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.
In the first 2 methods, the return value will be identical for all objects, thus it will be inefficient. In the 3rd case the value will be based on the variable which will be less likely to return same hash code.