As a former student who took the AP Computer Science exam long ago without taking any class associated with it, I know how to learn the material quickly. I can teach you the basics of Java in as little as two weeks; it's actually quite easy to learn. You won't be able to write the next Facebook, but you'll be familiar enough with the language to do any assignment in a college computer science class. You'll be able to read Javadocs and learn the various nooks and crannies of the language.