An AsyncTask.

DownloadTask.java

class DownloadTask extends AsyncTask<String, Void, File> {

  protected File doInBackground(String... args) {
    final String url = args[0];
    try {
      byte[] fileContent = downloadFile(url);
      File file = writeToFile(fileContent);
      return file;
    } catch (Exception e) {
      // ???
    }
  }
  
  protected void onPostExecute(File file) {
    Context context = getContext(); // ???
    Toast.makeText(context, 
        "Downloaded: " + file.getAbsolutePath(), 
        Toast.LENGTH_SHORT)
        .show();
  }
}