private void initHandler() {
        mouseHandler          = mouseEvent -> {
            final Object SOURCE = mouseEvent.getSource();
            if (MouseEvent.MOUSE_PRESSED == mouseEvent.getEventType()) {
                MenuItem menuItem = items.get(SOURCE);
                if (menuItem.isSelectable()) {
                    menuItem.setSelected(!menuItem.isSelected());
                    if (menuItem.isSelected()) {
                        fireItemEvent(new ItemEvent(menuItem, this, null, ItemEvent.ITEM_SELECTED));
                    } else {
                        fireItemEvent(new ItemEvent(menuItem, this, null, ItemEvent.ITEM_DESELECTED));
                    }
                } else {
                    click(menuItem);
                    fireItemEvent(new ItemEvent(menuItem, this, null, ItemEvent.ITEM_CLICKED));
                }
            }
        };
    }