## 18.3 实例应用 正如在简介中所提及的，使用JFreeChart的applet可以在下面链接中看到： [http://www.object-refinery.com/jfreechart/applet.html](http://www.object-refinery.com/jfreechart/applet.html) 运行applet应用时，需要两个方面饿支持。一是代码方式创建applet，二是HTML文件用来调用applet。 ### 18.3.1 HTML 因为applet需要引入额外的jar文件，所以在HTML中使用applet是显得非常重要。HTML applet标签如下： ``` <APPLET ARCHIVE="jfreechart-1.0.6-applet-demo.jar, jfreechart-1.0.6.jar,jcommon-1.0.9.jar" CODE="demo.applet.Applet1" width=640 height=260 ALT="You should see an applet, not this text."> </APPLET> ``` 注意这里有三个jar需要引入，第一个包含了applet类，另外两个jar文件是JFreeChart和JCommon类库。我们需要在HTML文件中将applet标签引入。 ### 18.3.2 源代码 实例applet的源代码见下（代码中我们使用了很少的applet特殊的代码，仅仅扩展了JApplet）： ``` package demo; import java.awt.BasicStroke; import java.awt.Color; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JApplet; import javax.swing.Timer; import org.jfree.chart.ChartPanel; import org.jfree.chart.JFreeChart; import org.jfree.chart.axis.DateAxis; import org.jfree.chart.axis.NumberAxis; import org.jfree.chart.plot.XYPlot; import org.jfree.chart.renderer.xy.XYItemRenderer; import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer; import org.jfree.data.time.Millisecond; import org.jfree.data.time.TimeSeries; import org.jfree.data.time.TimeSeriesCollection; /** * A simple applet demo. */ public class Applet1 extends JApplet { /** Time series for total memory used. */ private TimeSeries total; /** Time series for free memory. */ private TimeSeries free; /** * Creates a new instance. */ public Applet1() { // create two series that automatically discard data more than // 30 seconds old... this.total = new TimeSeries("Total", Millisecond.class); this.total.setMaximumItemAge(30000); this.free = new TimeSeries("Free", Millisecond.class); this.free.setMaximumItemAge(30000); TimeSeriesCollection dataset = new TimeSeriesCollection(); dataset.addSeries(total); dataset.addSeries(free); DateAxis domain = new DateAxis("Time"); NumberAxis range = new NumberAxis("Memory"); XYItemRenderer renderer = new XYLineAndShapeRenderer(true, false); XYPlot plot = new XYPlot(dataset, domain, range, renderer); plot.setBackgroundPaint(Color.lightGray); plot.setDomainGridlinePaint(Color.white); plot.setRangeGridlinePaint(Color.white); renderer.setSeriesPaint(0, Color.red); renderer.setSeriesPaint(1, Color.green); renderer.setSeriesStroke(0, new BasicStroke(1.5f)); renderer.setSeriesStroke(1, new BasicStroke(1.5f)); domain.setAutoRange(true); domain.setLowerMargin(0.0); domain.setUpperMargin(0.0); domain.setTickLabelsVisible(true); range.setStandardTickUnits(NumberAxis.createIntegerTickUnits()); JFreeChart chart = new JFreeChart("Memory Usage", JFreeChart.DEFAULT_TITLE_FONT, plot, true); chart.setBackgroundPaint(Color.white); ChartPanel chartPanel = new ChartPanel(chart); chartPanel.setPopupMenu(null); getContentPane().add(chartPanel); new Applet1.DataGenerator().start(); } /** * Adds an observation to the ’total memory’ time series. * * @param y * the total memory used. */ private void addTotalObservation(double y) { total.add(new Millisecond(), y); } /** * Adds an observation to the ’free memory’ time series. * * @param y * the free memory. */ private void addFreeObservation(double y) { free.add(new Millisecond(), y); } /** * The data generator. */ class DataGenerator extends Timer implements ActionListener { /** * Constructor. */ DataGenerator() { super(100, null); addActionListener(this); } /** * Adds a new free/total memory reading to the dataset. * * @param event * the action event. */ public void actionPerformed(ActionEvent event) { long f = Runtime.getRuntime().freeMemory(); long t = Runtime.getRuntime().totalMemory(); addTotalObservation(t); addFreeObservation(f); } } } ```