JMenu弹出窗口有时仅适用

Question

I am having issue with JMenu popup. It only sometimes works. Sometimes I don't get a java popup at all. Sometimes my File and Edit options are completely missing. This is what my code looks like.

import javax.swing.*;

public class menu {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        JFrame f = new JFrame();
        f.setVisible(true);
        f.setSize(400,400);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLocationRelativeTo(null);

        JMenuBar mb = new JMenuBar();

        JMenu file = new JMenu ("File");
        mb.add(file);
        JMenu edit = new JMenu("Edit");
        mb.add(edit);

        f.setJMenuBar(mb);
    }

}

Answer 1

Call setVisible on the JFrame only after you have initialised the core UI...

JFrame f = new JFrame();
// Don't call this here...
//f.setVisible(true);
f.setSize(400,400);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLocationRelativeTo(null);

JMenuBar mb = new JMenuBar();

JMenu file = new JMenu ("File");
mb.add(file);
JMenu edit = new JMenu("Edit");
mb.add(edit);

f.setJMenuBar(mb);
// Call it here
f.setVisible(true);

Also, make sure you are creating/updating the UI only from within the context of the Event Dispatching Thread, see Initial Threads for more details