Question

我在代码下面遇到了一个问题

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);

        }
    }

}

和records对象包含不同类类型的Object

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

现在我需要按每个类中的stampDate变量对它们进行排序当我们在列表中有不同的类时，我们怎么能这样做

Answer 1

如果您的上述代码正确无误，则表示AddressRecord，CityRecord和UserRecord都延伸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
}

您只需为此课程编写Comparator。看起来应该是这样的：

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

只需使用受保护字段 stampDate 编写抽象类记录，即实现可比较并覆盖 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);
    }
}

然后使用您的记录类扩展此类：

public class AddressRecord extends Record{
...
}

public class CityRecord extends Record{
...
}

public class UserRecord extends Record{
...
}

Answer 3

如果您无法更改类，请编写比较器（Comparator<Object>），这将尝试查找字段stampDate并进行比较。比用它来排序列表。比较器实现：

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List上使用以下Comparator类。

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.
    }

}

Java ArrayList在动态对象字段的基础上排序？

4 个答案: