Count elements in a Java Arraylist

Question

I have a Arraylist calling for tracklist within the class Album, that contains a number of songs. I need to go through and return how many songs are within the album through a class I named contarMusica. For now I’ve done something like:

public class Album {
private int id;
private String Nome_album; 
Date Lancamento;
private Musica [] tracklist = new Musica[30];
static private int ultimo = 1;

//Contructor
public Album(int id, String nome_album, Date lancamento, Musica[] tracklist) {
    id=ultimo;
    ultimo++;
    Nome_album = nome_album;
    Lancamento = lancamento;
    this.tracklist = tracklist;
}


public void contarMusica(Musica m){

    int contador = 0;

            ...
}

Answer 1

You can use the attribute length, and you can access it to know the size of the array.

public void contarMusica(Musica m){

 int contador = 0;
 for (int i = 0; i < m.length; i ++)
 if (m[i] != null)
    contador ++;
 }

Answer 2

You could use it like this (Create the Get/Set and the same are already ready for various functionalities)

Class:

public class Album {
    private int id;
    private String Nome_album; 
    Date Lancamento;
    private Musica[] tracklist;
    static private int ultimo = 1;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getNome_album() {
        return Nome_album;
    }
    public void setNome_album(String Nome_album) {
        this.Nome_album = Nome_album;
    }
    public Musica[] getTracklist() {
        return tracklist;
    }
    public void setTracklist(Musica[] tracklist) {
        this.tracklist = tracklist;
    }
    public static int getUltimo() {
        return ultimo;
    }
    public static void setUltimo(int ultimo) {
        Album.ultimo = ultimo;
    }
    public Album(int id, String nome_album, Date lancamento, Musica[] tracklist) {
        id=ultimo;
        ultimo++;
        Nome_album = nome_album;
        Lancamento = lancamento;
        this.tracklist = tracklist;
    }
}

In the Codification:

Musica[] musica = new Musica[10];        
Album album = new Album(1, null, null, musica);

int totalMusica = album.getTracklist().length; // quantidade de música

I would do so:

Classes

public class Musica {
    private int id;
    private String nome;
    private int ano;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getNome() {
        return nome;
    }
    public void setNome(String nome) {
        this.nome = nome;
    }
    public int getAno() {
        return ano;
    }
    public void setAno(int ano) {
        this.ano = ano;
    }   
}

---

package classes;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
public class Album {
    private int id;
    private String nomeAlbum; 
    private Date lancamento;
    private List<Musica> tracklist;
    static private int ultimo = 1;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getNomeAlbum() {
        return nomeAlbum;
    }
    public void setNomeAlbum(String nomeAlbum) {
        this.nomeAlbum = nomeAlbum;
    }
    public Date getLancamento() {
        return lancamento;
    }
    public void setLancamento(Date lancamento) {
        this.lancamento = lancamento;
    }
    public List getTracklist() {
        return tracklist;
    }
    public void setTracklist(List tracklist) {
        this.tracklist = tracklist;
    }
    public static int getUltimo() {
        return ultimo;
    }
    public static void setUltimo(int ultimo) {
        Album.ultimo = ultimo;
    }
    //Contructor
    public Album(){
        this.tracklist = new ArrayList<>();
    }
    public Album(int id, String nomeAlbum, Date lancamento, List tracklist) {
        this.id = ultimo;        
        this.nomeAlbum = nomeAlbum;
        this.lancamento = lancamento;
        this.tracklist = tracklist;
    }
}

---

Testing

import classes.Album;
import classes.Musica;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
public class JavaApplication1 {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {           
       Musica music1 = new Musica();
       Musica music2 = new Musica();
       List<Musica> musicas = new ArrayList<>();
       musicas.add(music1);
       musicas.add(music2);       
       Album album = new Album(1, "Nome Album 1", new Date() , musicas);
       album.getTracklist().size(); // quantidade que estão na lista
    }
}

'Cause I’d do it like this?

Because, the List is dynamic so that you can add/remove/change songs from a particular album, one album may have more songs than the other and limit the list would be a mistake ...

Answer 3

int size = tracklist.lenght;