class Queue {
   QueueItem first;
   QueueItem last;
   void add(Thing t) {
      QueueItem newItem = new QueueItem(t);
      if (first == null) {
         first = newItem;
         last = newItem;
      }
      else {
         last.next = newItem;
         last = newItem;
      }
   }  // end of add()
   
   Thing get() {
      if (first == null)
         return null;
      else {
         QueueItem firstItem = first;
         first = first.next;
         return firstItem.myThing;
      }
   }  // end of get()
   
   void print() {
      if (first == null)
         System.out.println("Queue is empty");
      else {
         QueueItem item = first;
         while (item != null) {
            System.out.println(item.myThing.key 
               + ":" + item.myThing.value);
            item = item.next;
         }
      }
   }  // end of print()
}  // end of class Queue

class QueueItem {
   Thing myThing;
   QueueItem next;
   QueueItem(Thing t) {
      myThing = t;
   }
}  // end of class QueueItem