PooledSet<String> set = new PooledSet<>(); set.add("apple"); set.add("banana"); set.add("orange"); set.remove("banana"); MultiDictionary<String, Integer> dictionary = new MultiDictionary<>(); dictionary.put("fruit", 1); dictionary.put("fruit", 2); dictionary.put("fruit", 3); dictionary.put("vegetable", 4); dictionary.remove("fruit", 2);