The dots represent individual samples from the tablet. It is up to you to interpolate the samples to make continuous lines.
The simplest way to do this is to keep track of the last point and draw a line between that and the current point.
Not sure about Java projects, but the Tablet SDK for windows does all the handwriting/gesture recognition stuff for you. I'm not aware if similar SDKs exist for other platforms, so it's questionable whether it makes sense to provide access to that functionality in JPen...
