while (degrees < 0) { degrees += 360; }
  private static Rotation valueOf(int degrees) {    degrees = degrees % 360;    Rotation result;    if (degrees ==   0) { result = NOTHING; } else    if (degrees == -90) { result = LEFT   ; } else    if (degrees ==  90) { result = RIGHT  ; } else    if (degrees == 180) { result = OVER   ; } else {      throw new IllegalArgumentException();    }    return result;  }