public class MediaPlayerStudy extends Activity {
  private Button bplay,bpause,bstop;
  private MediaPlayer mp = new MediaPlayer();
  @Override
  public void onCreate(BundlesavedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    bplay =(Button)findViewById(R.id.play);
    bpause =(Button)findViewById(R.id.pause);
    bstop =(Button)findViewById(R.id.stop);
    bplay.setOnClickListener(new OnClickListener(){
      @Override
      public void onClick(View v) {
         try {
           mp.setDataSource("/sdcard/test.mp3");
           mp.prepare();
           mp.start();
         } catch (IllegalArgumentException e){
           e.printStackTrace();
         } catch (IllegalStateException e){
           e.printStackTrace();
         } catch (IOException e) {
           e.printStackTrace();
         }
         mp.setOnCompletionListener(new OnCompletionListener(){
           @Override
           public void onCompletion(MediaPlayer mp){
             mp.release();
           }
         });
      }
    });
    bpause.setOnClickListener(new OnClickListener(){
      @Override
      public void onClick(View v) {
         if(mp != null){
           mp.pause();
         }
      }
    });
    bstop.setOnClickListener(new OnClickListener(){
    @Override
    public void onClick(View v) {
       if(mp != null){
        mp.stop();
       }
    }
    });
  }
  @Override
  protected void onDestroy() {
    if(mp != null)
      mp.release();
    super.onDestroy();
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:Android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView android:layout_width="fill_parent"
    android:layout_height="wrap_content" android:text="@string/hello" />
    <Button android:text="play" android:id="@+id/play"
      android:layout_width="wrap_content"
android:layout_height="wrap_content"></Button>
    <Button android:text="pause" android:id="@+id/pause"
      android:layout_width="wrap_content"
android:layout_height="wrap_content"></Button>
    <Button android:text="stop" android:id="@+id/stop"
      android:layout_width="wrap_content"
android:layout_height="wrap_content"></Button>
  </LinearLayout>

MediaPlayer mp = new MediaPlayer();

MediaPlayer mp = MediaPlayer.create(this, R.raw.test);
//这时就不用调用setDataSource了

MediaPlayer.create(this,R.raw.test);

mp.setDataSource("/sdcard/test.mp3");

mp.setDataSource("http://www.citynorth.cn/music/confucius.mp3");