ADDITIONAL SYSTEM INFORMATION :
C:\>ver

Microsoft Windows [Version 10.0.19042.985]

C:\>java -version
openjdk version "11.0.11" 2021-04-20 LTS
OpenJDK Runtime Environment 18.9 (build 11.0.11+9-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.11+9-LTS, mixed mode)


A DESCRIPTION OF THE PROBLEM :
Changing the menubar in a frame does not free the unused menucomponents.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
After starting the example-application press the only button to toggle the menubar (severl times).
Stop when only the File-menu is shown.
Use VisualVM or other tool to see the current instances.
There should be only 1 JMenuBar, 1 JMenu and 1 JMenuItem.
This is true for the Motif-LookAndFeel (USE_WINDOWS_LAF = false)
but not for the Windows-LookAndFeel (USE_WINDOWS_LAF = true)
Use 'static boolean USE_WINDOWS_LAF = true;' to switch between test (restart application neccessary).



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
There should be only 1 JMenuBar, 1 JMenu and 1 JMenuItem (ok with Motif).

ACTUAL -
This is not true when the Windows-LookAndFeel is used.


---------- BEGIN SOURCE ----------
public class MenuTest
  extends JFrame {

  // --- switch for L&F -> Windows-L&F leaks JMenuBar, JMenu, JMenuItem
  static boolean USE_WINDOWS_LAF = true;

  private static final String PREFIX = "PREFIX";

  private JPanel pnl;
  private boolean doFullMenu;
  // --- just to have it like in a real app
  private JMenuBar mMenuBar;
  private JMenu mFile;
  private JMenu mEdit;
  private JMenu mView;
  private JMenu mHelp;
  private JMenuItem miFile_New;
  private JMenuItem miFile_Open;
  private JMenuItem miFile_Print;
  private JMenuItem miFile_SwitchMenu;

  public MenuTest() {
    super("MenuTest " + UIManager.getLookAndFeel().getDescription() + " ("
      + UIManager.getLookAndFeel().getName() + ")");
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    createContent();
  }

  private Action a(final String name, final ActionListener al) {
    return new AbstractAction(name) {
      @Override
      public void actionPerformed(final ActionEvent e) {
        al.actionPerformed(e);
      }
    };
  }

  private void createContent() {
    pnl = new JPanel(new GridLayout(1, 0));
    pnl.add(new JButton(a("switch menubar", ae -> installMB())));
    getContentPane().add(pnl);
    installMB();
    setMinimumSize(new Dimension(300, 100));
  }

  private void setMnem(final boolean forced, final boolean add2FLM,
    final AbstractButton ab, final String key) {
    final String mk = key + "_Mnem";
    final String mv = mk.substring(0, 1).toLowerCase();
    if (forced || !mv.equals(mk)) {
      final char c = mv.charAt(0);
      ab.setMnemonic(c);
    }
  }

  private JMenu crm(final String key) {
    final String miText = key;
    final JMenu m = new JMenu(miText);
    m.setName(PREFIX + "." + key);
    setMnem(true, true, m, key);
    return m;
  }

  private JMenuItem crmi(final String key, final String cmd, final KeyStroke ks,
    final ActionListener al) {
    final String miText = key;
    final JMenuItem mi = new JMenuItem(miText);
    mi.setName(PREFIX + "." + key);
    if (cmd != null)
      mi.setActionCommand(cmd);
    setMnem(false, false, mi, key);
    if (ks != null)
      mi.setAccelerator(ks);
    if (al != null)
      mi.addActionListener(al);
    return mi;
  }

  private final class ALSwitchMenu
    implements ActionListener {
    @Override
    public void actionPerformed(final ActionEvent e) {
      performSwitchMenu(e);
    }
  }

  private final class ALExit
    implements ActionListener {
    @Override
    public void actionPerformed(final ActionEvent e) {
      performExit(e);
    }
  }

  private void installMB() {
    // --- set null is neccessary !
    mMenuBar = null;
    mFile = null;
    mEdit = null;
    mView = null;
    mHelp = null;
    miFile_New = null;
    miFile_Open = null;
    miFile_Print = null;
    miFile_SwitchMenu = null;

    final JMenuBar mb = mMenuBar = new JMenuBar();
    mb.add(mFile = crm("File"));
    if (doFullMenu) {
      mb.add(mEdit = crm("Edit"));
      mb.add(mView = crm("View"));
      mb.add(mHelp = crm("Help"));
      mFile.add(miFile_New =
        crmi("New", "miFile_New", KeyStroke.getKeyStroke("alt N"), null));
      mFile.add(miFile_Open = crmi("Open", "miFile_Open", null, null));
      mFile.add(miFile_Print = crmi("Print", "miFile_Print", null, null));
      mFile.addSeparator();

      mFile.add(miFile_SwitchMenu =
        crmi("Switch menu", "miFile_SwitchMenu", null, new ALSwitchMenu()));
    }

    mFile.add(crmi("Exit", "miFile_Exit", null, new ALExit()));

    setJMenuBar(mb);
    revalidate();

    doFullMenu = !doFullMenu;
  }

  private void performSwitchMenu(final ActionEvent e) {
    installMB();
  }

  private void performExit(final ActionEvent e) {
    dispose();
  }

  public static void main(final String[] args) {
    if (USE_WINDOWS_LAF) {
      try {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
      } catch (final Exception e) {
        e.printStackTrace();
      }
    }
    EventQueue.invokeLater(() -> {
      final MenuTest mt = new MenuTest();
      mt.pack();
      mt.setVisible(true);
    });
  }
}

---------- END SOURCE ----------

FREQUENCY : always