/**
* initialize the move down button
*/
private void initMoveDownButton() {
// move down button
MoveDownSelectionTableAction moveDownAction = new MoveDownSelectionTableAction(mainTable);
moveDownButton.setAction(moveDownAction);
addButtonToButtonPanel(moveDownButton);
addToMainTableKeyBindings(moveDownAction);
popupMenu.add(new JMenuItem(moveDownAction));
}