所以，我有這個代碼public class MultiThreadedWindow extends JFrame implements ActionListener {    FormatRtsp parser = new FormatRtsp();    private JPanel topPanel = new JPanel();    private JPanel statusPanel = new JPanel();    private JButton btnPlay = new JButton("Conectar");    private JButton btnStop = new JButton("Desconectar");    private JButton btnPause = new JButton("Pausar");    private MediaPlayerFactory[] factory;    private EmbeddedMediaPlayer[] mediaPlayer;    int Video_Width = 500;    int Video_Height = 300;    int Num_Video = 4;    public MultiThreadedWindow() {        this.setExtendedState(JFrame.MAXIMIZED_BOTH);        this.setLayout(new BorderLayout());        this.setVisible(true);        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        Canvas[] videoCanvas = new Canvas[Num_Video];        JPanel mainPanel = new JPanel(new FlowLayout());        JPanel[] vidPanel = new JPanel[Num_Video];        for (int i = 0; i < Num_Video; i++) {            vidPanel[i] = new JPanel();            videoCanvas[i] = new Canvas();            vidPanel[i].setPreferredSize(new Dimension(Video_Width, Video_Height));            vidPanel[i].setBackground(Color.black);            vidPanel[i].setLayout(new BorderLayout());            videoCanvas[i].setBackground(Color.black);            vidPanel[i].add(videoCanvas[i], BorderLayout.CENTER);            mainPanel.add(vidPanel[i]);        }這是一個使用 VLCj 顯示 4 個攝像機的項目。我試圖研究文檔，甚至在 Stackoverflow 中通過多個流看到它，但我發(fā)現(xiàn)它令人困惑。我研究了很多，但無法確定空指針異常在哪里。它應該顯示一個帶有 4 個畫布的 JFrame。我能夠執(zhí)行相同的代碼聲明 4 個工廠和 4 個媒體播放器，但我認為這不是正確的方法。我想了解我缺少什么。謝謝你。錯誤：Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException    at core.MultiThreadedWindow.<init>(MultiThreadedWindow.java:56)