try this
try(Realm realm = Realm.getDefaultInstance()) { realm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { RealmList<News> _newsList = new RealmList<>(); _newsList.addAll(myCustomArrayList); realm.insertOrUpdate(_newsList); // <-- insert unmanaged to Realm } }); }

In case if you're using @PrimaryKey then `insertOrUpdate` will do the trick
try(Realm realm = Realm.getDefaultInstance()) { realm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { RealmList<News> _newsList = new RealmList<>(); _newsList.addAll(myCustomArrayList); realm.insertOrUpdate(_newsList); // <-- insert unmanaged to Realm } }); }