Will the memory size of the stack and heap change if multiple threads are created in the application?

Stack — yes, a separate stack is created for each new thread to store local variables, call parameters, and return addresses.

Heap — no, the heap is a shared resource for all threads in the application. Objects created on the heap are accessible to all threads, and synchronization is required for safe access to shared data. The size of the heap can increase as new objects are created, but this is not directly dependent on the number of threads, rather on the overall memory consumption by objects.