1.List集合中取出某一属性的值的集合
List<Order> list = new ArrayList<User>();
List<String> orderNoList=list.stream().map(User::getOrderNo).collect(Collectors.toList());
List<String> idList=list.stream().map(Order::getId()).collect(Collectors.toList());
2.判断list中是否包含某个对象
List<Integer> AList=new ArrayList<>();
Integer i =0;
bool b = AList.contains(i);
3.List中追加list
List result =new ArrayList<>();
List selectProductCommentModelList = new ArrayList<>();
result.addAll(selectProductCommentModelList);
4.判断是否有值
list.isEmpty();
