/** An instance of this class represents a queue capable of holding items
**  of the specified type T (the generic type parameter).
**  The underlying implementation makes use of a linked structure of
**  objects arising from the Link1 class.
**
**  Author: R. McCloskey
**  Date: January 2020
*/
public class QueueViaLink1<T> implements Queue<T> {

   // instance variables
   // ------------------

   protected Link1<T> front; // reference to object holding front item on queue 
   protected Link1<T> rear;  // reference to object holding rear item on queue
   private int numItems;    // # of items on the queue


   // constructors
   // ------------

   /* Establishes this queue as being empty.
   */
   public QueueViaLink1() { clear(); }


   // observers
   // ---------

   public int sizeOf() { return numItems; }

   public boolean isEmpty() { return sizeOf() == 0; }

   public boolean isFull() { return false; }

   public T frontOf() { return front.item; }

   @Override
   public String toString() {
      Link1 pntr = front;
      StringBuilder result = new StringBuilder("[ ");
      for (int i=0; i != numItems; i++) {
         result.append(pntr.item + " ");
         pntr = pntr.next;
      }
      return result.append(']').toString();
   }


   // mutators
   // --------

   public void clear() { front = null; rear = null; numItems = 0; }

   public void enqueue( T item ) { 
      Link1<T> newRear = new Link1(item, null);
      if (isEmpty())
         { front = newRear; }
      else
         { rear.next = newRear; }
      rear = newRear;
      numItems = numItems + 1;
   }

   public T dequeue() { 
      T result = front.item;
      front = front.next; 
      numItems = numItems - 1;
      return result;
   }

}