Do you know Java.. like..really know it.. if you have not done much coding with it other than a class on it.. then you really don't know it. Writing an app on Android is not terribly hard.. you can start pretty quickly with their documents and get something running in 1/2 an hour. That said, to actually know enough java to be useful, takes many months, if not longer to really learn it and use it. Memorizing the apis that you wont use often is not required.. google and other references can quickly help you with that. But knowing the language, the JVM, classpath, classloaders, what works, what doesnt, and the primary apis that are used (collections for example) are fundamental and really need to be understood to be able to write a decent app. Despite what many coders think (and sadly do), Java still has to be managed correctly.. resources closed, objects released/nulled, etc. Too many are taught that Java means no worries about memory management.. too often that results in memory leaks and lost resources.
All that said, if you're just trying to build say a simple hello app, or a picture browser, or maybe mess around with putting a dot on a google map, those aren't terribly hard and there are good examples out there that you can basically lift the code, build, run, and then dissect and learn from it. I don't recommend you try learning the fundamentals of Java that way, but you can at least go mess around with Android now, using the emulator if you don't have a device, and get some pretty simple apps working quickly.
There are tons of good books out there. Oriely and Manning are pretty good sources as was the Sun Press. I'd try to find a more recent publication on Android though.. 2.1 and later API coverage, 2.2 if possible as it's quickly becoming the majority installation on devices right now, and 2.2 brought in a lot of nice stuff.
Join some forums too, but try to stay away from total noob questions like "How do I write a hello program.." or "how do I write an Android app". You can find tons of info on google that will get you started very quickly and answer all those basic questions in minutes. Forums are usually best for more specific questions when you're stuck on something or asking opinions on a way to do something, for example.
Good luck.
