Set 差集/交集/并集

        Set<Integer> set1 = Sets.newHashSet(1, 2, 3);
        Set<Integer> set2 = Sets.newHashSet(1, 2, 6);

        //差集
        Sets.SetView<Integer> difference = Sets.difference(set1, set2);
        System.out.println("差集: " +difference);//[2, 3]
        System.out.println("差集: " +Sets.difference(set2, set1));//[4, 6]

        //交集
        Sets.SetView<Integer> intersection = Sets.intersection(set1, set2);
        System.out.println("交集: " +intersection); //[1]

        //并集
        Sets.SetView<Integer> union = Sets.union(set1, set2);
        System.out.println("并集: " +union); //[1, 2, 3, 4, 6]

        System.out.println(intersection.size());
        List<Integer> collect = new ArrayList<>(intersection);
        System.out.println(collect);