public void undo()
 {
     if (prevSpeed == CeilingFan.HIGH)
     {
         ceilingFan.high();
     }
     else if (prevSpeed == CeilingFan.MEDIUM)
     {
         ceilingFan.medium();
     }
     else if (prevSpeed == CeilingFan.LOW)
     {
         ceilingFan.low();
     }
     else if (prevSpeed == CeilingFan.OFF)
     {
         ceilingFan.off();
     }
 }
 public void execute()
 {
     prevSpeed = ceilingFan.getSpeed();
     ceilingFan.low();
 }