Multiple axes on the same data

To avoid duplicating data, you can use the XYPlot method mapDatasetToRangeAxes() to map a dataset index to a list of axis indices. In the example below, meters is the principle axis, and the range of the corresponding feet axis is scaled accordingly, as shown here. Note that invokeLater() is required to ensure that the feet axis is scaled after any change in the meters axis.

import java.awt.EventQueue;
import java.util.Arrays;
import java.util.List;
import javax.swing.JFrame;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.AxisLocation;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.ValueAxis;
import org.jfree.chart.event.AxisChangeEvent;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYItemRenderer;
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;

/**
 * @see https://stackoverflow.com/q/13358758/230513
 */
public class AxisTest {

    private static final int N = 5;
    private static final double FEET_PER_METER = 3.28084;

    private static XYDataset createDataset() {
        XYSeriesCollection data = new XYSeriesCollection();
        final XYSeries series = new XYSeries("Data");
        for (int i = -N; i < N * N; i++) {
            series.add(i, i);
        }
        data.addSeries(series);
        return data;
    }

    private JFreeChart createChart(XYDataset dataset) {
        NumberAxis meters = new NumberAxis("Meters");
        NumberAxis feet = new NumberAxis("Feet");
        ValueAxis domain = new NumberAxis();
        XYItemRenderer renderer = new XYLineAndShapeRenderer();
        XYPlot plot = new XYPlot(dataset, domain, meters, renderer);
        plot.setRangeAxis(1, feet);
        plot.setRangeAxisLocation(1, AxisLocation.BOTTOM_OR_LEFT);
        List<Integer> axes = Arrays.asList(0, 1);
        plot.mapDatasetToRangeAxes(0, axes);
        scaleRange(feet, meters);
        meters.addChangeListener((AxisChangeEvent event) -> {
            EventQueue.invokeLater(() -> {
                scaleRange(feet, meters);
            });
        });
        JFreeChart chart = new JFreeChart("Axis Test",
            JFreeChart.DEFAULT_TITLE_FONT, plot, true);
        return chart;
    }

    private void scaleRange(NumberAxis feet, NumberAxis meters) {
        feet.setRange(meters.getLowerBound() * FEET_PER_METER,
            meters.getUpperBound() * FEET_PER_METER);
    }

    private void display() {
        JFrame f = new JFrame("AxisTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new ChartPanel(createChart(createDataset())));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            new AxisTest().display();
        });
    }
}

Alternatively, you can use a JCheckBox to flip between the two series, meters & feet, as shown in this related example. Using the methods available to XYLineAndShapeRenderer, you can hide a second series’ lines, shapes and legend. The series itself must be visible to establish the axis range.