Integer的源码
/*
* Copyright (c) 1994, 2010, 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} class wraps a value of the primitive type
* {@code int} in an object. An object of type {@code Integer}
* contains a single field whose type is {@code int}.
*
* <p>In addition, this class provides several methods for converting
* an {@code int} to a {@code String} and a {@code String} to an
* {@code int}, as well as other constants and methods useful when
* dealing with an {@code int}.
*
* <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
* @author Joseph D. Darcy
* @since JDK1.0
*/
public final class Integer extends Number implements Comparable<Integer> {
/**
* A constant holding the minimum value an {@code int} can
* have, -2<sup>31</sup>.
*/
public static final int MIN_VALUE = 0x80000000;
/**
* A constant holding the maximum value an {@code int} can
* have, 2<sup>31</sup>-1.
*/
public static final int MAX_VALUE = 0x7fffffff;
/**
* The {@code Class} instance representing the primitive type
* {@code int}.
*
* @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}
* or larger than {@code Character.MAX_RADIX}, then the radix
* {@code 10} is used instead.
*
* <p>If the first argument is negative, the first element of the
* result is the ASCII minus character {@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>'\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>
* {@code 0123456789abcdefghijklmnopqrstuvwxyz}
* </blockquote>
*
* These are <code>'\u0030'</code> through
* <code>'\u0039'</code> and <code>'\u0061'</code> through
* <code>'\u007A'</code>. If {@code radix} 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}. If uppercase letters are
* desired, the {@link java.lang.String#toUpperCase()} method may
* be called on the result:
*
* <blockquote>
* {@code Integer.toString(n, 16).toUpperCase()}
* </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}s. If the unsigned magnitude is zero, it is
* represented by a single zero character {@code '0'}
* (<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>
* {@code 0123456789abcdef}
* </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>
* {@code Integer.toHexString(n).toUpperCase()}
* </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}s.
*
* <p>If the unsigned magnitude is zero, it is represented by a
* single zero character {@code '0'}
* (<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>
* {@code 01234567}
* </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}s.
* If the unsigned magnitude is zero, it is represented by a
* single zero character {@code '0'}
* (<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>'\u0030'</code>) and {@code '1'}
* (<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} 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(buf, true);
}
/**
* 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>'\u002D'</code>) to
* indicate a negative value or an ASCII plus sign {@code '+'}
* (<code>'\u002B'</code>) to indicate a positive value. The
* resulting integer value is returned.
*
* <p>An exception of type {@code NumberFormatException} is
* thrown if any of the following situations occurs:
* <ul>
* <li>The first argument is {@code null} 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>'\u002D'</code>) or plus sign
* {@code '+'} (<code>'\u002B'</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}.
* </ul>
*
* <p>Examples:
* <blockquote><pre>
* parseInt("0", 10) returns 0
* parseInt("473", 10) returns 473
* parseInt("+42", 10) returns 42
* 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} containing the integer
* representation to be parsed
* @param radix the radix to be used while parsing {@code s}.
* @return the integer represented by the string argument in the
* specified radix.
* @exception NumberFormatException if the {@code String}
* does not contain a parsable {@code int}.
*/
public static int parseInt(String s, int radix)
throws NumberFormatException
{
/*
* WARNING: This method may be invoked early during VM initialization
* before IntegerCache is initialized. Care must be taken to not use
* the valueOf method.
*/
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, len = s.length();
int limit = -Integer.MAX_VALUE;
int multmin;
int digit;
if (len > 0) {
char firstChar = s.charAt(0);
if (firstChar < '0') { // Possible leading "+" or "-"
if (firstChar == '-') {
negative = true;
limit = Integer.MIN_VALUE;
} else if (firstChar != '+')
throw NumberFormatException.forInputString(s);
if (len == 1) // Cannot have lone "+" or "-"
throw NumberFormatException.forInputString(s);
i++;
}
multmin = limit / radix;
while (i < len) {
// 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);
}
return negative ? result : -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>'\u002D'</code>) to indicate a negative value or an
* ASCII plus sign {@code '+'} (<code>'\u002B'</code>) to
* indicate a positive 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} containing the {@code int}
* 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} object holding the value
* extracted from the specified {@code String} 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} object that
* represents the integer value specified by the string.
*
* <p>In other words, this method returns an {@code Integer}
* object equal to the value of:
*
* <blockquote>
* {@code new Integer(Integer.parseInt(s, radix))}
* </blockquote>
*
* @param s the string to be parsed.
* @param radix the radix to be used in interpreting {@code s}
* @return an {@code Integer} object holding the value
* represented by the string argument in the specified
* radix.
