Thread: Could someone give me some insight as to how to do this?

I am working on an assignment and I am having trouble figuring out exactly how to do it. I have already done a good bit of it, but I keep getting stuck.

Here is the assignment:

Implement*the*following*classes*in*Java:
MusicCollection
This*class*represents*a*collection*of*music*albums *(see*below).*It*should*provide*the*following
public*methods:
● void addAlbum(Album album)*—*adds*the*supplied*album*to*the*collection
● void removeAlbum(Album album)*—*removes*the*supplied*album*from*the*colle ction
● Album[] albumsByArtist(String artist)*—*returns*an*array*of*Album*objects*from
the*collection*that*match*the*artist*supplied.
● Album[] albumsByYear(int year)*—*returns*an*array*of*Album*objects*from*the
collection*that*match*the*year*supplied.
In*addition,*MusicCollection*must*implement*the*It erable<Album>*interface.*This*requires
you*implement*the*following*method:
● Iterator<Album> iterator()*—*returns*an*Iterator<Album>*object*tha t*iterates
through*the*albums*in*the*collection*in*order*of*a rtist*and*year
Album
This*class*represents*a*music*album.*It*should*pro vide*the*following*public*methods:
● Album(String artist, String title, int year)*—*constructor*accepting*the*artist
name,*the*title*of*the*album,*and*the*year*it*was* released
● String getArtistName()*—*returns*the*name*of*the*artist
● String getTitle()*—*returns*the*title*of*the*album
● int getYear()*—*returns*the*release*year
● boolean equals(Album otherAlbum)*—*returns*true*if*other*album*is*the*s ame*album
from*the*same*artist*and*the*same*year
● String toString()*—*returns*a*string*representing*the*alb ums*information.*The*string
should*look*like*this:*“Artist*Name***Album*Title* (Year)”
In*addition,*Album*must*implement*the*Comparable<A lbum>*interface.*This*requires*you
implement*the*following*method:
● int compareTo(Album otherAlbum)*—*compares*the*album*with*the*supplied
otherAlbum*argument.*Returns**1*if*otherAlbum*shou ld*be*sorted*after*the*album,*0*if
they*are*same*album,*and*1*if*otherAlbum*should*be *sorted*before.*The*sorting*should*be
based*on*artist,*then*year,*then*album.

Here is what I have for the two classes so far:

Album Class:

import java.io.*;
import java.util.*;
 
 
/**
 *
 * @author Jared
 */
public class Album {
    //Variables
    String Artist;
    String Title;
    int Year = 0;
 
    public Album(String artist, String title, int year){
        Artist = artist;
        Title = title;
        Year = year;
    }
 
    public String getArtistName() {
        return Artist;
    }
 
    public String getTitle() {
        return Title;
    }
 
    public int getYear() {
        return Year;
    }
 
    public boolean equals(Album otherAlbum) {
        String otherArtist = otherAlbum.getArtistName();
        String otherTitle = otherAlbum.getTitle();
        int otherYear =  otherAlbum.getYear();
 
        if (Artist.equals(otherArtist) && Title.equals(otherTitle) && Year == otherYear) {
            return true;
        }
        else{
            return false;
        }
    }
 
    @Override
    public String toString() {
        String artistInfo = Artist + " - " + Title +"(" + Year + ")";
        return artistInfo;
    }
 
    public int compareTo(Album otherAlbum) {
        String otherArtist = otherAlbum.getArtistName();
        String otherTitle = otherAlbum.getTitle();
        int otherYear =  otherAlbum.getYear();
 
        if(Album.equals(otherAlbum)){
            return 0;
        }
 
        else if (Artist.equals(otherArtist) ) {
            if (Year > otherYear){
                return -1;
            }
            else if (Year < otherYear){
                return 1;
            }
        }
       /* 
        * 
        else if (Artist.equals(otherArtist) && Year == otherYear && ! Album.equals(otherAlbum)) {
            if (){
 
            }
        }
        return 0;
        * 
        */
    }
}

The place that I cannot figure out how to do is the last method, the compareTo method.


MusicCollection class:

import java.io.*;
import java.util.*;
 
 
 
/**
 *
 * @author Jared
 */
public class MusicCollection impliments Iterable<Album> {
    public ArrayList<Album> musicCollection = new ArrayList<> ();
 
 
    public void addAlbum(Album album){
        musicCollection.add(album);
    }
 
    public void removeAlbum(Album album) {
 
    }
 
    public Album[] albumsByArtist(String artist){
 
    }
 
    public Album[] albumsByYear(int year) {
 
    }
 
    public Iterator<Album> iterator(){
 
    }
}

I can't figure out how to do the last four methods. My teacher did not really cover Iterator.


If someone could help me understand what to do, I would very much appreciate it. Thank you.

That is in the Album class, the only part of that class that I needed help with is the last one. Its the MusicCollection class that I need help with the last four methods. Sorry for the confusion.

