10.3 实例应用

10.3.1 概述

实例MemoryUsageDemo.java文档可以从下面的链接中获得：

http://www.object-refinery.com/jfreechart/premium/index.html

页面需要输入购买JFreeChart开发指南时需要的用户名和密码。

10.3.2 创建一个dataset

创建的实例代码数据源，包含了一个单一的时序集合，集合内有两个TimeSeries对象（一个是计算总内存，另一个是计算剩余内存）。代码如下：

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(this.total);
dataset.addSeries(this.free);

每个时间系列的maximumItemAge属性设置为30000毫秒（30秒）。因此任何时候添加到新系列的新数据，都是30秒前记录的老数据。

10.3.3 创建一个图表

图表的创建（定制）都遵循所有图表创建的标准模式。创建动态图也是一样，没有任何特殊的步骤。除了我们将autoRange属性设置为true之外。同时，这也有利于维护图表使用的数据源的引用。

10.3.4 更新一个dataset

在本实例演示中，通过向两个时序图添加的数据来更新数据源，该数据的添加有一个独立的线程Timer管理。代码如下：

class DataGenerator extends Timer implements ActionListener {
    DataGenerator(int i) {
        super(i, null);
        addActionListener(this);
    }
    public void actionPerformed(ActionEvent actionevent) {
        long l = Runtime.getRuntime().freeMemory();
        long l_0_ = Runtime.getRuntime().totalMemory();
        MemoryUsageDemo.this.addTotalObservation((double) l_0_);
        MemoryUsageDemo.this.addFreeObservation((double) l);
    }
}

注意JFreeChart在画图表和数据源更新代码之间没有使用线程同步，因此是不安全的。另一点需要注意的是，曾做过一个关于JFreeChart内存泄露问题的测试，将JFreeChart的实例在一个机器上连续运行6天。随着图表的不断更新，我们就可以看到垃圾收集器所产生的影响。六天之后，发现总内存的使用量保持不变。当JFreChart产生并丢弃的临时对象（垃圾对象）时，剩余可用内存减少了。增加的使用内存量是垃圾收集器工作时所使用的。

10.3.5 全部代码

下面是全部的实例代码：

/* MemoryUsageDemo - Decompiled by JODE
* Visit http://jode.sourceforge.net/
*/
package demo;
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
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.XYLineAndShapeRenderer;
import org.jfree.data.time.Millisecond;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.ui.RectangleInsets;
public class MemoryUsageDemo extends JPanel {
    private static final long serialVersionUID = 6776712838359498649L;
    private TimeSeries total;
    private TimeSeries free;
    /* synthetic */
    static Class class$org$jfree$data$time$Millisecond;
    class DataGenerator extends Timer implements ActionListener {
        private static final long serialVersionUID = 1L;
        DataGenerator(int i) {
            super(i, null);
            addActionListener(this);
        }
        public void actionPerformed(ActionEvent actionevent) {
            long l = Runtime.getRuntime().freeMemory();
            long l_0_ = Runtime.getRuntime().totalMemory();
            MemoryUsageDemo.this.addTotalObservation((double) l_0_);
            MemoryUsageDemo.this.addFreeObservation((double) l);
        }
    }
    public MemoryUsageDemo(int i) {
        super(new BorderLayout());
        total = new TimeSeries(
            "Total Memory",
            (class$org$jfree$data$time$Millisecond == null ? (class$org$jfree$data$time$Millisecond = class$("org.jfree.data.time.Millisecond"))
            : class$org$jfree$data$time$Millisecond));
        total.setMaximumItemAge((long) i);
        free = new TimeSeries(
            "Free Memory",
            (class$org$jfree$data$time$Millisecond == null ? (class$org$jfree$data$time$Millisecond = class$("org.jfree.data.time.Millisecond"))
            : class$org$jfree$data$time$Millisecond));
        free.setMaximumItemAge((long) i);
        TimeSeriesCollection timeseriescollection = new TimeSeriesCollection();
        timeseriescollection.addSeries(total);
        timeseriescollection.addSeries(free);
        DateAxis dateaxis = new DateAxis("Time");
        NumberAxis numberaxis = new NumberAxis("Memory");
        dateaxis.setTickLabelFont(new Font("SansSerif", 0, 12));
        numberaxis.setTickLabelFont(new Font("SansSerif", 0, 12));
        dateaxis.setLabelFont(new Font("SansSerif", 0, 14));
        numberaxis.setLabelFont(new Font("SansSerif", 0, 14));
        XYLineAndShapeRenderer xylineandshaperenderer = new XYLineAndShapeRenderer(
            true, false);
        xylineandshaperenderer.setSeriesPaint(0, Color.red);
        xylineandshaperenderer.setSeriesPaint(1, Color.green);
        xylineandshaperenderer.setSeriesStroke(0, new BasicStroke(3.0F, 0, 2));
        xylineandshaperenderer.setSeriesStroke(1, new BasicStroke(3.0F, 0, 2));
        XYPlot xyplot = new XYPlot(timeseriescollection, dateaxis, numberaxis,
            xylineandshaperenderer);
        xyplot.setBackgroundPaint(Color.lightGray);
        xyplot.setDomainGridlinePaint(Color.white);
        xyplot.setRangeGridlinePaint(Color.white);
        xyplot.setAxisOffset(new RectangleInsets(5.0, 5.0, 5.0, 5.0));
        dateaxis.setAutoRange(true);
        dateaxis.setLowerMargin(0.0);
        dateaxis.setUpperMargin(0.0);
        dateaxis.setTickLabelsVisible(true);
        numberaxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits());
        JFreeChart jfreechart = new JFreeChart("JVM Memory Usage", new Font(
            "SansSerif", 1, 24), xyplot, true);
        jfreechart.setBackgroundPaint(Color.white);
        ChartPanel chartpanel = new ChartPanel(jfreechart, true);
        chartpanel.setBorder(BorderFactory.createCompoundBorder(BorderFactory
            .createEmptyBorder(4, 4, 4, 4), BorderFactory
            .createLineBorder(Color.black)));
        add(chartpanel);
    }
    private void addTotalObservation(double d) {
        total.add(new Millisecond(), d);
    }
    private void addFreeObservation(double d) {
        free.add(new Millisecond(), d);
    }
    public static void main(String[] strings) {
        JFrame jframe = new JFrame("Memory Usage Demo");
        MemoryUsageDemo memoryusagedemo = new MemoryUsageDemo(30000);
        jframe.getContentPane().add(memoryusagedemo, "Center");
        jframe.setBounds(200, 120, 600, 280);
        jframe.setVisible(true);
        memoryusagedemo.new DataGenerator(100).start();
        jframe.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent windowevent) {
                System.exit(0);
            }
        });
    }
    /* synthetic */static Class class$(String string) {
        Class var_class;
        try {
            var_class = Class.forName(string);
        } catch (ClassNotFoundException classnotfoundexception) {
            throw new NoClassDefFoundError(classnotfoundexception.getMessage());
        }
        return var_class;
    }
}