org.apache.commons.collections4.CollectionUtils

        {// 集合判空
            List<Integer> list = new ArrayList<>();
            list.add(2);
            list.add(1);
            list.add(3);

            if (CollectionUtils.isEmpty(list)) {
                System.out.println("集合为空");
            }

            if (CollectionUtils.isNotEmpty(list)) {
                System.out.println("集合不为空");
            }
        }

        {// 对两个集合进行操作
            List<Integer> list = new ArrayList<>();
            list.add(2);
            list.add(1);
            list.add(3);

            List<Integer> list2 = new ArrayList<>();
            list2.add(2);
            list2.add(4);

            //获取并集
            Collection<Integer> unionList = CollectionUtils.union(list, list2);
            System.out.println(unionList);

            //获取交集
            Collection<Integer> intersectionList = CollectionUtils.intersection(list, list2);
            System.out.println(intersectionList);

            //获取交集的补集
            Collection<Integer> disjunctionList = CollectionUtils.disjunction(list, list2);
            System.out.println(disjunctionList);

            //获取差集
            Collection<Integer> subtractList = CollectionUtils.subtract(list, list2);
            System.out.println(subtractList);
        }