Поскольку

/**
* Returns whether or not this mouse event is the popup menu
* trigger event for the platform.
* <p><b>Note</b>: Popup menus are triggered differently
* on different systems. Therefore, <code>isPopupTrigger</code>
* should be checked in both <code>mousePressed</code>
* and <code>mouseReleased</code>
* for proper cross-platform functionality.
*
* @return boolean, true if this event is the popup menu trigger
* for this platform
*/

то можно написать такой слушатель

class PopupListener
extends MouseAdapter
{
JPopupMenu popup;

PopupListener(JPopupMenu popupMenu)
{
popup = popupMenu;
}

public void mousePressed(MouseEvent e)
{
maybeShowPopup(e);
}

public void mouseReleased(MouseEvent e)
{
maybeShowPopup(e);
}

private void maybeShowPopup(MouseEvent e)
{
if (e.isPopupTrigger())
{
popup.show(e.getComponent(), e.getX(), e.getY());
}
}
}

взято из примера, ничего не обещаю

Nai tiruvantel ar varyuvantel i Valar tieyanna nu vilya

Вообще такой проверки не нужно, потому что на данной платформе не обязательно правая конпка вызывает. Используется e.isPopupTrigger()

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