ASC 和 DESC 顺序的自定义比较器实现

Question

I'm trying to find a way to define an unique implementation of java.util.Comparator usable for both ascending and descending ordering purpose.

I have defined a class Golf.java that represents Volkswagen's car. I also defined a Comparator that order Golf instances by horses power ( int variable). I was wondering if it's possible to use the same comparator for both ascending and descending ordering.

GolfHorsePowerComparator.java

package test2.comparator;

import test2.dto.Golf;
import java.util.Comparator;

public class GolfHorsePowerComparator implements Comparator<Golf> {

    @Override
    public int compare(Golf a, Golf b) {
        return a.getHorsePower() > b.getHorsePower() ? 1 : a.getHorsePower() == b.getHorsePower() ? 0 : -1;
    }

}

Given a list of Golf how could I sort them ascending or descending using the same java.util.Comparator implementation?

Answer 1

You can use Collections::reverseOrder to sort in desc order. Eg:

GolfHorsePowerComparator golfHorsePowerComparator = new GolfHorsePowerComparator();
Collections.sort(golfList, Collections.reverseOrder(golfHorsePowerComparator));

Answer 2

Yes, look at documentation . Comparator has a reversed method. You can simply do this:

list.stream().sorted(comparator).collect(Collectors.toList());
list.stream().sorted(comparator.reversed()).collect(Collectors.toList());

The first one sorts ascending, the second - descending.