From the API
public boolean renameTo(File dest)
Renames the file denoted by this abstract pathname.
Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.
Note that the Files class defines the move method to move or rename a file in a platform independent manner.
dest - The new abstract pathname for the named file
true if and only if the renaming succeeded; false otherwise
SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.lang.String) method denies write access to either the old or new pathnames
NullPointerException - If parameter dest is null