This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
File.renameTo does not change the File object. If it returns true it renames the file, yes, but the File object is immutable and stays exactly the same. Instead of using the old value of f you should reassign it: