Function will process message in handler thread, not the main thread

// first we create the class and implement the callback interface
public class GetMessageClass implements Handler.Callback {
 
    @Override
    public boolean handleMessage(@NonNull Message msg) {
        // parse the message using the message key
        Bundle bundle = msg.getData();
        String string = bundle.getString("mykey");
        Log.v("javademo3","got the message: " + string);
        return false;
    }
}

Then in the main activity:

public class MainActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // after we have a class with a callback, we create a thread for the handler.
        // every handler has a looper which actually calls the handler:
        HandlerThread handlerThread = new HandlerThread("myHandlerThread");
        handlerThread.start();
        Looper looper = handlerThread.getLooper();
        // create an instance of the class
        GetMessageClass getMessageClass = new GetMessageClass();
        // create a new handler and assign it to the looper in the handler thread
        Handler handler = new Handler(looper, getMessageClass);
 
        // boilerplate to send a message
        Message msg = handler.obtainMessage(); // ?
        Bundle bundle = new Bundle();
        bundle.putString("mykey", "hello");
        msg.setData(bundle);
        handler.sendMessage(msg);
    }
}