JFreeChart時序圖

時序圖表顯示的數據點在相等的時間間隔序列變化。本章演示了如何從一個給定的業務數據使用JFreeChart，建立時序圖。

業務數據

讓我們考慮通過使用標準 Java API 的 Math.random()產生的各種亂數。我們使用這些數字產生一個時間序列圖。可以生成用於發生錯誤的總數在自己的網站給定的時間間隔類似的圖表。

基於AWT的應用

下麵是創建由Math.random()產生的數字時間的代碼在給定時間內的序列圖。

import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.data.general.SeriesException;
import org.jfree.data.time.Second;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.data.xy.XYDataset;
import org.jfree.ui.ApplicationFrame;
import org.jfree.ui.RefineryUtilities;

public class TimeSeries_AWT extends ApplicationFrame
{
   public TimeSeries_AWT( final String title )
   {
      super( title );
      final XYDataset dataset = createDataset( );
      final JFreeChart chart = createChart( dataset );
      final ChartPanel chartPanel = new ChartPanel( chart );
      chartPanel.setPreferredSize( new java.awt.Dimension( 560 , 370 ) );
      chartPanel.setMouseZoomable( true , false );
      setContentPane( chartPanel );
   }

   private XYDataset createDataset( )
   {
      final TimeSeries series = new TimeSeries( "Random Data" );
      Second current = new Second( );
      double value = 100.0;
      for (int i = 0; i < 4000; i++)
      {
         try
         {
            value = value + Math.random( ) - 0.5;
            series.add(current, new Double( value ) );
            current = ( Second ) current.next( );
         }
         catch ( SeriesException e )
         {
            System.err.println("Error adding to series");
         }
      }

      return new TimeSeriesCollection(series);
   }

   private JFreeChart createChart( final XYDataset dataset )
   {
      return ChartFactory.createTimeSeriesChart(
      "Computing Test",
      "Seconds",
      "Value",
      dataset,
      false,
      false,
      false);
   }

   public static void main( final String[ ] args )
   {
      final String title = "Time Series Management";
      final TimeSeries_AWT demo = new TimeSeries_AWT( title );
      demo.pack( );
      RefineryUtilities.positionFrameRandomly( demo );
      demo.setVisible( true );
   }
}   

保存上面的Java代碼在TimeSeries_AWT.java檔，然後從命令提示符下編譯並運行它，如下所示：

$javac TimeSeries_AWT.java
$java TImeSeries_AWT

如果一切順利，它會編譯並運行生成以下時序圖：

創建JPEG圖像

讓我們重新編寫上面的例子，在命令行生成JPEG圖像。

import java.io.*;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.JFreeChart;
import org.jfree.data.general.SeriesException;
import org.jfree.data.time.Second;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.data.xy.XYDataset;
import org.jfree.chart.ChartUtilities;

public class TimeSeriesChart
{
   public static void main( final String[ ] args )throws Exception
   {
      final TimeSeries series = new TimeSeries( "Random Data" );
      Second current = new Second();
      double value = 100.0;
      for ( int i = 0 ; i < 4000 ; i++ )
      {
         try
         {
            value = value + Math.random( ) - 0.5;
            series.add( current , new Double( value ) );
            current = ( Second ) current.next( );
         }
         catch ( SeriesException e )
         {
            System.err.println( "Error adding to series" );
         }
      }
      final XYDataset dataset=( XYDataset )new TimeSeriesCollection(series);
      JFreeChart timechart = ChartFactory.createTimeSeriesChart(
         "Computing Test",
         "Seconds",
         "Value",
         dataset,
         false,
         false,
         false);

      int width = 560; /* Width of the image */
      int height = 370; /* Height of the image */
      File timeChart = new File( "TimeChart.jpeg" );
      ChartUtilities.saveChartAsJPEG( timeChart, timechart, width, height );
   }
}

繼續上面的Java代碼保存在TimeSeriesChart.java檔中，然後從命令提示符下編譯並運行它，如下所示：

$javac TimeSeriesChart.java
$java TimeSeriesChart

如果一切正常，它會編譯並運行在當前的目錄中創建JPEG圖像檔TimeChart.jpeg檔。