This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The IllException is not at all designed to extend an Exception. The point of providing your own Exceptions is to make handling them easier in your project. But that object is never used as an Exception.