String shortpath = "";
        StringTokenizer tokenizer = new StringTokenizer(longpath, "\\");
        while(tokenizer.hasMoreTokens() == true)
        {
            String temp = tokenizer.nextToken();
            if(temp.length() >= 8)
                temp = temp.substring(0, 6) + "~1";
            shortpath += temp + "\\";
        }

There is Microsoft's algorithm, for converting a regular (long) filename to a DOS (short) filename, which you can probably find on MSDN. The most basic operation is indeed to construct an "8.3" abbreviation by appending "~1" to the first 6 chars, then dropping everything else, up to the first (?) ".", and taking only the first 3 chars after that, for the "extension". But the algorithm continues, if you have a lot of files with similar names, for instance (after you run out of "~2", "~3", ...).

But then, there is the entirely different operation, of taking a directory in a FAT32/NTFS filesystem, and getting the actual (short and long) names stored for the files in it (as in "DIR /X"), IF the filesystem has generated a short name for each file (I think in the NTFS version used in WindowsXP, the short name is no longer generated and stored, by default, for every file?).

So, using Microsoft's algorithm you can predict what the short name should be, but retrieving the actual short name from the directory is a different operation. The two should match, except in the newer filesystems e.g. NTFS under WinXP, where there may no longer be a short name stored for a given file (I think you can still create and store the short name for a given file, on demand if needed?).

Caution, I think there may be a problem with this solution (not that I know a better one) or at least there was when I looked into this last.

First is handling spaces ... you need to know to drop em. So if you create a folder called "this is the first test" it will have a short name of THISIS~1.

The second issue though is more tricky. If originally there were three folders called:

"this is the first test"
"this is the second test"
"this is the third test"

They would have short names of THISIS~1, THISIS~2, and THISIS~3. So far, fine.

But, what happens if the "this is the first test" folder is deleted? On my system I show the two remaining folders listed as THISIS~2 and THISIS~3. That is, the short name seems to be cooked in when the folder is created.

Which you might think is good if you are hard coding the path name into your application.

However, if you come along later and see only the two folders, you might assume they were ~1 and ~2, not ~2 and ~3, and using the ~2 to access the 'second' directory would result in the wrong one.

Worse, if you create a new folder called "this is the fourth test" it's short name is THISIS~1, not ~4. You can just imagine what that would do to your application.

Confusing, huh?

I would be searching at MSDN and Technet (microsoft.com) if I were needing some serious information about this ....

As I wrote (a year and a half ago! nice long conversation here :-), the NTFS filesystem has a second name slot, for storing a "short" ("8dot3") name, for a file, BUT it may be empty.
And I remember reading somewhere, that under Windows XP now (maybe under Windows 2000 too? unlike NT4 and earlier), the default is NOT to compute and store a short name anymore, unless you change a configuration parameter for the filesystem (? I forget; maybe it was an argument to the "CONVERT" command?).

If you do "HELP DIR" in a command prompt, look at the comment for the "/X" option. In Windows 2000 now it says:

This displays the short names generated for non-8dot3 file names.
The format is that of /N with the short name inserted before the long name.
If no short name is present, blanks are displayed in its place.

So you could indeed get into a situation like the one described, where short names were generated at one time, but then files were removed, etc., and your current computation of short names could be off, from the actual stored previously computed short names, because of the way they depend on sequential numbers ...... pretty yucky.

5 minutes at microsoft.com will come up with:

1. registry key "NtfsDisable8dot3NameCreation"

2. Win32 API function "GetShortPathName" (<http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/getshortpathname.asp?frame=true>),
including remark "When an application calls this function and specifies a path on a volume that does not support 8.3 aliases, the function fails with ERROR_INVALID_PARAMETER if the path is longer than 67 bytes."

... and so on ...