threaded progames

So guys I hear of many people saying single threaded programs suck. I personally program in java and i have a question. Even when i make a single thread program in java and then look @ it via jconsole it appears to have ~5-10 threads up at any time. Does that mean it's already multi-threaded and really wouldn't make a shit load of a difference since i'm already using multiple cores?

guy so i have this game with a large map 1000x1000x1000 stored in memory. I have to then update all of the cells of the map and i have a few choices. I can make it one single thread that takes a long long long time to finish or i can split it up into ~5000 threads that check their own section of the map.


which is a better idea and should i take another approach?