Queue(FIFO) implementation using Java

A queue is a collection that is based on the first-in-first-out (FIFO) policy.

• dequeue() - get an item from the queue.
• enqueue() - insert item into the queue.

1. public class Queue<Item> implements Iterable<Item>
2. {
3. private Node first; // link to least recently added node
4. private Node last; // link to most recently added node
5. private int N; // number of items on the queue
6. private class Node
7. { // nested class to define nodes
8. Item item;
9. Node next;
10. }
11. public boolean isEmpty() { return first == null; } // Or: N == 0.
12. public int size() { return N; }
13. public void enqueue(Item item)
14. { // Add item to the end of the list.
15. Node oldlast = last;
16. last = new Node();
17. last.item = item;
18. last.next = null;
19. if (isEmpty()) first = last;
20. else oldlast.next = last;
21. N++;
22. }
23. public Item dequeue()
24. { // Remove item from the beginning of the list.
25. Item item = first.item;
26. first = first.next;
27. if (isEmpty()) last = null;
28. N--;
29. return item;
30. }
31. }