DataLine声级计不显示

Question

我正在尝试从DataLine文档示例中获取的这段代码。据我了解，在播放声音时，它应该显示一个振幅电平计，但事实并非如此。它会打开声音文件并正确播放，并在一个小窗口中显示有关该文件的一些数据，但没有仪表。

也许我不了解它的工作方式。你能帮我理解吗？

DataLineInfoGUI类：

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.sound.sampled.*;


 public class DataLineInfoGUI extends JPanel {

PCMFilePlayer player;
JButton startButton;

  public DataLineInfoGUI (File f) {
 super();
     try {
       player = new PCMFilePlayer (f);
   } catch (Exception ioe) {
        add (new JLabel ("Error: " +
                        ioe.getMessage()));
       return;
   }
   DataLine line = player.getLine();
   // layout
   // line 1: name
   setLayout (new BoxLayout (this, BoxLayout.Y_AXIS));
   add (new JLabel ("File:  " + 
                     player.getFile().getName()));
    // line 2: levels
   add (new DataLineLevelMeter (line));
  // line 3: format info as textarea
AudioFormat format = line.getFormat();
 JTextArea ta = new JTextArea();
  ta.setBorder (new TitledBorder ("Format"));
 ta.append ("Encoding: " + 
          format.getEncoding().toString() + "\n");
  ta.append ("Bits/sample: " +
             format.getSampleSizeInBits() + "\n");
  ta.append ("Channels: " +
            format.getChannels() + "\n");
 ta.append ("Endianness: " + 
              (format.isBigEndian() ? " big " : "little") + "\n");
   ta.append ("Frame size: " + 
              format.getFrameSize() + "\n");
    ta.append ("Frame rate: " +
              format.getFrameRate() + "\n");
   add (ta);

  // now start playing
    player.start();
 }
   public static void main (String[] args) {
   JFileChooser chooser = new JFileChooser();
   chooser.showOpenDialog(null);
  File file = chooser.getSelectedFile();
   DataLineInfoGUI demo = 
       new DataLineInfoGUI (file);

    JFrame f = new JFrame ("JavaSound info");
    f.getContentPane().add (demo);
   f.pack();
    f.setVisible(true);
 }

      class DataLineLevelMeter extends JPanel {
   DataLine line;
   float level = 0.0f;
          public DataLineLevelMeter (DataLine l) {
                line = l;
               Timer timer =
                new Timer (50,
                             new ActionListener (){
                                 public void actionPerformed (ActionEvent e) 
{
                               level = line.getLevel();
                               repaint();
                           }
                       });
       timer.start();
   }
          public void paint (Graphics g) {
        Dimension d = getSize();
        g.setColor (Color.green);

       int meterWidth = (int) (level * (float) d.width);
        g.fillRect (0, 0, meterWidth, d.height);
  }

}

}

PCMFilePlayer类：

import javax.sound.sampled.*;
import java.io.*;

public class PCMFilePlayer implements Runnable {
File file;
AudioInputStream in;
SourceDataLine line;
int frameSize;
byte[] buffer = new byte [32 * 1024]; // 32k is arbitrary
Thread playThread;
boolean playing;
boolean notYetEOF;

public PCMFilePlayer (File f)
    throws IOException,
           UnsupportedAudioFileException,
           LineUnavailableException {
    file = f;
    in = AudioSystem.getAudioInputStream (f);
    AudioFormat format = in.getFormat();
    AudioFormat.Encoding formatEncoding = format.getEncoding();
    if (! (formatEncoding.equals (AudioFormat.Encoding.PCM_SIGNED) ||
           formatEncoding.equals (AudioFormat.Encoding.PCM_UNSIGNED)))
        throw new UnsupportedAudioFileException (
                                                 file.getName() + " is not 
    PCM audio");
    System.out.println ("got PCM format");
    frameSize = format.getFrameSize();
    DataLine.Info info =
        new DataLine.Info (SourceDataLine.class, format);
    System.out.println ("got info");
    line = (SourceDataLine) AudioSystem.getLine (info);
    System.out.println ("got line");
    line.open();
    System.out.println ("opened line");
    playThread = new Thread (this);
    playing = false;
    notYetEOF = true;
    playThread.start();
}

public void run() {
    int readPoint = 0;
    int bytesRead = 0;

    try {
        while (notYetEOF) {
            if (playing) {
                bytesRead = in.read (buffer,
                                     readPoint,
                                     buffer.length - readPoint);
                if (bytesRead == -1) {
                    notYetEOF = false;
                    break;
                }
                // how many frames did we get,
                // and how many are left over?
                int frames = bytesRead / frameSize;
                int leftover = bytesRead % frameSize;
                // send to line
                line.write (buffer, readPoint, bytesRead-leftover);
                // save the leftover bytes
                System.arraycopy (buffer, bytesRead,
                                  buffer, 0,
                                  leftover);
                readPoint = leftover;

            } else {
                // if not playing
                // Thread.yield();
                try { Thread.sleep (10);} 
                catch (InterruptedException ie) {}
            }
        } // while notYetEOF
        System.out.println ("reached eof");
        line.drain();
        line.stop();
    } catch (IOException ioe) {
        ioe.printStackTrace();
    } finally {
        // line.close();
    }
} // run


public void start() {
    playing = true;
    if (! playThread.isAlive())
        playThread.start();
    line.start();
}

public void stop() {
    playing = false;
    line.stop();
}

public SourceDataLine getLine() {
    return line;
}

public File getFile() {
    return file;
}
}