Java ArrayList根據動態對象字段排序嗎？

Question

我遇到以下代碼問題

public void columnsList(List<TableRecord> records){

    for(TableRecord record : records){
        Table table = record.getTable();
        //Do sort here on stampDate
        Field[] fields = table.fields();
        for(Field field : fields){
            field.getName();
            record.getValue(field);

        }
    }

}

並records對象包含不同類類型的對象

List<TableRecord> records = new List<TableRecord>();
records.add(new AddressRecord());
records.add(new CityRecord());
records.add(new UserRecord());

現在我需要如何根據每個類中的stampDate變量對它們進行排序，當列表中有不同的類時我們該怎么做

Answer 1

如果你上面的代碼是正確的，這意味着AddressRecord ， CityRecord和UserRecord所有擴展TableRecord ：

class AddressRecord extends TableRecord {
    // other fields and methods here
}
class CityRecord extends TableRecord {
    // other fields and methods here
}
class UserRecord extends TableRecord {
    // other fields and methods here
}

您只需要為此類編寫一個Comparator 。 它看起來應該像這樣：

class TableRecord {
    private Date timeStamp;

    public Date getTimeStamp() {
        return timeStamp;
    }
// other fields and methods here
}

class RecordStampDateComparator implements Comparator<TableRecord>{

    public int compare(TableRecord tr1, TableRecord tr2) {
        Date tr1Date = tr1.getTimeStamp();
        Date tr2Date = tr2.getTimeStamp();   
        return tr1Date.compareTo(tr2Date);
    }
}

Answer 2

只需編寫帶有受保護字段stampDate的抽象類Record 即可 ，該類實現Comparable並重寫compareTo方法。

public abstract class Record implements Comparable<Record> {
    protected Date stampDate;

    @Override
    public int compareTo(Record anotherRecord){
        return this.stampDate.compareTo(anotherRecord.stampDate);
    }
}

然后用您的記錄類擴展該類：

public class AddressRecord extends Record{
...
}

public class CityRecord extends Record{
...
}

public class UserRecord extends Record{
...
}

Answer 3

如果您不能更改類，請編寫比較器（ Comparator<Object> ），這將嘗試查找字段stampDate並對其進行比較。 比用它來排序列表。 比較器實現：

import java.util.Comparator;
import java.util.Date;


public class StampDateComparator implements Comparator<Object> {

@Override
public int compare(Object o1, Object o2) {

    try {
        Date d1 = (Date) o1.getClass().getDeclaredField("stampDate").get(o1);
        Date d2 = (Date) o2.getClass().getDeclaredField("stampDate").get(o2);
        return compare(d1, d2);
    } catch (SecurityException e) {
        throw new RuntimeException(e);
    } catch (NoSuchFieldException e) {
        throw new RuntimeException("Missing variable stampDate");
    }catch (ClassCastException e) {
        throw new RuntimeException("stampDate is not a Date");
    } catch (IllegalArgumentException e) {
        //shoud not happen
        throw new RuntimeException(e);
    } catch (IllegalAccessException e) {
        throw new RuntimeException(e);
    }
}

}

Answer 4

在列表上使用以下Comparator類。

class TableRecordCompare implements Comparator<TableRecord>{
     if(TableRecord instanceof AddressRecord){
       // return compareTo for sample data of address.
     }
     else if(TableRecord instanceof CityRecord){
     // return compareTo for sample data of CityRecord.
      }
     else{
     // return compareTo for sample data of UserRecord.
    }

}