JAVA8 List> list中再装一个list转成一个list操作

  List<Integer> collect = IntStream.range(1, 10).boxed().collect(Collectors.toList());
  List<Integer> collect1 = IntStream.range(10, 20).boxed().collect(Collectors.toList());

  List<List<Integer>> lists = new ArrayList<>();
  lists.add(collect);
  lists.add(collect1);
  ArrayList<Integer> collect2 = lists.stream().collect(ArrayList::new, ArrayList::addAll, ArrayList::addAll);
  System.out.println(collect2);