Well i just got it, id like to say thanks for all the help, it was quite a little change.

public static void main(String[] args){

        String input = null;
        String Output = null;

        String In = JOptionPane.showInputDialog(null," Please enter a file plus its dot format");

        int index = In.lastIndexOf('.');

      String one = In.substring(index + 1);

        JOptionPane.showMessageDialog(null," You choose the " +one + " format");

Using the 'lastIndexOf' was a good idea. In that way you can handle inputs such as: "file.name.txt";

why don't you save it as something like .bat .doc .html .ppt etc

if this does not work send me an e-mail at my PC shop