如何结合2个或更多的对象在一个列表中基于这些对象的某些字段

Question

如果标题听起来很模糊，我很抱歉。

我有个目标-

    public class AccountInfo {
        private String accountId;
        private Double vat;
        private Double totalFee;
        private Date invoiceDate;
    }

还有这些物品的清单-

List<AccountInfo> AccountInfoLst;

我想通过合并具有相同帐户ID的对象来操作这个列表，方法是将vat字段和总计费用字段相加，前提是它们也具有相同的发票日期。

如果两个对象具有相同的帐户ID但不同的发票日期，则它们不应合并。

Answer 1

在重复的列表上迭代，将它们合并到一个AcCountInfo并删除所有重复的列表。

由于Date已被弃用，我们使用了java。时间LocalDate。

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class AccountInfo {
    private String accountId;

    private Double vat;
    private Double totalFee;
    private LocalDate invoiceDate;

    public Double getVat() {
        return vat;
    }

    public void setVat(Double vat) {
        this.vat = vat;
    }

    public Double getTotalFee() {
        return totalFee;
    }

    public void setTotalFee(Double totalFee) {
        this.totalFee = totalFee;
    }

    public LocalDate getInvoiceDate() {
        return invoiceDate;
    }

    public void setInvoiceDate(LocalDate invoiceDate) {
        this.invoiceDate = invoiceDate;
    }

    public AccountInfo(String accountId, Double vat, Double totalFee, LocalDate invoiceDate) {
        this.accountId = accountId;
        this.vat = vat;
        this.totalFee = totalFee;
        this.invoiceDate = invoiceDate;
    }

    public String getAccountId() {
        return accountId;
    }

    public void setAccountId(String accountId) {
        this.accountId = accountId;
    }

    public String toString() {
        return accountId + " " + vat + " " + totalFee + " " + invoiceDate;
    }

    public boolean areEquals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        AccountInfo that = (AccountInfo) o;
        var thatInvoiceDate = that.getInvoiceDate();
        var thisInvoiceDate = getInvoiceDate();
        return that.getAccountId().equals(getAccountId()) && thatInvoiceDate.isEqual(thisInvoiceDate);
    }

    @Override
    public int hashCode() {
        return Objects.hash(accountId, vat, totalFee, invoiceDate);
    }
}

public class MainClass {
    public static void main(String... $) {
        var out = System.out;
        
        List<AccountInfo> accounts = Stream.of(new AccountInfo("A", 20.2, 200.4, LocalDate.of(2022, 11, 3))
                , new AccountInfo("A", 20.2, 200.4, LocalDate.of(2022, 11, 3)),
                new AccountInfo("B", 20.2, 200.4, LocalDate.of(2023, 11, 2)),
                new AccountInfo("B", 20.2, 200.4, LocalDate.of(2023, 11, 2))).collect(Collectors.toList());
        
        //Iterating over all the accounts
        for (int i = 0; i < accounts.size(); i++) {
            var account = accounts.get(i);
            ArrayList<AccountInfo> duplicates = new ArrayList<>();
            for (int j = i + 1; j < accounts.size(); j++) {
                var acc = accounts.get(j);
                if (acc.areEquals(account))
                    duplicates.add(acc);
            }
//            out.println(i + " " + indices);
            //Merging all duplicates to account
            for (AccountInfo acc : duplicates) {
                account.setTotalFee(acc.getTotalFee() + account.getTotalFee());
                account.setVat(acc.getVat() + account.getVat());
            }
            //Removing all duplicates
            accounts.removeAll(duplicates);
        }
        //printing accounts after removal of duplicates
        out.println(accounts);
    }
}

[A 40.4 400.8 2022-11-03, B 40.4 400.8 2023-11-02]

Answer 2

如果你想利用流来做这件事，其中一种可能的方法是收集数据到地图，使用一个组合了accountId和invoiceDate的对象作为键。

将合并映射到同一密钥的所有帐户。

在帐户ID或发票日期中不同的帐户将保持不变。

    public static void main(String[] args) {
        List<AccountInfo> result = List.of(
                    new AccountInfo("123", 80., 180., LocalDate.now()),
                    new AccountInfo("123", 120., 590., LocalDate.now()),
                    new AccountInfo("123", 30., 120., LocalDate.now().minusDays(3))
                )
                .stream()
                .collect(Collectors.toMap(
                        AccountWrapper::new,
                        UnaryOperator.identity(),
                        (acc1, acc2) -> new AccountInfo(
                                acc1.getAccountId(),
                                acc1.getVat() + acc2.getVat(),
                                acc1.getTotalFee() + acc2.getTotalFee(),
                                acc1.getInvoiceDate())
                ))
                .values().stream()
                .collect(Collectors.toList());

        result.forEach(System.out::println);
    }



    public record AccountWrapper(String accountId, LocalDate invoiceDate) {
        public AccountWrapper(AccountInfo info) {
            this(info.getAccountId(), info.getInvoiceDate());
        }
    }

输出

AccountInfo{accountId='123', vat=200.0, totalFee=770.0, invoiceDate=2022-02-09}
AccountInfo{accountId='123', vat=30.0, totalFee=120.0, invoiceDate=2022-02-06}