LibGDX NullPointer Exception when trying to load Music

Question

I'm working out of the book Learning Libgdx Game Development on Chapter 10 dealing with adding music and sound to the game. I tried Googling around to see if anyone else came across the same null pointer issue with adding the music but no luck.

Essentially trying to load in a Music track from a different class called Assets to run in my main game.

I see the assets are loaded, it prints out on the console. So I don't think it is an issue with not finding the file.

com.woodgdx.game.Assets: # of assets loaded: 9
com.woodgdx.game.Assets: asset: ../core/assets/sounds/jump_with_feather.wav
com.woodgdx.game.Assets: asset: ../core/assets/canyonbunny.pack.png
com.woodgdx.game.Assets: asset: ../core/assets/music/keith303_-_brand_new_highscore.mp3
com.woodgdx.game.Assets: asset: ../core/assets/sounds/live_lost.wav
com.woodgdx.game.Assets: asset: ../core/assets/canyonbunny.pack2.png
com.woodgdx.game.Assets: asset: ../core/assets/sounds/pickup_feather.wav
com.woodgdx.game.Assets: asset: ../core/assets/sounds/jump.wav
com.woodgdx.game.Assets: asset: ../core/assets/canyonbunny.pack.atlas
com.woodgdx.game.Assets: asset: ../core/assets/sounds/pickup_coin.wav

So I'm not really sure what is going on...

The error itself is..

Exception in thread "LWJGL Application" java.lang.NullPointerException
    at com.woodgdx.game.woodGdxGame.create(woodGdxGame.java:29)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:147)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:124)

Main class

package com.woodgdx.game;

import com.badlogic.gdx.Application;
import com.badlogic.gdx.Game;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.assets.AssetManager;
import com.woodgdx.game.Assets;
import com.woodgdx.game.screens.MenuScreen;
import com.woodgdx.game.util.AudioManager;
import com.woodgdx.game.util.GamePreferences;

/**
 * The main game file with the main
 * engine methods
 * @author xxxx
 */
public class woodGdxGame extends Game
{
    @Override
    public void create()
    {
        // Set Libgdx log level
        Gdx.app.setLogLevel(Application.LOG_DEBUG);
        // Load assets
        Assets.instance.init(new AssetManager());
        // Load preferences for audio settings and start playing music
        GamePreferences.instance.load();
        AudioManager.instance.play(Assets.instance.music.song01);
        // Start game at menu screen
        setScreen(new MenuScreen(this));
    }
}

The error occurs on this line..

AudioManager.instance.play(Assets.instance.music.song01);

My Assets class contains this inner class. The way the book had it, I got the same error when I made it it's own class.

    /**
     * Music for game loaded
     * @author xxxx
     *
     */
    public class AssetMusic
    {
        //Our music object
        public final Music song01;

        /**
         * Retrieves the music file for the music
         * @param am
         */
        public AssetMusic(AssetManager am)
        {
            song01 = am.get("../core/assets/music/keith303_-_brand_new_highscore.mp3", Music.class);
        }
    }

Then here is the AudioManager class they does play a little role in here.

/**
 * Manages the playing and organization
 * of audio files
 * @author xxxx
 *
 */
public class AudioManager
{
    public static final AudioManager instance = new AudioManager();

    private Music playingMusic;

    // singleton: prevent instantiation from other classes
    private AudioManager()
    {
    }

    /**
     * Play sound with default vol, pitch, and pan (0)
     * @param sound
     */
    public void play(Sound sound)
    {
        play(sound, 1);
    }

    /**
     * Play sound with default pitch and pan (0) but different vol
     * @param sound
     * @param volume
     */
    public void play(Sound sound, float volume)
    {
        play(sound, volume, 1);
    }

    /**
     * Play sound with default pan (0) with different pitch and vol
     * @param sound
     * @param volume
     * @param pitch
     */
    public void play(Sound sound, float volume, float pitch)
    {
        play(sound, volume, pitch, 0);
    }

    /**
     * Plays sound with a vol, pitch, and pan activated
     * @param sound
     * @param volume
     * @param pitch
     * @param pan
     */
    public void play(Sound sound, float volume, float pitch, float pan)
    {
        //If sound is muted, dont play
        if (!GamePreferences.instance.sound)
            return;
        sound.play(GamePreferences.instance.volSound * volume, pitch, pan);
    }

    /**
     * Plays music on loop
     * @param music
     */
    public void play(Music music)
    {
        stopMusic();
        playingMusic = music;
        if (GamePreferences.instance.music)
        {
            music.setLooping(true);
            music.setVolume(GamePreferences.instance.volMusic);
            music.play();
        }
    }

    /**
     * Ends the music loop of doom
     */
    public void stopMusic()
    {
        if (playingMusic != null)
            playingMusic.stop();
    }

    /**
     * Checks settings for muted music, vol level
     */
    public void onSettingsUpdated()
    {
        //No music available
        if (playingMusic == null)
            return;
        //Sets volume
        playingMusic.setVolume(GamePreferences.instance.volMusic);
        //Checks if music is not muted
        if (GamePreferences.instance.music)
        {
            //If music isn't playing, play it
            if (!playingMusic.isPlaying())
                playingMusic.play();
        }
        //Mute music if selected so
        else
        {
            playingMusic.pause();
        }
    }
}

Answer 1

Forgot to add in the music and sound for the initialization for the Assets class. I was thinking it was something with the files but it just wasn't initialized.

Add this to the init() method of Assets

sounds = new AssetSounds(assetManager);
music = new AssetMusic(assetManager);