question: public boolean subscribeTopic ( @ NonNull Context context , @ NonNull String [ ] newTopics ) { if ( ! initialized ) init ( context ) ; if ( newTopics . length == 0 ) return false ; if ( null == topics ) { topics = new ArrayList < > ( ) ; } for ( String topic : newTopics ) { if ( topics . contains ( topic ) ) { return false ; } topics . add ( topic ) ; } saveSubscibedTopics ( context ) ; Intent intent = new Intent ( context , RegistrationIntentService . class ) ; intent . setAction ( RegistrationIntentService . ACTION_SUBSCRIBE ) ; intent . putExtra ( RegistrationIntentService . EXTRA_TOPIC_LIST , newTopics ) ; context . startService ( intent ) ; return true ; }
target:  Subscribe to a list of topics.