Java - Collection Framework LIFO Implementation

Description

LIFO Implementation
Demo

class LIFOImplementation<Item> {

  // top of stack (most recently added node)
  private Nodes first;
  // number of items
  int counter;//from ww w  .j a v a 2s. com

  private class Nodes {
    Item item;
    Nodes next;
  }

  public boolean isEmpty() {
    return first == null;
  } // Or: N == 0.

  public int size() {
    return counter;
  }

  // Add item to top of stack.
  public void push(Item item) {
    Nodes oldfirst = first;
    first = new Nodes();
    first.item = item;
    first.next = oldfirst;
    counter++;
  }

  public Item pop() { // Remove item from top of stack.
    Item item = first.item;
    first = first.next;
    counter--;
    return item;
  }
}

public class Main {
  public static void main(String args[]) {
    LIFOImplementation lifo = new LIFOImplementation();

    lifo.push(3);
    lifo.push(1);
    lifo.push(7);
    lifo.push(4);

    System.out.println(lifo.pop());
    System.out.println(lifo.pop());
    lifo.push(4);
    lifo.push(3);
    System.out.println(lifo.pop());
    System.out.println(lifo.pop());
    System.out.println(lifo.pop());
    // System.out.println(lifo.pop());
    // System.out.println(lifo.pop());
    // System.out.println(lifo.pop());
  }

}