In fact the waters north of Australia are not especially treacherous, and Australia was located and the indigenous peoples contacted by Indonesian mariners, certainly by the late 17th century and possibly earlier. The Indonesians, who were based in Makassar, a major port in Sulawesi, came in search of trepang (sea cucumbers), which were an expensive and sought-after Chinese delicacy that came into vogue after c. 1600, and a considerable industry evolved to catch and process them. Among other things, this resulted in a number of Australian Aborigines travelling to Indonesia and beyond – when the first English explorers penetrated the interior of Arnhem land in the first half of the 19th century, they encountered an English-speaking Aborigine who had picked up the language during a visit to Singapore.

I wrote more about the trepang trade and Australian contact with Indonesia (and hence, via trade links, effectively with China and Japan) in an essay that's available here if you are interested in finding out more, and you can learn a lot more about the society and culture of Makassar and South Sulawesi in this AMA, led by /u/PangeranDipanagara.