HogeService.java

package com.example.hoge;

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

class HogeService {
  
  
      private <T extends UpdatableRecord> List<T> getUpdatableRecords(
            List<T> existingList,
            List<T> addedList,
            LocalDateTime endDate
    ) {
        var existingUniqueIdToMap = existingList.stream().collect(Collectors.toMap(T::getUniqueKey, data -> data));
        var updatableRecords = new ArrayList<T>();
        addedList.forEach(data -> {
            var existingData = existingUniqueIdToMap.get(data.getUniqueKey());
            if (existingData == null) {
                updatableRecords.add(data);
            } else {
                if (!existingData.isSame(data)) {
                    existingData.setEndDate(endDate);

                    updatableRecords.add(data);
                    updatableRecords.add(existingData);
                }
            }
        });
        return updatableRecords;
    }
}

UpdatableRecord.java

package com.example.hoge;

import java.time.LocalDateTime;

public interface UpdatableRecord {
    String getUniqueKey();

    <T extends UpdatableRecord> Boolean isSame(T other);

    void setEndDate(LocalDateTime endDate);
}