/** Implementa una Queue usando una DLL. */

public class DLLQueue implements Queue {

	 private DLLNode head, tail;  // Nodi fittizi di testa/cdoa

	 /** Crea una coda vuota. */ 
	 public DLLQueue() {
		  head = new DLLNode( null );
		  tail = new DLLNode( null );
		  tail.insertAfter( head );
	 }

	 /* --- METODI DI Queue --- */

	 public void enqueue( Object o ) {
		  DLLNode node = new DLLNode( o );
		  node.insertBefore( tail );
	 }

	 public Object dequeue() {
		  if ( isEmpty() ) return null;
		  DLLNode node = head.getNext();
		  node.remove();
		  return node.getContent();
	 }

	 public boolean isEmpty() {
		  return ( head.getNext().getNext() == null );
	 }

	 /** Main di test. Inserisce gli argomenti in coda e li rimuove 
		  stampandoli. */
	 static public void main( String arg[] ) {
		  Queue q = new DLLQueue();

		  for ( int i = 0; i < arg.length; i++ )
				q.enqueue( arg[i] );

		  while (! ( q.isEmpty() ) ) 
				System.out.println( q.dequeue() );
	 }
	 
}