public void init(GameContainer gc, StateBasedGame sbg) throws SlickException{
    BossInt = new Music("OST/bossintronly.wav");
    Boss1 = new Music("OST/bossloop.wav");
    Boss1.setVolume(0.5f);
    BossInt.setVolume(0.5f);

    BossInt.play();
}

if (BossInt.playing() == false) {
        Boss1.loop();
}

if (BossInt.playing() == false && Boss1.playing() == false) {
    Boss1.loop();
}