Java 8-初始化列表（列表）

Question

I have a question concerning Java 8 and Lists. Is it possible to initialise a List easier than my code below is?

final List<List<ScheduleIntervalContainer>> weekScheduler = new ArrayList<>();

weekScheduler.add(0, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(1, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(2, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(3, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(4, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(5, new ArrayList<ScheduleIntervalContainer>());
weekScheduler.add(6, new ArrayList<ScheduleIntervalContainer>());

Answer 1

Personally I would just use a for loop:

List<List<ScheduleIntervalContainer>> weekScheduler = new ArrayList<>();
for (int i = 0; i < 7; i++)
    weekScheduler.add(new ArrayList<>());

However, if you want a Java 8 solution:

List<List<ScheduleIntervalContainer>> weekScheduler 
        = Stream.generate(ArrayList<ScheduleIntervalContainer>::new)
                .limit(7)
                .collect(Collectors.toList());

Answer 2

You can use:

List<List<ScheduleIntervalContainer>> weekScheduler = 
     IntStream.rangeClosed(0, 6).mapToObj(i -> new ArrayList<ScheduleIntervalContainer>())
                                .collect(Collectors.toList());

This will create a Stream of int values going from 0 to 6 (included), map each of those ints to a new ArrayList of your class and collect the result to a List .

Answer 3

You can use a loop or an IntStream.

final List<List<ScheduleIntervalContainer>> weekScheduler = new ArrayList<>();
IntStream.range(0, 7).forEach(day -> weekScheduler.add(new ArrayList<>()));

Answer 4

Whenever I code with lists, I use a for loop to speed up the declaration. In your case, I would heavily suggest a loop of any kind, but a for loop would probably be the easiest.