When using the Mac menubar via System.setProperty("apple.laf.useScreenMenuBar", "true") and using an accelerator key that contains the COMMAND button (i.e. InputEvent.META_DOWN_MASK) the actionPerformed() method of an action contained in a JCheckBoxMenuItem is called twice.

The problem does not seem to occur with other modifiers (like SHIFT).

This probably should have been fixed by JDK-8152492, but apparently wasn't, as the fix explicitly does not work for checkboxes (see http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/ee787ce3d454).

The problem does not occur in Java 8.

Code to reproduce:

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;

public class DoubleActionTest {

    public static void main(String[] args) {
        System.setProperty("apple.laf.useScreenMenuBar", "true");
        
        final JFrame frame = new JFrame();
        final JMenuBar menubar = new JMenuBar();
        final JMenu fileMenu = new JMenu("OPEN ME");
        final MyAction myAction = new MyAction();
        final JCheckBoxMenuItem menuItem = new JCheckBoxMenuItem(myAction);
        fileMenu.add(menuItem);
        menubar.add(fileMenu);
        frame.setJMenuBar(menubar);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        SwingUtilities.invokeLater(() -> {
            frame.setBounds(200, 200, 200, 200);
            frame.setVisible(true);
        });
    }

    private static class MyAction extends AbstractAction {

        MyAction() {
            putValue(Action.NAME, "HIT MY ACCELERATOR KEY");
            putValue(Action.ACCELERATOR_KEY, KeyStroke.getKeyStroke(KeyEvent.VK_E, InputEvent.META_DOWN_MASK));
        }

        @Override
        public void actionPerformed(final ActionEvent e) {
            System.out.println("Action! called with modifiers: " + e.getModifiers() + "\n" + e);
        }
    }
}

Run the code and hit the accelerator key (COMMAND+E). On system out you should see a single line of output, but you see two. The first one for the correct call and a second one that is the result of an internal ItemEvent (state changed). The second one should not happen.