Iterator Design Pattern

Definition:

•       Iterator pattern falls under behavioural pattern category.

•       In object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.

•       This pattern is used to get a way to access the elements of a collection object in sequential manner without any need to know its underlying representation.

•       What Iterator patterns is NOT? -  repeat task / solving solution

Purpose:

•       Easy access to elements of container.

•       Avoid data tampering at client side

•       Perform simultaneous Iterators

Why Iterator Pattern (Problem statement):

•       Consider an application used to print the details of a bank (its name and its manager name). For now only 3 banks details are known, and this is how it prints.

        Display(bank1.BankName);

     Display(bank1.Locatioin);

     Display(bank2.BankName);

     Display(bank2.Location);

•       Let’s say now 100 bank details are known, now the complexity arises, as the application will now need to print all the 100 bank details one by one.

•       To overcome the above issue, we can use the Iterator pattern.

Implementation:

•       Step 1: Store all the objects ( all bank details ) in a container (list).

                private ArrayList m_ArrBank = new ArrayList();

                 m_ArrBank .Add(new Bank("ABC", “Location1"));

                 m_ArrBank .Add(new Bank("XYZ", " Location2"));

                 m_ArrBank .Add(new Bank("TUV", "Location3”));

•       Step2: Access all the elements of the list by using an Iterator ( i.e. by using foreach)

                 foreach (Bank item in m_ArrBank )  // Iterator

                 {

                      Display(item.Location);

                      Display(item.BankName);

                 }

UML :

Example in C# :

Examples of Iterator :

  C++
        Template Library Containers implement their iterators
        Template Library algorithm are defines in terms iterator
  C#
        IEnumerable and IEnumurator are used
  Java
        SDK defines iterator interface
        Collections implement their iterators
  SQL
        Cursor is an iterator.
  TV Remote control

Types of Iterator :

•       Internal Iterator

•       External Iterator

•       Single Integral Iterator

•       Multiple Integral Iterator