如何在 compareTo() 中做更多的比较？

Question

我的练习说我应该用一些方法实现 class 歌曲。（见下文）之后我应该用给定的比较编写一个方法：

歌曲 1 < 歌曲 2 当且仅当

song1.singer < song2.singer
song1.singer = song2.singer ∧ song1.title < song2.title
song1.singer = song2.singer ∧ song1.title = song2.title ∧ song1.year > song2.year

歌曲 1 = 歌曲 2 当且仅当

song1.singer = song2.singer ∧ song1.title=song2.title ∧ song1.year = song2.year

歌曲 1 > 歌曲 2 其他

我实现了第一个比较并且它有效但我不知道如何写下其他的。你有什么提示吗？？我只能使用 Comparable，不能使用 Comparator！

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;


public class Songs implements Comparable<Songs>{

private String singer;
private String title;
private Integer year;


Songs(String singer, String title, int year){

        this.singer = singer;
        this.title  = title;
        this.year   = year;

    }
public String getSinger(){

        return this.singer;
    }
public String getTitle(){

        return this.title;
    }
public int getYear(){

        return this.year;
    }

public String getCompleteName(){

        return this.singer+"\t"+this.title.toString()+" - "+this.year.toString();
    }





public int compareTo(Songs o) {

        if (o.getSinger() == this.getSinger() ) {
              return 0;
            }
        if (this.getSinger()==null) {
              return 1;
            }
         if (o.getSinger() == null) {
              return -1;
            }
         return this.getSinger().compareTo(o.getSinger());




}



    public static void main(String[] args) {


        List<Songs> list = new ArrayList<Songs>();

        list.add(new Songs ("Birdman","Breathe", 1994));
        list.add(new Songs ("Lgoony","Nebel", 2012));
        list.add(new Songs ("Recondite","Cleric",2015));
        list.add(new Songs ("Alpha", "Beta", 1023));
        list.add(new Songs ("Cleric", "zoom", 1999));
        list.add(new Songs ("Cleric", "boom", 1999));

        Collections.sort(list);

        for (Songs x : list) {
              System.out.println(x.getCompleteName());
        }
}




}

Answer 1

你可以通过这个实现你的目标:

@Override
public int compareTo(Songs o) {

    int compare;
    if ((compare = this.getSinger().compareTo(o.getSinger())) != 0) {
        return compare;
    } else if ((compare = this.getTitle().compareTo(o.getTitle())) != 0) {
        return compare;
    }
    return this.getYear() - o.getYear();
}

Answer 2

我会这样做

@Override
public int compareTo(Songs song) {
    int val=0 ;
    if(!singer.equals(song.getSinger())){
    return singer.compareTo(song.getSinger());
    }
    else if (!title.equals(song.getTitle())){
        return title.compareTo(song.getTitle());}
        else  {return -1*song.getYear().compareTo(year);}

    }

如何在 compareTo() 中做更多的比较？

How to do more comparisons in compareTo()?

java

comparable