" java.lang.IllegalArgumentException: uri.getScheme() == null! " error using JavaFX to play audio

The constructor for Media requires a URL, so you'd need something starting with http:// or file://

btn.setOnAction(e -> {
  Media m = new Media(Paths.get("04.mp3").toUri().toString());
  new MediaPlayer(m).play();
});`

See http://docs.oracle.com/javase/8/javafx/media-tutorial/simpleplayer.htm

It also helps that both Path and File objects can be converted to URLs.