String to Integer (atoi)

  //String to Integer (atoi) Total Accepted: 58433 Total Submissions: 453312 My Submissions Question Solution 
//Implement atoi to convert a string to an integer.
//
//Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.
//
//Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.
//
//Update (2015-02-10):
//The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button  to reset your code definition.
//
//spoilers alert... click to show requirements for atoi.
public class StringtoInteger {


public static void main(String[] args) {
// TODO Auto-generated method stub


}
 public int myAtoi(String str) {
 //注意空和空格
    if(str==null)
    {
        return 0;
    }
    str = str.trim();
    if(str.length()==0)
        return 0;
    //注意+，-
    boolean isNeg = false;
    int i = 0;
    if(str.charAt(0)=='-' || str.charAt(0)=='+')
    {
        i++;
        if(str.charAt(0)=='-')
            isNeg = true;
    }
    int res = 0;
    while(i<str.length()){
    //判断是数字吗
        if(str.charAt(i)<'0'||str.charAt(i)>'9')
            break;
        int digit = (int)(str.charAt(i)-'0');
        //判断越界
        if(isNeg && res>-((Integer.MIN_VALUE+digit)/10))
            return Integer.MIN_VALUE;
        else if(!isNeg && res>(Integer.MAX_VALUE-digit)/10)
            return Integer.MAX_VALUE;
        res = res*10+digit;
        i++;
    }
    return isNeg?-res:res;
   }


}