Stack(LIFO) implementation in java (linkedlist)

A stack is a collection that is based on the last-in-first-out (LIFO) policy.

• push() -  push an item into stack.
• pop() - get an item and remove it from the top.

(This Stack implementation is based on a linked-list data structure)

1. public class Stack<Item> implements Iterable<Item>
2. {
3.  // top of stack (most recently added node)
4. private Node first;
5.  // number of items
6. private int N;
7. private class Node
8. {
9. Item item;
10. Node next;
11. }
12. public boolean isEmpty() { return first == null; } // Or: N == 0.
13. public int size() { return N; }
14. // Add item to top of stack.
15. public void push(Item item)
16. { 
17. Node oldfirst = first;
18. first = new Node();
19. first.item = item;
20. first.next = oldfirst;
21. N++;
22. }
23. public Item pop()
24. { // Remove item from top of stack.
25. Item item = first.item;
26. first = first.next;
27. N--;
28. return item;
29. }
30. }