Problem with the challenge...

package com.teamtreehouse;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

import java.util.ArrayDeque;
import java.util.Map;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.ArrayList;
import java.util.Queue;

public class KaraokeMachine {
    private SongBook mSongBook;
    private BufferedReader mReader;
    private Queue<SongRequest> mSongRequestQueue;
    private Map<String, String> mMenu;

    public KaraokeMachine(SongBook songBook) {
        mSongBook = songBook;
        mReader = new BufferedReader(new InputStreamReader(System.in));
        mSongRequestQueue = new ArrayDeque<>();
        mMenu = new LinkedHashMap<String, String>();

        mMenu.put("add", "Adding a new song to the song book.");
        mMenu.put("choose", "Choose an artist for you to sing.");
        mMenu.put("play", "Play next song in the queue.");
        mMenu.put("quit", "Exit the program.");
    }

    private String promptAction() throws IOException {
        System.out.printf("There are %d song available and %d in the queue. Your options are: %n%n", mSongBook.getSongCount(), mSongRequestQueue.size());

        for (Map.Entry<String, String> option : mMenu.entrySet()) {
            System.out.printf("%s - %s %n", option.getKey(), option.getValue());
        }

        System.out.printf("%nWhat do you whant to do: ");
        String choice = mReader.readLine();

        return choice.trim().toLowerCase();
    }

    public void run() {
        String choice = "";

        do {
            try {
                choice = promptAction();

                switch (choice) {
                    case "add":
                        Song song = promptNewSong();
                        mSongBook.addSong(song);
                        System.out.printf("New song %s is added to the song book. %n%n%n", song);
                        break;
                    case "choose":
                        String singerName = promptForSingerName();
                        String artist = promptArtist();
                        Song artistSong = promptSongForArtist(artist);
                        SongRequest songRequest = new SongRequest(singerName, artistSong);

                        if (mSongRequestQueue.contains(songRequest)) {
                            System.out.printf("%n%nWhoops! %s already requested %s! %n%n%n", singerName, artist);
                            break;
                        }

                        mSongRequestQueue.add(songRequest);
                        System.out.printf("You chose: %s %n%n%n", artistSong);
                        break;
                    case "play":
                        playNext();
                        break;
                    case "quit":
                        System.out.println("Thank you come again!");
                        break;
                    default:
                        System.out.printf("Unknown command '%s'. Try again. %n%n%n", choice);
                        break;
                }
            } catch (IOException ioe) {
                System.out.println("Problem with input.");
                ioe.printStackTrace();
            }
        } while (!choice.equals("quit"));
    }

    private String promptForSingerName() throws IOException {
        System.out.printf("Enter the singer's name: ");
        return mReader.readLine();
    }

    public Song promptNewSong() throws IOException {
        System.out.printf("%nEnter the artists name: ");
        String artist = mReader.readLine();
        System.out.printf("Enter the title: ");
        String title = mReader.readLine();
        System.out.printf("Enter the video URL: ");
        String videoUrl = mReader.readLine();

        return new Song(artist, title, videoUrl);
    }

    private String promptArtist() throws IOException {
        System.out.printf("%nAvailable artists: %n");
        List<String> artists = new ArrayList<>(mSongBook.getArtists());
        int index = promptForIndex(artists);

        return artists.get(index);
    }

    private Song promptSongForArtist(String artist) throws IOException {
        List<Song> songs = mSongBook.getSongsForArtist(artist);
        List<String> songTitles = new ArrayList<>();

        for (Song song : songs) {
            songTitles.add(song.getTitle());
        }

        System.out.printf("%nAvaliable songs for %s: %n", artist);
        int index = promptForIndex(songTitles);

        return songs.get(index);
    }

    private int promptForIndex(List<String> options) throws IOException {
        int counter = 1;

        for (String option : options) {
            System.out.printf("%d. ) %s. %n", counter, option);
            counter++;
        }

        System.out.printf("%nYour choice: ");
        String optionAsString = mReader.readLine();
        int choice = Integer.parseInt(optionAsString.trim());

        return choice - 1;
    }

    public void playNext() {
        SongRequest songRequest = mSongRequestQueue.poll();

        if (songRequest == null) {
            System.out.printf("%n%n%nThere are no more songs in the queue! %n%n%n%n");
        } else {
            Song song = songRequest.getSong();
            System.out.printf("%n%n%nReady %s? Open %s to hear %s by %s. %n%n%n%n", songRequest.getSingerName(), song.getVideoUrl(), song.getTitle(), song.getArtist());
        }
    }
}