign<sub>opt</sub> DecimalNumeral</i>
* <dd><i>Sign<sub>opt</sub></i> <code>0x</code> <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> <code>0X</code> <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> <code>#</code> <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> <code>0</code> <i>OctalDigits</i>
* <p>
* <dt><i>Sign:</i>
* <dd><code>-</code>
* </dl>
* </blockquote>
*
* <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
* are defined in <a href="http://java.sun.com/docs/books/jls/second_edition/html/lexical.doc.html#48282">§3.10.1</a>
* of the <a href="http://java.sun.com/docs/books/jls/html/">Java
* Language Specification</a>.
* <p>
* The sequence of characters following an (optional) negative
* sign and/or radix specifier ("<code>0x</code>",
* "<code>0X</code>", "<code>#</code>", or
* leading zero) is parsed as by the <code>Integer.parseInt</code>
* method with the indicated radix (10, 16, or 8).  This sequence
* of characters must represent a positive value or a {@link
* NumberFormatException} will be thrown.  The result is negated
* if first character of the specified <code>String</code> is the
* minus sign.  No whitespace characters are permitted in the
* <code>String</code>.
*
* @param     nm the <code>String</code> to decode.
* @return    a <code>Integer</code> object holding the <code>int</code>
*         value represented by <code>nm</code>
* @exception NumberFormatException  if the <code>String</code> does not
*            contain a parsable integer.
* @see java.lang.Integer#parseInt(java.lang.String, int)
*/
public static Integer decode(String nm) throws NumberFormatException {
int radix = 10;
int index = 0;
boolean negative = false;
Integer result;

// Handle minus sign, if present
if (nm.startsWith("-")) {
negative = true;
index++;
}

// Handle radix specifier, if present
if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
index += 2;
radix = 16;
}
else if (nm.startsWith("#", index)) {
index ++;
radix = 16;
}
else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
index ++;
radix = 8;
}

if (nm.startsWith("-", index))
throw new NumberFormatException("Negative sign in wrong position");

try {
result = Integer.valueOf(nm.substring(index), radix);
result = negative ? Integer.valueOf(-result.intValue()) : result;
} catch (NumberFormatException e) {
// If number is Integer.MIN_VALUE, we'll end up here. The next line
// handles this case, and causes any genuine format error to be
// rethrown.
String constant = negative ? "-" + nm.substring(index)
: nm.substring(index);
result = Integer.valueOf(constant, radix);
}
return result;
}

/**
* Compares two <code>Integer</code> objects numerically.
*
* @param   anotherInteger   the <code>Integer</code> to be compared.
* @return  the value <code>0</code> if this <code>Integer</code> is
*      equal to the argument <code>Integer</code>; a value less than
*      <code>0</code> if this <code>Integer</code> is numerically less
*      than the argument <code>Integer</code>; and a value greater
*      than <code>0</code> if this <code>Integer</code> is numerically
*       greater than the argument <code>Integer</code> (signed
*       comparison).
* @since   1.2
*/
public int compareTo(Integer anotherInteger) {
int thisVal = this.value;
int anotherVal = anotherInteger.value;
return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1));
}

// Bit twiddling

/**
* The number of bits used to represent an <tt>int</tt> value in two's
* complement binary form.
*
* @since 1.5
*/
public static final int SIZE = 32;

/**
* Returns an <tt>int</tt> value with at most a single one-bit, in the
* position of the highest-order ("leftmost") one-bit in the specified
* <tt>int</tt> value.  Returns zero if the specified value has no
* one-bits in its two's complement binary representation, that is, if it
* is equal to zero.
*
* @return an <tt>int</tt> value with a single one-bit, in the position
*     of the highest-order one-bit in the specified value, or zero if
*     the specified value is itself equal to zero.
* @since 1.5
*/
public static int highestOneBit(int i) {
// HD, Figure 3-1
i |= (i >>  1);
i |= (i >>  2);
i |= (i >>  4);
i |= (i >>  8);
i |= (i >> 16);
return i - (i >>> 1);
}

/**
* Returns an <tt>int</tt> value with at most a single one-bit, in the
* position of the lowest-order ("rightmost") one-bit in the specified
* <tt>int</tt> value.  Returns zero if the specified value has no
* one-bits in its two's complement binary representation, that is, if it
* is equal to zero.
*
* @return an <tt>int</tt> value with a single one-bit, in the position
*     of the lowest-order one-bit in the specified value, or zero if
*     the specified value is itself equal to zero.
* @since 1.5
*/
public static int lowestOneBit(int i) {
// HD, Section 2-1
return i & -i;
}

/**
* Returns the number of zero bits preceding the highest-order
* ("leftmost") one-bit in the two's complement binary representation
* of the specified <tt>int</tt> value.  Returns 32 if the
* specified value has no one-bits in its two's complement representation,
* in other words if it is equal to zero.
*
* <p>Note that this method is closely related to the logarithm base 2.
* For all positive <tt>int</tt> values x:
* <ul>
* <li>floor(log<sub>2</sub>(x)) = <tt>31 - numberOfLeadingZeros(x)</tt>
* <li>ceil(log<sub>2</sub>(x)) = <tt>32 - numberOfLeadingZeros(x - 1)</tt>
* </ul>
*
* @return the number of zero bits preceding the highest-order
*     ("leftmost") one-bit in the two's complement binary representation
*     of the specified <tt>int</tt> value, or 32 if the value
*     is equal to zero.
* @since 1.5
*/
public static int numberOfLeadingZeros(int i) {
// HD, Figure 5-6
if (i == 0)
return 32;
int n = 1;
if (i >>> 16 == 0) { n += 16; i <<= 16; }
if (i >>> 24 == 0) { n +=  8; i <<=  8; }
if (i >>> 28 == 0) { n +=  4; i <<=  4; }
if (i >>> 30 == 0) { n +=  2; i <<=  2; }
n -= i >>> 31;
return n;
}

