Android superuser shutdown/reboot commands not doing anything

I am trying to make an app that can shutdown/reboot your phone at the touch of a button. I found a command online for reboot:

public void rebootPhone() {
    try {
        Runtime.getRuntime().exec("su");
        Runtime.getRuntime().exec(开发者_开发知识库"reboot");
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

I understand this requires root (for the "su" superuser command); My phone has been rooted so I can gain su access. However when this method is run (after I press 'yes' on the prompt to allow su access) the phone does not reboot, nothing happens! Is there something else i need to include to make the phone reboot?

Also, what is the su command for shutdown (i.e. to just turn your phone off)? I can't find it anywhere on the net.

You can't "su" in one process and "reboot" in another expecting it to have super user status. The command "su -c reboot" might work for you though.