JAVA threads (different stacks) synchronization

Question

I have a question regarding synchronization of code that is executed by several threads:

As far as I know each thread has its own stack, hence, non-static variables

Answer 1

Only primitive types, such as int are guaranteed to be allocated on the stack. Objects and arrays are all typically stored in the heap unless Escape Analysis determines the scope of the object is 'restricted to the scope of the procedure'.