(import '(java.io File))

(.renameTo (File. "input.txt") (File. "output.txt"))
(.renameTo (File. "docs") (File. "mydocs"))

(.renameTo 
 (File. (str (File/separator) "input.txt"))
 (File. (str (File/separator) "output.txt")))
(.renameTo 
 (File. (str (File/separator) "docs"))
 (File. (str (File/separator) "mydocs")))