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Java Java Data Structures Efficiency! Queueing

Sean Flanagan
Sean Flanagan
33,234 Points

Error in KaraokeMachine

Hi. I've got a problem with KaraokeMachine.

package com.teamtreehouse;

import com.teamtreehouse.model.Song;
import com.teamtreehouse.model.SongBook;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Deque;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Queue;

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

  public KaraokeMachine(SongBook songBook) {
    mSongBook = songBook;
    mReader = new BufferedReader(new InputStreamReader(System.in));
    mSongQueue = new ArrayDeque<Song>(); //Error here
    mMenu = new HashMap<String, String>();
    mMenu.put("add", "Add a new song to the song book");
    mMenu.put("play", "Play the next song in the queue");
    mMenu.put("choose", "Choose a song to sing!");
    mMenu.put("quit", "Give up. Exit the program");

  private String promptAction() throws IOException {
    System.out.printf("There are %d songs available and %d in the queue. Your options are: %n",
    for (Map.Entry<String, String> option : mMenu.entrySet()) {
      System.out.printf("%s - %s %n",
    System.out.print("What do you want 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();
            System.out.printf("%s added! %n%n", song);
          case "choose":
            String artist = promptArtist();
            Song artistSong = promptSongForArtist(artist);
            System.out.printf("You chose: %s %n", artistSong);
          case "play":
          case "quit":
            System.out.println("Thanks for playing!");
            System.out.printf("Unknown choice: '%s'. Try again. %n%n%n",
      } catch(IOException ioe) {
        System.out.println("Problem with input");
    } while (!choice.equals("quit"));

  private Song promptNewSong() throws IOException {
    System.out.print("Enter the artist's name: ");
    String artist = mReader.readLine();
    System.out.print("Enter the title: ");
    String title = mReader.readLine();
    System.out.print("Enter the video URL: ");
    String videoUrl = mReader.readLine();
    return new Song(artist, title, videoUrl);

  private String promptArtist() throws IOException {
    System.out.println("Available artists: ");
    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) {
    System.out.printf("Available 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);
    System.out.print("Your choice: ");
    String optionAsString = mReader.readLine();
    int choice = Integer.parseInt(optionAsString.trim());
    return choice - 1;

  public void playNext() {
    Song song = mSongQueue.poll();
    if (song == null) {
      System.out.println("Sorry there are no songs in the queue. " + " Use choose from the menu to         add some");
    } else {
      System.out.printf("%n%n%n Open %s to hear %s by %s %n%n%n",



./com/teamtreehouse/KaraokeMachine.java:25: error: cannot find symbol                            
    mSongQueue = new ArrayDeque<Song>();                                                         
  symbol:   class ArrayDeque                                                                     
  location: class KaraokeMachine                                                                 
1 error 

Any help would be appreciated. :-)

1 Answer

Jacob Bergdahl
Jacob Bergdahl
29,118 Points

Add the following import: java.util.ArrayDeque

Sean Flanagan
Sean Flanagan
33,234 Points

That fixed it. Thanks Jacob. :-)