Java null constructor

Question

So I have two classes called songs and albums, here they are:

    public class Songs {
    private String title;
    private Double duration;

    public Songs(String title, Double duration) {
        this.title = title;
        this.duration = duration;
    }

    public Songs(){}


    public String getTitle() {
        return title;
    }



    public Double getDuration() {
        return duration;
    }


    public static Songs addSong(String title, Double duration){
        return new Songs(title,duration);

    }
}



    import java.util.ArrayList;
import java.util.LinkedList;

public class Albums {
    private ArrayList<Songs> albums;
    private String name;
    private String title;

    public Albums(String name, String title) {
        this.albums = new ArrayList<>();
        this.name = name;
        this.title = title;
    }

    public boolean addSong(Songs songs){
        if(findSong(songs.getTitle())==null){
            this.albums.add(songs);
            return true;
        }else{
            System.out.println("Song alredy exist!");
            return false;
        }

    }

      private Songs findSong(String songName){
        for(int i=0;i<this.albums.size();i++){
            Songs currentSong = this.albums.get(i);
            if(currentSong.equals(songName)){
                return currentSong;
            }
        }
        return null;
    }
}

The problem is the main, maybe my logic is not right, if I'm missing something please tell me:

 public class Main {

    public static void main(String[] args) {
        Albums albums = new Albums("Alexandru", "Doi dsadcopii");
        Songs songs = new Songs("Patrascu",4.44);
        songs.addSong("Dorin",11.11);
        albums.addSong(songs);

        songs.addSong("Dorin",11.11);
        albums.addSong(songs);


        songs.addSong("Dorinsads",11.11);
        albums.addSong(songs);


        songs.addSong("Dorisadsan",11.11);
        albums.addSong(songs);



        System.out.println(songs.getTitle());

        albums.addSong(songs);

        albums.printSongs();
    }
}

Why I'm getting the same value ? why those values from the .addSong where not added in the list ? This is my code to print the list:

    public void  printSongs() {
    for (int i = 0; i < this.albums.size(); i++) {
        System.out.println(i + 1 + "-->" + this.albums.get(i).getTitle() + "--->" + this.albums.get(i).getDuration());
    }

}

For sure I'm missing something but I dont know exactly where, any ideas how to fix this ? Thanks! :D The problem is when I'm using the .printSongs() method it prints the first value

addSong doesn't add a Songs, it only creates a new object, and you just ignore it. — Bart Friederichs
– Bart Friederichs, Commented Aug 19, 2017 at 10:04
words are important. Change to singular Song and Album. Then thing about multiply (Album has many Song) ... so album.add(Song) etc — Jacek Cz
– Jacek Cz, Commented Aug 19, 2017 at 10:06
Since addSong creates a new object, which is not saved anywhere, your 'songs' variable remains unchanged and you are basically adding the same object 5 times. — The Javatar
– The Javatar, Commented Aug 19, 2017 at 10:11
What does the term "null constructor" in your title have to do with your question? — Mark Rotteveel
– Mark Rotteveel, Commented Aug 19, 2017 at 10:20

Dorian Gray · Accepted Answer · 2017-08-19 10:08:58Z

2

From your class Songs:

public static Songs addSong(String title, Double duration){
    return new Songs(title,duration);
}

This is just returning a new Song, it is not adding it to the internal List.

You can just add them to the album directly, like

Albums albums = new Albums("Alexandru", "Doi dsadcopii");
albums.addSong(new Songs("Patrascu",4.44));
albums.addSong(new Songs("Dorin",11.11));

answered Aug 19, 2017 at 10:08

Dorian Gray

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Comments

Murat Karagöz · Accepted Answer · 2017-08-19 10:05:21Z

0

Your Song#addSong method is plain wrong. You are creating new Sound objects there. In fact you don't need to do that. Remove that method and use it like this

Albums albums = new Albums("Alexandru", "Doi dsadcopii");
albums.addSong(new Songs("Patrascu",4.44));
albums.addSong(new Songs("Dorin",11.11));

etc.

answered Aug 19, 2017 at 10:05

Murat Karagöz

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Comments

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2017-08-21 05:07:58Z

0

Please Use modified below Main class.

public class Main {

    public static void main(String[] args) {
        Albums albums = new Albums("Alexandru", "Doi dsadcopii");
        Songs songs = new Songs();
        songs=songs.addSong("Patrascu",4.44);
        albums.addSong(songs);
        songs=songs.addSong("Dorin",11.11);
        albums.addSong(songs);

        songs=songs.addSong("Dorin",11.11);
        albums.addSong(songs);



        songs=songs.addSong("Dorinsads",11.11);
        albums.addSong(songs);


        songs=songs.addSong("Dorisadsan",11.11);
        albums.addSong(songs);

        System.out.println(songs.getTitle());

        albums.addSong(songs);

        albums.printSongs();
    }
}

edited Aug 21, 2017 at 5:07

ΦXocę 웃 Пepeúpa ツ

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answered Aug 21, 2017 at 5:04

Kumar Panchal

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Comments

HK boy · Accepted Answer · 2019-11-07 12:20:41Z

0

Assuming that by

songs.addSong("Dorin",11.11);

, you meant

Songs.addSong("Dorin",11.11);

. This is happening because you are not reassigning songs reference. Replace every statement

songs.addSong("Dorin",11.11);

with

songs=Songs.addSong("Dorin",11.11);

and it will work. Further observation is that your logic in 'findSong()' for equality will always yield false.

edited Nov 7, 2019 at 12:20

HK boy

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answered Aug 19, 2017 at 10:11

Sunil Singhal

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