How to do more comparisons in compareTo()?

Question

My exercise says that i should implement a class called songs with a few methods. (see below) Afterwards i should code a method with given comparisons:

song1 < song2 if and only if

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

song1 = song2 if and only if

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

song1 > song2 other

I implement the first comparison and it works but i have no idea how to write down the others. Do you have any hints?? I'm only allowed to use Comparable , not 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

You can achieve your goal by this :

@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

I will do it this way

@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);}

    }