Subclassing "Not inteded for subclassing"

Frank Benoit keinfarbton at
Wed Oct 15 12:24:46 PDT 2008

Aarti_pl schrieb:
> Frank Benoit pisze:
>> Simen Haugen schrieb:
>>> I see dwt also have the "Not intended for subclassing", but the classes
>>> are not marked final.
>>> It shouldn't be any problems subclassing as long as you're careful,
>>> right?
>>> Right now I want to subclass Text and automatically add a dynamic
>>> tooltip. The same type of text box should be used many places in my
>>> application. I know I can just bind each time, but is it really
>>> dangerous to do this kind of subclassing to save typing?
>>> Or is there a easier way to solve these kind of things?
>> Hehe, i don't know why, but i simply forgot about making them 'final'.
>> Perhaps i should do that :)
>> Well, some of them are subclassed within SWT, but they shall not be
>> subclasses by user code. (Decorations, Scrollable, ..)
>> I think, they are not intended for subclassing, because of ...
>> 1. So you do not depend on protected/private API and the SWT project is
>> free in changing it in a future version.
>> 2. So you do not used protected/private API which may be platform
>> dependent. There are examples of this.
>> 3. So you do not accidentally change any behavior of the widget, which
>> might be expected from other classes, like layouts or widget containers.
>> I am convinced, the SWT devs are very good designers and they choose
>> this restriction for good reason.
>> Perhaps you can do this by composition instead of inheritance.
>> Do you have code examples of what you want to do?
> Frank, please do not make them final! :-O
> I use a few subclassed SWT widgets in my code, and have no problem with
> them.
> To subclass widget it is enough to override method checkSubclass() with
> empty body:
> @Override
> protected void checkSubclass() {
> }
> I think that there should be no problem with subclassing as long as you
> use there only public interface of SWT.
> Finally it is sometimes more convenient to keep updating subclassed
> widget (because of possible SWT api changes), than make them as
> aggregated composites and redirect all necessary methods from original
> widget to new widget. That's why I think even SWT doesn't declare them
> final...
> Best Regards
> Marcin Kuszczak
> (aarti_pl)

ok, i see

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