Implement a sample application in Java that uses the Observer pattern to simulate a news agency notifying its subscribers whenever a new news article is published.

$1.$ News Agency

a$.$ Create a $`$NewsAgency$`$ class that maintains a list of subscribers $($observers$).$

b$.$ Implement the $`$Subject$`$ interface from the $`$java$.$util.Observer$`$ package, which includes the $`$addObserver$`,`$removeObserver$`,$ and $`$notifyObservers$`$ methods.

c$.$ Implement a method $`$publishNewsArticle$`$ that accepts a $`$NewsArticle$`$ object as a parameter and calls the $`$notifyObservers$`$ method to notify all registered subscribers.

$2.$ News Article

a$.$ Create a $`$NewsArticle$`$ class that represents a news article with properties such as title, content, author, and

publication date.

b$.$ Implement appropriate constructors and getter methods for accessing the article details.

$3.$ Subscriber

a$.$ Create a $`$Subscriber$`$ class that implements the $`$Observer$`$ interface from the $`$java$.$util.Observer$`$ package.

b$.$ Implement the $`$update$`$ method, which will be called by the $`$NewsAgency$`$ when a new news article is published.

c$.$ Within the $`$update$`$ method, cast the received argument to a $`$NewsArticle$`$ object and display the details of the published news article.

$4.$ Main Class

a$.$ In your main program $(`$Main$`$ class$),$ create an instance of the $`$NewsAgency$`$ class.

b$.$ Create instances of several $`$Subscriber$`$ objects representing different subscribers.

c$.$ Register the subscribers with the $`$NewsAgency$`$ by calling the $`$addObserver$`$ method.

d$.$ Create one or more $`$NewsArticle$`$ objects representing different news articles.

e$.$ Publish the news articles using the $`$NewsAgency$`$ by calling the $`$publishNewsArticle$`$ method and passing the $`$NewsArticle$`$ object as an argument.

f$.$ Observe how the registered subscribers are notified and display the details of the published news articles.

g$.$ Demonstrate the ability to unregister a subscriber from the $`$NewsAgency$`$ by calling the $`$removeObserver$`$ method.