New to Java

Hey, First of all I have to apologise for posting in wrong place,but I guess might some one has used the jflex. Is jflex only works with files.
what i m passing a string on run time i.e. "jflex advantages". and in string i m looking for jflex. It reads each character but at the end of this string neither its giving any result nor giving any exception. i m new to jflex. can any body give me a simple example.