How to correctly setup a Cancelable event

I have a custom event with the @Cancelable annotation, that I want to only do something if it isn't canceled.

At the moment, I'm doing something like:

if (!event.isCanceled()) {

	//Do Something

}

Which obviously doesn't work. How would I go about making an event that when fired, only runs code if it isn't cancelled?

Thanks for your help!