I started learning java and android app building a while back. Everywhere I looked they said
Learn java first and then start learning to make android application.
I suggest a different approach.
Don't learn java completely before jumping into android development. You just need to know only java basics to get started with android.
Select a java video tutorial on YouTube. See how it works. Then jump straight into android. Learn what you need to know about java along with android. This way you will save a lot of time and learn both things to the extent where you will find you have wasted far lesser time.
Suggested books to learn Java for android development and android app development.
For java: Head First Java, 2nd Edition
For Android: Beginning Android (Expert's Voice in Open Source) , Hello, Android Publisher: Pragmatic Bookshelf 3th (third) edition Text Only and Android Programming Tutorials, 3rd Edition
Hope this will help a few.