/**
* Returns the number of zero bits following the lowest-order ("rightmost")
* one-bit in the two's complement binary representation of the specified
* <tt>int</tt> value.  Returns 32 if the specified value has no
* one-bits in its two's complement representation, in other words if it is
* equal to zero.
*
* @return the number of zero bits following the lowest-order ("rightmost")
*     one-bit in the two's complement binary representation of the
*     specified <tt>int</tt> value, or 32 if the value is equal
*     to zero.
* @since 1.5
*/
public static int numberOfTrailingZeros(int i) {
// HD, Figure 5-14
int y;
if (i == 0) return 32;
int n = 31;
y = i <<16; if (y != 0) { n = n -16; i = y; }
y = i << 8; if (y != 0) { n = n - 8; i = y; }
y = i << 4; if (y != 0) { n = n - 4; i = y; }
y = i << 2; if (y != 0) { n = n - 2; i = y; }
return n - ((i << 1) >>> 31);
}

/**
* Returns the number of one-bits in the two's complement binary
* representation of the specified <tt>int</tt> value.  This function is
* sometimes referred to as the <i>population count</i>.
*
* @return the number of one-bits in the two's complement binary
*     representation of the specified <tt>int</tt> value.
* @since 1.5
*/
public static int bitCount(int i) {
// HD, Figure 5-2
i = i - ((i >>> 1) & 0x55555555);
i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
i = (i + (i >>> 4)) & 0x0f0f0f0f;
i = i + (i >>> 8);
i = i + (i >>> 16);
return i & 0x3f;
}

/**
* Returns the value obtained by rotating the two's complement binary
* representation of the specified <tt>int</tt> value left by the
* specified number of bits.  (Bits shifted out of the left hand, or
* high-order, side reenter on the right, or low-order.)
*
* <p>Note that left rotation with a negative distance is equivalent to
* right rotation: <tt>rotateLeft(val, -distance) == rotateRight(val,
* distance)</tt>.  Note also that rotation by any multiple of 32 is a
* no-op, so all but the last five bits of the rotation distance can be
* ignored, even if the distance is negative: <tt>rotateLeft(val,
* distance) == rotateLeft(val, distance & 0x1F)</tt>.
*
* @return the value obtained by rotating the two's complement binary
*     representation of the specified <tt>int</tt> value left by the
*     specified number of bits.
* @since 1.5
*/
public static int rotateLeft(int i, int distance) {
return (i << distance) | (i >>> -distance);
}

/**
* Returns the value obtained by rotating the two's complement binary
* representation of the specified <tt>int</tt> value right by the
* specified number of bits.  (Bits shifted out of the right hand, or
* low-order, side reenter on the left, or high-order.)
*
* <p>Note that right rotation with a negative distance is equivalent to
* left rotation: <tt>rotateRight(val, -distance) == rotateLeft(val,
* distance)</tt>.  Note also that rotation by any multiple of 32 is a
* no-op, so all but the last five bits of the rotation distance can be
* ignored, even if the distance is negative: <tt>rotateRight(val,
* distance) == rotateRight(val, distance & 0x1F)</tt>.
*
* @return the value obtained by rotating the two's complement binary
*     representation of the specified <tt>int</tt> value right by the
*     specified number of bits.
* @since 1.5
*/
public static int rotateRight(int i, int distance) {
return (i >>> distance) | (i << -distance);
}

/**
* Returns the value obtained by reversing the order of the bits in the
* two's complement binary representation of the specified <tt>int</tt>
* value.
*
* @return the value obtained by reversing order of the bits in the
*     specified <tt>int</tt> value.
* @since 1.5
*/
public static int reverse(int i) {
// HD, Figure 7-1
i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
i = (i & 0x33333333) << 2 | (i >>> 2) & 0x33333333;
i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
i = (i << 24) | ((i & 0xff00) << 8) |
((i >>> 8) & 0xff00) | (i >>> 24);
return i;
}

/**
* Returns the signum function of the specified <tt>int</tt> value.  (The
* return value is -1 if the specified value is negative; 0 if the
* specified value is zero; and 1 if the specified value is positive.)
*
* @return the signum function of the specified <tt>int</tt> value.
* @since 1.5
*/
public static int signum(int i) {
// HD, Section 2-7
return (i >> 31) | (-i >>> 31);
}

/**
* Returns the value obtained by reversing the order of the bytes in the
* two's complement representation of the specified <tt>int</tt> value.
*
* @return the value obtained by reversing the bytes in the specified
*     <tt>int</tt> value.
* @since 1.5
*/
public static int reverseBytes(int i) {
return ((i >>> 24)           ) |
((i >>   8) &   0xFF00) |
((i <<   8) & 0xFF0000) |
((i << 24));
}

/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 1360826667806852920L;
}