从AsyncTask中获取数据的问题

public class GetData extends AsyncTask<String, Void, String> 
{ 
    DataDownloadListener dataDownloadListener; 
    public GetData() 
    { 

    } 
    public void setDataDownloadListener(DataDownloadListener dataDownloadListener) { 
        this.dataDownloadListener = dataDownloadListener; 
    } 
    @Override 
    protected Object doInBackground(Object... param)  
    { 

        return null; 
    } 
    @Override 
    protected void onPostExecute(Object results) 
    {        
        if(results != null) 
        {                
        dataDownloadListener.dataDownloadedSuccessfully(results); 
        } 
        else 
        dataDownloadListener.dataDownloadFailed(); 
    } 
    public static interface DataDownloadListener { 
        void dataDownloadedSuccessfully(Object data); 
        void dataDownloadFailed(); 
    } 
}
在Activity中使用：

GetData getdata = new GetData(); 
getdata.setDataDownloadListener(new DataDownloadListener() 
{ 
    @SuppressWarnings("unchecked") 
    @Override 
    public void dataDownloadedSuccessfully(Object data) { 

    } 
    @Override 
    public void dataDownloadFailed() { 

    } 
}); 
getdata.execute("");