把字符串转换成整数 --剑指offer

public class Solution {
    public  int StrToInt(String str) {
        if (str.length() == 0 ||str == null){
            return 0;
        }
        long result = 0;
        
        for(int i=0;i < str.length();i ++){
            char c=str.charAt(i);
            if(c >= ‘0‘ && c <= ‘9‘){
                result = result*10 + c-‘0‘;
            }else if(result != 0){
                return 0;
            }
        }
        result=str.charAt(0)==‘-‘? -result:result;
        if(result > Integer.MAX_VALUE || result < Integer.MIN_VALUE){
            return 0;
        }
        return (int)result;
    }
}