The documentation for the setAutoscrolls method in JComponent says:

If <i>true</i> this component will automatically scroll its contents
when dragged, if contained in a component that supports scrolling,
such as JViewport

This has to be expanded to explain for developers who subclass JComponent that

setAutoscrolls(true)

won't do the job (it is not enough). Looking at the source one might guess that the method only creates a Autoscroller which doesn't scroll (despite its name) but only generates timer events which it translates into mouseDragged events.

The documentation needs to say that one needs a mouseMotionListener who does the actual scrollRectToVisible call.