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Program 1
using System.Collections;
namespace Templates.Observer {

 public class Subject {                             
   // Subject instance variables

   private ArrayList observers = new ArrayList();   

   public void Attach(Observer o){                  

   public void Detach(Observer o){

   public void Notify(){                            
     foreach(Observer o in observers) o.Update();   

   public SubjectState GetState(){                  
     return new SubjectState();                     

 public class SubjectState {                        
   // Selected state of the subject
The subject class.
The list of observers.
A method that handles subscription.
A method that updates all
observers that subcribe to events
from this subject.
A method that may supply additional
information to an observer upon 
A sketch of the class SubjectState.