java - Androidでクラスのインスタンスを作成してonCreateメソッドを実行するにはどうすればよいですか

Question

MainActivity.java と SongLoad.java があります。のコードMainActivity.javaは

 public class MainActivity extends Activity {

public static final int LOADREQUEST = 100;
private String callerClass = "DoubleMode";

ImageButton loadPlaylist1,loadPlaylist2;
ImageButton play1,play2;


SongLoad songloader = new SongLoad(callerClass);
MusicPlayerService musicplayer = new MusicPlayerService();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.homescreen);
    loadPlaylist1 = (ImageButton)findViewById(R.id.load_button1);
    loadPlaylist2 = (ImageButton)findViewById(R.id.load_button2);
    play1 = (ImageButton)findViewById(R.id.play1);
    play2 = (ImageButton)findViewById(R.id.play2);
}

public void onLoad(View v) {
    int loadButtonPressed = v.getId();
    songloader.playListGenerator();
    musicplayer.songLoader(songloader.songIndex, loadButtonPressed);.. soon       

SongLoad.java

public class SongLoad extends ListActivity{
public int songIndex = 0;
public String selectedSongPath;
public String callerClass;
final String MEDIA_PATH = new String(Environment.getExternalStorageDirectory().getPath());
public ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
ArrayList<HashMap<String, String>> songsListData = new ArrayList<HashMap<String, String>>();
SongLoad(String callerClass) {
    this.callerClass = callerClass; 
}
SongLoad() {

}

@Override
public void onCreate(Bundle savedInstanceState)  {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    if(callerClass == "DoubleMode")
    {
        setContentView(R.layout.playlist);
    }
}

public void playListGenerator() {

    mediaScanner(); 
    for (int i = 0; i < songsList.size(); i++)  {
        // creating new HashMap
        HashMap<String, String> song = songsList.get(i);

        // adding HashList to ArrayList
        songsListData.add(song);
    }

    // Adding menuItems to ListView
    ListAdapter adapter = new SimpleAdapter(this, songsListData,
            R.layout.playlist_item, new String[] { "songTitle" }, new int[] {
                    R.id.songTitle });

    setListAdapter(adapter);

    // selecting single ListView item
    ListView lv = getListView();
    // listening to single listitem click
    lv.setOnItemClickListener(new OnItemClickListener() {

    @Override
    public void onItemClick(AdapterView<?> parent, View view,int position, long id) {
        // getting listitem index
        songIndex = position;
        selectedSongPath = songsList.get(songIndex).get("songPath");

    }
    });
}

今私の質問は、SongLoad.java のオブジェクトを作成し、playListGenerator onCreate メソッドを呼び出すと呼び出されるということです。しかし、私はそれを実行したい。それ、どうやったら出来るの？