QueryCollectionAddtoList.java

 CollectionReference colRef = fStore.collection("Users");
        colRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if(task.isSuccessful()){
                    for(QueryDocumentSnapshot userData : task.getResult()){
                        //Log.d(TAG, "onComplete: " + userData.getData());
                        User user = new User();
                        user.setName(userData.getString("name"));
                        user.setEmail(userData.getString("email"));
                        user.setProfileUrl(userData.getString("profileUrl"));
                        allUsers.add(user);
                    }

                    //Log.d(TAG, "onCreateView: " + allUsers.get(0).getName());
                    adapter = new UserListAdapter(allUsers);
                    friendList.setAdapter(adapter);
                }
            }


        });

QueryFirebaseSingleDocument.java

        DocumentReference docRef = fStore.collection("Users").document(fAuth.getCurrentUser().getUid());
        docRef.addSnapshotListener(new EventListener<DocumentSnapshot>() {
            @Override
            public void onEvent(@Nullable DocumentSnapshot value, @Nullable FirebaseFirestoreException error) {
               if(value != null && value.exists()){
                   Log.d(TAG, "onEvent: " + value.getData());
               }else {
                   Log.d(TAG, "onEvent: Data is Null");
               }

               if(error != null){
                   Log.w(TAG, "onEvent: Listen Failed. ", error);
                   return;
               }
            }
        });