Check your logs, you may have your java running in 32bit mode.
Latest "java auto-update" reverted my system to 32bit java, and I had on purpose ONLY 64bit installed before,
but yeah it seems like they only update 32bit and this has then a higher version number and priority than your 64bit variant and it wont get used.
So, best bet would be:
Get latest 64bit JDK and check your memory settings.
- Andy