The premises are not all correcting.


So in your case, the first call was passing reference x "by value",
and you had a copy of x, called Z in the method, which was pointing to the object.


This is correct


You assign null to the object, now both z and x point to a memory block containing a null.


This is mistaken.
You assign Null to the Z variable, the object is not touched.


Don't know whether this has something to do with reference counting,


This is very simple: by Value increment RefCount semaphore, by Reference not change RefCount semaphore.

To the end you have understood all. Very good.

Hi Dragan.