public Balloon(double radius, double fullness) {
        if (radius <=0) {
            throw new IllegalArgumentException(
                    "Illegal radius, must me positive");
        } else {
            this.radius = radius;
        }

        if (fullness < 0 || fullness > 1) {
            throw new IllegalArgumentException(
                    "Illegal fullness, must me 0..1");
        } else {
            this.fullness = fullness;
        }
    }