Java Stream流之求和的實現

BigDecimal:

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

int、double、long:

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

補充:java8-Stream流之數值函數(求和、最大值、最小值、平均值)

我就廢話不多說瞭,大傢還是直接看代碼吧~

//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;
 }

以上為個人經驗,希望能給大傢一個參考,也希望大傢多多支持WalkonNet。如有錯誤或未考慮完全的地方,望不吝賜教。

推薦閱讀: