java JMenu栏未出现在GUI中

Question

这是一个新手问题，但我正在努力让这个JMenu栏显示在拆分窗格上方。有人能帮我解释一下我做错了什么吗？据我所知，我添加了JMenu及其下拉菜单

非常感谢您为我的问题提供的解决方案和帮助

以下是我的代码：

public class JavaAssignmentPanel {

    JMenuBar setupMenu() {

        JMenuBar menuBar = new JMenuBar(); //menubar
        JMenu menu1 = new JMenu("Menu"); //menu
        menuBar.add(menu1); //add menu to gui
        JMenuItem menuItem1 = new JMenuItem("Item 1", KeyEvent.VK_1); //create drop down menu
        menu1.add(menuItem1); //adds drop down menu to gui

        //execute code when selected
        menuItem1.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                //  panel.showText("Example1 text - normally read from file");
            }
        });

        return menuBar;
    }

    public static void main(String[] args) throws FileNotFoundException {

        window window = new window();

    }

    private static class window extends JFrame {

        public window() throws FileNotFoundException {

            JPanel leftScrollPane = new JPanel();
            JPanel rightPane = new JPanel();
            JSplitPane splitPane;

            this.setVisible(true);
            this.setSize(400, 400);
            this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            splitPane = new JSplitPane();
            splitPane.setOrientation(JSplitPane.HORIZONTAL_SPLIT);
            splitPane.setDividerSize(10);
            splitPane.setDividerLocation(100);
            splitPane.setLeftComponent(leftScrollPane);
            splitPane.setRightComponent(rightPane);
            splitPane.setOneTouchExpandable(true);
            splitPane.setDividerLocation(200);

            Dimension minimumSize = new Dimension(100, 50);

            leftScrollPane.setSize(400, 400);

            splitPane.setPreferredSize(new Dimension(400, 200));
            splitPane.setLeftComponent(leftScrollPane);
            splitPane.setRightComponent(rightPane);
            this.add(splitPane);

        }
    }

}

Answer 1

必须在JFrame中设置JMenuBar

查看代码，您可以通过将setupMenu方法设置为静态，并在window类中调用它，如下所示：

this.setJMenuBar(setupMenu());

代码：

public class JavaAssignmentPanel {

// making this method as static
static JMenuBar setupMenu() {

    JMenuBar menuBar = new JMenuBar(); // menubar
    JMenu menu1 = new JMenu("Menu"); // menu
    menuBar.add(menu1); // add menu to gui
    JMenuItem menuItem1 = new JMenuItem("Item 1", KeyEvent.VK_1); // create
                                                                    // drop
                                                                    // down
                                                                    // menu
    menu1.add(menuItem1); // adds drop down menu to gui

    // execute code when selected
    menuItem1.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {

            // panel.showText("Example1 text - normally read from file");
        }
    });

    return menuBar;
}

public static void main(String[] args) throws FileNotFoundException {

    window window = new window();

}

private static class window extends JFrame {

    public window() throws FileNotFoundException {

        JPanel leftScrollPane = new JPanel();
        JPanel rightPane = new JPanel();
        JSplitPane splitPane;

        this.setVisible(true);
        this.setSize(400, 400);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // calling setupMenu method to set the JMenuBar in JFrame
        this.setJMenuBar(setupMenu());

        splitPane = new JSplitPane();
        splitPane.setOrientation(JSplitPane.HORIZONTAL_SPLIT);
        splitPane.setDividerSize(10);
        splitPane.setDividerLocation(100);
        splitPane.setLeftComponent(leftScrollPane);
        splitPane.setRightComponent(rightPane);
        splitPane.setOneTouchExpandable(true);
        splitPane.setDividerLocation(200);

        Dimension minimumSize = new Dimension(100, 50);

        leftScrollPane.setSize(400, 400);

        splitPane.setPreferredSize(new Dimension(400, 200));
        splitPane.setLeftComponent(leftScrollPane);
        splitPane.setRightComponent(rightPane);
        this.add(splitPane);

    }
}}

Answer 2

我查看了您的代码，并做了以下更改：

向setupMenu（）添加了一个修饰符（

public static JMenuBar setupMenu() { ... }

通过调用JFrames构造函数中的this.setJMenuBar(setupMenu());将菜单栏添加到JFrame中

我还将JFrame的大小增加到1280x720以查看更改

This是我所做的所有更改的类

我还鼓励你总是根据Java Code Conventions来命名你的类，它是驼色大小写，以大写字母（Uppper Camel Case）开头。这使你的代码更容易阅读

Answer 3

定义方法setupMenu()，该方法返回JMenuBar。但菜单栏必须添加到窗口中

它可以通过

this.setJMenuBar(setupMenu());

作为window()构造函数中的最后一个命令（即this.add(splitPane);之后）

Answer 4

所以我可能完全失明了，但我看不到你在班上其他任何地方调用setupMenu方法。你需要告诉程序你正在给jframe添加一个菜单栏