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("");