It's worth pointing out that volatile doesn't mean atomic:
volatile int a;

++a; // Still two separate accesses to a

I didn't fully understood volatile until I read about it in the book
Java Concurrency In Practice
<http://virtualinfinity.net/wordpress/technical-book-recommendations/java-concurr
ency-in-practice/>

The only real use I've found for it is for a simple
you-should-shut-down-now flag to a tight-looped thread.  That thread
only needs to read, and other threads only need to write.

Thanks for that. I was not aware the guarantee was new to java 5. The
book I am learning from (Thinking in Java by Bruce Excel) was in its
final stages as java 5 came out, so although it does mention java 5 I
did not fully get this point. This does indeed make it convenient to
make a cheap check which would otherwise be done (more expensively)
using a private data member and synchronized getters and setters.

I have made some other enquires and apparently this change was made so
that double checking locking could be fixed. Can anyone else here
confirm that please?

-Andrew Marlow