You want to know about all the top-level directories, such as C: and D: on MS-Windows.

Use the static method File.listRoots( ) .

Speaking of directory listings, you surely know that all modern desktop computing systems arrange files into hierarchies of directories. But you might not know that on Unix all filenames are somehow “under” the single root directory named /, while on Microsoft platforms there is a root directory named in each disk drive (A: for the first floppy, C: for the first hard drive, and other letters for CD-ROM and network drivers). If you need to know about all the files on all the disks, then, you should find out what “directory root” names exist on the particular platform. The static method listRoots( ) returns (in an array of File objects) the available filesystem roots on whatever platform you are running on. Here is a short program to list these, along with its output:

C:> type DirRoots.java
import java.io.*;

public class DirRoots {
    public static void main(String argh_my_aching_fingers[]) {
        File[] drives = File.listRoots(  ); // Get list of names
        for (int i=0; i<drives.length; i++)
            System.out.println(drives[i]);    // Print the list
    }
}
C:> java DirRoots
A:
C:
D:
C:>

As you can see, the program listed my floppy drive (even though the floppy drive was not only empty, but left at home while I wrote this recipe on my notebook computer in a parking lot), the hard disk drive, and the CD-ROM drive.

On Unix there is only one:

$ java DirRoots
/
$

One thing that is “left out” of the list of roots is the so-called UNC filename. UNC filenames are used on Microsoft platforms to refer to a network-available resource that hasn’t been mounted locally on a particular drive letter. For example, my server (running Unix with the Samba SMB fileserver software) is named darian (made from my surname and first name), and my home directory on that machine is exported or shared with the name ian, so I could refer to a directory named book in my home directory under the UNC name \darianianook. Such a filename would be valid in any Java filename context (assuming you’re running on MS-Windows), but you would not learn about it from the File.listRoots( ) method.