collection和lambda数据处理实战

• 需求描述：电商订单数据处理，根据下⾯的list1和list2 共11个订单

统计出同时被两个⼈购买的商品列表(交集)
统计出两个⼈购买商品的差集
统计出全部被购买商品的去重并集
统计两个⼈的分别购买订单的平均价格
统计两个⼈的分别购买订单的总价格

• 代码案例

public class VideoOrder {

    private String tradeNo;

    private int money;

    private String title;

    public VideoOrder(String tradeNo, String title, int money) {
        this.tradeNo = tradeNo;
        this.title = title;
        this.money = money;
    }

    public String getTradeNo() {
        return tradeNo;
    }

    public void setTradeNo(String tradeNo) {
        this.tradeNo = tradeNo;
    }

    public int getMoney() {
        return money;
    }

    public void setMoney(int money) {
        this.money = money;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof  VideoOrder){
            VideoOrder o1 =  (VideoOrder)obj;
            return title.equals(o1.title);
        }
        return super.equals(obj);
    }
    
    @Override
    public int hashCode() {
        return title.hashCode();
    }
    
    @Override
    public String toString() {
        return "VideoOrder{" +
                "title='" + title + '\'' +
                '}';
    }
}

public class Main {

    public static void main(String[] args) throws Exception {

        //总价 35
        List<VideoOrder> videoOrders1 = Arrays.asList(
                new VideoOrder("20190242812", "springboot教程", 3),
                new VideoOrder("20194350812", "微服务SpringCloud", 5),
                new VideoOrder("20190814232", "Redis教程", 9),
                new VideoOrder("20190523812", "网页开发教程", 9),
                new VideoOrder("201932324", "百万并发实战Netty", 9));

        //总价 54
        List<VideoOrder> videoOrders2 = Arrays.asList(
                new VideoOrder("2019024285312", "springboot教程", 3),
                new VideoOrder("2019081453232", "Redis教程", 9),
                new VideoOrder("20190522338312", "网页开发教程", 9),
                new VideoOrder("2019435230812", "Jmeter压力测试", 5),
                new VideoOrder("2019323542411", "Git+Jenkins持续集成", 7),
                new VideoOrder("2019323542424", "Idea全套教程", 21));
        
        //两个订单平均价格
        double videoOrderAvg1 =  videoOrders1.stream().collect(Collectors.averagingInt(VideoOrder::getMoney)).doubleValue();
        System.out.println("订单列表1平均价格="+videoOrderAvg1);

        double videoOrderAvg2 =  videoOrders2.stream().collect(Collectors.averagingInt(VideoOrder::getMoney)).doubleValue();
        System.out.println("订单列表2平均价格="+videoOrderAvg2);
        
        //订单总价
        int totalMoney1 =  videoOrders1.stream().collect(Collectors.summingInt(VideoOrder::getMoney)).intValue();
        System.out.println("订单列表1总价="+totalMoney1);

        int totalMoney2 =  videoOrders2.stream().collect(Collectors.summingInt(VideoOrder::getMoney)).intValue();
        System.out.println("订单列表2总价="+totalMoney2);
        
        //交集
        List<VideoOrder> intersectionList = videoOrders1.stream().filter(videoOrders2::contains).collect(Collectors.toList());
        System.out.println(intersectionList);
        
        //差集1
        List<VideoOrder> diffList1 =  videoOrders1.stream().filter(obj->!videoOrders2.contains(obj)).collect(Collectors.toList());
        System.out.println("差集1="+diffList1);

        List<VideoOrder> diffList2 =  videoOrders2.stream().filter(obj->!videoOrders1.contains(obj)).collect(Collectors.toList());
        System.out.println("差集2="+diffList2);
        
        //并集
        List<VideoOrder> allVideoOrder = videoOrders1.parallelStream().collect(Collectors.toList());
        allVideoOrder.addAll(videoOrders2);
        System.out.println("并集="+allVideoOrder);
        
        List<VideoOrder> allVideoOrderDistinct = allVideoOrder.parallelStream().distinct().collect(Collectors.toList());
        System.out.println("去重并集="+allVideoOrderDistinct);
    }
    
}