Where does Java process ID's(pid) are stored ?

Got to 'Run' command,
Type  %temp%  and hit enter.

This will open up the 'Temp' folder in your local user App data.

Look for a folder hsperfdata_<systemLoginName>

example:  hsperfdata_KK1205

Complete path looks like below:
C:\Users\KK1205\AppData\Local\Temp\hsperfdata_KK1205

Inside of 'hsperfdata_KK1205' you can find currently running java process id's.