The documentation for File.createNewFile say "This method, in combination with the deleteOnExit() method, can therefore serve as the basis for a simple but reliable cooperative file-locking protocol."  This statement is false and dangerously misguided.

If you mark the file as deleteOnExit *before* invoking createNewFile but the file already exists, you run the risk of deleting a file you didn't create and dropping someone elses lock!  On the other hand, if you mark the file *after* creating it, you lose atomicity: if the program exits before the file is marked, it won't get deleted and the lock will be "wedged".

Luckily, a proper file-locking facility was added in release 1.4 (java.nio.channels Class FileLock).  The disinformative notation on File.createNewFile should be replaced by something like this:

"Note: this method should <i>not</i> be used for file-locking, as the resulting protocol cannot be made to work reliably.  The {@link java.nio.channels.FileLock FileLock} facility should be used instead."

Perhaps this note should be added to the doc comment for File.deleteOnExit as well.