Description

Lab 01: PlayListApp

In this lab, you will:

• Work with a basic music playlist.
• Complete the partial implementation of the playlist, which aggregates a set of Tack objects.
• Create a controller for the playlist, which controls various data-flow to a playlist instance, separating-out this responsibility from the playlist itself.
•
… which will result in the following outcomes:

• A reminder of the function of:
o getter and setter methods and class constructers. o Use of Predicate.
o Overridden methods.
• Introduction to the basic use of a Controller class

Table of Contents
1.1 Preliminary 3
1.2 Exercise 1 3
1.3 Exercise 2 5
1.4 Exercise 3 6

Figure 1: PlayListAppStarter project ……………………………………………………………………………… 3
Figure 2: Target output from the TrackTest class ……………………………………………………………. 4
Figure 3: Configuring Netbeans ……………………………………………………………………………………. 4

1.1 Preliminary

• Download the lab1.zip file < Lab1_PlaylistAppStarter.zip> from GCULearn and unzip.

• Launch NetBeans 8 and open the Lab1_PlaylistAppStarter project.

Figure 1: Lab1_PlayListAppStarter
Note the structure of the application with packages folders for model and controllers. Currently there are syntax errors in some of the classes which are addressed in the following exercises.

1.2 Exercise 1
Open the Track class, in the model folder, and note the attributes: trackId, trackTitle, trackArtist and trackLength.
a. Add in the missing getters and setters for attributes.
Note the class variable – lastAllocatedTrackId – which is used to generate a value for the trackId attribute when a new Track object is created. You can see how this is used in the two constructor methods: in both cases, a new Track object is being created so a new value for trackId is required.
public Track(String trackTitle, String trackArtist, int trackLength)
{
this.trackId = ++lastAllocatedTrackId; this.trackTitle = trackTitle; this.trackArtist = trackArtist; this.trackLength = trackLength;
}

b. Create a new constructor method which accepts parameter values for all attributes.
public Track(int trackId, String trackTitle,
String trackArtist, int trackLength) { … }

Note the private methods: getTrackLengthMinutes() and getTrackLengthSeconds() which split the trackLength value into separate values for minutes and seconds. These methods are called from the toString() method which provides a String version of the current values of attributes for the object. This method is preceded by the @Override annotation to indicate that a toString() method is inherited from the Object class and we are overriding this to provide a customised version.
c. Run the TrackTest class and ensure that you can create, update and display tracks.

Figure 2: Target output from the TrackTest class

Figure 3: Configuring Netbeans

1.3 Exercise 2
We are working towards a basic Playlist app so next we have to create a Playlist class, in the model folder, which aggregates a collection of Tracks.
a. Add a new class to the model folder called Playlist and declare attributes as follows:

playlistName – String playlistAuthor – String
playlistTracks – ArrayList of Track

b. Three constructors are required: a parameterless constructor detailed below; a constructor which accepts name and author; and, a third constructor which accepts values for all three attributes.

public Playlist() {
this.playlistName = “New Playlist”; this.playlistAuthor = “Unknown”;
this.playlistTracks = new ArrayList<Track>(); }

Create the other two constructors.

c. Add getters and setters for each of the attributes.

d. Add a toString() method which uses the private method getNumberedTracks() detailed below:

private String getNumberedTracks() { String numberedTracks = ” “; int number = 1;
for (Track track : this.playlistTracks) { numberedTracks += Integer.toString(number++) + “:
” +
track.toString() + ” “;
}
return numberedTracks;
}

e. We also require methods to add and remove tracks from the playlist. The addTrackToPlaylist() method is straightforward and simply involves accepting a track as a parameter and adding it to the playlistTracks attribute:

public void addTrackToPlaylist(Track track) { this.playlistTracks.add(track); }

The removal process is more complex. As a taste of things to come I have implemented this using a Predicate object which will search the list for a track that matches a supplied trackId and then removes it from the list. Later, we will see how this works:

public void removeTrackFromPlaylist(int trackId) { Predicate<Track> trackPredicate =
t-> t.getTrackId() == trackId; this.playlistTracks.removeIf(trackPredicate); }

Add these methods.

f. Run the PlaylistTest class to create a playlist and add and remove tracks.
1.4 Exercise 3
We are now going to introduce the concept of a controller class which will interpret user requests and, through interacting with model classes, generate suitable responses. Now the app simply has to create a controller object and then run it; from then on the controller object carries out all the work.
a. Open the PlaylistAppStarter class and note its use of the
PlaylistController object:

public static void main(String[] args) { PlaylistAppStarter playlistApp = new PlaylistAppStarter(); playlistAppStarter.run();
}

public static void run() {
System.out.println(“PlaylistApp ======== “);

PlaylistController playlistController = new PlaylistController();

playlistController.run();

System.out.println(“Thank you for using
PlaylistApp. “);
}

b. Open the PlaylistController class and note it has a Playlist attribute.

private final Playlist playlist;

Note the PlaylistController constructor uses an InputHelper object to ask for a playlist name and author; using these values in creating the Playlist object:

public PlaylistController() {
InputHelper inputHelper = new InputHelper(); String playlistName =
inputHelper.readString(“Enter Playlist
Name”);
String playlistAuthor =
inputHelper.readString(“Enter Playlist
Author”);

playlist = new Playlist(playlistName, playlistAuthor);
}

Examine the InputHelper class which contains methods for reading strings and numbers from the standard input stream.

c. Examine the run() method; note, it uses a private method displayPlaylistMenu() to display options for adding and removing tracks.

public void run() { boolean finished = false; do {
System.out.println(playlist); char choice = displayPlaylistMenu(); switch (choice) { case ‘A’: addTrack(); break; case ‘B’: deleteTrack(); break; case ‘F’: finished = true;
}
} while (!finished);
}

private char displayPlaylistMenu() {
InputHelper inputHelper = new InputHelper();
System.out.print(” A. Add a new track”);
System.out.print(” B. Delete a track”); System.out.print(” F. Finish “); return inputHelper.readCharacter(“Enter choice”,
“ABF”);
}

d. Examine the addTrack() method which is used to get new track details from the user – using an InputHelper object – and then executes the addTrackToPlaylist() method on the Playlist object.

private void addTrack() {
InputHelper inputHelper = new InputHelper(); String trackTitle =
inputHelper.readString(“Enter Track Title”); String trackArtist =
inputHelper.readString(“Enter Track Artist”); int trackMinutes =
inputHelper.readInt(“Enter Track Minutes”, 60,
0);
int trackSeconds =
inputHelper.readInt(“Enter Track Seconds”, 60,
0);
Track newTrack = new Track(trackTitle, trackArtist, trackMinutes * 60 + trackSeconds);
playlist.addTrackToPlaylist(newTrack);
}

e. Implement the deleteTrack() method:

• Create an InputHelper object
• Read an integer between 1 and 100 representing the track id to delete
• Call the appropriate Playlist method using the track id

f. Run the PlaylistAppStarter class and ensure that you can create a playlist, add and remove tracks.