在J2ME应用里控制移动设备的音量

下边的代码描述了如何在J2ME应用里控制移动设备的音量，VolumeControl类可以用来控制播放器Player类的音量

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.Ticker;
import javax.microedition.media.*;

public class VolumeControlDemo extends MIDlet implements CommandListener {

    private Display display;
    private Command exit, incr, decr;
    Form frm;

    VolumeControl vc;
    int vol;
    Player player;

    public VolumeControlDemo() {
        display = Display.getDisplay(this);

    }

    public void startApp() {

        frm = new Form("VolumeControlDemo  Demo");

        exit = new Command("Exit", Command.EXIT, 1);
        decr = new Command("Decrease", Command.EXIT, 1);
        incr = new Command("Increase", Command.EXIT, 1);
        frm.addCommand(exit);
        frm.addCommand(decr);
        frm.addCommand(incr);

        frm.setCommandListener(this);

        display.setCurrent(frm);

        try {

            // 创建播放器Player对象
            player = Manager.createPlayer("/demo.wav");

            // 设置循环计数器
            player.setLoopCount( -1);

            // 播放
            player.start();
            Control cs[];

            // 获得播放器的所有控制对象
            cs = player.getControls();

            for (int i = 0; i < cs.length; i++) {
                if (cs[i] instanceof VolumeControl) {
                    // 获得音量控制类实例
                    vc = (VolumeControl) cs[i];
                }
            }

        } catch (Exception e) {}

    }

    public void pauseApp() {

    }

    public void destroyApp(boolean un) {

    }

    public void commandAction(Command cmd, Displayable d) {
        try {
            if (decr) {
                if (vol > 0) {
                    vol--;
                }
                vc.setLevel(vol);
            } else {
                if (vol < 99) {
                    vol--;
                }
                vc.setLevel(vol);
            }

            frm.appent("vol=" + vc.getLevel());
        } catch (Exception e) {}

    }
}