/**
   realizza una coda, usando sue pile.

   @author Adriano Luchetta
   @version 21-Nov-2005
   @version 3-Dic-2004
*/
public class QueueByStacks implements Queue
{
   //parte privata
   Stack pila;
   
   //parte pubblica
   public QueueByStacks()
   {
      pila = new ArStack();
   }
   
   public boolean isEmpty()
   {
      return pila.isEmpty();
   }
   
   public void makeEmpty()
   {
      pila.makeEmpty();
   }
   
   public int size()
   {
      return pila.size();
   }

   public void enqueue(Object obj)
   {
      pila.push(obj);
   }

   public Object front() throws EmptyQueueException
   {
      if (isEmpty())
         throw new EmptyQueueException();

      Stack tmpPila = new ArStack();
      while (!pila.isEmpty())
         tmpPila.push(pila.pop());

      Object obj = tmpPila.top();
      
      while (!tmpPila.isEmpty())
         pila.push(tmpPila.pop());
         
      return obj;
   }
   
   public Object dequeue() throws EmptyQueueException
   {
       if (isEmpty())
         throw new EmptyQueueException();

      Stack tmpPila = new ArStack();
      while (!pila.isEmpty())
         tmpPila.push(pila.pop());

      Object obj = tmpPila.pop();
      
      while (!tmpPila.isEmpty())
         pila.push(tmpPila.pop());
         
      return obj;
   }
}