This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
As vierda was talking about covariant returns, the return type of a method in subclass should be subclass of the return type of the method in the super class. Animal is a super class of cat so it works fine, but int is not a super class of long.