所以这个while循环几乎什么都不做，直到我改变bgmPlaying的值。它工作正常。但是，如果我删除了//上面测试的部分（没有任何换行符），它就不起作用。
这段代码实际上会检查音乐是打开还是关闭。
当我删除System.out.println（）部分???
时，知道它为什么停止工作这是我的代码：
import java.io.File;
import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.FloatControl;
/**
* This class simply plays a background music in a seperate thread
* @author Mohammad Nafis
* @version 1.0
* @since 04-03-2018
*
*/
public class AudioPlayer implements Runnable{
/**
* this boolean indicates whether the background music is playing
*/
private boolean bgmPlaying = true;
public void stopBGM() {
bgmPlaying = false;
}
public void playBGM() {
bgmPlaying = true;
}
/**
* this is an overridden method from Runnable interface that executes when a thread starts
*/
@Override
public void run() {
try {
File soundFile = new File("sounds/epic_battle_music.wav");
AudioInputStream ais = AudioSystem.getAudioInputStream(soundFile);
AudioFormat format = ais.getFormat();
DataLine.Info info = new DataLine.Info(Clip.class, format);
Clip clip = (Clip)AudioSystem.getLine(info);
clip.open(ais);
clip.loop(Clip.LOOP_CONTINUOUSLY);
//controlling the volume
FloatControl gainControl = (FloatControl) clip.getControl(FloatControl.Type.MASTER_GAIN);
gainControl.setValue(-20);
clip.start();
while(true) {
if(bgmPlaying) {
gainControl.setValue(-20);
} else {
gainControl.setValue(-80);
}
while(bgmPlaying) {
//testing
System.out.println("BGM is on: ");
if(bgmPlaying == false) {
gainControl.setValue(-80);
break;
}
}
while(!bgmPlaying) {
//testing
System.out.println("BGM is off: ");
if(bgmPlaying == true) {
gainControl.setValue(-20);
break;
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
此代码位于我的Controller类中，用于调用停止和播放方法。
//adding action listener
window.getpausebutton().addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ev) {
new Thread(new SoundEffect("sounds/clickSound.wav")).start();
bgm.stopBGM();
}
});
window.getplaybutton().addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ev) {
new Thread(new SoundEffect("sounds/clickSound.wav")).start();
bgm.playBGM();
}
});
答案 0 :(得分：1)
使用volatile和Thread.sleep确实是解决问题的方法，尽管它应该可行。但更大的问题是代码忙 - 等待变量的状态改变，并取决于两个线程之间的共享状态。使用volatile或synchronized您可以管理这些问题，但有更好的方法。
在java.util.concurrent包中有用于处理并发的电源工具。与之相比，线程，易失性，休眠（以及等待和通知）就像原始的手工工具。其中一个强大的工具是BlockingQueue及其各种实现，它们可以让你在Java中实现类似Actor Model的东西。
在Actor模型中，actor会相互发送消息以进行操作，但它们永远不会共享内存。您可以定义一些简单的消息，如PLAY，MUTE和STOP，并将这些消息从您的控制线程发送到您的播放器线程。如果您使用BlockingQueue，播放器看到消息就没有问题，并且它不必忙 - 等待消息到达。它可以简单地尝试take来自队列的消息，如果没有消息等待，它将一直阻塞，直到消息可用。
以下是您在代码中实现的方法：
public enum Command {
PLAY, STOP, MUTE;
}
import java.io.File;
import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.FloatControl;
import java.util.Objects;
import java.util.Scanner;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
/**
* This class simply plays a background music in a separate thread
*
* @author Mohammad Nafis
* @version 1.0
* @since 04-03-2018
*/
public class AudioPlayer implements Runnable {
private final String filename;
private final BlockingQueue<Command> commandQueue =
new LinkedBlockingQueue<>();
public final static int LOUD = -20;
public final static int QUIET = -80;
public AudioPlayer(String filename) {
this.filename = Objects.requireNonNull(filename);
}
public void perform(Command command) throws InterruptedException {
commandQueue.put(Objects.requireNonNull(command));
}
@Override
public void run() {
try {
File soundFile = new File(filename);
AudioInputStream ais = AudioSystem.getAudioInputStream(soundFile);
AudioFormat format = ais.getFormat();
DataLine.Info info = new DataLine.Info(Clip.class, format);
Clip clip = (Clip)AudioSystem.getLine(info);
clip.open(ais);
clip.loop(Clip.LOOP_CONTINUOUSLY);
//controlling the volume
FloatControl gainControl = (FloatControl)
clip.getControl(FloatControl.Type.MASTER_GAIN);
gainControl.setValue(LOUD);
clip.start();
forever: while (true) {
switch (commandQueue.take()) {
case PLAY:
gainControl.setValue(LOUD);
break;
case MUTE:
gainControl.setValue(QUIET);
break;
case STOP:
break forever;
}
}
clip.stop();
clip.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
AudioPlayer player = new AudioPlayer(args[0]);
Thread thread = new Thread(player);
thread.start();
Scanner in = new Scanner(System.in);
String cmd = "";
System.out.println("Type mute or play. Or stop to exit.");
do {
System.out.print(": ");
System.out.flush();
cmd = in.nextLine();
if ("play".equals(cmd)) player.perform(Command.PLAY);
else if ("mute".equals(cmd)) player.perform(Command.MUTE);
else if ("stop".equals(cmd)) player.perform(Command.STOP);
else System.out.println("I didn't understand that, sorry.");
} while (!"stop".equals(cmd));
player.perform(Command.STOP);
thread.join();
System.out.println("Be seeing you.");
}
}
一些注意事项：
clip.stop()和clip.close()的调用，以便音频系统不会保持后台线程运行，从而阻止程序退出。perform(Command)方法虽然位于AudioPlayer类中，但会在调用它的控件线程上执行，但这没关系。因为队列是为并发而设计的，所以在控制线程上排队的命令将立即在播放器线程上可见。无需Thread.sleep。AudioPlayer，perform构造函数和null方法都会抛出。