package Audio;

import javax.sound.sampled.*;

public class AudioPlayer {

private Clip clip;

public AudioPlayer(String s) {

    try {

        AudioInputStream ais = AudioSystem.getAudioInputStream(getClass().getResourceAsStream(s));
        AudioFormat baseFormat = ais.getFormat();
        AudioFormat decodeFormat = new AudioFormat(
            AudioFormat.Encoding.PCM_SIGNED,
            baseFormat.getSampleRate(),
            16,
            baseFormat.getChannels(),
            baseFormat.getChannels() * 2,
            baseFormat.getSampleRate(),
            false
        );
        AudioInputStream dais =
            AudioSystem.getAudioInputStream(
                decodeFormat, ais);
        clip = AudioSystem.getClip();
        clip.open(dais);
    }
    catch(Exception e) {
        e.printStackTrace();
    }

}

public void play() {
    if(clip == null) return;
    stop();
    clip.setFramePosition(0);
    clip.start();
}

public void stop() {
    if(clip.isRunning()) clip.stop();
}

public void close() {
    stop();
    clip.close();
}
}

[...]
import Audio.AudioPlayer;
[...]
    private AudioPlayer bgMusic;
[...]
        bgMusic = new AudioPlayer("Resources/Musics/menu.mp3");
        bgMusic.play();

java.lang.NullPointerException
at javazoom.spi.mpeg.sampled.file.MpegAudioFileReader.getAudioInputStream(Unknown Source)
at javax.sound.sampled.AudioSystem.getAudioInputStream(Unknown Source)
at Audio.AudioPlayer.<init>(AudioPlayer.java:13)
at GameState.MenuState.<init>(MenuState.java:38)
at GameState.GameStateManager.loadState(GameStateManager.java:30)
at GameState.GameStateManager.<init>(GameStateManager.java:24)
at main.GamePanel.init(GamePanel.java:64)
at main.GamePanel.run(GamePanel.java:70)
at java.lang.Thread.run(Unknown Source)