title: Add extension with jFileChooser
body: <p>I'm creating a program which will create files with different extensions. For that, i'm using the <code>JFileChooser</code>. I've set the <code>FileFilter</code> to accept only my desired extensions, but when I select one, I still have to add the extension in the name of the file myself. How can I solve that? Many thanks!</p>