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.
You can only directly extend one class, yes. That class may extend another class, etc, so you may have many classes that are indirectly extended, but only one direct superclass. This seems like an introductory Java question, so I'm moving this thread to Java in General - Beginner.