If the argument is not null, sets the receiver's default
button to the argument, and if the argument is null, sets
the receiver's default button to the first button which
was set as the receiver's default button (called the
<em>saved default button</em>). If no default button had
previously been set, or the saved default button was
disposed, the receiver's default button will be set to
null.
<p>
The default button is the button that is selected when
the receiver is active and the user presses ENTER.
</p>
@param button the new default button
@exception IllegalArgumentException <ul>
<li>ERROR_INVALID_ARGUMENT - if the button has been disposed</li>
<li>ERROR_INVALID_PARENT - if the control is not in the same widget tree</li>
</ul>
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
If the argument is not null, sets the receiver's default button to the argument, and if the argument is null, sets the receiver's default button to the first button which was set as the receiver's default button (called the <em>saved default button</em>). If no default button had previously been set, or the saved default button was disposed, the receiver's default button will be set to null. <p> The default button is the button that is selected when the receiver is active and the user presses ENTER. </p>
@param button the new default button
@exception IllegalArgumentException <ul> <li>ERROR_INVALID_ARGUMENT - if the button has been disposed</li> <li>ERROR_INVALID_PARENT - if the control is not in the same widget tree</li> </ul> @exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>