Android Studio trouble w/ declaration in Main Activity

I’m still troubled w/ declarations other than the pure ported/created Processing stuff.
I have a running ported App, which I wanted to extend w/ a Background Network task, because networking in the main thread is prohibited.
I created a background task, wich I believe is OK.

public class listen {

   public AsyncTask async_client;

    public void receive() {

        async_client = new AsyncTask<Void, Void, Void>() {

            protected Void doInBackground(Void... params) {
                boolean run = true;
                try {
            ...some code here
                } catch (IOException e) {
                    ... and here
                    run = false;

                return null;
        if (Build.VERSION.SDK_INT >= 11) async_client.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        else async_client.execute();

I tried to activate this background thread in my main activity like this

public class MainActivity extends AppCompatActivity {
  private PApplet sketch;
  protected void onCreate(Bundle savedInstanceState) {
    FrameLayout frame = new FrameLayout(this);
    setContentView(frame, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,

    sketch = new MiniEFIS();

    PFragment fragment = new PFragment(sketch);
    fragment.setView(frame, this);
    listen client = new listen();

Is this the right place? There are no errors at compile time!
I am receiving a runtime exception (and crash) wIth the error
java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.Void[]
and I don’t know, if the declaration is wrong, or in a wrong place, or what ??
Any help welcome.
Thank you in advance

@lve0200 ====
That is very simple; your Listen class is not good; with android varArgs (used in the asynkTask)are waiting for an array, (String or what you want for the first one) and you are only creating an object.If you want i can put code.

thanks anyway, but after taking another deep dive into the dev docu, I found it, myself. Its just about replicating other peoples code, thinking it would be easier…