使用Java 8流重構循環和條件

Question

我有一個類似的代碼片段：

List<Ticket> lowestPriceTickets(List<Info> infos, Ticket lowestPriceTicket) {
    List<Ticket> allLowestPriceTickets = new ArrayList<>();

    for (Info info : infos)
    {
        if (info.getTicketTypeList() != null)
        {
            for (Ticket ticket : info.getTicketTypeList())
            {
                if (lowestPriceTicket.getCode().order() == ticket.getCode().order())
                {
                    allLowestPriceTickets.add(ticket);
                }
            }
        }
    }
    return allLowestPriceTickets;
}

我正在嘗試使用Java 8流來重構它，但是之后卡住了

infos.stream()
                .filter(info -> info.getTicketTypeList() != null)
                .map(Info::getTicketTypeList)

因為我想過濾每張Ticket但請參閱Stream<List<Ticket>> ，有人可以建議如何實現此方法嗎？ 謝謝！

Answer 1

您需要在兩者之間使用flatMap將Ticket對象的列表轉換為流，以便可以過濾Ticket 。 您可以引用以下代碼（帶有內聯注釋）以使用流獲得結果：

List<Ticket> ticketsList = infos.stream()
   .filter(info -> info.getTicketTypeList() != null)//filter the list if null
   .map(info -> info.getTicketTypeList())//get the tickettype list
   .flatMap(ticketsList -> ticketsList.stream())//convert to stream of tickets
   .filter(lowestPriceTicket -> 
       lowestPriceTicket.getCode().order() == 
          ticket.getCode().order())//check if it matches with the given ticket
   .collect(Collectors.toList());//now collect it to a List<Ticket>