Java Stream流之求和的实现

BigDecimal:

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

int、double、long:

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

补充：java8-Stream流之数值函数（求和、最大值、最小值、平均值）

我就废话不多说了，大家还是直接看代码吧~

//todo stream流的使用
 //todo filter：过滤操作；保留符合过滤条件的对象；这是一个中间操作；后面可以带最终操作
 //todo mapToInt: 将数据根据double类型来处理；
 public static void main(String[] args) {
  List<SalesOrder> list = createSalesOrder();
  //获取集合中城市为上海的数量
  System.out.println(\"mapToInt获取和:\"+list.stream().filter(s -> s.getConsigneeCity().equals(\"上海\"))
   .mapToInt(SalesOrder::getCreateUserId).sum());
  //利用stream流中的函数获取相关数值信息
  IntSummaryStatistics summaryStatistics = list.stream().filter(s -> s.getConsigneeCity().equals(\"上海\"))
   .mapToInt(SalesOrder::getCreateUserId).summaryStatistics();
  System.out.println(\"summaryStatistics函数获取数量:\"+summaryStatistics.getCount());
  System.out.println(\"summaryStatistics函数获取平均值:\"+summaryStatistics.getAverage());
  System.out.println(\"summaryStatistics函数获取最大值:\"+summaryStatistics.getMax());
  System.out.println(\"summaryStatistics函数获取最小值:\"+summaryStatistics.getMin());
  System.out.println(\"summaryStatistics函数获取和\"+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(\"广州\");
  salesOrder.setCreateUserId(30);
  list.add(salesOrder);
  salesOrder = new SalesOrder();
  salesOrder.setConsigneeCity(\"杭州\");
  salesOrder.setCreateUserId(40);
  list.add(salesOrder);
  return list;
 }