/** Program 6.23 Linked Queue Representation */

/*----------------------------------------------------------------*/

  class QueueNode {
    Object    item;
    QueueNode  link;
  }

/*----------------------------------------------------------------*/

  class Queue {

     private QueueNode front;        // front contains a reference to the
                                               // front item of the queue
     private QueueNode rear;          // rear contains a reference to the
                                                // rear item of the queue
     private int count;               // the number of items in the queue
  
 /*-----------------*/

   // Java's automatically defined no-arg constructor suffices

 /*-----------------*/

   public boolean empty() {
     return (count == 0);
   }

 /*-----------------*/
 
   public void insert(Object newItem) {
   
     QueueNode temp = new QueueNode();
   
     temp.item = newItem;
     temp.link = null;
     if (rear == null) {
       front = rear = temp;
     } else {
       rear.link = temp;
       rear = temp;
     }
     count++;
   
   } //end insert

 /*-----------------*/

   
   public Object remove() {

     if (count == 0) {              // if the queue is empty, return null
       return null;
     } else {                         // otherwise, return the front item
       Object tempItem = front.item;
       front = front.link;
       if (front == null) {
         rear = null;
       }
       count--;
       return tempItem;
     }

   } //end remove

 /*-----------------*/