Where to start in JAVA/Android programming?

My major right now is Electrical Engineering. I have interest in programming and have learned some java. I've read through entire books and took a programs and algorithms cl based on JAVA. I also have interest in Android os . So my question is that I would like to fool around with creating apps for android based on JAVA, but don't know where to start.I have did several of the easy programs like making an e-person or creating a quiz. I have a descent overview knowledge JAVA. But lets say that I have an idea for an app. I wouldn't know where to start. So what should I do in preparing? What type of material should I have? where would I get other related or useful source code? I could use maybe some good website or forums to check out.