java - Storing firebase values into an array? Keep getting zero -

i trying store userid's uidmatches. when first println getting correct string array of matches, when second 1 says uidmatches array has nothing in it... "[ ]". don't see how possible.

 private void populatelistview() {     final arraylist<string> uidmatches = new arraylist<string>();     final arraylist<profile> match_profiles = new arraylist<profile>();     users = database.getreference("users");     user = firebaseauth.getinstance().getcurrentuser();     matches = database.getreference("matches").child(user.getuid());      // returns uid's profiles matched    matches.addvalueeventlistener(new valueeventlistener() {         @override         public void ondatachange(datasnapshot datasnapshot) {             (datasnapshot child : datasnapshot.getchildren()) {                 string match = child.getvalue().tostring();                 uidmatches.add(match.tostring());                system.out.println("here matches 1: " + uidmatches);             }         }          @override         public void oncancelled(databaseerror databaseerror) {          }     });     system.out.println("here matches 2: " + uidmatches);    // loop profiles match each "uidmatches" uid  (int x=0; x<uidmatches.size(); x++)     {         users.child(uidmatches.get(x)).addvalueeventlistener(new     valueeventlistener() {             @override             public void ondatachange(datasnapshot datasnapshot) {                 (datasnapshot child : datasnapshot.getchildren())                 {                     profile profile = child.getvalue(profile.class);                     match_profiles.add(profile);                 }             }              @override             public void oncancelled(databaseerror databaseerror) {              }         });     } } 

picture of firebase setup. blocked out users unique id's generated fb login

this isn't firebase issue it's java problem. println @ end of code gets run when code first starts when array empty. other println gets fired ondatachange after results populated.