10.3 實例應用 · Java 開源項目中文文檔

## 10.3 實例應用 ### 10.3.1 概述實例MemoryUsageDemo.java文檔可以從下面的鏈接中獲得： [http://www.object-refinery.com/jfreechart/premium/index.html](http://www.object-refinery.com/jfreechart/premium/index.html) 頁面需要輸入購買JFreeChart開發指南時需要的用戶名和密碼。 ### 10.3.2 創建一個dataset 創建的實例代碼數據源，包含了一個單一的時序集合，集合內有兩個TimeSeries對象（一個是計算總內存，另一個是計算剩余內存）。代碼如下： ``` 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); ``` 每個時間系列的maximumItemAge屬性設置為30000毫秒（30秒）。因此任何時候添加到新系列的新數據，都是30秒前記錄的老數據。 ### 10.3.3 創建一個圖表圖表的創建（定制）都遵循所有圖表創建的標準模式。創建動態圖也是一樣，沒有任何特殊的步驟。除了我們將autoRange屬性設置為true之外。同時，這也有利于維護圖表使用的數據源的引用。 ### 10.3.4 更新一個dataset 在本實例演示中，通過向兩個時序圖添加的數據來更新數據源，該數據的添加有一個獨立的線程Timer管理。代碼如下： ``` 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在畫圖表和數據源更新代碼之間沒有使用線程同步，因此是不安全的。另一點需要注意的是，曾做過一個關于JFreeChart內存泄露問題的測試，將JFreeChart的實例在一個機器上連續運行6天。隨著圖表的不斷更新，我們就可以看到垃圾收集器所產生的影響。六天之后，發現總內存的使用量保持不變。當JFreChart產生并丟棄的臨時對象（垃圾對象）時，剩余可用內存減少了。增加的使用內存量是垃圾收集器工作時所使用的。 ### 10.3.5 全部代碼下面是全部的實例代碼： ``` /* 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; } } ```