Java CompareTo Method

Question

does anyone know how the string compareTo method actually works? I am trying to use a binary search to find a word in an arraylist with a specific prefix.
i know that the compareTo method returns a 1 0 or -1 based on what the result of the comparison is but im interested in teh actual way that the comparison takes place.
Since i will be comparing a prefix to a complete word, i would like to know if this would cause any problems due to the difference in string lengths.
Do you guys have any other idea on how i can use a very fast searching method to search a sorted arraylist of words to see if any word with a specific prefix exists?

Answer 1

i did that but i would still have to use compareTo because if the middle element does not have the prefix i am looking for then i would have to know if its on the right half or the left half of the Arraylist by comparing. right?
     public static int bSearch(ArrayList list, String pref)
          int result = -1;
          int low = 0;
          int high = list.size()-1;
          String s="";
          while(low <= high || result==-1)
               int mid = (low + high)/2;
               s = (String)list.get(mid);
               if(s.startsWith(pref)==true)
                    result = mid;
               else if(pref.compareTo(list.get(mid))<0)
                    high = mid - 1;
               else
                    low = mid + 1;
          return result;
     }this is what i got so far but i am not sure if using compareTo method the way i am using it will work or not.