This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Say you have this:
File f = new File("./folder1/folder2");
f.mkdir() will create only folder2 and only if folder1 already exists on the specified path
f.mkdirs() will create the entire path: if folder1 doesn't exist it will create it and the it will create the subfolder folder2