public void undo() {
   if (prevStatus == DVDPlayer.Pull) {
     DVDplayer.Pull();
   } else if (prevStatus == DVDPlayer.Play) {
     DVDplayer.Play();
   } else if (prevStatus == DVDPlayer.Off) {
     DVDplayer.Off();
   } else if (prevStatus == DVDPlayer.On) {
     DVDplayer.On();
   } else if (prevStatus == DVDPlayer.Stop) {
     DVDplayer.Stop();
   }
 }
 public void execute() {
   prevStatus = DVDplayer.getStatus();
   DVDplayer.Off();
 }