* @exception NumberFormatException if the {@code String}
* does not contain a parsable {@code int}.
*/
public static Integer valueOf(String s, int radix) throws NumberFormatException {
return Integer.valueOf(parseInt(s,radix));
}
/**
* Returns an {@code Integer} object holding the
* value of the specified {@code String}. 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} object that represents the integer value
* specified by the string.
*
* <p>In other words, this method returns an {@code Integer}
* object equal to the value of:
*
* <blockquote>
* {@code new Integer(Integer.parseInt(s))}
* </blockquote>
*
* @param s the string to be parsed.
* @return an {@code Integer} 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. The size of the cache
* may be controlled by the -XX:AutoBoxCacheMax=<size> option.
* During VM initialization, java.lang.Integer.IntegerCache.high property
* may be set and saved in the private system properties in the
* sun.misc.VM class.
*/
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
}
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 an {@code Integer} instance representing the specified
* {@code int} value. If a new {@code Integer} 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.
*
* This method will always cache values in the range -128 to 127,
* inclusive, and may cache other values outside of this range.
*
* @param i an {@code int} value.
* @return an {@code Integer} instance representing {@code i}.
* @since 1.5
*/
public static Integer valueOf(int i) {
assert IntegerCache.high >= 127;
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
/**
* The value of the {@code Integer}.
*
* @serial
*/
private final int value;
/**
* Constructs a newly allocated {@code Integer} object that
* represents the specified {@code int} value.
*
* @param value the value to be represented by the
* {@code Integer} object.
*/
public Integer(int value) {
this.value = value;
}
/**
* Constructs a newly allocated {@code Integer} object that
* represents the {@code int} value indicated by the
* {@code String} parameter. The string is converted to an
* {@code int} value in exactly the manner used by the
* {@code parseInt} method for radix 10.
*
* @param s the {@code String} to be converted to an
* {@code Integer}.
* @exception NumberFormatException if the {@code String} 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} as a
* {@code byte}.
*/
public byte byteValue() {
return (byte)value;
}
/**
* Returns the value of this {@code Integer} as a
* {@code short}.
*/
public short shortValue() {
return (short)value;
}
/**
* Returns the value of this {@code Integer} as an
* {@code int}.
*/
public int intValue() {
return value;
}
/**
* Returns the value of this {@code Integer} as a
* {@code long}.
*/
public long longValue() {
return (long)value;
}
/**
* Returns the value of this {@code Integer} as a
* {@code float}.
*/
public float floatValue() {
return (float)value;
}
/**
* Returns the value of this {@code Integer} as a
* {@code double}.
*/
public double doubleValue() {
return (double)value;
}
/**
* Returns a {@code String} object representing this
* {@code Integer}'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 toString(value);
}
/**
* Returns a hash code for this {@code Integer}.
*
* @return a hash code value for this object, equal to the
* primitive {@code int} value represented by this
* {@code Integer} object.
*/
public int hashCode() {
return value;
}
/**
* Compares this object to the specified object. The result is
* {@code true} if and only if the argument is not
* {@code null} and is an {@code Integer} object that
* contains the same {@code int} value as this object.
*
* @param obj the object to compare with.
* @return {@code true} if the objects are the same;
* {@code false} 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} object representing this value is
* returned. Details of possible numeric formats can be found with
* the definition of {@code getProperty}.
*
* <p>If there is no property with the specified name, if the specified name
* is empty or {@code null}, or if the property does not have
* the correct numeric format, then {@code null} is returned.
*
* <p>In other words, this method returns an {@code Integer}
* object equal to the value of:
*
* <blockquote>
* {@code getInteger(nm, null)}
* </blockquote>
*
* @param nm property name.
* @return the {@code Integer} 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} object representing this value is
* returned. Details of possible numeric formats can be found with
* the definition of {@code getProperty}.
*
* <p>The second argument is the default value. An {@code Integer} 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}.
*
* <p>In other words, this method returns an {@code Integer} object
* equal to the value of:
*
* <blockquote>
* {@code getInteger(nm, new Integer(val))}
* </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}
* object when the default value is not needed.
*
* @param nm property name.
* @param val default value.
* @return the {@code Integer} 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} method,
* and an {@code Integer} object representing this value is
* returned.
*
* <ul><li>If the property value begins with the two ASCII characters
* {@code 0x} or the ASCII character {@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} 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}.
*
* @param nm property name.
* @param val default value.
* @return the {@code Integer} 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} into an {@code Integer}.
