Question

Is it required to synchronize write access to an array in Java if each thread writes to a separate cell space?

EDIT: Specifically, the array is either a primitive Array or an immutable object array. Ex. An int array or a String array.

Answer 1

No, synchronization is not needed.

It is defined in JLS §17.6 Word Tearing:

One implementation consideration for Java virtual machines is that every field and array element is considered distinct; updates to one field or element must not interact with reads or updates of any other field or element. In particular, two threads that update adjacent elements of a byte array separately must not interfere or interact and do not need synchronization to ensure sequential consistency.