TopItems { public static List<RecommendedItem> getTopItems(int howMany, LongPrimitiveIterator possibleItemIDs, IDRescorer rescorer, Estimator<Long> estimator) throws TasteException { Preconditions.checkArgument(possibleItemIDs != null, "possibleItemIDs is null"); Preconditions.checkArgument(estimator != null, "estimator is null"); Queue<RecommendedItem> topItems = new PriorityQueue<>(howMany + 1, Collections.reverseOrder(ByValueRecommendedItemComparator.getInstance())); boolean full = false; double lowestTopValue = Double.NEGATIVE_INFINITY; while (possibleItemIDs.hasNext()) { long itemID = possibleItemIDs.next(); if (rescorer == null || !rescorer.isFiltered(itemID)) { double preference; try { preference = estimator.estimate(itemID); } catch (NoSuchItemException nsie) { continue; } double rescoredPref = rescorer == null ? preference : rescorer.rescore(itemID, preference); if (!Double.isNaN(rescoredPref) && (!full || rescoredPref > lowestTopValue)) { topItems.add(new GenericRecommendedItem(itemID, (float) rescoredPref)); if (full) { topItems.poll(); } else if (topItems.size() > howMany) { full = true; topItems.poll(); } lowestTopValue = topItems.peek().getValue(); } } } int size = topItems.size(); if (size == 0) { return Collections.emptyList(); } List<RecommendedItem> result = new ArrayList<>(size); result.addAll(topItems); Collections.sort(result, ByValueRecommendedItemComparator.getInstance()); return result; } private  TopItems(); static List<RecommendedItem> getTopItems(int howMany,
                                                  LongPrimitiveIterator possibleItemIDs,
                                                  IDRescorer rescorer,
                                                  Estimator<Long> estimator); static long[] getTopUsers(int howMany,
                                   LongPrimitiveIterator allUserIDs,
                                   IDRescorer rescorer,
                                   Estimator<Long> estimator); static List<GenericItemSimilarity.ItemItemSimilarity> getTopItemItemSimilarities(
    int howMany, Iterator<GenericItemSimilarity.ItemItemSimilarity> allSimilarities); static List<GenericUserSimilarity.UserUserSimilarity> getTopUserUserSimilarities(
    int howMany, Iterator<GenericUserSimilarity.UserUserSimilarity> allSimilarities);  }
@Test public void testTopItemsRandom() throws Exception { long[] ids = new long[100]; for (int i = 0; i < 100; i++) { ids[i] = i; } LongPrimitiveIterator possibleItemIds = new LongPrimitiveArrayIterator(ids); final Random random = RandomUtils.getRandom(); TopItems.Estimator<Long> estimator = new TopItems.Estimator<Long>() { @Override public double estimate(Long thing) { return random.nextDouble(); } }; List<RecommendedItem> topItems = TopItems.getTopItems(10, possibleItemIds, null, estimator); assertEquals(10, topItems.size()); double last = 2.0; for (RecommendedItem topItem : topItems) { assertTrue(topItem.getValue() <= last); last = topItem.getItemID(); } }