android thread exits when app in background code example

Example: how to run a background thread in android

Thread thread = new Thread() {
  @Override
  public void run() {
      try { Thread.sleep(2000); }
      catch (InterruptedException e) {}

      runOnUiThread(new Runnable() {
          @Override
          public void run() {
              textView.setText("OK");
          }
      });
  }
};
thread.start();