Oops. Looking at the code, I see that my "fix" won't work, because Jobe ignores the memorylimit parameter in the case of Java (which asks for silly amounts of virtual memory when it starts, but doesn't use most of it).
Assuming you have access to Jobe as a sysadmin, you could try the following fix instead. Around line 17 of <jobehome>/application/libraries/java_task.php you'll find a line like:
$params['memorylimit'] = 2500; // 2.5GB - JVM is greedy!
Change that to
$params['memorylimit'] = 0; // Disregard memory limit - let JVM manage memory
As I said in the previous posting, this doesn't mean student submissions can gobble unlimited memory, as memory limits are set by the JVM (and can be configured by a question author using java command parameters like -Xss and -Xmx)
I'll be pushing this change (and quite a few others) to github within the next 24 hours, so if it's not urgent you could hold off until then.