How can I set/update the PATH variable from within a Java application on Windows?

Something equivalent to this command line:

set PATH=%PATH%;C:\Something\bin

To run my application, something has to be in a PATH variable. So I want at the program beginning catch exceptions if the program fails to start and display some wizard for the user to select the installation folder of a program that needs to be in a PATH. Then I would take that folder's absolute path and add it to the PATH variable and start my application again.

That "something" is VLC media player. I need its installation folder in the PATH variable (for example: C:\Program Files\VideoLAN\VLC). My application is a single executable .jar file and in order to use it, VLC needs to be in a PATH. So when the user first starts my application, that little wizard would pop up to select the VLC folder, and then I would update PATH with it.

You can execute commands using the Process object, and you can also read the output of that using a BufferedReader. Here's a quick example that may help you out:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

    public static void main(String args[]) {
        try {
            Process proc = Runtime.getRuntime().exec("cmd set PATH=%PATH%;C:\\Something\\bin");
            proc.waitFor();
            BufferedReader reader = new BufferedReader(new InputStreamReader(proc.getInputStream()));

            String line = reader.readLine();
            while (line != null) {
                // Handle what you want it to do here
                line = reader.readLine();
            }
        }
        catch (IOException e1) {
            // Handle your exception here
        }
        catch(InterruptedException e2) {
            // Handle your exception here
        }

        System.out.println("Path has been changed");
    }
}