How to retrieve a list of directories QUICKLY in Java?

Question

Suppose a very simple program that lists out all the subdirectories of a given directory. Sound simple enough? Except the only way to list all subdirectories in Java is to u

Answer 1

Do you know the finite list of possible subdirectory names? If so, use a loop over all possible names and check for directory's existence.

Otherwise, you can not get ONLY directory names in most underlying OSs (e.g. in Unix, the directory listing is merely reading contents of "directory" file, so there's no way to find "just directories" quickly without listing all the files).

However, in NIO.2 in Java7 (see http://java.sun.com/developer/technicalArticles/javase/nio/#3 ), there's a way to have a streaming directory list so you don't get a full array of file elements cluttering your memory/network.