Java比较器使用.reverseOrder()但具有内部类

问题描述

我正在创建一个简单的程序来了解Java Comparator类.我已经按顺序对Arraylist进行了排序，但是现在我想按降序对列表进行排序，但是由于使用了实现Comparator<Song>的内部类(歌曲是一首歌，所以在调用.reverseOrder()方法时遇到了问题包含getter和setter方法的类.

I am creating a simple program to learn about the Java Comparator class. I have sorted an Arraylist into order but now I want to sort the list in descending order but am having problems in where to call the .reverseOrder() method as I have used an inner class that implements Comparator<Song> (song being a song class which houses getters and setter methods).

这是我的SongSort类，其中包含排序过程等；

Here is my SongSort class which houses the sorting process etc.;

import java.util.*;
import java.io.*;

public class SongSort
{
    ArrayList<Song> songList = new ArrayList<Song>();

    public void main(String[] args)
    {
        new SongSort().go();
    }

    class ArtistCompare implements Comparator<Song>
    {
        public int compare(Song one, Song two)
        {
            return one.getRating().compareTo(two.getRating());
        }
    }


    public void go()
    {

        getSongs();
        System.out.println(songList);
        //Collections.sort(songList); 
        System.out.println(songList);

        ArtistCompare artistCompare = new ArtistCompare();
        Collections.sort(songList, artistCompare);
        System.out.println(songList);
    }



    public void getSongs()
    {
        try{
            File file = new File("SongListMore.txt");
            BufferedReader reader = new BufferedReader(new FileReader(file));
            String line = null;

            while((line = reader.readLine()) != null)
               {
                   addSong(line);
               }
            }
            catch(Exception ex)
            {
                ex.printStackTrace();
            }
        }

        public void addSong(String lineToParse)
        {
            String [] tokens = lineToParse.split("/");
            Song nextSong = new Song(tokens[0],  tokens[1], tokens[2], tokens[3]);
            songList.add(nextSong);

    }

}

这是我简单的Song类；

public class Song //implements Comparable<Song>
{
    private String title;
    private String artist;
    private String rating;
    private String bpm;

    public Song(String t, String a, String r, String b)
    {
        title = t;
        artist = a;
        rating = r;
        bpm = b;
    }

    public String getTitle()
    {
        return title;
    }

    public String getArtist()
    {
        return artist;
    }
    public String getRating()
    {
        return rating;
    }
    public String getBpm()
    {
        return bpm;
    }

    public String toString()
    {
       return ("Title : " + title + "," +  " Artist : " + artist +  " Rating : " + rating);
    }
}

有人可以帮我弄清楚我将在SongSort类中调用reverseOrder()方法的地方，因为它无法编译吗?

Can anyone help me figure out where I will call the reverseOrder() method in the SongSort class, as it won't compile?

推荐答案

ArtistCompare artistCompare = new ArtistCompare();
Collections.sort(songList, Collections.reverseOrder(artistCompare));

编辑2015年7月

由于此答案仍然受到关注，因此这里进行了一个小更新:

As this answer still gets some attention, here a small update:

使用Java SE 8，创建反向比较器变得更加容易:

With Java SE 8 it's becoming easier to create a reversed comparator:

Comparator<Song> songRatingComparator = Comparator.comparing(Song::getRating);
Collections.sort(songList, songRatingComparator.reversed());

您当然也可以使用Streams框架:

And you can, of course, also use the Streams framework:

List<Song> sortedSongList = songList.stream()
.sorted(Comparator.comparing(Song::getRating).reversed())
.collect(Collectors.toList());

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