java每月跟踪器

Question

   Date     Name   Sale  Discount  Product
2021-02-01   LV    143     14       P1
2021-02-18   PS    473     25       P2
2021-02-01   LV    65      5        P3
2021-02-22   XB    143     14       P1
2021-02-27   PS    143     14       P1
2021-03-03   LV    263     46       P3
2021-03-16   XB    765     38       P2

Answer 1

除了map，您还可以使用现代的日期时间API和streamAPI。

您可以定义数据类，如下所示

class Transaction {
    LocalDate date;
    String name;
    int sale;
    int discount;
    String product;
    YearMonth tranYearMon;

    public Transaction(LocalDate date, String name, int sale, int discount, String product) {
        this.date = date;
        this.name = name;
        this.sale = sale;
        this.discount = discount;
        this.product = product;
        this.tranYearMon = YearMonth.of(date.getYear(), date.getMonth());
    }

    // Getters, setters, toString etc.
}

现在，在processing类中，您可以将数据分组，如

import java.time.LocalDate;
import java.time.YearMonth;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<Transaction> list = List.of(
                    new Transaction(LocalDate.parse("2021-02-01"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-02-18"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-02-01"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-02-22"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-02-27"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-03-03"), "LV", 143, 14, "P1"),
                    new Transaction(LocalDate.parse("2021-03-16"), "LV", 143, 14, "P1")
                );
        
        Map<YearMonth, List<Transaction>> map = list.stream().collect(Collectors.groupingBy(t ->t.getTranYearMon()));
        System.out.println(map);
    }
}