實現一個購買商品后,對數據進行處理統計的功能.

將購買的商品信息保存在Orders類中

public class Orders {private String name;private double price;private int amount;public Orders(String name, double price, int amount) {this.name = name;this.price = price;this.amount = amount;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}public int getAmount() {return amount;}public void setAmount(int amount) {this.amount = amount;}

通過map()處理數據,輸出購買每一件商品的總價

public static void main(String[] args) {List<Orders> list = new ArrayList<>();list.add(new Orders("dq csdn", 60.00, 80));list.add(new Orders("dq android", 100.20, 73));list.add(new Orders("dq java", 72.02, 15));//計算購買每一件商品的總價list.stream().map((x) -> x.getAmount() * x.getPrice()).forEach(System.out::println);}

通過reduce()對map()處理后的數據進行統計

 double all = list.stream().map((x) -> x.getAmount() * x.getPrice()).reduce((x, y) -> x + y).get();System.out.println(String.format("%.2f", all));

使用DoubleStream接口中DoubleSummaryStatistics類進行數據統計

        DoubleSummaryStatistics statistics=list.stream().mapToDouble((x)->x.getAmount()* x.getPrice()).summaryStatistics();System.out.println("商品品種"+statistics.getCount()+"商品總花費"+statistics.getSum()+"商品平均花費"+statistics.getAverage()+"最高花費"+statistics.getMax()+"最低花費"+statistics.getMin());

總代碼:

import java.util.ArrayList;
import java.util.DoubleSummaryStatistics;
import java.util.List;public class Orders {private String name;private double price;private int amount;public Orders(String name, double price, int amount) {this.name = name;this.price = price;this.amount = amount;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}public int getAmount() {return amount;}public void setAmount(int amount) {this.amount = amount;}public static void main(String[] args) {List<Orders> list = new ArrayList<>();list.add(new Orders("dq csdn", 60.00, 80));list.add(new Orders("dq android", 100.20, 73));list.add(new Orders("dq java", 72.02, 15));DoubleSummaryStatistics statistics=list.stream().mapToDouble((x)->x.getAmount()* x.getPrice()).summaryStatistics();System.out.println("商品品種"+statistics.getCount()+"商品總花費"+statistics.getSum()+"商品平均花費"+statistics.getAverage()+"最高花費"+statistics.getMax()+"最低花費"+statistics.getMin());}
}

參考<<第一行代碼>>第13章