导致Jfreechart带有滚动条

Question

我想在图表中添加一个滚动条，以便查看不适合屏幕的大数据集，因为要保留所有的xtick。然而，我收到了以下错误消息：

Exception in thread "main" java.lang.NullPointerException
at MySlidingCategoryDatasetDemo2$DemoPanel.createChart(MySlidingCategoryDatasetDemo2.java:96)
at MySlidingCategoryDatasetDemo2$DemoPanel.<init>(MySlidingCategoryDatasetDemo2.java:148)
at MySlidingCategoryDatasetDemo2.createDemoPanel(MySlidingCategoryDatasetDemo2.java:170)
at MySlidingCategoryDatasetDemo2.<init>(MySlidingCategoryDatasetDemo2.java:166)
at MySlidingCategoryDatasetDemo2.main(MySlidingCategoryDatasetDemo2.java:174)

带有以下代码：

import java.awt.*;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import org.jfree.chart.*;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.ValueAxis;
import org.jfree.chart.event.ChartChangeListener;
import org.jfree.chart.plot.CombinedDomainXYPlot;
import org.jfree.chart.plot.Plot;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.StandardXYItemRenderer;
import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer;
import org.jfree.data.category.*;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;
import org.jfree.ui.ApplicationFrame;
import org.jfree.ui.RefineryUtilities;
public class MySlidingCategoryDatasetDemo2 extends ApplicationFrame {
static class DemoPanel extends JPanel implements ChangeListener {
    private static XYDataset createDataset() {
    XYSeries xyseries = new XYSeries("First");
    xyseries.add(1.0D, 1.0D);
    xyseries.add(2D, 4D);
    xyseries.add(3D, 3D);
    xyseries.add(4D, 5D);
    xyseries.add(5D, 5D);
    xyseries.add(6D, 7D);
    xyseries.add(7D, 7D);
    xyseries.add(8D, 8D);
    xyseries.add(9D, 8D);
    xyseries.add(10D, 8D);
    xyseries.add(11D, 8D);
    xyseries.add(12D, 8D);
    xyseries.add(13D, 8D);
    xyseries.add(14D, 8D);
    xyseries.add(15D, 8D);
    xyseries.add(16D, 25D);
    xyseries.add(17D, 8D);
    xyseries.add(18D, 5D);
    xyseries.add(19D, 7D);
    xyseries.add(20D, 6D);
    xyseries.add(21D, 8D);
    xyseries.add(22D, 4D);
    xyseries.add(23D, 4D);
    xyseries.add(24D, 2D);
    xyseries.add(25D, 1.0D);
    xyseries.add(26D, 8D);
    xyseries.add(27D, 8D);
    xyseries.add(28D, 8D);
    xyseries.add(29D, 8D);
    xyseries.add(30D, 8D);
    xyseries.add(31D, 8D);
    xyseries.add(32D, 25D);
    xyseries.add(33D, 8D);
    xyseries.add(34D, 5D);
    xyseries.add(35D, 7D);
    xyseries.add(36D, 6D);
    xyseries.add(37D, 8D);
    xyseries.add(38D, 4D);
    xyseries.add(39D, 4D);
    xyseries.add(40D, 2D);
    xyseries.add(41D, 1.0D);
    XYSeriesCollection xyseriescollection = new XYSeriesCollection();
    xyseriescollection.addSeries(xyseries);
    return xyseriescollection;
    }
    private static JFreeChart createChart(XYDataset xydataset) {
    final CombinedDomainXYPlot xyplot = new CombinedDomainXYPlot();
    NumberAxis rangeAxis1 = new NumberAxis();
    rangeAxis1.setLowerBound(0);
    rangeAxis1.setUpperBound(30);
    final XYPlot subplot1 = new XYPlot(xydataset, null, rangeAxis1,
        new StandardXYItemRenderer());
    xyplot.add(subplot1);
    final JFreeChart jfreechart = new JFreeChart("Hello",
        JFreeChart.DEFAULT_TITLE_FONT, xyplot, true);
    // JFreeChart jfreechart =
    // ChartFactory.createXYLineChart("Line Chart Demo 2", "X", "Y",
    // xydataset, PlotOrientation.VERTICAL, true, true, false);
