在JVM7中凍結，但在JVM6中凍結

Question

一位朋友最近要求我製作一個簡單的蜂鳴器程序，並在我爲他寫的內容中發現了一個奇怪的「錯誤」。

如果按下鍵並且蜂鳴器在幾秒鐘內迅速復位，他會觀察到復位後第一次按鍵和「蜂鳴」指示之間出現的程序的2到3秒鐘凍結。他具有以下Java安裝：

build 1.7.0_25-b16 

不過，我並不在我的電腦上遇到此問題，用下面的Java安裝：

$ java -version 
java version "1.6.0_51" 
Java(TM) SE Runtime Environment (build 1.6.0_51-b11-457-10M4509) 
Java HotSpot(TM) 64-Bit Server VM (build 20.51-b01-457, mixed mode) 

一旦解凍，程序返回相應的鍵（即不是按下的最後一個鍵，而是在重置之後和凍結之前推動的第一個鍵）。這表明問題不在聆聽者身上，而在於對聆聽者的反應。

有什麼想法可能會導致這種現象？在此先感謝您的幫助。

的源代碼：

/** 
* Buzzer.java 
* 
* Buzzer 
*/ 
package org.lexingtonma.lhs.nhb; 

import java.awt.Color; 
import java.awt.DefaultKeyboardFocusManager; 
import java.awt.Font; 
import java.awt.KeyEventDispatcher; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 

import javax.sound.sampled.AudioSystem; 
import javax.sound.sampled.Clip; 
import javax.sound.sampled.LineUnavailableException; 
import javax.swing.JButton; 
import javax.swing.JFrame; 
import javax.swing.JOptionPane; 
import javax.swing.JPanel; 
import javax.swing.JTextField; 


/** 
* @author Arman D. Bilge 
* 
*/ 
public class Buzzer extends JFrame implements KeyListener { 

    private static final long serialVersionUID = 7492374642744742658L; 
    private static final String BUZZ_A = "BuzzA.wav"; 
    private static final String BUZZ_B = "BuzzB.wav"; 
    private Clip buzz = null; 
    private boolean listening = true; 
    private final JTextField display = new JTextField(3); 
    private final JButton reset = new JButton("Reset"); 

    { 

     DefaultKeyboardFocusManager.getCurrentKeyboardFocusManager() 
      .addKeyEventDispatcher(new KeyEventDispatcher() { 
       public boolean dispatchKeyEvent(KeyEvent e) { 
        keyTyped(e); 
        return false; 
       } 
      }); 
     setTitle("Buzzer"); 
     final JPanel panel = new JPanel(); 
     setSize(256, 162); 
     setDefaultCloseOperation(EXIT_ON_CLOSE); 
     display.setFont(new Font("Helvetica", Font.BOLD, 64)); 
     display.setForeground(Color.WHITE); 
     display.setVisible(true); 
     display.setEditable(false); 
     display.setHorizontalAlignment(JTextField.CENTER); 
     panel.add(display); 
     reset.addActionListener(new ActionListener() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       display.setText(""); 
       display.setBackground(Color.WHITE); 
       listening = true; 
       reset.setEnabled(false); 
      } 
     }); 
     reset.setEnabled(false); 
     panel.add(reset); 
     add(panel); 
     try { 
      buzz = AudioSystem.getClip(); 
     } catch (LineUnavailableException e) { 
      JOptionPane.showMessageDialog(this, e.getLocalizedMessage(), "FATAL ERROR", JOptionPane.ERROR_MESSAGE); 
     } 
    } 

    public static final void main(String args[]) { 
     Buzzer b = new Buzzer(); 
     b.setVisible(true); 
    } 

    public void keyPressed(KeyEvent e) { 
     // Do nothing   
    } 

    public void keyReleased(KeyEvent e) { 
     // Do nothing   
    } 

    public void keyTyped(KeyEvent e) { 
     final char c = e.getKeyChar(); 
     if (listening && Character.isLetterOrDigit(c)) { 
      buzz.close(); 
      listening = false; 
      if (Character.isDigit(c)) { 
       display.setBackground(Color.RED); 
       try { 
        buzz.open(AudioSystem.getAudioInputStream(getClass().getResource(BUZZ_A))); 
        buzz.start(); 
       } catch (Exception ex) { 
        JOptionPane.showMessageDialog(this, ex.getLocalizedMessage(), "FATAL ERROR", JOptionPane.ERROR_MESSAGE); 
        System.exit(1); 
       } 
      } else { 
       display.setBackground(Color.BLUE); 
       try { 
        buzz.open(AudioSystem.getAudioInputStream(getClass().getResource(BUZZ_B))); 
        buzz.start(); 
       } catch (Exception ex) { 
        JOptionPane.showMessageDialog(this, ex.getLocalizedMessage(), "FATAL ERROR", JOptionPane.ERROR_MESSAGE); 
        System.exit(1); 
       } 
      } 
      display.setText("" + c); 
      reset.setEnabled(true); 
     } 

    } 

} 

罐：https://www.dropbox.com/s/62fl2i97m9hrx9m/Buzzer.jar

Answer 1

每次創建一個新的Clip對象並丟棄舊對象會更安全。試試這個方法

public static void play(String name) { 
    try{ 
    AudioInputStream sounds = AudioSystem.getAudioInputStream(Buzzer.class.getResource(name)); 
    final Clip clip = AudioSystem.getClip(); 
    clip.addLineListener(new LineListener() { 
     public void update(LineEvent e) { 
      LineEvent.Type type = e.getType(); 
      if(type == type.STOP) clip.close(); 
     } 
    }); 
    clip.open(sounds); 
    clip.start(); 
    } catch(Exception e){ 
     e.printStackTrace(); 
    } 

}

Answer 2

至於有人建議，你可以給一個鍵綁定嘗試看看是否有幫助。這只是顯示如何使用Enter鍵完成此操作。

public class Buzzer extends JFrame { 
private static final String enter = "ENTER"; 
    public Buzzer() { 
     // Key bound AbstractAction item 
     enterAction = new EnterAction(); 
     // Gets the JFrame InputMap and pairs the key to the action 
     this.getInputMap().put(KeyStroke.getKeyStroke(enter), "doEnterAction"); 
     // This line pairs the AbstractAction enterAction to the action "doEnterAction" 
     this.getActionMap().put("doEnterAction", enterAction); 
    } 

    private class EnterAction extends AbstractAction { 
     @Override 
     public void actionPerformed(ActionEvent e) { 
      System.out.println("Enter was pressed."); 
     } 
    } 
} 

其實我不記得這是否會工作時，應用到一個JFrame，你可能需要做一個JPanel首次把這些申請。只需用面板名稱替換「this」即可。