Question

名为MyCustomClass的自定义类具有joda LocalDateTime的属性。我需要创建一个java.util.Comparator类来比较MyCustomClass的{{1}}属性的实例，其类型为TimeStamp。我已经阅读了几篇关于此的帖子（包括this one），我已经尝试了所有方法，但答案中显示的方法似乎都不起作用。例如，以下几种方法会抛出编译错误：

LocalDateTime

我打算在代码中的其他地方使用它：

import java.time.temporal.ChronoUnit;
import java.util.Comparator;

import org.joda.time.DateTime;
import org.joda.time.Duration;
import org.joda.time.Period;

import my.app.model.MyCustomClass;

public class MyCustomClassComparator implements Comparator<MyCustomClass>{
    public int compare(MyCustomClass mcc1, MyCustomClass mcc2) {
        //this first attempt throws a return type error for the method.
        return Period.fieldDifference(mcc2.getTimestamp(), mcc1.getTimestamp());
        //This next attempt says that LocalDateTimes are not valid arguments
        Duration.between(mcc2.getTimestamp(), mcc1.getTimestamp());
        //The next approach also says LocalDateTimes are not valid arguments.
        DateTime.parse(mcc2.getTimestamp()), mcc1.getTimestamp()).getSeconds();
        //This boilerplate approach says the minus sign is not valid for LocalDateTime
        return mcc1.getTimestamp() - mcc2.getTimestamp();
    }
}

如何根据Joda List<MyCustomClass> mccs = new ArrayList<MyCustomClass>(); // Sort by time stamp: Collections.sort(mccs, new MyCustomClassComparator());属性编写Comparator类来比较MyCustomClass的实例？

Answer 1

LocalDateTime实现了comparable接口，因此您可以实现比较符：

public class MyCustomClassComparator implements Comparator<MyCustomClass> {
    @Override
    public int compare(final MyCustomClass mcc1, final MyCustomClass mcc2) {
        return mcc1.getTimestamp().compareTo(mcc2.getTimestamp());
    }
}

Answer 2

如果您需要的只是一个比较器实例：

类似于Iłya Bursov的答案，因为LocalDateTime实现了可比性，所以您可以使用Comparator.comparing

Comparator.comparing(MyCustomClass::getTimestamp)

用于两个LocalDateTimes的java比较器

2 个答案: