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;

    }

}