horse nettle

The most likely explanation is an escaped cultivar. In general, though, people don't really pay attention to plants. If a cultivated plant escapes and starts wreaking havoc on the populations of endemic species, most people don't even notice. For instance, where I live (the Pacific Northwest USA), there is a plant called Scotch Brush (Cytisus scoparius) that is not endemic, but was imported because someone thought it looked pretty. I guess when it started to root itself outside his garden, he just didn't pay attention, and now the stuff is everywhere. When I see a nightshade flower in your area, it's like seeing a conifer in the desert, but most people just see another flower.

After a bit of research on this, there doesn't seem to be any member of the Solanaceae family endemic to Indonesia, which means this must have been imported. Furthermore, unless it is a "Strawberry, cucumber, pepper(capsicum), tomato, eggplant and grape, summer squash and melon which meets the standards established by the Minister of Agriculture, Forestry and Fisheries", it is likely an illegal or unintentional import. http://www.pps.go.jp/english/law/list2.html#f.3

I agree. Solanaceae for sure, and likely in the genus Solanum.

Looks like a type of Horse Nettle found in the states.