public static void main(String[] args) {
		ConcreteAggregate a=new ConcreteAggregate();
		a.set("Item A");
		a.set("Item B");
		a.set("Item C");
		a.set("Item D");
		
		ConcreteIterator i=new ConcreteIterator(a);
		System.out.println("Iterating over collection:");
		Object item=i.first();
		while(item!=null){
			System.out.println(item);
			item=i.next();
		}
	}