第五周笔记

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

/**
* Class SoundEngine provides functionality to process sound files.
* SoundEngine类提供了处理声音文件的功能。
* Sounds can be loaded, played, paused, resumed, and stopped.
* 声音可以被加载，播放，暂停，恢复，并停止。
*
* The sound engine can play multiple sounds simultaniously, but only
* the last sound loaded can be controlled (pased, resumed, etc.).
* 音乐播放器的声音可以播放多种声音simultaniously，但只有最后一声负载可以被控制（过时，恢复等）。
*
* The sound engine accepts files in WAV, AIFF, and AU formats (although
* not all WAV files - it depends on the encoding in the file).
* 音乐播放器接受WAV文件，AIFF，au格式（虽然不是所有的WAV文件，这取决于编码的文件）。
*
* @author Michael Kolling and David J Barnes
* @version 1.0
*/
public class SoundEngine
{
// the following three fields hold information about the sound clip
//以下三个字段保存有关该声音剪辑的信息
// currently loaded in this engine
private Clip currentSoundClip = null;
private int currentSoundDuration = 0;
private int currentSoundFrameLength = 0;

/**
* Create a SoundEngine that can play sound files.
*/
public SoundEngine()
{
}

/**
* Load and play a specified sound file. If the file is not in a
* recognised file format, false is returned. Otherwise the sound
* is started and true is returned. The method returns immediately
* after the sound starts (not after the sound finishes).
* 加载并播放指定的声音文件。如果文件不在确认文件格式，错误返回。否则声音开始和正确就返回。
* 方法立即返回声音开始后（声音结束后）。
* @param soundFile The file to be loaded.
* @return True, if the sound file could be loaded, false otherwise.
*/
public boolean play(File soundFile)
{
if(loadSound(soundFile)) {
currentSoundClip.start();
return true;
}
else {
return false;
}
}

/**
* Stop the currently playing sound (if there is one playing). If no
* sound is playing, this method has no effect.
*/
public void stop()
{
if(currentSoundClip != null) {
currentSoundClip.stop();
currentSoundClip = null;
}
}

/**
* Pause the currently playing sound. If no sound is currently playing,
* calling this method has no effect.
*/
public void pause()
{
if(currentSoundClip != null) {
currentSoundClip.stop();
}
}

/**
* Resume the currently paused sound. If no sound is currently paused,
* this method has no effect.
*/
public void resume()
{
if(currentSoundClip != null) {
currentSoundClip.start();
}
}

/**
* Set the current playing position in the currently playing sound to 'value'.
* 'value' is a percentage value (0 to 100). If there is no sound currently
* playing, this method has no effect.
*
* @param value The target position in the sound file, as a percentage.
*/
public void seek(int value)
{
if(currentSoundClip != null) {
int seekPosition = currentSoundFrameLength / 100 * value;
currentSoundClip.setFramePosition(seekPosition);
}
}

/**
* Set the playback volume of the current sound. If no sound is currently
* loaded, this method has no effect.
*
* @param vol Volume level as a percentage (0..100).
*/
public void setVolume(int vol)
{
if(currentSoundClip == null) {
return;
}
if(vol < 0 || vol > 100) {
vol = 100;
}

double val = vol / 100.0;

try {
FloatControl volControl =
(FloatControl) currentSoundClip.getControl(FloatControl.Type.MASTER_GAIN);
float dB = (float)(Math.log(val == 0.0 ? 0.0001 : val) / Math.log(10.0) * 20.0);
volControl.setValue(dB);
} catch (Exception ex) {
System.out.println("could not set volume");
}
}

/**
* Return the duration of the currently loaded sound clip.
*
* @return The duration of the current sound, or 0 if no sound has been loaded.
*/
public int getDuration()
{
return currentSoundDuration;
}

/**
* Load the sound file supplied by the parameter into this sound engine.
*
* @return True if successful, false if the file could not be decoded.
*/
private boolean loadSound(File file)
{
currentSoundDuration = 0;

try {
AudioInputStream stream = AudioSystem.getAudioInputStream(file);
AudioFormat format = stream.getFormat();

// we cannot play ALAW/ULAW, so we convert them to PCM
//
if ((format.getEncoding() == AudioFormat.Encoding.ULAW) ||
(format.getEncoding() == AudioFormat.Encoding.ALAW))
{
AudioFormat tmp = new AudioFormat(
AudioFormat.Encoding.PCM_SIGNED,
format.getSampleRate(),
format.getSampleSizeInBits() * 2,
format.getChannels(),
format.getFrameSize() * 2,
format.getFrameRate(),
true);
stream = AudioSystem.getAudioInputStream(tmp, stream);
format = tmp;
}
DataLine.Info info = new DataLine.Info(Clip.class,
stream.getFormat(),
((int) stream.getFrameLength() *
format.getFrameSize()));

currentSoundClip = (Clip) AudioSystem.getLine(info);
currentSoundClip.open(stream);
currentSoundFrameLength = (int) stream.getFrameLength();
currentSoundDuration = (int) (currentSoundClip.getBufferSize() /
(currentSoundClip.getFormat().getFrameSize() *
currentSoundClip.getFormat().getFrameRate()));
return true;
} catch (Exception ex) {
currentSoundClip = null;
return false;
}
}
}