Question

Hello ive added two new functions to the implementation of an interface.

this is the implementation file…

import au.edu.uow.Collection.Album;
import java.util.ArrayList;

public class CDAlbum implements Album {
    private String Title;
    private String Genre;
    private String Artist;
    private String MediaType;
    private ArrayList<String> trackList;

    public CDAlbum(String TempTitle, String TempGenre, String TempArtist, ArrayList<String> TempTracklist, String TempMediaType){
        //Set initail variable values
        Title = TempTitle;
        Genre = TempGenre;
        Artist = TempArtist;
        trackList = TempTracklist;
        MediaType = TempMediaType;
    }
    //Accessor Functions
    public String getMediaType(){
        //Return Media Type
        return MediaType;
    }
    public String getTitle(){
        //Return Title
        return Title;
    }
    public String getGenre(){
        //Return Genre
        return Genre;
    }
    public String getArtist(){
        //Return Artist
        return Artist;
    }
    public ArrayList<String> getTrackList(){
        //Return Tracklist
        return trackList;
    }
}

The bottom two functions are the added functions( getArtist(), getTrackList())
the problem im having is that when i try to call these functions from a class file it give me the following errors.

./au/edu/uow/UserInterface/UserInterface.java:95: cannot find symbol
symbol  : method getArtist()
location: interface au.edu.uow.Collection.Album
            System.out.println(albumCollection.get(number).getArtist());
                                                          ^
./au/edu/uow/UserInterface/UserInterface.java:98: cannot find symbol
symbol  : method getTrackList()
location: interface au.edu.uow.Collection.Album
            ArrayList<String> trackList = albumCollection.get(number).getTrackList();

When i call the functions

import au.edu.uow.Collection.Album;

System.out.println(albumCollection.get(number).getArtist());

//Access the track titles
ArrayList<String> trackList = albumCollection.get(number).getTrackList();
//Output collection
int arrayListSize = trackList.size();
for(int i = 0; i < arrayListSize; i++)
{
    System.out.println( i + ": " + trackList.get(i));
}

Answer 1

Album specifies neither getArtist nor getTrackList:

public interface Album {
    /**
     * This method returns the media type of the album. 
     * @return the media type of the album, either CD or DVD
     * @see #getTitle()
     * @see #getGenre()
     */
     String getMediaType();

    /**
     * This method returns the title of the album. 
     * @return the title of the album
     * @see #getMediaType()
     * @see #getGenre()
     */
     String getTitle();

    /**
     * This method returns the genre of the album. 
     * @return the genre of the album
     * @see #getTitle()
     * @see #getMediaType()
     */
    String getGenre();

}

… only CDAlbum does.

You can determine whether the Album is a CDAlbum or DVDAlbum by checking Album.getMediaType; then, if it is a CD, you can cast to CDAlbum and invoke getArtist and getTrackList then.

for (final Album album : albumCollection) {
  final String type = album.getMediaType();
  System.out.print(type + " album: " + album.getTitle()
      + " (" + album.getGenre() + ") - ");
  if (type.equals("CD")) {
    final CDAlbum cd = (CDAlbum) album;
    System.out.println(cd.getArtist());
    int n = 0;
    for (final String track : cd.getTrackList()) {
      System.out.printf("#%2d - %s\n", ++n, track);
    }
  } else {
    final DVDAlbum dvd = (DVDAlbum) album;
    System.out.println(dvd.getDirector());
    System.out.println(dvd.getPlotOutline());
  }
}