How to detect OS from within java?

hi,
i have a method that reads all the classes in a directory. to do this i use the code
File dir = new File(DIRECTORY_PATH);
the variable DIRECTORY_PATH is a windows based directory path and so if i port my app to a mac it will not work 'cos of the different directory structure.
is there any way i could detect the OS before this method is called so i can change the directory path structure?
many thanks in advance
benny

im reading all the classes available in a dir.
i then populate a list box with the classes available
the user can then select the classes he wants created from this list.the code goes something like this:
File dir = new File(DIRECTORY_PATH);
String [] classes = dir.list( new FilenameFilter()); //filter gets files ending with .class
then i populate the list with these, user selects wanted classes and presses create.
then i use Class.forName() to create the specified classes.
will this work on both OS? is there a better way to do this if not?

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How to detect OS from within java?

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