Asynchronous GET on REST with okhttp3 - rest

Question

I am trying to perform an asynchronous GET-request on my openHAB-project. I have done it before and reused parts of my code to create a new Android app, but it is not working.
In theory I want the state of the "GastSwitch"-item to be written into a String (gastSwitchState) to then be used as a trigger for opening a different activity. If the result of the request is "OFF" the app is supposed to keep running, but stay in the MainActivity.
When debugging it seems like the getGastSwitchState-method is jumped entirely after the enqeue-Method is called. Can someone explain to me, why my code seems to leave out half of the method?
I know that this way of doing it should work, but I can't find where I went wrong.
//connect with REST-API in openHAB :
// GET Status GastSwitch: if Switch = "ON" go to MeetingActivity
//Timer to GET the GastSwitch-status every 30 seconds:
TimerTask gastSwitchTimerTask = new TimerTask() {
public void run() {
try {
getGastSwitchState("myURLforOpenHABGastSwitchState", new Callback() {
#Override
public void getParameter(String string) {
if (gastSwitch.equals("ON")) {
Intent activityIntent = new Intent(getApplicationContext(), MeetingActivity.class);
startActivity(activityIntent);
}
}
});
} catch (IOException e) {
e.printStackTrace();
tvLog.setText(e.toString());
}
}
};
// Timer for GETting the GastSwitch-state every 30 seconds
long emergencyDelay = 1000 * 30 * 1;
Timer gastSwitchTimer = new Timer();
gastSwitchTimer.schedule(gastSwitchTimerTask, 0, emergencyDelay);
}
//Method for GETting the GastSwitch-state from REST-API:
void getGastSwitchState(String url, final Callback callback) throws IOException {
OkHttpClient client = new OkHttpClient().newBuilder()
.build();
okhttp3.Request request = new okhttp3.Request.Builder()
.url(url)
.method("GET", null)
.addHeader("AuthToken", "")
.build();
client.newCall(request)
.enqueue(new okhttp3.Callback() {
#Override
public void onResponse(#NotNull okhttp3.Call call, #NotNull Response response) throws IOException {
if (response.isSuccessful()) {
final String res = response.body().string();
MainActivity.this.runOnUiThread(new Runnable() {
#Override
public void run() {
gastSwitch = res;
tvLog.setText(gastSwitch);
callback.getParameter(gastSwitch);
}
});
}
}
#Override
public void onFailure(#NotNull okhttp3.Call call, #NotNull IOException e) {
runOnUiThread(new Runnable() {
#Override
public void run() {
}
});
}
});