Ok, for starters, I am having trouble figuring out how to do this compareTo method. I have tried to logically work through it with if statements but I keep getting stuck. This is what I have so far:

public int compareTo(Album otherAlbum) {
        String otherArtist = otherAlbum.getArtistName();
        String otherTitle = otherAlbum.getTitle();
        int otherYear =  otherAlbum.getYear();
 
        if(Album.equals(otherAlbum)){
            return 0;
        }
 
        else if (Artist.equals(otherArtist) ) {
            if (Year > otherYear){
                return -1;
            }
            else if (Year < otherYear){
                return 1;
            }
        }
       /* 
        * 
        else if (Artist.equals(otherArtist) && Year == otherYear && ! Album.equals(otherAlbum)) {
            if (){
 
            }
        }
        return 0;
        * 
        */
    }

Okay, here is what I have gotten so far. I only have one more thing that needs to be implemented.

Album Class:

import java.io.*;
import java.util.*;
 
/**
 *
 * @author Jared
 */
public class Album {
    //Variables
    public String Artist;
    public String Title;
    public int Year = 0;
 
    public Album(String artist, String title, int year){
        Artist = artist;
        Title = title;
        Year = year;
    }
 
    public String getArtistName() {
        return Artist;
    }
 
    public String getTitle() {
        return Title;
    }
 
    public int getYear() {
        return Year;
    }
 
    public boolean equals(Album otherAlbum) {
        String otherArtist = otherAlbum.getArtistName();
        String otherTitle = otherAlbum.getTitle();
        int otherYear =  otherAlbum.getYear();
 
        if (Artist.equals(otherArtist) && Title.equals(otherTitle) && Year == otherYear) {
            return true;
        }
        else{
            return false;
        }
    }
 
    @Override
    public String toString() {
        String artistInfo = Artist + " - " + Title +"(" + Year + ")";
        return artistInfo;
    }
 
    public int compareTo(Album otherAlbum) {
        String otherArtist = otherAlbum.getArtistName();
        String otherTitle = otherAlbum.getTitle();
        int otherYear =  otherAlbum.getYear();
 
        if (Artist.equals(otherArtist) && Title.equals(otherTitle) && Year == otherYear){
            return 0;
        }
        else if (! Artist.equals(otherArtist)) {
            int compare = Artist.compareToIgnoreCase(otherArtist);
 
            if (compare < 0){
                return -1;
            }
            else if (compare > 0){
                return 1;
            }
        }
 
        else if (Artist.equals(otherArtist) ) {
            if (Year > otherYear){
                return -1;
            }
            else if (Year < otherYear){
                return 1;
            }
        }
 
        else if (Artist.equals(otherArtist) && Year == otherYear && ! Title.equals(otherTitle)) {
            int compare = Title.compareToIgnoreCase(otherTitle);
 
            if (compare < 0){
                return -1;
            }
            else if (compare > 0){
                return 1;
            }           
        }
        return 0;
    }
}

MusicCollection Class:
 
import java.io.*;
import java.util.*;
 
/**
 *
 * @author Jared
 */
public class MusicCollection implements Iterable<Album> {
    public ArrayList<Album> musicCollection = new ArrayList<> ();
 
 
    public  void addAlbum(Album album){
        musicCollection.add(album);
    }
 
    public void removeAlbum(Album album) {
        musicCollection.remove(album);
    }
 
    public Album[] albumsByArtist(String artist){
        String Artist = artist;
        Album[] albumsByArtist;
        ArrayList<Album> tempArrayList = new ArrayList<> ();
        for (int i = 0; i < musicCollection.size(); i++ ){
            if (Artist.equals(musicCollection.get(i).getArtistName())) {
                tempArrayList.add(musicCollection.get(i));
            }
        }
        albumsByArtist = (Album[]) tempArrayList.toArray();
        return albumsByArtist;
    }
 
    public Album[] albumsByYear(int year) {
        int Year = year;
        Album[] albumsByYear;
        ArrayList<Album> tempArrayList = new ArrayList<> ();
        for (int i = 0; i < musicCollection.size(); i++){
            if (Year == musicCollection.get(i).getYear()){
                tempArrayList.add(musicCollection.get(i));
            }
        }
        albumsByYear = (Album[]) tempArrayList.toArray();
        return albumsByYear;
    }
 
    /**
     *
     * @return
     */
    @Override
    public Iterator<Album> iterator(){
 
    }
}

I don't understand how to implement the iterator for the MusicCollection class. My teacher said that since I was using an ArrayList, that it would generate it for me, but I still do not understand how to write it.

Here is the directions for it:

In addition, MusicCollection must implement the Iterable<Album> interface. This requires
you implement the following method:
● Iterator<Album> iterator() — returns an Iterator<Album> object that iterates
through the albums in the collection in order of artist and year

Hey, I apologize that my understanding of what a iterator is or does is poor. We have not really covered it.

Is this what you are talking about?

    /**
     *
     * @return
     */
    @Override
    public Iterator<Album> iterator(){
        Iterator<Album> it = musicCollection.iterator();
        while (it.hasNext()){
            Album obj = it.next();
 
        }
        return null;
    }

I am just confused as how to implement it. I feel like that is doing what I am suppose to do, Im just not sure. Thanks.

The Album class doesn't contain an iterator. Only the MusicCollection class contains an iterator. Since the ArrayList aready has a built in iterator, then do I even need to define an iterator for the ArrayList?