// file FIFOQueue.java
//  FIFO Queue implemented as singly linked list with pointers to begin 
//  and end

class Node<T>  {
   protected T value;
   protected Node<T>  next;
  }
  
public class FIFOQueue<T> {
   private Node<T> first;
   private Node<T> last;

   public boolean empty() { return (first == null); }

   public void add(T x) {
        Node<T> n = new Node<T>();
        n.value = x;
        if (empty()) first = n;
          else last.next = n;
        last = n;
        }

   public T pop() {
        if (empty()) { 
           System.out.println("Cannot pop empty queue");
           return null;
           }
        T x = first.value;
        first = first.next;
        return x;
      }

   public String toString() {
        String s = "[";
        Node n = first;
        while (n != null)  {
           s = s + n.value.toString() + " ";
           n = n.next; 
          }
        return s + "]";
    }

  public static void main(String[] args) {
      FIFOQueue<Integer> q = new FIFOQueue<Integer>();
      q.add(4);
      q.add(14);
      q.add(23);
      q.pop();
      q.add(28);
      q.add(34);
      q.pop();
      System.out.println(q.toString());
}
}