When I generate javadoc for my Android project in Eclipse, there are lots of warnings like
cannot find symbol
symbol : class TextView
and
By now (August 2020), Google has published a package-list
on its Android developer documentation. Hence, simply linking to https://developer.android.com/reference/ or https://d.android.com/reference/ will work (just tried this with success).
Minor glitch: if you open the generated Javadoc and try to follow a link to an Android class (or one of the standard Java classes, which will also link to the Android documentation) and you are in frame mode, your browser might refuse to follow the link, as the Android site does not allow embedding in another page. Firefox then gives you the alternative of opening the target document in a new tab.