報錯部分代碼如下：public class BeatBox { JPanel mainPanel; ArrayList<JCheckBox> checkboxList; Sequencer sequencer; Sequence sequence; Track track; JFrame theFrame; String[] instrumentNames = {"Bass Drum", "Closed Hi-Hat", "Open Hi-Hat", "Acoustic Snare", "Crash Cymbal", "Hand Clap", "High Tom", "Hi Bongo", "Maracas", "Whistle", "Low Conga", "Cowbell", "Vibraslap", "Low-mid Tom", "High Agogo", "Open Hi Conga"}; //實際的樂器關鍵字，例如說35是Bass Drum，42是Closed Hi-Hat int[] instruments = {35, 42, 46, 38, 49, 39, 50, 60, 70, 72, 64, 56, 58, 47, 67, 63}; public static void main(String[] args) { new BeatBox().buildGUI(); } public void buildGUI() { theFrame = new JFrame("Cyber BeatBox"); theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); BorderLayout layout = new BorderLayout(); ? //創建布局對象? JPanel background = new JPanel(layout); //設定面板上擺設組件時的空白邊緣 background.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10)); checkboxList = new ArrayList<JCheckBox>(); Box buttonBox = new Box(BoxLayout.Y_AXIS); JButton start = new JButton("Start"); start.addActionListener(new MyStartListener()); buttonBox.add(start); JButton stop = new JButton("Stop"); stop.addActionListener(new MyStopListener()); buttonBox.add(stop); JButton upTempo = new JButton("Tempo Up"); upTempo.addActionListener(new MyUpTempoListener()); buttonBox.add(upTempo);