JFreechart series tool tip above shape annotation

I suspect you are adding the shape annotations to the plot, where they are drawn last. Instead, add them to the renderer in Layer.BACKGROUND. As shown below, the circle does not obscure the tool tip at (20, 20). Note also how (10, 10) is not affected by the line annotation, while (30, 30) is obscured by the arc.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.geom.Arc2D;
import java.awt.geom.Ellipse2D;
import java.util.Random;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartFrame;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.annotations.XYLineAnnotation;
import org.jfree.chart.annotations.XYShapeAnnotation;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;
import org.jfree.ui.Layer;

/**
 * @see http://stackoverflow.com/questions/6797012
 * @see http://stackoverflow.com/questions/6604211
 */
public class ArcTest {

    private static final Random r = new Random();
    private static final Color blue = Color.blue;
    private static final BasicStroke stroke = new BasicStroke(2.0f);
    private static final double PI = 180d;
    private static final int X = 8;
    private static final int Y = 0;
    private static final int W = 6 * X;
    private static final int H = 3 * X;

    public static void main(String[] args) {
        JFreeChart chart = ChartFactory.createXYLineChart(
            "ArcTest", "X", "Y", createDataset(),
            PlotOrientation.VERTICAL, true, true, false);
        XYPlot plot = chart.getXYPlot();

        XYLineAndShapeRenderer renderer =
            (XYLineAndShapeRenderer) plot.getRenderer();
        renderer.setBaseShapesVisible(true);
        Ellipse2D.Double circle = new Ellipse2D.Double(X, X, 20, 20);
        renderer.addAnnotation(new XYShapeAnnotation(
            circle, stroke, blue), Layer.BACKGROUND);

        XYLineAnnotation line = new XYLineAnnotation(X, Y, X, H, stroke, blue);
        plot.addAnnotation(line);
        Arc2D.Double arc = new Arc2D.Double(X, Y, W, 2 * H, PI, PI, Arc2D.OPEN);
        plot.addAnnotation(new XYShapeAnnotation(arc, stroke, blue));

        ChartFrame frame = new ChartFrame("Test", chart);
        frame.pack();
        frame.setVisible(true);
    }

    private static XYDataset createDataset() {
        XYSeriesCollection result = new XYSeriesCollection();
        XYSeries series = new XYSeries("ArcTest");
        series.add(0, 0);
        series.add(10, 10);
        series.add(20, 20);
        series.add(30, 30);
        series.add(W, W);
        result.addSeries(series);
        return result;
    }
}