Java Memory : Runtime.getRuntime().maxMemory()

Question

Runtime.getRuntime().maxMemory() 

shows which memory ? Is it Survivor , Eden , Old, Permanent ?

Answer 1

It is the maximum size of the heap. It is loosely based on the -mx or -Xmx command line argument but for reasons I don't understand can be 1-5% less (It doesn't seem to be ever exactly the same)

What this doesn't include is the perm gen, the direct memory, memory mapped files, stack spaces or shared libraries.

While it doesn't include everything is it usually 80-90% the total memory usable for most applications.