java.util.Collections

        List<Integer> list = new ArrayList<>();
        list.add(2);
        list.add(1);
        list.add(3);

        Collections.sort(list);//升序
        System.out.println(list);
        Collections.reverse(list);//降序
        System.out.println(list);

        Integer max = Collections.max(list);//获取最大值
        Integer min = Collections.min(list);//获取最小值
        System.out.println(max);
        System.out.println(min);

        List<Integer> integers = Collections.synchronizedList(list);//将ArrayList转换成线程安全集合
        System.out.println(integers);

        List<Object> emptyList = Collections.emptyList();//返回空集合
        System.out.println(emptyList);

        int i = Collections.binarySearch(list, 3);//二分查找
        System.out.println(i);

        List<Integer> integers2 = Collections.unmodifiableList(list);//转换成不可修改集合
        integers2.add(4);
        System.out.println(integers2);