String to Integer

string2Int.java

package wcy.leetcode.gist;

/**
 * Created by ChauyanWang on 12/19/14.
 */
public class string2Int {
    public int atoi(String number) {
        if (number == null || number.length() == 0) return 0;

        double result = 0;
        int startIndex = 0;
        boolean isNegative = false;

        // skip header / tail space char
        number = number.trim();
        if(number.charAt(0) == '+')
            startIndex ++ ;
        else if (number.charAt(0) == '-'){
            isNegative = true;
            startIndex ++ ;
        }

        while(startIndex < number.length() &&
                number.charAt(startIndex) >= '0' &&
                number.charAt(startIndex) <= '9') {
            result = result * 10 + (number.charAt(startIndex) - '0');
            startIndex ++;
        }

        if(isNegative) result = -result;
        if(result > Integer.MAX_VALUE) return Integer.MAX_VALUE;
        else if(result < Integer.MIN_VALUE) return Integer.MIN_VALUE;

        return (int)result;

    }
}