Pubnub hereNow: Issues with variable scope & threads - multithreading

Question

Here is my code.
I am trying to check if a subscriber with a specific ID is subscribed to my channel.
public class HubActions {
private boolean reply;
public boolean isConnected(String id, String chan) {
String subKey = "sub-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
String pubKey = "pub-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
Pubnub pubnub = new Pubnub(pubKey, subKey);
Callback callback = new Callback() {
public void successCallback(String channel, Object response) {
System.out.println(response.toString());
try {
JSONObject json = new JSONObject(response.toString());
JSONArray uuids = new JSONArray();
uuids = json.getJSONArray("uuids");
for(int i=0;i<json.getInt("occupancy");i++) {
if(uuids.get(i).equals(id)) {
System.out.println("Yup!");
reply = true;
break;
}
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void errorCallback(String channel, PubnubError error) {
System.out.println(error.toString());
}
};
pubnub.hereNow(chan, callback);
return reply;
}
public static void main(String[] args) {
boolean b = new HubActions().isConnected("2", "2_sub");
System.out.println(b);
}
}
Here is my output
false
{"occupancy":2,"service":"Presence","message":"OK","status":200,"uuids":["2","3bbe065c-d84a-4529-a641-26d05439e71d"]}
Yup!
I dont understand why false is returned even though the function clearly assigns true to value of boolean variable reply
I understand that when we create an instance of pubnub 2 threads are initialized. I think it might be that the threads are still processing while the function returns the default value of variable reply
But how do I resolve this?

Answer 1

This is an async issue. You are calling hereNow, and it is returning immediately and then you are outputting the value of reply while the successCallback is getting called asynchronously and running the loop.
That is why you see the value of reply get displayed before the Yup is displayed. Do this instead:
public class HubActions {
private boolean reply;
public boolean isConnected(String id, String chan) {
String subKey = "sub-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
String pubKey = "pub-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
Pubnub pubnub = new Pubnub(pubKey, subKey);
Callback callback = new Callback() {
public void successCallback(String channel, Object response) {
System.out.println(response.toString());
try {
JSONObject json = new JSONObject(response.toString());
JSONArray uuids = new JSONArray();
uuids = json.getJSONArray("uuids");
for(int i=0;i<json.getInt("occupancy");i++) {
if(uuids.get(i).equals(id)) {
System.out.println("Yup!");
reply = true;
break;
}
}
// output value of reply here
// or implement your own listener for the
// caller to receive the update
System.out.println(reply);
}
catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void errorCallback(String channel, PubnubError error) {
System.out.println(error.toString());
}
};
pubnub.hereNow(chan, callback);
return reply;
}
public static void main(String[] args) {
boolean b = new HubActions().isConnected("2", "2_sub");
// b will always be false due to async nature of code
// must implement a listener to get the result from this scope
// System.out.println(b);
}
}
In the above code, I am punting on the real solution, which is to implement a listener pattern the successCallback code and call to notify the orginal caller in main.
All I did was comment out your System.out.println(b) as that will always be false and doing System.out.println(reply) in the successCallback after the for loop has terminated.