Default heap memory size allocated with Java 7 on OSX

[Paul Taylor]

How does Java 7 decide on the max value of heap memory allocated (-Xmx) 
if not specified on an OSX bundle, I've read the manual page and it gave 
no indication. It seems to be allocated more than the default on Java 6 
and I wonder if it varies with the memory available on the machine, that 
would be very useful to me because my application is memory bound, but I 
cannot set the default too high because then the application would fail 
to run at all on lower specification machines.

Paul