DLList L = new DLList();
L.Push("A");
L.Push("B");
String s = L.Pop();

のように使います。Pop()のかわりにPopLast()を使えばキューになります。

import java.io.*;

public class DLList {
  ListItem head = null;
  ListItem tail = null;

  /* constructor */
  DLList() {}

  boolean IsEmpty() { return (head == null); }
  Object Head() { return head.inf(); }
  Object Hail() { return tail.inf(); }

  /* Methods for Stack operation */
  public void Push(Object o) 
    {
      ListItem r = new ListItem(o); 
      r.next = head;
      if (head != null) head.prev = r;
      if (tail == null) tail = r;
      head = r;
    }

  public Object Pop()
    { if (head == null) return null;
      Object ret = head.inf();
      head = head.next;
      if (head == null) tail = null;
      return ret;
    } 

  public Object PopLast()
    { if (tail == null) return null;
      Object ret = tail.inf();
      tail = tail.prev;
      if (tail == null) head = null;
      return ret;
    }

  /* Definition of list boxes */
  class ListItem 
  {
    Object   obj;
    ListItem (Object o) { obj = o; } 
    ListItem prev;
    ListItem next;
    public Object inf() { return obj; }
  }
}