Hmmm... considering that I do not know Java, and I am in the .Net forum, I think I will stick to the Validation control that is already built (thanks to .Nets rich toolset).
Thank you tho, with the RequiredFieldValidator for the radio button list and a CustomValidator for a dropdown list it seems to be working. However, they do not work at the same time.
For instance, I come to the page, enter data, click the button, and the RadioList validator error pops up. But both controls should be invalid. If I correct the RadioList and click the button I then get the error for the DropDownList, but why does my customer need to click twice to see the errors?