atoi -- Java version

public int atoi(String str) {
 if (str == null || str.length() < 1)
  return 0;
 
 // trim white spaces
 str = str.trim();
 
 char flag = '+';
 
 // check negative or positive
 int i = 0;
 if (str.charAt(0) == '-') {
  flag = '-';
  i++;
 } else if (str.charAt(0) == '+') {
  i++;
 }
 // use double to store result
 double result = 0;
 
 // calculate value
 while (str.length() > i && str.charAt(i) >= '0' && str.charAt(i) <= '9') {
  result = result * 10 + (str.charAt(i) - '0');
  i++;
 }
 
 if (flag == '-')
  result = -result;
 
 // handle max and min
 if (result > Integer.MAX_VALUE)
  return Integer.MAX_VALUE;
 
 if (result < Integer.MIN_VALUE)
  return Integer.MIN_VALUE;
 
 return (int) result;
}