在NetBeans中，如何将jMenuBar添加到JPanel？

Question

I am having problems and I don't really understand why. I have a JFrame and a JPanel and everything works properly. I am trying to add a jMenuBar into the JPanel and I cannot get it to show up. It is being placed under "Other Components" and does not show up during runtime. any suggestions?

edit: It seems that the appropriate answer is NetBeans cannot add a JMenu to a JFrame. I wanted to add this to the first post because the appropriate answer below was down-voted.

Answer 1

JMenuBar is added to the JFrame by using setJMenuBar(...) method.

Small code to help your cause :

import javax.swing.*;

public class MenuBarTest extends JFrame
{
    public MenuBarTest()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JPanel contentPane = new JPanel();
        contentPane.setBackground(java.awt.Color.WHITE);
        JMenuBar menuBar = new JMenuBar();
        JMenu menu = new JMenu("File");
        JMenuItem menuItem = new JMenuItem("Open");

        menu.add(menuItem);
        menuBar.add(menu);

        setContentPane(contentPane);
        setJMenuBar(menuBar);
        setSize(200, 200);
        setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new MenuBarTest();
            }
        });
    }
}

Answer 2

其中一个聪明的方法是双击JFrame，它在项目栏上，这个出现了新窗口，实际的JFrame在左侧调色板上出现了所有摆动的组件，你只需将项目拖放到此框架代码将由nb自动生成，您还可以通过右键单击该项目来添加事件

Answer 3

For vextorspace who states:

JMenuBar can only be added to JFrames, JDialogs, and JApplets.

This example shows that it is easy to add JMenuBar to a JPanel (or any container for that matter):

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class MenuBarEg {
   private static void createAndShowGui() {
      final JFrame frame = new JFrame("MenuBar Exampe");

      JMenuItem barItem = new JMenuItem(new AbstractAction("Bar") {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            JOptionPane.showMessageDialog(frame, "Hello from bar!");
         }
      });
      JMenu fooMenu = new JMenu("Foo");
      fooMenu.add(barItem);
      JMenuBar menuBar = new JMenuBar();
      menuBar.add(fooMenu);

      JPanel menuBarHoldingPanel = new JPanel(new BorderLayout());
      menuBarHoldingPanel.add(menuBar, BorderLayout.PAGE_START);

      JPanel mainPanel = new JPanel(new GridLayout(0, 1));

      // rigid area just as a place-holder
      mainPanel.add(Box.createRigidArea(new Dimension(400, 150)));
      mainPanel.add(menuBarHoldingPanel);

      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Not only is this easy to do, there are many cases where this is desirable.

Answer 4

Since a JMenuBar derives from JComponent it can be added to any container (usually one using BorderLayout to the BorderLayout.PAGE_START position), it is most commonly added to JApplet, JDialog, JFrame, JInternalFrame, JRootPane via the setJMenuBar(...) method.

http://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html

Just a small addition :

A menu bar contains one or more menus and has a customary, platform-dependent location — usually along the top of a window.