Java Stream流之求和的實現

BigDecimal bb =list.stream().map(Plan::getAmount).reduce(BigDecimal.ZERO,BigDecimal::add);

double max = list.stream().mapToDouble(User::getHeight).sum();

//todo stream流的使用
 //todo filter：過濾操作；保留符合過濾條件的對象；這是一個中間操作；後面可以帶最終操作
 //todo mapToInt: 將數據根據double類型來處理；
 public static void main(String[] args) {
  List<SalesOrder> list = createSalesOrder();
  //獲取集合中城市為上海的數量
  System.out.println("mapToInt獲取和:"+list.stream().filter(s -> s.getConsigneeCity().equals("上海"))
   .mapToInt(SalesOrder::getCreateUserId).sum());
  //利用stream流中的函數獲取相關數值信息
  IntSummaryStatistics summaryStatistics = list.stream().filter(s -> s.getConsigneeCity().equals("上海"))
   .mapToInt(SalesOrder::getCreateUserId).summaryStatistics();
  System.out.println("summaryStatistics函數獲取數量:"+summaryStatistics.getCount());
  System.out.println("summaryStatistics函數獲取平均值:"+summaryStatistics.getAverage());
  System.out.println("summaryStatistics函數獲取最大值:"+summaryStatistics.getMax());
  System.out.println("summaryStatistics函數獲取最小值:"+summaryStatistics.getMin());
  System.out.println("summaryStatistics函數獲取和"+summaryStatistics.getSum());
 }
 
static List<SalesOrder> createSalesOrder(){
  List<SalesOrder> list = new LinkedList<>();
  SalesOrder salesOrder = new SalesOrder();
  salesOrder.setCreateUserId(12);
  salesOrder.setConsigneeCity("上海");
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity("上海");
  salesOrder.setCreateUserId(24);
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity("北京");
  salesOrder.setCreateUserId(18);
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity("深圳");
  salesOrder.setCreateUserId(16);
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity("廣州");
  salesOrder.setCreateUserId(30);
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity("杭州");
  salesOrder.setCreateUserId(40);
  list.add(salesOrder);
  return list;
 }