Annotating points on line graph with JFreeChart?

I'm using JFreeChart to make a line graph. There are some points that I want to mark, or annotate, with circles of different sizes. I tried ShapeAnnotation, but even after I addAnnotation, it's not visible. I was able to make a pointer annotation, though. Here's the relevant code:

 XYShapeAnnotation annotation = new XYShapeAnnotation(new Ellipse2D.Float(100.0f, 100.0f, 100.0f, 100.0f), new BasicStroke(1.0f), Color.blue);
XYPointerAnnotation pointer = new XYPointerAnnotation("arrow", 0.5,0.5,0.0);
xyDataset.addSeries(series1); //
xyDataset.addSeries(series2); // random lists of numbers
xyDataset.addSeries(series3); //
JFreeChart chart = ChartFactory.createXYLineChart ("XYLi开发者_JAVA百科ne Chart using JFreeChart","Age","Weight",xyDataset,PlotOrientation.VERTICAL,true,true,false);
chart.getXYPlot().addAnnotation(pointer);
chart.getXYPlot().addAnnotation(annotation);

I think I should have more code to make the ellipse annotation visible because I never specified coordinates like I did with the pointer. I went through the JFreeChart API and couldn't find it. Help?

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It's hard to say why your XYShapeAnnotation fails without seeing your data; an sscce would help. As a starting point, you might look at the examples here and here for comparison.