I am afraid that the answers was not my solution.
in javadoc documentation there is option for documenting multiple packages,
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javadoc.html
I first extracted android source.zip file and then I used javadoc command in command-prompt. like so:
javadoc -J-Xmx1024m -d [DESTINATION] -sourcpath [SOURCE OF PACKAGES] -subpackages [PACKAGES]
-J-Xmx1024m is allocation of memory to VM and for multiple packages under src/ folder should be used like this,
-subpackages android:androidx:java and so