For example:
new File("/home").getParent() returns null. ("/" would be nice)
new File("//home").getParent() returns "/".

new File("/").list() returns:
 "//net"
 "//home" ("/home" would be nicer, at least there is getCanonicalPath() now)

 and lots more.

From a program's point of view, there is no way to navigate up to find "/".
("/home" seems to be the root (null parent) when starting from "/home/hefner")

Windows of course has an even bigger set of problems.
(e.g., does "C:\" have a parent, and if not, is there any way to obtain
 a list of drives?)