Java Sound offers FloatControl instances for various sound line functionality, and both a MASTER_GAIN & VOLUME control type.

Can these controls be used to change the system volume?

解决方案

No, it cannot. Here is source adapted from an answer to Adjusting master volume on coderanch. The source iterates the available lines, checks if they have a control of the right type, and if so, puts them in a GUI attached to a JSlider

import java.awt.*;

import javax.swing.*;

import javax.sound.sampled.*;

import javax.swing.event.ChangeEvent;

import javax.swing.event.ChangeListener;

public class SoundMixer {

public Component getGui() {

JPanel gui = new JPanel(new GridLayout(0,1));

Mixer.Info[] mixers = AudioSystem.getMixerInfo();

System.out.println(

"There are " + mixers.length + " mixer info objects");

for (Mixer.Info mixerInfo : mixers) {

System.out.println("mixer name: " + mixerInfo.getName());

Mixer mixer = AudioSystem.getMixer(mixerInfo);

Line.Info[] lineInfos = mixer.getSourceLineInfo();

for (Line.Info lineInfo : lineInfos) {

System.out.println(" Line.Info: " + lineInfo);

try {

Line line = mixer.getLine(lineInfo);

FloatControl volCtrl = (FloatControl)line.getControl(

FloatControl.Type.MASTER_GAIN);

VolumeSlider vs = new VolumeSlider(volCtrl);

gui.add( new JLabel(volCtrl.toString()) );

gui.add( vs.getVolume() );

System.out.println(

" volCtrl.getValue() = " + volCtrl.getValue());

} catch (LineUnavailableException e) {

e.printStackTrace();

} catch (IllegalArgumentException iaEx) {

System.out.println(" " + iaEx);

}

}

}

return gui;

}

public static void main(String[] args) {

Runnable r = new Runnable() {

@Override

public void run() {

SoundMixer sm = new SoundMixer();

Component c = sm.getGui();

JOptionPane.showMessageDialog(null, c);

}

};

// Swing GUIs should be created and updated on the EDT

// http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html

SwingUtilities.invokeLater(r);

}

}

class VolumeSlider {

JSlider volume;

VolumeSlider(final FloatControl volumeControl) {

volume = new JSlider(

(int) volumeControl.getMinimum() * 100,

(int) volumeControl.getMaximum() * 100,

(int) volumeControl.getValue() * 100);

ChangeListener listener = new ChangeListener() {

@Override

public void stateChanged(ChangeEvent e) {

float val = volume.getValue() / 100f;

volumeControl.setValue(val);

System.out.println(

"Setting volume of " + volumeControl.toString() +

" to " + val);

}

};

volume.addChangeListener(listener);

}

public JSlider getVolume() {

return volume;

}

}

On this Windows 7 machine I get two controls, both from the "Java Sound Audio Engine". Neither has any effect on the current system volume.

run:

There are 4 mixer info objects

mixer name: Primary Sound Driver

Line.Info: interface SourceDataLine supporting 8 audio formats, and buffers of at least 32 bytes

java.lang.IllegalArgumentException: Unsupported control type: Master Gain

Line.Info: interface Clip supporting 8 audio formats, and buffers of at least 32 bytes

java.lang.IllegalArgumentException: Unsupported control type: Master Gain

mixer name: Speakers (VIA High Definition Audio)

Line.Info: interface SourceDataLine supporting 8 audio formats, and buffers of at least 32 bytes

java.lang.IllegalArgumentException: Unsupported control type: Master Gain

Line.Info: interface Clip supporting 8 audio formats, and buffers of at least 32 bytes

java.lang.IllegalArgumentException: Unsupported control type: Master Gain

mixer name: Java Sound Audio Engine

Line.Info: interface SourceDataLine supporting 8 audio formats

volCtrl.getValue() = 0.0

Line.Info: interface Clip supporting 8 audio formats, and buffers of 0 to 4194304 bytes

volCtrl.getValue() = 0.0

mixer name: Port Speakers (VIA High Definition A

Setting volume of Master Gain with current value: 0.0 dB (range: -80.0 - 13.9794) to 0.0

Setting volume of Master Gain with current value: 0.0 dB (range: -80.0 - 13.9794) to -0.41

Setting volume of Master Gain with current value: 0.0 dB (range: -80.0 - 13.9794) to -0.68

...

Swap FloatControl.Type.MASTER_GAIN for FloatControl.Type.VOLUME to see.. no controls.