Are Stack objects shared between different parts of a program or does each instance exist independently?

In Java, objects of type Stack (for example, java.util.Stack) are regular objects, and each instance exists independently.

This means that if you create multiple Stack objects, each one stores its own data and is not automatically shared between different parts of the program.

Example:

Stack<Integer> stack1 = new Stack<>();
Stack<Integer> stack2 = new Stack<>();

stack1.push(1);
stack2.push(2);

System.out.println(stack1.peek()); // Will output 1
System.out.println(stack2.peek()); // Will output 2

If you need to share data between different parts of the program, you should pass a reference to the same object or use static data structures.