Checks that this class can be subclassed.
<p>
The SWT class library is intended to be subclassed
only at specific, controlled points (most notably,
<code>Composite</code> and <code>Canvas</code> when
implementing new widgets). This method enforces this
rule unless it is overridden.
</p><p>
<em>IMPORTANT:</em> By providing an implementation of this
method that allows a subclass of a class which does not
normally allow subclassing to be created, the implementer
agrees to be fully responsible for the fact that any such
subclass will likely fail between SWT releases and will be
strongly platform specific. No support is provided for
user-written classes which are implemented in this fashion.
</p><p>
The ability to subclass outside of the allowed SWT classes
is intended purely to enable those not on the SWT development
team to implement patches in order to get around specific
limitations in advance of when those limitations can be
addressed by the team. Subclassing should not be attempted
without an intimate and detailed understanding of the hierarchy.
</p>
@exception SWTException <ul>
<li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li>
</ul>
Checks that this class can be subclassed. <p> The SWT class library is intended to be subclassed only at specific, controlled points (most notably, <code>Composite</code> and <code>Canvas</code> when implementing new widgets). This method enforces this rule unless it is overridden. </p><p> <em>IMPORTANT:</em> By providing an implementation of this method that allows a subclass of a class which does not normally allow subclassing to be created, the implementer agrees to be fully responsible for the fact that any such subclass will likely fail between SWT releases and will be strongly platform specific. No support is provided for user-written classes which are implemented in this fashion. </p><p> The ability to subclass outside of the allowed SWT classes is intended purely to enable those not on the SWT development team to implement patches in order to get around specific limitations in advance of when those limitations can be addressed by the team. Subclassing should not be attempted without an intimate and detailed understanding of the hierarchy. </p>
@exception SWTException <ul> <li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li> </ul>