This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
and readLine() returns "" (the empty String) then yes, charAt() will throw a StringIndexOutOfBoundsException, as there is no 0th character in an empty String. Note also that at end-of-file, readLine() returns null, and you need to watch for that as well. Better to write something like