why my applet not inited?

有一段APPLET程序如下:
import java.applet.*;

import java.awt.*;

public class Sound extends java.applet.Applet{

private AudioClip sound;

private Button bPlay,bLoop,bStop;

private String play;

public void init(){

play=new String(getParameter("File"));

sound=getAudioClip(getDocumentBase(),play);

bPlay=new Button("Play");

add(bPlay);

bLoop=new Button("LoopPlay");

add(bLoop);

bStop=new Button("StopPlay");

add(bStop);

}


public boolean action(Event e,Object o){

if(e.target==bPlay)
{
sound.play();

}
else if(e.target==bLoop)
{
sound.loop();

}
else if(e.target==bStop)
{
sound.stop();

}
return true;

}

}
编译后,在页面里却显示:
小应用程序Sound notinited
why?