Constructs a new instance of this class given its parent
(which must be a <code>MenuItem</code>) and sets the style
for the instance so that the instance will be a drop-down
menu on the given parent's parent menu.
<p>
After constructing a drop-down menu, it can be set into its parentItem
using <code>parentItem.setMenu(menu)</code>.
</p>
@param parentItem a menu item which will be the parent of the new instance (cannot be null)
@exception IllegalArgumentException <ul>
<li>ERROR_NULL_ARGUMENT - if the parent is null</li>
</ul>
@exception SWTException <ul>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent</li>
<li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li>
</ul>
Constructs a new instance of this class given its parent (which must be a <code>MenuItem</code>) and sets the style for the instance so that the instance will be a drop-down menu on the given parent's parent menu. <p> After constructing a drop-down menu, it can be set into its parentItem using <code>parentItem.setMenu(menu)</code>. </p>
@param parentItem a menu item which will be the parent of the new instance (cannot be null)
@exception IllegalArgumentException <ul> <li>ERROR_NULL_ARGUMENT - if the parent is null</li> </ul> @exception SWTException <ul> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent</li> <li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li> </ul>
@see SWT#DROP_DOWN @see Widget#checkSubclass @see Widget#getStyle