/**
* 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;
}
}
/**
* 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));
}
--------------------编程问答--------------------
/**
* Returns the numeric value of the specified character (Unicode
* code point) in the specified radix.
*
* <p>If the radix is not in the range <code>MIN_RADIX</code> <=
* <code>radix</code> <= <code>MAX_RADIX</code> or if the
* character is not a valid digit in the specified
* radix, <code>-1</code> is returned. A character is a valid digit
* if at least one of the following is true:
* <ul>
* <li>The method {@link #isDigit(int) isDigit(codePoint)} is <code>true</code> of the character
* and the Unicode decimal digit value of the character (or its
* single-character decomposition) is less than the specified radix.
* In this case the decimal digit value is returned.
* <li>The character is one of the uppercase Latin letters
* <code>'A'</code> through <code>'Z'</code> and its code is less than
* <code>radix + 'A' - 10</code>.
* In this case, <code>ch - 'A' + 10</code>
* is returned.
* <li>The character is one of the lowercase Latin letters
* <code>'a'</code> through <code>'z'</code> and its code is less than
* <code>radix + 'a' - 10</code>.
* In this case, <code>ch - 'a' + 10</code>
* is returned.
* </ul>
*
* @param codePoint the character (Unicode code point) to be converted.
* @param radix the radix.
* @return the numeric value represented by the character in the
* specified radix.
* @see java.lang.Character#forDigit(int, int)
* @see java.lang.Character#isDigit(int)
* @since 1.5
*/
public static int digit(int codePoint, int radix) {
int digit = -1;