One day, a teacher of Wisma Bahasa asked his student about his activity on the last weekend,”Apa acara Anda akhir minggu lalu?”. He answer,” Saya saja membaca buku di hotel” (I just read a book in hotel). In this sentence the use of saja is incorrect. It should be “Saya membaca buku saja di hotel”.The meaning of word hanya and saja are different.
Both of those words can not be switched their position and meaning each other in a sentence. The function of word hanya and saja in a sentence are also different. Word hanya explaines a word or a group of word that followed. And word saja explaines a word or a group of word that preceded.
The correct examples of the use of word hanya and saja according to the rule of bahasa Indonesia are:
(1) Saya hanya memiliki dua orang anak.
(2) Saya memiliki dua orang anak saja.
(3) Orang itu hanya memikirkan diri sendiri.
(4) Orang itu memikirkan diri sendiri saja. (source: Pusat Bahasa)