I've been stuck for days with a problem i have no idea how to solve

package com.teamtreehouse;
import com.teamtreehouse.model.SongBook;
import com.teamtreehouse.model.Song;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Map;
import java.util.HashMap;
import java.util.ArrayList;
import java.util.List;
import java.util.ArrayDeque;
import java.util.Queue;

public class KaraokeMachine{

  private SongBook mSongBook;
  private BufferedReader mReader;
  private Map<String,String> mMenu;
  private Queue<Song> mSongQueue;

  public KaraokeMachine(SongBook songBook){
mSongBook=songBook;
 // esto convierte bytes a chars cuando realmente lo necesitamos
//para ayudar a la eficiencia
    mReader= new BufferedReader(new InputStreamReader(System.in));
    mSongQueue = new ArrayDeque<Song>();
    mMenu = new HashMap<String,String>();
    // los mapas string string sirven mucho para hacer menus
    mMenu.put("add","Add a new son to the song book");    
    mMenu.put("play","Play next song in the queue");
    mMenu.put("choose","Choose a song to sing!");
    mMenu.put("quit","Give up. Exit the program");
  }

private String promptAction()throw IOException{
  //no es mi problema la exception
System.out.printf("There are %d songs available and %d in the queue. your options are%n",mSongBook.getSongCount(),mSongQueue.size());
  for(Map.Entry<String,String> option: mMenu.entrySet()){
  System.out.printf("%s - %s %n",option.getKey(),option.getValue());}
  System.out.print("What do you want to do: ");
  String choice= mReader.readLine();
  return choice.trim().toLowerCase();//trim recorta los espacios al final y al principio
  }

  public void run(){
  String choice = "";
  do {
    try{
  choice = promptAction();//en vez de hacer ifs usamos switch
      switch(choice){
    case "add":
      Song song =promptNewSong();
      mSongBook.addSong(song);
      System.out.printf("%s has been added! %n%n",song);
      break;
        case"choose":
        String artist = promptArtist();
        Song artistSong=promptSongForArtist(artist);
        //TODO: ADD TO A SONG QUEUE,done
        mSongQueue.add(artistSong);
        System.out.printf("you chose: %s %n",artistSong);
        break;
        case "play":
        playNext();
        break;
      case "quit":
      System.out.println("Thanks for playing!");
        break;
    default : 
      System.out.printf("unknown choice: '%s'. Try again.  %n%n%n",choice);
    }
    }catch(IOException ioe){
    System.out.println("problem with input");
    ioe.printStackTrace();
    }
  }while(!choice.equals("quit"));
    }

  private Song promptNewSong()throw 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 url =mReader.readLine();
  return new Song(artist,title,url);   
  }

  private String promptArtist() throw 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){
  songTitles.add(song.getTitle());
  }
    System.out.printf("Available songs for %s: %n",artist);
  int index=promptForIndex(songTitles);
  return songs.get(index);
  }


  private int promptForIndex(List<String> options)throw IOException{
  int counter = 1;
  for (String option : options){
  System.out.printf("%d.) %s %n",counter,option);
  counter ++;
  }
   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" ,song.getVideoUrl()
         ,song.getTitle()
          ,song.getArtist());
  }

  }
}