java8-Stream流之数值函数（求和、最大值、最小值、平均值）

今天药忘吃喽~ 2021-11-29 10:54 2242阅读 0赞

//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;
        }

![20190721224050728.png][]

[20190721224050728.png]: /images/20211129/251ffdc9a83b41929cb3b4718d0d4cb3.png