JFreeChart是JAVA平台上的一个开放的图表绘制类库。它完全使用JAVA语言编写，是为applications, applets, servlets 以及JSP等使用所设计。JFreeChart可生成饼图(pie charts)、柱状图(bar charts)、散点图(scatter plots)、时序图(time series)、甘特图(Gantt charts)等等多种图表，并且可以产生PNG和JPEG格式的输出，还可以与PDF和EXCEL关联。

JFreeChart截止2011年2月22日为止的相当不错的java图形解决方案，基本能够解决目前的图形方面的需求。本文着重对JFreeChart在Swing客户端界面实现柱形图进行介绍，其它统计图表的使用方法类似，读者可以参考JFreeChart提供的API。程序实现的效果如图：

Java代码：

package Test.JFreeChar;

import java.awt.Color;

import java.awt.Dimension;

import java.awt.GradientPaint;

import javax.swing.JPanel;

import org.jfree.chart.ChartFactory;

import org.jfree.chart.ChartPanel;

import org.jfree.chart.JFreeChart;

import org.jfree.chart.axis.CategoryAxis;

import org.jfree.chart.axis.CategoryLabelPositions;

import org.jfree.chart.axis.NumberAxis;

import org.jfree.chart.labels.StandardCategorySeriesLabelGenerator;

import org.jfree.chart.plot.CategoryPlot;

import org.jfree.chart.plot.PlotOrientation;

import org.jfree.chart.renderer.category.BarRenderer;

import org.jfree.data.category.CategoryDataset;

import org.jfree.data.category.DefaultCategoryDataset;

import org.jfree.ui.ApplicationFrame;

import org.jfree.ui.RefineryUtilities;

/**

* JFreeChar柱形图

*

*/

public class BarChartDemo extends ApplicationFrame {

private static final long serialVersionUID = 1L;

public BarChartDemo(String paramString) {

super(paramString);

JPanel localJPanel = createDemoPanel();

localJPanel.setPreferredSize(new Dimension(500, 270));

setContentPane(localJPanel);

}

/**

* 准备绘制柱形图使用的数据集

*/

private static CategoryDataset createDataset() {

String str1 = "First";

String str2 = "Second";

String str3 = "Third";

String str4 = "Category 1";

String str5 = "Category 2";

String str6 = "Category 3";

String str7 = "Category 4";

String str8 = "Category 5";

DefaultCategoryDataset localDefaultCategoryDataset = new DefaultCategoryDataset();

localDefaultCategoryDataset.addValue(1.0D, str1, str4);

localDefaultCategoryDataset.addValue(4.0D, str1, str5);

localDefaultCategoryDataset.addValue(3.0D, str1, str6);

localDefaultCategoryDataset.addValue(5.0D, str1, str7);

localDefaultCategoryDataset.addValue(5.0D, str1, str8);

localDefaultCategoryDataset.addValue(5.0D, str2, str4);

localDefaultCategoryDataset.addValue(7.0D, str2, str5);

localDefaultCategoryDataset.addValue(6.0D, str2, str6);

localDefaultCategoryDataset.addValue(8.0D, str2, str7);

localDefaultCategoryDataset.addValue(4.0D, str2, str8);

localDefaultCategoryDataset.addValue(4.0D, str3, str4);

localDefaultCategoryDataset.addValue(3.0D, str3, str5);

localDefaultCategoryDataset.addValue(2.0D, str3, str6);

localDefaultCategoryDataset.addValue(3.0D, str3, str7);

localDefaultCategoryDataset.addValue(6.0D, str3, str8);

return localDefaultCategoryDataset;

}

/**

* 创建JFreeChart

* @param paramCategoryDataset 数据集

* @return

*/

private static JFreeChart createChart(CategoryDataset paramCategoryDataset) {

JFreeChart localJFreeChart = ChartFactory.createBarChart(

"Bar Chart Demo 1", "Category", "Value", paramCategoryDataset,

PlotOrientation.VERTICAL, true, true, false);

CategoryPlot localCategoryPlot = (CategoryPlot) localJFreeChart

.getPlot();

localCategoryPlot.setDomainGridlinesVisible(true);

localCategoryPlot.setRangeCrosshairVisible(true);

localCategoryPlot.setRangeCrosshairPaint(Color.blue);

NumberAxis localNumberAxis = (NumberAxis) localCategoryPlot

.getRangeAxis();

localNumberAxis.setStandardTickUnits(NumberAxis

.createIntegerTickUnits());

BarRenderer localBarRenderer = (BarRenderer) localCategoryPlot

.getRenderer();

localBarRenderer.setDrawBarOutline(false);

GradientPaint localGradientPaint1 = new GradientPaint(0.0F, 0.0F,

Color.blue, 0.0F, 0.0F, new Color(0, 0, 64));

GradientPaint localGradientPaint2 = new GradientPaint(0.0F, 0.0F,

Color.green, 0.0F, 0.0F, new Color(0, 64, 0));

GradientPaint localGradientPaint3 = new GradientPaint(0.0F, 0.0F,

Color.red, 0.0F, 0.0F, new Color(64, 0, 0));

localBarRenderer.setSeriesPaint(0, localGradientPaint1);

localBarRenderer.setSeriesPaint(1, localGradientPaint2);

localBarRenderer.setSeriesPaint(2, localGradientPaint3);

localBarRenderer

.setLegendItemToolTipGenerator(new StandardCategorySeriesLabelGenerator(

"Tooltip: {0}"));

CategoryAxis localCategoryAxis = localCategoryPlot.getDomainAxis();

localCategoryAxis.setCategoryLabelPositions(CategoryLabelPositions

.createUpRotationLabelPositions(0.5235987755982988D));

return localJFreeChart;

}

/**

* 创建显示柱形图的面板

* @return

*/

public static JPanel createDemoPanel() {

JFreeChart localJFreeChart = createChart(createDataset());

return new ChartPanel(localJFreeChart);

}

public static void main(String[] paramArrayOfString) {

BarChartDemo localBarChartDemo1 = new BarChartDemo(

"JFreeChart: BarChartDemo1.java");

localBarChartDemo1.pack();

RefineryUtilities.centerFrameOnScreen(localBarChartDemo1);

localBarChartDemo1.setVisible(true);

}

}

至此，使用JFreeChart实现的统计柱形图便完成了，JFreeChart为统计图的显示提供了方便的接口，后续文章将会介绍使用JFreeChart实现其它统计图。

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