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Observer pattern

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  • 1. Class report CLASS ASSIGNMENT- 2 OBSERVER PATTERN SHARE PRICE NOTIFICATION:Introduction:At first, we have to see what happens in this sort of share price notificationsystem, i.e. what features we have to focus on.Now,let’s see the criteria that we have to maintain in our program. When auser or client is registering ,he/she has to be added to the userlist. At the sametime, the preservation of the very information comes in mind.But,if we think deeply, we can see that it’s not the responsibility of the user tokeep the registration information always in mind.Rather, the company is fullyresponsible in respect of holding its users’ information.Now, the questioncomes where will I keep the subscription info?So, let,s go through the wholeproblem in brief.There must be a Company class.Let’s, see what may be there….. Page 1 of 9
  • 2. Class reportCompany:Company name:Supportive information:Userlist;Shareprice:So, some methods may be present like;Registration();ChangeShare();NotifyUsers();Again, there must be a User class.The features may be ….User:Name:Description:Functions like;ReceiveNotification(); -may be present.Another class named Share may be present. But, it’s not mandatory to take itas a class .Rather, we can easily include it in the Company class.Actually, what functions will play the key role can easily be detected.As, Page 2 of 9
  • 3. Class reportCompany UserNotifyUser(); ReceiveNotification();However; let’s focus, how we will troubleshoot the problem.Company Class:At first , we have to create a registration method in Company class in order tomaintain the generic registration issues.As for example;Registration(User us){Userlist.add(us);}Now, we have to maintain a suitable connection with the users who are addedto the userlist. If there is any change found in the share price then thecompany has to notify the users about the possible change. As,ChangeShare(double price){If (shareprice !=price){Shareprice=price;NotifyUser();}} Page 3 of 9
  • 4. Class reportNotifyUser(){For all users in userlist{//loop;User.ReceiveNotification(shareprice,company name);}}User Class:Now, after being called by NotifyUser() method, the ReceiveNotification()method becomes active. So, it somehow sends the message that it has beennotifed. As,ReceiveNotification(double price,company name){Print(“I have been notified”);}So, what we clearly see here is that , Company notifies user. User observe notification. Hence, company – user observation process.That’s why, this way of solving a problem is termed as “Observer Pattern”.Now,We have described the criteria in respect to one company only until now. Ifwe have to do the same thing in respect to many companies, then we just haveto add an abstract class namely AddCompany with some common featuresextending the companies seperately with the extra features. Page 4 of 9
  • 5. Class reportLikewise, AddCompany Company1 Company2 ...............Similarly,We can use the same concept in case of multiple users,likewise; Page 5 of 9
  • 6. Class report AddUser User1 User2 .........The main code to solve the problem is shown below:Main Code:User Class:public class User { public static void main(String[ ] args) { Company cmp1 = new Company("Yahoo", 5000000); Company cmp2 = new Company("Apple", 4000000); ShareHolder sh1 = new ShareHolder("Mahedi", cmp1); cmp1.addShareHolder(sh1); ShareHolder sh2 = new ShareHolder("Mahfuj", cmp1); cmp1.addShareHolder(sh2); Page 6 of 9
  • 7. Class report ShareHolder sh3 = new ShareHolder("Anik", cmp2); cmp2.addShareHolder(sh3); cmp1.changePrice(7000000); cmp2.changePrice(6000000); }}Company Class:import java.util.ArrayList;public class Company { private double sharePrice; private ArrayList<ShareHolder> sh; private String companyName; public Company(String cn,double sPrice){ companyName = cn; sharePrice = sPrice; sh = new ArrayList<ShareHolder>(); } public void addShareHolder(ShareHolder sh){ this.sh.add(sh); } Page 7 of 9
  • 8. Class report public void changePrice(double sPrice){ if(this.sharePrice != sPrice){ java.util.Iterator<ShareHolder> itr = sh.iterator(); while(itr.hasNext()){ itr.next().receiveNotification(getCompanyName(),sPrice); } } } public String getCompanyName() { return companyName; } }Shareholder Class://This class is not mandatory.We can add the shareholder information in thecompany class even.//import java.util.ArrayList;public class ShareHolder { private String holderName; private ArrayList<Company> regCom; public ShareHolder(String hn,Company cm){ holderName = hn; regCom = new ArrayList<Company>(); } public void registerTo(Company cm){ this.regCom.add(cm); } Page 8 of 9
  • 9. Class report public void receiveNotification(String cName,double sPrice){ System.out.println(this.holderName + " is notified as sharePrice of " + cName + " is changed to " + sPrice); } }……………………………………………………………………………..X………………………………………………………………………………… Page 9 of 9