Converting to base 10

Question

My instructions were:
Write a function, public int convertToBase10(String s) which takes a
String that represents the String form of a binary number and returns an int which
is equal to this number in base 10. For example, convertToBase10(�1001�)
returns 9.
Can anyone point me in the right direction?
double sum = 0, exp = 0;
public int convertToBase10(String s) {
     if (s.length() >= 1)
     String current = charAt(s.length());
     int num = Integer.parseInt(current);
     sum = sum + (java.lang.Math.pow(2,exp) * num);
     exp++;
     convertToBase10(s.substring(0,(s.length() - 1)));
     return sum;
}

Answer 1

                String str = "1001";
          int num = 0;
          for (int x=0; x<str.length(); x++){
               int c = str.charAt(x)-48;
               int d = (int)Math.pow(2,x);
               num = num + c * d;
          System.out.println(num);str.charAt(x) always returns me the ASCII.
Anyways this works.