Question

Create UML class diagram extension for an array data structure support of the iterator pattern. • Write pseudo code to support iterator pattern for an array data structure

Answer 1

UML CLASS DIAGRAM

// A Java program to demonstrate implementation

// of iterator pattern with the example of

// notifications

// A simple Notification class

class Notification

{

               // To store notification message

               String notification;

               public Notification(String notification)

               {

                              this.notification = notification;

               }

               public String getNotification()

               {

                              return notification;

               }

}

// Collection interface

interface Collection

{

               public Iterator createIterator();

}

// Collection of notifications

class NotificationCollection implements Collection

{

               static final int MAX_ITEMS = 6;

               int numberOfItems = 0;

               Notification[] notificationList;

               public NotificationCollection()

               {

                              notificationList = new Notification[MAX_ITEMS];

                              // Let us add some dummy notifications

                              addItem("Notification 1");

                              addItem("Notification 2");

                              addItem("Notification 3");

               }

               public void addItem(String str)

               {

                              Notification notification = new Notification(str);

                              if (numberOfItems >= MAX_ITEMS)

                                             System.err.println("Full");

                              else

                              {

                                             notificationList[numberOfItems] = notification;

                                             numberOfItems = numberOfItems + 1;

                              }

               }

               public Iterator createIterator()

               {

                              return new NotificationIterator(notificationList);

               }

}

// We could also use Java.Util.Iterator

interface Iterator

{

               // indicates whether there are more elements to

               // iterate over

               boolean hasNext();

               // returns the next element

               Object next();

}

// Notification iterator

class NotificationIterator implements Iterator

{

               Notification[] notificationList;

               // maintains curr pos of iterator over the array

               int pos = 0;

               // Constructor takes the array of notifiactionList are

               // going to iterate over.

               public NotificationIterator (Notification[] notificationList)

               {

                              this.notificationList = notificationList;

               }

               public Object next()

               {

                              // return next element in the array and increment pos

                              Notification notification = notificationList[pos];

                              pos += 1;

                              return notification;

               }

               public boolean hasNext()

               {

                              if (pos >= notificationList.length ||

                                             notificationList[pos] == null)

                                             return false;

                              else

                                             return true;

               }

}

// Contains collection of notifications as an object of

// NotificationCollection

class NotificationBar

{

               NotificationCollection notifications;

               public NotificationBar(NotificationCollection notifications)

               {

                              this.notifications = notifications;

               }

               public void printNotifications()

               {

                              Iterator iterator = notifications.createIterator();

                              System.out.println("-------NOTIFICATION BAR------------");

                              while (iterator.hasNext())

                              {

                                             Notification n = (Notification)iterator.next();

                                             System.out.println(n.getNotification());

                              }

               }

}

// Driver class

class Main

{

               public static void main(String args[])

               {

                              NotificationCollection nc = new NotificationCollection();

                              NotificationBar nb = new NotificationBar(nc);

                              nb.printNotifications();

               }

}