NetBeans Options Panel validation

I have a class that extends org.netbeans.spi.options.OptionPanelController. 

When a user clicks OK, the following method gets called:


Code:
    @Override
    public void applyChanges() { ... }



I have some items on the options panel that take a really long time to validate, and I'd like to wait until they press OK to validate them. Is there a way to keep the form from closing after they press OK? Here's a basic idea of what I want:



Code:
    @Override
    public void applyChanges() { 
    // do my slow, slow, slow validation
    // if valid, save and allow form to close return
    // otherwise, show invalid validation results on the page and don't let the form close
 }



How can I do this?

Thanks,
   Karl