* 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} <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> {@code 0X} <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> {@code #} <i>HexDigits</i>
* <dd><i>Sign<sub>opt</sub></i> {@code 0} <i>OctalDigits</i>
* <p>
* <dt><i>Sign:</i>
* <dd>{@code -}
* <dd>{@code +}
* </dl>
* </blockquote>
*
* <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
* are as defined in section 3.10.1 of
* <cite>The Java™ Language Specification</cite>,
* except that underscores are not accepted between digits.
*
* <p>The sequence of characters following an optional
* sign and/or radix specifier ("{@code 0x}", "{@code 0X}",
* "{@code #}", or leading zero) is parsed as by the {@code
* Integer.parseInt} 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} is the minus sign. No whitespace characters are
* permitted in the {@code String}.
*
* @param nm the {@code String} to decode.
* @return an {@code Integer} object holding the {@code int}
* value represented by {@code nm}
* @exception NumberFormatException if the {@code String} 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;
if (nm.length() == 0)
throw new NumberFormatException("Zero length string");
char firstChar = nm.charAt(0);
// Handle sign, if present
if (firstChar == '-') {
negative = true;
index++;
} else if (firstChar == '+')
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) || nm.startsWith("+", index))
throw new NumberFormatException("Sign character 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} objects numerically.
*
* @param anotherInteger the {@code Integer} to be compared.
* @return the value {@code 0} if this {@code Integer} is
* equal to the argument {@code Integer}; a value less than
* {@code 0} if this {@code Integer} is numerically less
* than the argument {@code Integer}; and a value greater
* than {@code 0} if this {@code Integer} is numerically
* greater than the argument {@code Integer} (signed
* comparison).
* @since 1.2
*/
public int compareTo(Integer anotherInteger) {
return compare(this.value, anotherInteger.value);
}
/**
* Compares two {@code int} values numerically.
* The value returned is identical to what would be returned by:
* <pre>
* Integer.valueOf(x).compareTo(Integer.valueOf(y))
* </pre>
*
* @param x the first {@code int} to compare
* @param y the second {@code int} to compare
* @return the value {@code 0} if {@code x == y};
* a value less than {@code 0} if {@code x < y}; and
* a value greater than {@code 0} if {@code x > y}
* @since 1.7
*/
public static int compare(int x, int y) {
return (x < y) ? -1 : ((x == y) ? 0 : 1);
}
// Bit twiddling
/**
* The number of bits used to represent an {@code int} value in two's
* complement binary form.
*
* @since 1.5
*/
public static final int SIZE = 32;
/**
* Returns an {@code int} value with at most a single one-bit, in the
* position of the highest-order ("leftmost") one-bit in the specified
* {@code int} 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 {@code int} 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); //向右移动一位，然后与自己或运算，相当于使最高位的1的右边一位也置成1
i |= (i >> 2); //把最高位1的右边三位，置成1
i |= (i >> 4); //把最高位1的右边七位，置成1
i |= (i >> 8); //把最高位1的右边十五位，置成1
i |= (i >> 16); //把最高位1的右边三十一位，置成1，因为整数32位，已经足够了
return i - (i >>> 1); //无符号右移动一位，然后把最高位腾为0，想剪得到最高位
}
/**
* Returns an {@code int} value with at most a single one-bit, in the
* position of the lowest-order ("rightmost") one-bit in the specified
* {@code int} 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 {@code int} 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 {@code int} 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 {@code int} values x:
* <ul>
* <li>floor(log<sub>2</sub>(x)) = {@code 31 - numberOfLeadingZeros(x)}
* <li>ceil(log<sub>2</sub>(x)) = {@code 32 - numberOfLeadingZeros(x - 1)}
* </ul>
*
* @return the number of zero bits preceding the highest-order
* ("leftmost") one-bit in the two's complement binary representation
* of the specified {@code int} 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
* {@code int} 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 {@code int} 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 {@code int} 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 {@code int} 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 {@code int} 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: {@code rotateLeft(val, -distance) == rotateRight(val,
* distance)}. 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: {@code rotateLeft(val,
* distance) == rotateLeft(val, distance & 0x1F)}.
*
* @return the value obtained by rotating the two's complement binary
* representation of the specified {@code int} 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 {@code int} 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: {@code rotateRight(val, -distance) == rotateLeft(val,
* distance)}. 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: {@code rotateRight(val,
* distance) == rotateRight(val, distance & 0x1F)}.
*
* @return the value obtained by rotating the two's complement binary
* representation of the specified {@code int} 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 {@code int}
* value.
*
* @return the value obtained by reversing order of the bits in the
* specified {@code int} 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 {@code int} 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 {@code int} 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 {@code int} value.
*
* @return the value obtained by reversing the bytes in the specified
* {@code int} 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;
}