JFreeChart x axis scale

Based on this example, here's an sscce that uses setTickUnit() to adjust the domain axis tick unit dynamically, starting from the value 5.

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.SpinnerNumberModel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.NumberTickUnit;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/** @see https://stackoverflow.com/a/14167983/230513 */
public class SSCCE {

    private static final int COUNT = 100;
    private static final int UNITS = 5;
    private static final Random r = new Random();

    public static void main(String[] args) {
        XYSeries series = new XYSeries("Data");
        for (int i = 0; i < COUNT; i++) {
            series.add(i, r.nextGaussian());
        }
        XYSeriesCollection data = new XYSeriesCollection(series);
        final JFreeChart chart = ChartFactory.createXYLineChart("TickUnits",
            "X", "Y", data, PlotOrientation.VERTICAL, true, true, false);
        XYPlot plot = (XYPlot) chart.getPlot();
        final NumberAxis xAxis = (NumberAxis) plot.getDomainAxis();
        xAxis.setTickUnit(new NumberTickUnit(UNITS));
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame f = new JFrame("TickUnitDemo");
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.add(new ChartPanel(chart));
                final JSpinner spinner = new JSpinner(
                    new SpinnerNumberModel(UNITS, 1, COUNT, 1));
                spinner.addChangeListener(new ChangeListener() {

                    @Override
                    public void stateChanged(ChangeEvent e) {
                        JSpinner s = (JSpinner) e.getSource();
                        Number n = (Number) s.getValue();
                        xAxis.setTickUnit(new NumberTickUnit(n.intValue()));
                    }
                });
                JPanel p = new JPanel();
                p.add(new JLabel(chart.getTitle().getText()));
                p.add(spinner);
                f.add(p, BorderLayout.SOUTH);
                f.pack();
                f.setLocationRelativeTo(null);
                f.setVisible(true);
            }
        });

    }
}

You should use NumberAxis, which contains a lot of methods to define the scale of your chart.

Example :

// Create an XY Line chart
XYSeries series = new XYSeries("Random Data");
series.add(1.0, 500.2);
series.add(10.0, 694.1);
XYSeriesCollection data = new XYSeriesCollection(series);
JFreeChart chart = ChartFactory.createXYLineChart("XY Series Demo", "X", "Y", data,
                                                  PlotOrientation.VERTICAL, 
                                                  true, true, false);

// Create an NumberAxis
NumberAxis xAxis = new NumberAxis();
xAxis.setTickUnit(new NumberTickUnit(2));

// Assign it to the chart
XYPlot plot = (XYPlot) chart.getPlot();
plot.setDomainAxis(xAxis);