@Override
    public void undo() {
        if(prevSpeed==CeiligFan.HIGH){
            ceilingFan.high();
        }else if(prevSpeed==CeiligFan.MEDIUM){
            ceilingFan.medium();
        }
        else if(prevSpeed==CeiligFan.LOW){
            ceilingFan.low();
        }
        else if(prevSpeed==CeiligFan.OFF){
            ceilingFan.OFF();
        }
    }