This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
strictfp is an implementation detail, so it only allowed to be used in the classes that implement the interface. That is, you cannot force the implementor of your interface to use the strictfp feature.