atoi 字符串 转换为 数字 leetcode

package String;  /**  * @Title: atoi.java  * @Package String  * @Description: TODO * @author nutc * @date 2013-8-28 上午10:33:33  * @version V1.0  */public class atoi {public static void main(String args[]) {atoi l = new atoi();String s = "345e980";System.out.println(Integer.MAX_VALUE);System.out.println(Integer.MIN_VALUE);System.out.println(" "+l.atoi(s));// PINALSIGYAHRPISystem.out.println(" "+l.atoi2(s));// PINALSIGYAHRPI}public int atoi(String str) {        int len = str.length();        if (len == 0) return 0;        int ret = 0;        boolean signal = true;        int i = 0;        while (i < len && str.charAt(i) == ' ') {  //空格            i++;            }        if (i < len && str.charAt(i) == '-') {             signal = false;            i++;        } else if (i < len && str.charAt(i) == '+') {  //注意还有+号！            i++;        } else if (str.charAt(i) < '0' || str.charAt(i) > '9') return 0;        int count = 0;        while (i < len && str.charAt(i) >= '0' && str.charAt(i) <= '9') {            if (signal) {//MAX 2147483647  MIN -2147483648                if (count == 10 || ret>214748364  || (ret == 214748364 && str.charAt(i) >= '7')) return Integer.MAX_VALUE;                ret = ret * 10 + (str.charAt(i) - '0');            } else {                if (count == 10 || (ret<-214748364 ) || ( (ret == -214748364 && str.charAt(i) >= '8') )) return Integer.MIN_VALUE;                ret = ret * 10 - (str.charAt(i) - '0');            }//            System.out.println(ret);            i++;            count++;        }        return ret;    }public int atoi2(String s) {    //取巧的方式        s = s.trim();          long value = 0;    //用long！！        boolean isPositive = true;                    for (int i = 0; i < s.length(); i++) {              if (i == 0 && (s.charAt(i) == '+' || s.charAt(i) == '-')) {                  if (s.charAt(i) == '-') {                      isPositive = false;                  }                  continue;              }              if (s.charAt(i) < '0' || s.charAt(i) > '9') break;              value = 10 * value + s.charAt(i) - '0';          }          value = isPositive == true ? value : value * -1;          if (value < -2147483648) {              return -2147483648;          } else if (value > 2147483647) {              return 2147483647;          } else {              return (int) value;          }      } }