Since there seems to be no debugging tools for JFreeChart (1.0.19), I've managed to produce an SSCCE that exhibits the problem. Everything looks right to me but no lines are being drawn and the legend is missing, which I suspect is related. I'm hoping some new eyes can spot what I am missing. Here is the Chart class:
Here is main:
As an aside, note the time of 19:00 in the lower left. I have no idea where that comes from either. Again that might be a clue. TIA.
As earlier said, I don't use JFreeChart but I ran your code with some modifications (Threda#sleep raises a red flag in a GUI program, changd that part to use a Swing Timer, and also created the JFrame etc. on the EDT).
You see, that's not really an SSCCE. For one, you have a method addMarker(String id_,String name_) that's not used. To create a SSCCE, it's always better to start afresh and add only as much code as is necessary to show the problem. That makes it (much) easier for someone to be able to help you.
It could be that data points are being added to the LinkedHashMap after the series has been created with zero entries, but I haven't looked to see what the JFreeChart javadocs say about that.
There are no new questions, but there may be new answers.
Thanks. The addMarker method is irrlevent and can be removed since it is not used in this context. I didn't have a problem with the sleep and I didn't know any other way of spacing the datapoints out so they are at least 1 minute apart (produces a duplicate entry error). From what I read adding datapoints automatically triggers a repaint and is valid. Indeed, I have seen examples of real time plots.