As I've read last weekend in the fantastic book "Clean Code", it'd be much faster to use AtomicInteger or AtomicLong instead of synchronization blocks around each access to an int or long.
The key difference is, that a synchronization block will in any case acquire and release a lock. The atomic classes use "optimistic locking", a CPU operation that only changes a value if it still has not changed since the last read.
In most cases the value has not changed since the last visit so the operation is just as fast as a normal operation. If it had changed, then we read again and try to change again.
 Clean Code: A Handbook of Agile Software Craftsmanship (Robert C. Martin)