Java for Android programming

A complete understanding of the basics would be desirable.
Specifically the following topics:

• Declarations and Access Control
• ObjectOrientation
• Assignments
• Operators
• Flow Control, Exceptions, and Assertions
• Strings, I/O, Formatting, and Parsing
• Generics and Collections
• InnerClasses
• Threads

But if you know already the basics ( classes, objects, inheritance, interfaces ) I think you're ok to start.
You don't need to learn specific libraries ( like swing, or others ) because you won't use them in Android.

http://stackoverflow.com/questions/2981495/how-much-java-should-i-have-learnt-before-trying-android-programming