//version 1(use library function)
public class Solution {
    /**
     * @param str a string
     * @return an integer
     */
    public int stringToInteger(String str) {
        return Integer.valueOf(str);
    }
}

//version 2
public class Solution {
    /**
     * @param str a string
     * @return an integer
     */
    public int stringToInteger(String str) {
        // Write your code here
        int integer = 0;
        int Minus = 0;

        if (str.charAt(0) == '-'){
            Minus = 1;
        }

        for (int i = Minus; i < str.length(); i++){
            integer = integer * 10 + str.charAt(i)-'0';
        }

        if (Minus == 1){
            integer = -integer;
        }
        return integer;
    }
}