Java IO.pdf - Nguyen Dang Binh

12.2.2.1 Absolute paths
Java I/O
On Unix all mounted disks, whether local or mounted over the network, are combined into a
single virtual filesystem. The root of this filesystem is the directory called /. You generally do
not need to concern yourself with which physical disk any particular directory resides on, as
long as that disk has sufficient space. Absolute paths always begin with the root directory, /.
On Windows and the Mac, there is no root directory. Each mounted disk partition or network
server is a separate and independent filesystem. On Windows, these disks are assigned drive
letters. A: is normally the floppy drive. B: is the second floppy drive (less common these
days, since fewer systems have multiple floppy drives.) C: is the primary boot disk. D: is
often reserved for a CD-ROM, though it can be an additional hard disk or partition as well. E:
through Z: can be used for further disks, partitions, or network servers. A full pathname
begins with the drive letter where the file resides, e.g.,
C:\PUBLIC\HTML\JAVAFAQ\INDEX.HTM.
On Windows 95, 98 and NT, an additional level is possible by specifying remote machines on
the network like this: \\BIO\C\PUBLIC\HTML\ JAVAFAQ\INDEX.HTM. This path refers to a
file called INDEX.HTM in the directory JAVAFAQ in the directory HTML in the directory
PUBLIC on the C drive of the machine BIO. Java 1.1 does not provide a pure Java means to
get a list of all the available volumes on Windows; the best you can do is check all possible
drive letters and catch any IOExceptions that occur. Java 2 does add a File.listRoots()
method that returns all the roots of the local system.
Like Windows, the Macintosh does not have a true root from which all mounted disks and
servers can be accessed. Each disk or disk partition and each server appear as a separate
volume, though the names are generally a little more descriptive than A, B, C, and D.
Macintosh virtual machines interpret a request to list the contents of the directory "/" as a
request for a list of all mounted volumes. You should be warned, however, that a single
Macintosh can have several volumes with the same name. This is rare on a single-user Mac
but relatively common in networked environments where file sharing can mount volumes on
other Macs with common names like Macintosh HD or untitled or Public Folder. This isn't a
problem for native code, which doesn't use names to identify volumes, but it's a real
showstopper for pure Java programs. To further complicate matters, the Mac's primary hard
drive may not be named Macintosh HD.
For these reasons and more, absolute pathnames are a royal pain to work with across
platforms. You should avoid hardcoding them in your programs whenever possible. Instead,
you should calculate them at runtime from system properties and user input.
12.2.2.2 Relative paths
The following are some examples of relative paths:
Unix html/index.html
DOS HTML\INDEX.HTM
Win32 html\index.html
MacOS :html:index.html
Unix index.html
DOS INDEX.HTM
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