// the original code for class Thermometer

    public int measure() {
        if (onoff == false) {
            try {
                throw IllegalStateException(" ");
            } catch (Exception ex) {
                Logger.getLogger(Thermometer.class.getName()).log(Level.SEVERE, null, ex);
            }
        } else {
            Random randoms = new Random();
            random = randoms.nextInt(61) - 30;

            return random;
        }
        return random;
    }

// my suggestion

    public int measure() {
        if (onoff) {
            return (int) (-30 + Math.random() * 60);
        }
        throw new IllegalStateException();
    }