why does java not use 100% CPU

[icecoffemix]

I also has this problem with fate extra, jpcsp doesn't utilize all the cores and stuck at low fps. I tried running the game on my friend's 2600K and it ran at full fps (60 or 30 with enable ge graphics only).

My spec :
AMD Phenom II X3 3.2GHz
ATi HD4850 1GB

I've included the log file. Thanks.