Java: Do all mutable variables need to be volatile when using locks?

Question

Does the following variable, x, need to be volatile?

Or does the manipulation within a utils.concurrent lock perform the same function as a synchronized block (ensuring it's written to memory, and not stored in cpu cache)?

myMethod(){
  myLock.lock();
  x++;
  myLock.unlock();
}

Answer 1

Such variables only need to be volatile if they're accessed elsewhere without a lock. For example, as a fast read-only access to a size variable. The lock methods do serve the same purpose as a synchronized block. See the "Memory Synchronization" section in the javadoc for the Lock class.