java - 将 DefaultCategoryDataset 转换为 CategoryDataset

Question

我正在尝试创建一个基本的条形图，当我编译它时，它会出现类似的错误

Exception in thread "main" java.lang.ClassCastException: org.jfree.data.category.DefaultCategoryDataset cannot be cast to org.jfree.data.CategoryDataset

这是我的代码

 package barchart;

import java.awt.Color;
import java.awt.Dimension;

import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.CategoryDataset;
import org.jfree.data.category.DefaultCategoryDataset;
import org.jfree.ui.ApplicationFrame;


public class BarChartDemo extends 
    public BarChartDemo(final String title) {

        super(title);

        final CategoryDataset dataset = createDataset();
        final JFreeChart chart = createChart(dataset);
        final ChartPanel chartPanel = new ChartPanel(chart);
        chartPanel.setPreferredSize(new Dimension(500, 270));
        setContentPane(chartPanel);

    }
    public static void main(String[] args) {
        BarChartDemo  br = new BarChartDemo("title");
        br.createDataset();
    }


    private CategoryDataset createDataset() {

        // row keys...
        final String series1 = "First";
        final String series2 = "Second";
        final String series3 = "Third";

        // column keys...
        final String category1 = "Category 1";
        final String category2 = "Category 2";
        final String category3 = "Category 3";
        final String category4 = "Category 4";
        final String category5 = "Category 5";

        // create the dataset...
        final DefaultCategoryDataset dataset = new DefaultCategoryDataset();

        dataset.addValue(1.0, series1, category1);
        dataset.addValue(4.0, series1, category2);
        dataset.addValue(3.0, series1, category3);
        dataset.addValue(5.0, series1, category4);
        dataset.addValue(5.0, series1, category5);

        dataset.addValue(5.0, series2, category1);
        dataset.addValue(7.0, series2, category2);
        dataset.addValue(6.0, series2, category3);
        dataset.addValue(8.0, series2, category4);
        dataset.addValue(4.0, series2, category5);

        dataset.addValue(4.0, series3, category1);
        dataset.addValue(3.0, series3, category2);
        dataset.addValue(2.0, series3, category3);
        dataset.addValue(3.0, series3, category4);
        dataset.addValue(6.0, series3, category5);

        return dataset;

    }


    private JFreeChart createChart(final CategoryDataset dataset) {

        // create the chart...
        final JFreeChart chart = ChartFactory.createBarChart(
            "Bar Chart Demo",         // chart title
            "Category",               // domain axis label
            "Value", (org.jfree.data.CategoryDataset) dataset,                  
            PlotOrientation.VERTICAL, // orientation
            true,                     // include legend
            true,                     // tooltips?
            false                     // URLs?
        );

        chart.setBackgroundPaint(Color.white);
        return chart;

    }
}

为什么我们不能将 DefaultCategoryDataset 转换为 CategoryDataset？我可以纠正这个问题吗？

Answer 1

CategoryDataset 的完全限定名称是org.jfree.data.category.CategoryDataset，但在这种情况下强制转换是多余的。

代码，经测试:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.CategoryDataset;
import org.jfree.data.category.DefaultCategoryDataset;
import org.jfree.ui.ApplicationFrame;

public class BarChartDemo extends ApplicationFrame {

    public BarChartDemo(final String title) {
        super(title);
        final CategoryDataset dataset = createDataset();
        final JFreeChart chart = createChart(dataset);
        final ChartPanel chartPanel = new ChartPanel(chart) {

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(500, 270);
            }
        };
        setContentPane(chartPanel);
        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                BarChartDemo br = new BarChartDemo("title");
            }
        });
    }

    private CategoryDataset createDataset() {
        // row keys...
        final String series1 = "First";
        final String series2 = "Second";
        final String series3 = "Third";

        // column keys...
        final String category1 = "Category 1";
        final String category2 = "Category 2";
        final String category3 = "Category 3";
        final String category4 = "Category 4";
        final String category5 = "Category 5";

        // create the dataset...
        final DefaultCategoryDataset dataset = new DefaultCategoryDataset();

        dataset.addValue(1.0, series1, category1);
        dataset.addValue(4.0, series1, category2);
        dataset.addValue(3.0, series1, category3);
        dataset.addValue(5.0, series1, category4);
        dataset.addValue(5.0, series1, category5);

        dataset.addValue(5.0, series2, category1);
        dataset.addValue(7.0, series2, category2);
        dataset.addValue(6.0, series2, category3);
        dataset.addValue(8.0, series2, category4);
        dataset.addValue(4.0, series2, category5);

        dataset.addValue(4.0, series3, category1);
        dataset.addValue(3.0, series3, category2);
        dataset.addValue(2.0, series3, category3);
        dataset.addValue(3.0, series3, category4);
        dataset.addValue(6.0, series3, category5);

        return dataset;
    }

    private JFreeChart createChart(final CategoryDataset dataset) {
        // create the chart...
        final JFreeChart chart = ChartFactory.createBarChart(
            "Bar Chart Demo", // chart title
            "Category", // domain axis label
            "Value", dataset,
            PlotOrientation.VERTICAL, // orientation
            true, // include legend
            true, // tooltips?
            false // URLs?
        );
        chart.setBackgroundPaint(Color.white);
        return chart;
    }
}