How is data moved between the stack and the heap?

Data is not transferred directly between the stack and the heap. The stack stores references to objects located in the heap, as well as primitive data types and method references. When accessing an object through a reference in the stack, the JVM follows the address in the heap to access the object's data.

• Stack: stores:
  • Local variables of primitive types.
  • References to objects in the heap.
  • Method arguments.
  • Return addresses from methods.
  • Operates on a LIFO (Last-In, First-Out) principle.
• Heap: stores:
  • All objects created with new.
  • Class instances.
  • Arrays.
  • Managed by the garbage collector.

Example:

// Stack:
// Variable 'a' (primitive type) is stored directly in the stack.
int a = 10;

// Stack:
// Variable 'str' (reference) is stored in the stack.
// The String object ("hello") is stored in the heap, and 'str' points to it.
String str = new String("hello");

Thus, there is no data movement as such. It involves passing references and accessing data in the heap through these references.