[App A] Figuring out what's going on with the multidimentional array of...

    theFrame.getContentPane().add(background);

    int numberOfInstruments = instruments.size();

    GridLayout grid = new GridLayout(numberOfInstruments, NUMBER_OF_BEATS);

    grid.setVgap(1);

    grid.setHgap(2);

    GridLayout grid = new GridLayout(numberOfInstruments, NUMBER_OF_BEATS, 2, 1);

    JPanel mainPanel = new JPanel(grid);

    background.add(BorderLayout.CENTER, mainPanel);

  }

  public void buildTrackAndStart() {

    List<Integer> trackList; // this will hold the instruments for each beat

    List<Integer> beatsForInstrument; // this will hold all the beats, on or off, for this instrument

    sequence.deleteTrack(track);

    track = sequence.createTrack();

    int numberOfInstruments = instruments.size();

    for (int i = 0; i < numberOfInstruments; i++) {

      trackList = new ArrayList<>();

      beatsForInstrument = new ArrayList<>();

      for (int j = 0; j < NUMBER_OF_BEATS; j++) {

        JCheckBox jc = checkboxList.get(j + (NUMBER_OF_BEATS * i));

        if (jc.isSelected()) {

          int key = instruments.get(i).getMidiValue();

          trackList.add(key);

          beatsForInstrument.add(instruments.get(i).getMidiValue());

        } else {

          trackList.add(null);  // because this slot should be empty in the track

          beatsForInstrument.add(null);  // because this slot should be empty in the track

        }

      } // close inner loop

      makeTracks(trackList);

    } // close outer loop

    track.add(makeEvent(192, 9, 1, 0, 15)); // - so we always go to full 16 beats

      }

      makeTracks(beatsForInstrument);

    }

    track.add(makeEvent(ShortMessage.PROGRAM_CHANGE, 9, 1, 0, 15)); // - so we always go to full 16 beats

    try {

      sequencer.setSequence(sequence);

      sequencer.setLoopCount(sequencer.LOOP_CONTINUOUSLY);

    }

  }

  public void makeTracks(List<Integer> list) {

    Iterator<Integer> it = list.iterator();

  public void makeTracks(List<Integer> instrumentsForBeat) {

    Iterator<Integer> it = instrumentsForBeat.iterator();

    for (int i = 0; i < NUMBER_OF_BEATS; i++) {

      Integer num = it.next();

      if (num != null) {