Define "Android developer". Downloading a sample app, learning how to modify it in some trivial way, and installing it on your phone will take less than a day. Would that make you an Android developer?
For a competent Java developer who's got a good grasp of computer science concepts in general I'd estimate the minimum time of study and experimentation needed to become a decent Android developer to be about 500 hours. That translates to be about 3 months of fulltime work.
Note that by "competent Java developer" I mean someone who's got a lot experience doing it (thousands of hours); my understanding is that the SCJA and SCJP exams are theoretical, so that doesn't count towards it.
Ulf Dittmer wrote:Not sure what you mean by "core Java knowledge" - thousands of hours of practical -not theoretical- knowledge? Because otherwise my estimation would not apply to you.
Yes,sir i have practical knowledge of following things at intermediate level:
Declarations and Access Control
Flow Control, Exceptions, and Assertions
Strings,Formatting, and Parsing
Generics and Collections