技術標籤：java基礎知識--第一行程式碼streamjava

實現一個購買商品後,對資料進行處理統計的功能.

將購買的商品資訊儲存在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()處理資料,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()處理後的資料進行統計

 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介面中DoubleSummaryStatistics類進行資料統計

        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());

總程式碼:

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<<第一行程式碼>>第13章