    // XYPlot xyplot = (XYPlot)jfreechart.getPlot();
    //
    xyplot.setDomainPannable(true);
    xyplot.setRangePannable(true);
    XYLineAndShapeRenderer xylineandshaperenderer = (XYLineAndShapeRenderer) xyplot
        .getRenderer();
    xylineandshaperenderer.setBaseShapesVisible(true);
    xylineandshaperenderer.setBaseShapesFilled(true);
    // NumberAxis numberaxis = (NumberAxis)xyplot.getRangeAxis();
    // numberaxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits());
    // numberaxis.setRange(0.0D, 100D);
    ValueAxis valueaxis = xyplot.getDomainAxis();
    // valueaxis.setLowerMargin(0.34999999999999998D);
    valueaxis.setLowerBound(0);
    valueaxis.setUpperBound(60);
    return jfreechart;
    }
    public void stateChanged(ChangeEvent changeevent) {
    // dataset.setFirstCategoryIndex(scroller.getValue());
    BoundedRangeModel scrollBarModel = scroller.getModel();
    try {
        Object src = changeevent.getSource();
        if (src == scrollBarModel) {
        int val = scrollBarModel.getValue();
        int ext = scrollBarModel.getExtent();
        System.out.println(val);
        System.out.println(ext);
        Plot plot = this.chartpanel.getChart().getPlot();
        if (plot instanceof XYPlot) {
            XYPlot hvp = (XYPlot) plot;
            ValueAxis axis = hvp.getDomainAxis();
            this.chartpanel.getChart().removeChangeListener(
                (ChartChangeListener) this);
            axis.setRange(val / this.xscrollFactor, (val + ext)
                / this.xscrollFactor);
            this.chartpanel.getChart().addChangeListener(
                (ChartChangeListener) this);
        }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    }
    JScrollBar scroller;
    SlidingCategoryDataset dataset;
    ChartPanel chartpanel;
    double xscrollFactor = 50;
    public DemoPanel() {
    super(new BorderLayout());
    JFreeChart jfreechart = createChart(createDataset());
    chartpanel = new ChartPanel(jfreechart);
    // chartpanel.setPreferredSize(new Dimension(400, 400));
    scroller = new JScrollBar(JScrollBar.HORIZONTAL);// (0, 0, 10, 0, 50);
    add(chartpanel);
    scroller.getModel().addChangeListener(this);
    JPanel jpanel = new JPanel(new BorderLayout());
    jpanel.add(scroller);
    jpanel.setBorder(BorderFactory.createEmptyBorder(2, 2, 2, 2));
    jpanel.setBackground(Color.white);
    add(jpanel, "South");
    }
}
public MySlidingCategoryDatasetDemo2(String s) {
    super(s);
    setDefaultCloseOperation(3);
    setContentPane(createDemoPanel());
}
public static JPanel createDemoPanel() {
    return new DemoPanel();
}
public static void main(String args[]) {
    MySlidingCategoryDatasetDemo2 slidingcategorydatasetdemo2 = new MySlidingCategoryDatasetDemo2(
        "JFreeChart: SlidingCategoryDatasetDemo2.java");
    slidingcategorydatasetdemo2.pack();
    RefineryUtilities.centerFrameOnScreen(slidingcategorydatasetdemo2);
    slidingcategorydatasetdemo2.setVisible(true);
}
}

我做错了什么？

提前谢谢。

Answer 1

NullPointerException的出现是因为名为xyplot的CombinedDomainXYPlot没有渲染器；只有它的子画面有渲染器。xyplot中唯一的子图形是名为subplot1的XYPlot，它具有类型为StandardXYItemRenderer的标准渲染器。你可以在createChart()中这样调节它：

StandardXYItemRenderer renderer =
    (StandardXYItemRenderer) subplot1.getRenderer();
renderer.setBaseShapesVisible(true);
renderer.setBaseShapesFilled(true);