Collection<Integer> (int maxIndex) { if (ourIndices != null) return ourIndices; final Random rnd = new Random(System.currentTimeMillis()); final int size = rnd.nextInt(maxIndex/2); ourIndices = new HashSet<>(); for (int c = 0; c < size; ++c) { final int id = rnd.nextInt(maxIndex); ourIndices.add(id); // System.out.println("\t" + id); } ourIndices.remove(1); ourIndices.remove(2); return ourIndices; }