How to allocate memory

Question

How to force Java to allocate enough memory for a 20 Million character String.

Answer 1

Actually it would be:
StringBuffer b = new StringBuffer(20000000);Probably.
But if you have a few extra bytes of overflow I believe the algorithm doubles the space. Might be a bit much just for a couple of bytes.
Allocating a 2200000000 element array is a bit more difficult... any ideas?2 Billion?
Yes, one idea. Don't do it. It isn't possible. On any OS.
Windows and earlier versions of Sun had an addressable limit of 4 gig (billion). Using a 2 billion elements would mean each element could only occupy 2 bytes of space. And there won't be much room for the program to do anything else.
And that is addressable space. On windows an application can't use more than 2 gig, the OS reserves the other 2 gig. And a Sun box still has to have the OS components that the program needs in the addressable space.
I am guessing that you could do this on C/C++ using the 64 bit addressable space of Solaris 8.
However, every Sun JVM, at least before 1.4, always limits the max heap size to less than 4 gig. And a java object will take far more than 2 bytes of space.
It might just be possible on a Solaris box, but only if the elements are 'characters' and nothing else. Since Java uses a UTF8 format, if the characters are actually latin, then it will only take 2 gig. And I believe one can tweak the JVM up above that. But the box will have to have more than 2 gig of memory. At least if you expect the program to do processing without thrashing the harddrive.