Tuesday, 17 September 2013

Observer Design Pattern - Implementation


Click here to watch in Youtube : https://www.youtube.com/watch?v=hBVlL64AEEs

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Observer Design Pattern - Implementation - Class Diagram





















Observer.java

public interface Observer
{
public void update( String availability );
}


Person.java

public class Person implements Observer
{
private String personName;

public Person( String personName, Subject subject )
{
this.personName = personName;
subject.registerObserver(this);
}

public String getPersonName()
{
return personName;
}

public void setPersonName( String personName )
{
this.personName = personName;
}

public void update( String availabiliy )
{
System.out.println("Hello " + personName + ", Product is now " + availabiliy + " on        
                                   flipkart");
}
}

Subject.java

public interface Subject
{
public void registerObserver( Observer observer );

public void removeObserver( Observer observer );

public void notifyObservers();
}

Product.java

import java.util.ArrayList;

public class Product implements Subject
{
private ArrayList<Observer> observers = new ArrayList<Observer>();
private String              productName;
private String              productType;
private String              productPrice;
private String              availability;

public Product( String productName, String productType, String productPrice, String availability )
{
super();
this.productName = productName;
this.productType = productType;
this.productPrice = productPrice;
this.availability = availability;
}

public ArrayList<Observer> getObservers()
{
return observers;
}

public void setObservers( ArrayList<Observer> observers )
{
this.observers = observers;
}

public String getProductName()
{
return productName;
}

public void setProductName( String productName )
{
this.productName = productName;
}

public String getProductType()
{
return productType;
}

public void setProductType( String productType )
{
this.productType = productType;
}

public String getProductPrice()
{
return productPrice;
}

public void setProductPrice( String productPrice )
{
this.productPrice = productPrice;
}

public String getAvailability()
{
return availability;
}

public void setAvailability( String availability )
{
this.availability = availability;
System.out.println("Availability changed from Not available to Available");
notifyObservers();
}

@Override
public void registerObserver( Observer observer )
{
observers.add(observer);

}

@Override
public void removeObserver( Observer observer )
{
observers.remove(observer);

}

@Override
public void notifyObservers()
{
System.out.println("Product Name :"
               + this.getProductName() + ", Product Type : " + this.productType + ", product Price : "
               + this.productPrice + " is available now.So notifying all the users ");
System.out.println();
for( Observer observer : observers )
{
observer.update(this.availability);
}

}
}

ObserverPatternMain.java

import java.util.ArrayList;
import java.util.Iterator;

public class ObserverPatternMain
{

public static void main( String[] args )
{
Product samsungLEDTV = new Product("Samsung LED TV", "LED TV","60000Rs", "Not available");
//Person david object will be created and person david object will be registered to the subject
Person david = new Person("David",samsungLEDTV);
//Person john object will be created and person john object will be registered to the subject
Person john = new Person("John",samsungLEDTV);

ArrayList<Observer> subscribers= samsungLEDTV.getObservers();
System.out.println("subscribers List : "+ subscribers);
for( Iterator<Observer> iterator = subscribers.iterator(); iterator.hasNext(); )
                {
               Person person = (Person) iterator.next();
               System.out.println("This person has subscribed : " + person.getPersonName());                
                }
System.out.println();
System.out.println("SamsungLED TV current state : "+samsungLEDTV.getAvailability());
System.out.println();
// Now product is available
samsungLEDTV.setAvailability("Available");
}

}

Output

subscribers List : [Person@119298d, Person@f72617]
This person has subscribed : David
This person has subscribed : John

SamsungLED TV current state : Not available

Availability changed from Not available to Available
Product Name :Samsung LED TV, Product Type : LED TV, product Price : 60000Rs is available now.So notifying all the users 

Hello David, Product is now Available on flipkart

2 comments:

  1. Hi Ram, Its good to under stand. Thanks, Sridhar/R

    ReplyDelete

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