当我使用运行文件进行测试时，NetBeans GUI的设计不一致

Question

当我选择运行文件来测试代码时，GUI应用程序的菜单栏不会始终显示。我使用的是NetBeans IDE版本7.0.1。我通过选择代码中的任何位置，右键单击鼠标并从结果菜单中选择Run File来测试代码。生成的GUI应用程序有菜单栏，但当我重新运行应用程序时，菜单栏不在那里，但当重新运行它时，会出现菜单栏。也许你可以测试一下，看看你在运行程序时是否遇到了同样的问题？在运行程序之前，是否有某种残余内存需要清除？这是代码：

public static void main(String[] args) {
    JFrame main = new JFrame("Main");
    main.setVisible(true);
    main.setSize(600, 600);
    main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel(new GridBagLayout());
    GridBagConstraints contraints = new GridBagConstraints();
    main.getContentPane().add(panel, BorderLayout.NORTH);
    contraints.gridx = 0;
    contraints.gridy = 0;
    contraints.insets = new Insets(0,0,0,0);
    //Adding labels and buttons
    JLabel enterUserName = new JLabel("Enter User Name:");
    contraints.gridx = 0;
    contraints.gridy = 1;
    contraints.insets = new Insets(1, 1, 1, 1);
    panel.add(enterUserName, contraints);
    JLabel enterPassWord = new JLabel("Enter Password:");
    contraints.gridx = 0;
    contraints.gridy = 2;
    contraints.insets = new Insets(1, 1, 1, 1);
    panel.add(enterPassWord, contraints);
    JButton logInButton = new JButton("Login");
    contraints.gridx = 0;
    contraints.gridy = 3;
    contraints.insets = new Insets(1, 1, 1, 1);
    panel.add(logInButton, contraints);
    logInButton.addActionListener(new helpAbout());

    //Adding menu bar and menubar items
    JMenuBar menuBar = new JMenuBar();
    main.setJMenuBar(menuBar);
    contraints.gridx = 0;
    contraints.gridy = 0;
    contraints.insets = new Insets(0, 0, 0, 0);
    JMenu file = new JMenu("File");
    menuBar.add(file, contraints);
    JMenu help = new JMenu("Help");
    menuBar.add(help, contraints);
    //Adding menu bar functionality
    JMenuItem exit = new JMenuItem("Exit");
    file.add(exit);
    exit.addActionListener(new fileExit());
    JMenuItem about = new JMenuItem("About");
    help.add(about);
    about.addActionListener(new helpAbout());
}
static class helpAbout implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        JFrame test = new JFrame("About");
        test.setVisible(true);
        test.setSize(200, 200);
        JLabel label2 = new JLabel("About");
        JPanel panel2 = new JPanel();
        test.add(panel2);
        panel2.add(label2);
    }
}
static class fileExit implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.exit(0);
    }
}

Answer 1

在构建框架后调用setVisible(true)。

如果将布局/控件添加到可见窗体（在其他情况下可能需要这样做），则需要在框架/面板上调用revalidate()。

Answer 2

代码行main.setVisible(true);必须是进入main method 的最后一个代码行