https://openjdk.java.net/ 
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package sun.security.util;


Utility class for holding parsing methods that can't be added
to the classes which form part of the language specification.

/**
 * Utility class for holding parsing methods that can't be added
 * to the classes which form part of the language specification.
 */
public final class Parsing {

    
Parses the string argument as an unsigned integer in the radix specified by the second argument. An unsigned integer maps the values usually associated with negative numbers to positive numbers larger than MAX_VALUE. The characters in the string must all be digits of the specified radix (as determined by whether Character.digit(char, int) returns a nonnegative value), except that the first character may be an ASCII plus sign '+' ('\u005Cu002B'). The resulting integer value is returned. 
An exception of type NumberFormatException is thrown if any of the following situations occurs: 
    

  • The first argument is null or is a string of length zero. 
  • The radix is either smaller than Character.MIN_RADIX or larger than Character.MAX_RADIX. 
  • Any character of the string is not a digit of the specified radix, except that the first character may be a plus sign '+' ('\u005Cu002B') provided that the string is longer than length 1. 
  • The value represented by the string is larger than the largest unsigned int, 232-1.



Params:
  • s –  the String containing the unsigned integer representation to be parsed
  • radix –  the radix to be used while parsing s.
Throws:
Returns:    the integer represented by the string argument in the
            specified radix.
/**
     * Parses the string argument as an unsigned integer in the radix
     * specified by the second argument.  An unsigned integer maps the
     * values usually associated with negative numbers to positive
     * numbers larger than {@code MAX_VALUE}.
     *
     * 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 plus
     * sign {@code '+'} ({@code '\u005Cu002B'}). 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 plus sign
     * {@code '+'} ({@code '\u005Cu002B'}) provided that the
     * string is longer than length 1.
     *
     * <li>The value represented by the string is larger than the
     * largest unsigned {@code int}, 2<sup>32</sup>-1.
     *
     * </ul>
     *
     *
     * @param      s   the {@code String} containing the unsigned 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.
     * @throws     NumberFormatException if the {@code String}
     *             does not contain a parsable {@code int}.
     */
    public static int parseUnsignedInt(String s, int radix)
                throws NumberFormatException {
        if (s == null)  {
            throw new NumberFormatException("null");
        }

        int len = s.length();
        if (len > 0) {
            char firstChar = s.charAt(0);
            if (firstChar == '-') {
                throw new
                    NumberFormatException(String.format("Illegal leading minus sign " +
                                                       "on unsigned string %s.", s));
            } else {
                if (len <= 5 || // Integer.MAX_VALUE in Character.MAX_RADIX is 6 digits
                    (radix == 10 && len <= 9) ) { // Integer.MAX_VALUE in base 10 is 10 digits
                    return Integer.parseInt(s, radix);
                } else {
                    long ell = Long.parseLong(s, radix);
                    if ((ell & 0xffff_ffff_0000_0000L) == 0) {
                        return (int) ell;
                    } else {
                        throw new
                            NumberFormatException(String.format("String value %s exceeds " +
                                                                "range of unsigned int.", s));
                    }
                }
            }
        } else {
            throw new NumberFormatException("For input string: \"" + s + "\"");
        }
    }

    
Parses the string argument as an unsigned decimal integer. The characters in the string must all be decimal digits, except that the first character may be an an ASCII plus sign 
'+' ('\u005Cu002B'). The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to the parseUnsignedInt(String, int) method. 
Params:
  • s –  a String containing the unsigned int representation to be parsed
Throws:
Returns:   the unsigned integer value represented by the argument in decimal.
/**
     * Parses the string argument as an unsigned decimal integer. The
     * characters in the string must all be decimal digits, except
     * that the first character may be an an ASCII plus sign {@code
     * '+'} ({@code '\u005Cu002B'}). The resulting integer value
     * is returned, exactly as if the argument and the radix 10 were
     * given as arguments to the {@link
     * #parseUnsignedInt(java.lang.String, int)} method.
     *
     * @param s   a {@code String} containing the unsigned {@code int}
     *            representation to be parsed
     * @return    the unsigned integer value represented by the argument in decimal.
     * @throws    NumberFormatException  if the string does not contain a
     *            parsable unsigned integer.
     */
    public static int parseUnsignedInt(String s) throws NumberFormatException {
        return parseUnsignedInt(s, 10);
    }

}