String和数字之间的转化

主要是JDK的代码，还是比较的经典，值得一看，例如：

package alg;

/**
 * @author zha 字符串之间的转化
 */
public class Alg3StringToint {

    /**
     * @param args
     */
    public static void main(String[] args) {
        String intv = "1232192373290";
//        int value = Integer.parseInt(intv);
//        System.out.println(value);
    }

    // JDK的源码还是比较好的研究对象
    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 new NumberFormatException(s);

                if (len == 1) // Cannot have lone "+" or "-"
                    throw new NumberFormatException(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 new NumberFormatException(s);
                }
                if (result < multmin) {
                    throw new NumberFormatException(s);
                }
                result *= radix;
                if (result < limit + digit) {
                    throw new NumberFormatException(s);
                }
                result -= digit;
            }
        } else {
            throw new NumberFormatException(s);
        }
        return negative ? result : -result;
    }
}