Returns <code>true</code> if the receiver is checked,
and false otherwise. When the parent does not have
the <code>CHECK style, return false.
@return the checked state of the checkbox
@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>
Returns <code>true</code> if the receiver is checked, and false otherwise. When the parent does not have the <code>CHECK style, return false.
@return the checked state of the checkbox
@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>